Dumping an Intel P8742AH

[Glen Slick via cctalk]

Anyone here have experience dumping the contents of an Intel P8742AH
OTP EPROM device?

I have one that I haven't been able to dump with either a BP
Microsystems BP-1610, or a Data-I/O UniSite device programmer. Both
have device entries for that specific device. Both report device
connection errors when attempting to read the device. The device pins
all look clean. I tried putting a machine pin socket between the
device and the programmer ZIF socket in case there was a flakey
connection, but that didn't make any difference.

I was told the device was working properly in the target system before
it was removed to dump its contents.

Looking at the UPI-41AH/42AH datasheet 210393-007 the P8742AH does
have a security bit which can be programmed. As far as I can tell
though, if the security bit is set the device should still respond to
the standard device verification algorithm, but just return the wrong
data, and the device manufacturer signature should still be able to be
read. Or does an Intel P8742AH not respond at all to the standard
device verification algorithm if the security bit is set?

I don't have the target system myself to reinstall the device and
verify that it actually works.

Re: HP 54200D oscope practically worthless?

[Glen Slick via cctalk]

On Thu, May 12, 2022 at 5:55 PM Eric Smith via cctalk
 wrote:
>
> These appear to be derived from the 1630/1631 logic analyzers, some models
> of which have 'scope capability, which works as you've described. They must
> have decided to offer models with only the scope and without the logic
> analzyer (except for a digital triggering option), which seems like a bad
> idea. Probably why I'd never heard of these before.
>

Without taking a close look at the specifications for any differences,
the scope capability of the 54200 might be basically the same as the
1631.

The 54201 scope adds a repetitive sampling capability that doesn't
appear to be present on the 54200 and 1631, which increases the
bandwidth up to 300MHz instead of 50MHz in the real-time sampling
mode.

Re: HP 54200D oscope practically worthless?

[Eric Smith via cctalk]

On Thu, May 12, 2022 at 12:25 PM Alexander Huemer via cctalk <
cctalk@classiccmp.org> wrote:

> On Thu, May 12, 2022 at 02:01:50PM -0400, William Sudbrink via cctalk
> wrote:
> > I picked up one of these in a batch of electronics.  Is it worth
> > repairing/investigating?
>
> The scope does what it is supposed to, you get a time-domain
> visualization of voltage.
> Though, they are awkward to use due to the lack of rotary encoders.
> Scaling horizontally or vertically requires you to go into a menu,
> navigate to the right option, do the actual scaling and go back.
> It's better than no scope at all, but not exactly the model you'd hunt.
>

These appear to be derived from the 1630/1631 logic analyzers, some models
of which have 'scope capability, which works as you've described. They must
have decided to offer models with only the scope and without the logic
analzyer (except for a digital triggering option), which seems like a bad
idea. Probably why I'd never heard of these before.

At the time they were current (early 1980s), the 1630/1631 family were
fairly reasonable logic analyzers, but the 1650/16500, 1660, 1670/16700,
etc. are far better. I wouldn't recommend that anyone _buy_ a 1630/1631
family logic analyzer at this late date, but if someone is giving one
away...

Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

>> 
>> If I am trying to calculate the height a sea harbour wall needs to be, can I
>> not consider the height of the tide and the height of the waves separately
>> and add them together, just to make it easier to work it out even though I
>> know that it would be physically impossible to distinguish the water that
>> makes up the tide from the water that makes up the waves?
>> 
> Using this analogy if you measured 10 waves at 10 feet high you would need
> a wall 100 feet high, correct? Or 20 waves at 7 feet it would need to be
> 140 feet. 
> Not valid at all.
>

The idea is to measure the maximum height of the waves on a windy day by
examining how far up they make splash marks on a vertical pole stuck in the
seabed for the purpose.  Then consult a tide table to see how high the tide
was at the time the wave measurement was made.  Subtracting the latter figure
from the former figure gives the height of the waves above the tide.  (This
is the AC component.  The tide is the DC component.)  Adding the height of
the highest expected tide to the figure calculated for the maximum height of
the waves would give a figure for the minimum height needed for the harbour
wall.

>
>> (It's not even that bad in the case of electric current because instruments
>> exist which can measure the DC component of a current and the AC component
>> of a current separately or together.)
> I have no idea what you are talking about. What instruments are you referring
> to? I’d like to read about them.
>

A suitable moving coil ammeter will register the average value of a current
flowing through it and will indicate which direction it is flowing in.  This
is the DC component of the current.  A suitable moving iron ammeter will
(crudely) register the RMS value of the AC current flowing through it.  I'm
not certain but as far as I recall, it will also register the actual value
of DC current.  There are probably lots of fancy computerised oscilloscope
like instruments that can be used to measure all sorts of oddball current
waveforms given suitable current probes.


>> 
>> How about we take a 3V doorbell transformer and make a circuit consisting
>> of the secondary of the transformer, a 6V battery and a 9V light bulb all
>> connected in series?  How would the current in this circuit be described?
>> A varying current? An AC current? A DC current?
>>
>
> The current would be described by ohm’s law. Incidentally, if the primary
> of a xformer was actually connected it would probably blow up the battery.
>

Maybe I should have stated that I was assuming that power is applied to the
primary for the test?  Perhaps I should have also stated that I am assuming
that the light bulb is selected such that the current it draws at it's rated
voltage will not exceed the capability of either the transformer or the
battery?  I don't expect anything to blow up assuming we are understanding
each other correctly which may not be a valid assumption.

>
> You would describe it as Open. If not, its just a 6 volt DC circuit.
>

I don't understand.

>
>> How about we use a 6V doorbell transformer and a 3V battery instead?  Would
>> that change how the current is described?
> No it wouldn’t.  
>
>> I would say that in both cases, the current flowing has an AC component and
>> it also has a DC component.
> As stated and not rectified it’s not a valid circuit.
> In ps circuits there is a fuse on the secondary side of the circuit usually
> after the rectifier-filter circuit to prevent any rectifier shorts from
> damaging other components.

The transformer secondary, battery and light bulb are all connected in series
ie in a circle, end to end.  The battery is not going to be bothered by the
AC current flowing through it and the presence of the light bulb will limit
the current to a safe value.

If the battery and the transformer secondary and the light bulb were connected
in parallel ie the two terminals of the battery were connected directly to the
two terminals of the transformer secondary and the two terminals of the light
bulb, that would be a different matter.  Either the transformer or the battery
or both could be damaged in this case.  This is not what I was suggesting.

>
> Well, the previous example seemed to imply that the output from a rectifier
> was pure dc.
>

Pretty much everything I have said is to try to illustrate that what flows
through the rectifier has a DC component and an AC component.

>
> Its not, it’s pulsed DC
>

Pulsed DC sounds like something that has a DC component and an AC component.

>
> so i thought you might be referring
> to the rectifier and associated filter and possibly regulator components as
> the whole rectifier”
> Sometimes in talking about electronics the specific function of a portion
> of connected components is cited. IE filter circuit,  Detector circuit,
> rectifier circuit. It’s just shorthand speak.
>

Sorry, I didn't follow.

I'm going to bow out at this point because I don't there is anything
further I can add

Re: Nicolet Computer interest

[dwight via cctalk]

It may have a processor inside. if it is the one I think it is, it uses 2900 
ALUs.
If you can send a picture I may be able to tell.
Dwight

From: cctalk  on behalf of dancohoe--- via 
cctalk 
Sent: Thursday, May 12, 2022 1:45 PM
To: 'dwight via cctalk' 
Subject: Nicolet Computer interest

Hi Dwight,

In 2010 I purchased a Nicolet LAS 12/70 Data and Signal Processor System box
on ebay.  I hoped it was a Nicolet computer but then could find nothing
online about it.

It's on the shelf here and I've never looked inside to see what's there.
It's ridiculously heavy.

I don't know if there's anything useful from it for you guys, but I can take
a look at what is on the inside and report back.

Regards,  Dan

Re: Recent purchase of NIC-80 computer.

[dwight via cctalk]

Hi Paul
 It may be a little slow for DSP. Its main thing was that the acquisition 
didn't require and processor time. It was designed before uPs. ( not counting 
what was used in the F16's ).
It is fun because it has a full front panel to toggle in a bootstrap. Then one 
can load with the serial. Mine also has a floppy drive ( something is broken 
right now ). I also have a Diablo 30 for it but haven't had time to play with 
it. The floppy was working at one time. I had to rewrite the low level code for 
the floppy from code I had for the diablo.
Bob has no mass storage yet. It is on his list of projects.
Dwight



From: Paul Koning 
Sent: Thursday, May 12, 2022 10:15 AM
To: dwight ; cctalk@classiccmp.org 
Subject: Re: Recent purchase of NIC-80 computer.



> On May 12, 2022, at 1:03 PM, dwight via cctalk  wrote:
>
> Hi All
> There was a Nicolet computer purchased recently on ebay:
> https://www.ebay.com/bfl/viewbids/363826255294?item=363826255294&rt=nc&_trksid=p2047675.l2565
> Looking at the buyers history, it looks like it was purchased by a collector.
> Bob Rosenbloom and I are wondering if anyone know who might have purchased it 
> and if they are expecting to restore it to operational status?
> These are an interesting computer being that it is a 20 bit word. It was also 
> designed specifically to do FFT's with specialized instructions like bit 
> reversing and hardware multiply and divide.

That may simply be a quite ordinary DSP processor.  Hardware multiply and in 
particular single cycle mul + add are typical DSP operations because you need 
them for FIR filters, one of the most common applications of a DSP.  And of 
course bit reverse for FFT, which has the nice property of being very easy in 
hardware.

paul

Re: DEC H7822 power supply

[Will Cooke via cctalk]

> On 05/12/2022 2:14 PM Peter Coghlan via cctalk  wrote:
> 
> 
> Wayne S wrote:
> >> On May 12, 2022, at 09:56, Peter Coghlan via cctalk 
> >>  wrote:
> >>
> >> Toby Thain via cctalk wrote:
>  On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
>  Given the normal usage that has evolved for the terms DC and AC rather 
>  than
>  their dictionary definitions, I would suggest that the current that gets
>  passed by a rectifier has both a DC component and an AC component. When
> 
> >>>
> >>> It does not, due to unidirectionality.
> >>>
> >>
> >> Consider the current through the rectifier as the sum of a "DC" current 
> >> plus
> >> an "AC" current. The "DC" current has a steady positive value and the "AC"
> >> current varies above and below zero with a magnitude less than or equal to
> >> that of the "DC" current.
> >
> > I’m really trying to understand what you’re getting at here.
> > In practical terms, The assumption that there is a sum of a DC and AC
> > component is incorrect.
> Why? What evidence do you have that the assumption is incorrect?
> 
> If I am trying to calculate the height a sea harbour wall needs to be, can I
> not consider the height of the tide and the height of the waves separately
> and add them together, just to make it easier to work it out even though I
> know that it would be physically impossible to distinguish the water that
> makes up the tide from the water that makes up the waves?
> 
> (It's not even that bad in the case of electric current because instruments
> exist which can measure the DC component of a current and the AC component
> of a current separately or together.)
> 
>
Peter,
You are quite correct.  It is called superposition.
https://en.wikipedia.org/wiki/Superposition_principle
It applies to all linear systems and is one of the principles that make many 
difficult problems practicable.
My background is primarily physics.  Superposition is extremely important there 
in many realms, including signal processing, electric circuits, and 
differential equations, among many others.

I'll say no more.  I didn't want to get into this quagmire, either.

Will

Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

Wayne S wrote:
>> On May 12, 2022, at 09:56, Peter Coghlan via cctalk  
>> wrote:
>> 
>> Toby Thain via cctalk wrote:
 On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
 Given the normal usage that has evolved for the terms DC and AC rather than
 their dictionary definitions, I would suggest that the current that gets
 passed by a rectifier has both a DC component and an AC component.  When
 
>>> 
>>> It does not, due to unidirectionality.
>>> 
>> 
>> Consider the current through the rectifier as the sum of a "DC" current plus
>> an "AC" current.  The "DC" current has a steady positive value and the "AC"
>> current varies above and below zero with a magnitude less than or equal to
>> that of the "DC" current.
>
> I’m really trying to understand what you’re getting at here.
> In practical terms, The assumption that there is a sum of a DC and AC
> component is incorrect.

Why? What evidence do you have that the assumption is incorrect?

If I am trying to calculate the height a sea harbour wall needs to be, can I
not consider the height of the tide and the height of the waves separately
and add them together, just to make it easier to work it out even though I
know that it would be physically impossible to distinguish the water that
makes up the tide from the water that makes up the waves?

(It's not even that bad in the case of electric current because instruments
exist which can measure the DC component of a current and the AC component
of a current separately or together.)

>
> There is no DC component in an AC wave. A wave is either AC meaning
> reversing polarity or it is DC meaning there is no reversal of polarity.
>

Can we agree that there is such a thing as an "AC current" and there
is such a thing as a "DC current" and the two of them can be added
together?

How about we take a 3V doorbell transformer and make a circuit consisting
of the secondary of the transformer, a 6V battery and a 9V light bulb all
connected in series?  How would the current in this circuit be described?
A varying current? An AC current? A DC current?

How about we use a 6V doorbell transformer and a 3V battery instead?  Would
that change how the current is described?

I would say that in both cases, the current flowing has an AC component and
it also has a DC component.

>
> And a rectifier does not sum anything.
>

I'm not saying the rectifier sums anything.  What I am saying is that the
current that goes through the rectifier can be considered as the sum of
two component currents.  It's just a way of looking at it, like considering
the tide and the waves separately in the harbour wall calculation.

>
> Are you maybe using “Rectifier” as the whole circuit?  A Rectifier
> can be a single component, like a diode used to pass one half of an
> alternating current or it can be a few components like 4 diodes connected
> as a bridge to pass both halfs.
>

Strictly speaking, a circuit involves a closed path for a current to flow in.
However, "circuit" also gets used to describe a substantial group of components
that needs to be connected to something else to form a fully closed path.  I
don't think a rectifier would be enough to be considered a whole circuit. 

>
> This may help to visualize.
> Do an experiment. If you have an Oscope take a small battery maybe 9 volt and
> wire the negative lead to the neg scope input. Touch the positive lead to the
> scope positive and watch the deflection. You should see a quick trace  rise
> and the trace should remain above the zero point.
> That is what pure DC looks like. No ripple at all. Power Supplies try to make
> that from your wall power input. 
> Next, untouch the positive and watch the trace fall. At no point does it fall
> below the zero line.
> NoW touch and untouch the positive as fast as you can and watch the trace.
> That is pulsating DC although with irregular frequency. That would be the
> output from the rectifier component.
> Reverse the leads and do it again.
> This will show the equivalent of a negative polarity.
>  
> If you have a variac, set it to 9 volts or so, plug in a light or something to
> provide a load and using your oscilloscope probes touch across the light and
> you should see a sine wave with regular frequency.  Notice the negative going
> half. That is AC.
> 
>
> It’s important to use a variac for safety ( or an isolation transformer very
> carefully) as wall voltages can hurt you.
>

A variac does not provide isolation.  If it is not wired correctly, it is
possible to end up scooping 9V from the live end of the mains supply instead
of from the neutral end.  If there is a bad connection or a break in the
winding near or at the neutral end, it is possible to end up with the whole
mains supply at the output.  I don't want to connect the earth lead of my
scope probe to the neutral output of a variac either.  If I were doing this,
I would prefer to use a transformer designed to provide an isolated fixed low
voltage output.

>
> This

Nicolet Computer interest

[dancohoe--- via cctalk]

Hi Dwight,

In 2010 I purchased a Nicolet LAS 12/70 Data and Signal Processor System box
on ebay.  I hoped it was a Nicolet computer but then could find nothing
online about it.  

It's on the shelf here and I've never looked inside to see what's there.
It's ridiculously heavy.

I don't know if there's anything useful from it for you guys, but I can take
a look at what is on the inside and report back.

Regards,  Dan

 

Re: HP 54200D oscope practically worthless?

[Jon Elson via cctalk]

On 5/12/22 13:01, William Sudbrink via cctalk wrote:

I picked up one of these in a batch of electronics.  Is it worth
repairing/investigating?
I don't see much on the web and they seem to go for practically nothing on
epay.
Is there something inherently wrong with them?


I have a 54200A that I got out of a dumpster.  The user 
interface is QUITE awful compared to modern digital scopes.  
Setting the trigger level requires going through several 
menus, for instance.


But, it is a decent scope except for the human-machine 
interface.


Jon

Lecture: The Danish Data History Association is on the move, 2022-05-14, 19:00

[Anke Stüber via cctalk]

Hi all,

you're invited to the Update computer club[0] public lecture series
"Updateringar"[1]!

When:  2022-05-14, 19:00 CEST
Where: https://bbb.cryptoparty.se/b/upd-0mo-m2u-aq8

The Danish Data History Association is on the move …
We, the Danish Data History Association (Dansk Datahistorisk Forening),
were founded more than 20 years ago and have primarily lived (quietly)
underground in a cellar in the outskirts of Copenhagen. In 2020 the
municipality of Ballerup, who were our hosts, decided to use the approx.
1000 m² for other purposes than us. Two years later – in February 2022 –
we had a "grand" opening of our new experimental data museum with a
600 m² exhibition. What happened? And what's the plan moving forward?
Michael Ørnø (DDHF)

The lecture is free and open to everyone.

Don't want to miss upcoming events? Subscribe to our low-traffic
announcement list here[2]!

Hope to see you there,
Anke

[0] https://www.dfupdate.se/en/
[1] https://wiki.dfupdate.se/projekt:updateringar
[2] https://lists.dfupdate.se/postorius/lists/announce.lists.dfupdate.se

RE: HP 54200D oscope practically worthless?

[William Sudbrink via cctalk]

Alexander Huemer wrote:

> The scope does what it is supposed to, you get a
> time-domain visualization of voltage.  Though, they
> are awkward to use due to the lack of rotary encoders.  
> Scaling horizontally or vertically requires you to go into
> a menu, navigate to the right option, do the actual
> scaling and go back.
> It's better than no scope at all

Yea, I have several other scopes, so I guess I won't
spend any time on it...

> but not exactly the model you'd hunt.

Anybody in the Washington, DC area want to pick it up
for a beer?

-Alex


-- 
This email has been checked for viruses by Avast antivirus software.
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Re: HP 54200D oscope practically worthless?

[Dennis Boone via cctalk]

 > The scope does what it is supposed to, you get a time-domain
 > visualization of voltage.  Though, they are awkward to use due to the
 > lack of rotary encoders.  Scaling horizontally or vertically requires
 > you to go into a menu, navigate to the right option, do the actual
 > scaling and go back.  It's better than no scope at all, but not
 > exactly the model you'd hunt.

It has HP-IB, and the manuals mention the HP desktop computers of that
era, so you could probably build a more facile interface on a modern
machine.

De

Re: HP 54200D oscope practically worthless?

[Alexander Huemer via cctalk]

On Thu, May 12, 2022 at 02:01:50PM -0400, William Sudbrink via cctalk wrote:
> I picked up one of these in a batch of electronics.  Is it worth
> repairing/investigating?
> I don't see much on the web and they seem to go for practically nothing on
> epay.
> Is there something inherently wrong with them?

The scope does what it is supposed to, you get a time-domain 
visualization of voltage.
Though, they are awkward to use due to the lack of rotary encoders.  
Scaling horizontally or vertically requires you to go into a menu, 
navigate to the right option, do the actual scaling and go back.
It's better than no scope at all, but not exactly the model you'd hunt.

-Alex

HP 54200D oscope practically worthless?

[William Sudbrink via cctalk]

I picked up one of these in a batch of electronics.  Is it worth
repairing/investigating?
I don't see much on the web and they seem to go for practically nothing on
epay.
Is there something inherently wrong with them?

Thanks,
Bill S.


-- 
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

Re: DEC H7822 power supply

[Toby Thain via cctalk]

On 2022-05-12 11:37 a.m., Peter Coghlan via cctalk wrote:

Toby Thain via cctalk wrote:

On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:


Given the normal usage that has evolved for the terms DC and AC 
rather than

their dictionary definitions, I would suggest that the current that gets
passed by a rectifier has both a DC component and an AC component.  When



It does not, due to unidirectionality.



Consider the current through the rectifier as the sum of a "DC" current 
plus

an "AC" current.  The "DC" current has a steady positive value and the "AC"
current varies above and below zero with a magnitude less than or equal to
that of the "DC" current.

When the two are summed, the result is a varying current which does not go
below zero.  This is what I mean by it having a DC component and an AC
component.


Sure, if you change the reference point, a DC signal under one reference 
("zero") potential becomes AC under a different potential. The 
definitions are relative to a reference, in order to define the current 
direction.





This sort of analysis often used in electronic engineering to break down
more complex entities into simpler ones which can be analysed separately
with greater ease.  Didn't somebody have a theorem or an axiom or something
that says this is a valid way to do it? I forget who.  It was a long time
ago.  Kirchoff maybe? No, it wasn't him, maybe he was the one that said
the sum of currents into and out of nodes is zero and stuff like that...
It is a particularly suitable strategy for the case in hand because a
transformer will not pass "DC" from primary to secondary so the effect of
this component can be ignored (except that it could cause the transformer
core to saturate which must be allowed for.  This is only relevant to the
designer of the power supply but if I don't mention it, someone will
surely tell me that I should have.)

(I am starting to regret making the effort to accurately describe this
unusual and confusing (to me anyway) circuit for the benefit of others who
might find themselves struggling with this power supply as I was and might
find some hints on how it operates to be helpful.)

Regards,
Peter Coghlan.

Re: Recent purchase of NIC-80 computer.

[Paul Koning via cctalk]

> On May 12, 2022, at 1:03 PM, dwight via cctalk  wrote:
> 
> Hi All
> There was a Nicolet computer purchased recently on ebay:
> https://www.ebay.com/bfl/viewbids/363826255294?item=363826255294&rt=nc&_trksid=p2047675.l2565
> Looking at the buyers history, it looks like it was purchased by a collector.
> Bob Rosenbloom and I are wondering if anyone know who might have purchased it 
> and if they are expecting to restore it to operational status?
> These are an interesting computer being that it is a 20 bit word. It was also 
> designed specifically to do FFT's with specialized instructions like bit 
> reversing and hardware multiply and divide.

That may simply be a quite ordinary DSP processor.  Hardware multiply and in 
particular single cycle mul + add are typical DSP operations because you need 
them for FIR filters, one of the most common applications of a DSP.  And of 
course bit reverse for FFT, which has the nice property of being very easy in 
hardware.

paul

Re: DEC H7822 power supply

[Paul Koning via cctalk]

> On May 12, 2022, at 11:37 AM, Peter Coghlan via cctalk 
>  wrote:
> 
> Toby Thain via cctalk wrote:
>> On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
>>> Given the normal usage that has evolved for the terms DC and AC rather than
>>> their dictionary definitions, I would suggest that the current that gets
>>> passed by a rectifier has both a DC component and an AC component.  When
>>> 
>> 
>> It does not, due to unidirectionality.
>> 
> 
> Consider the current through the rectifier as the sum of a "DC" current plus
> an "AC" current.  The "DC" current has a steady positive value and the "AC"
> current varies above and below zero with a magnitude less than or equal to
> that of the "DC" current.
> 
> When the two are summed, the result is a varying current which does not go
> below zero.  This is what I mean by it having a DC component and an AC
> component.

Sure, that's the standard way to look at a signal.  It becomes very obvious 
when you do a Fourier transform; you see a term at f=0 (the DC offset) and 
terms at f equal to multiples of the mains frequency.

paul

Recent purchase of NIC-80 computer.

[dwight via cctalk]

Hi All
 There was a Nicolet computer purchased recently on ebay:
https://www.ebay.com/bfl/viewbids/363826255294?item=363826255294&rt=nc&_trksid=p2047675.l2565
Looking at the buyers history, it looks like it was purchased by a collector.
Bob Rosenbloom and I are wondering if anyone know who might have purchased it 
and if they are expecting to restore it to operational status?
These are an interesting computer being that it is a 20 bit word. It was also 
designed specifically to do FFT's with specialized instructions like bit 
reversing and hardware multiply and divide.
It also has an built in A/D that can have different bandwidth, depending on 
sample size.
The original design was for NMR chemical analysis. But was especially useful 
for acquiring repeating sampled evens that had low signal to noise because of 
its hardware built in analog acquisition capable of multiple samples to 
accumulate multiple pass without requiring action by the processor.
We were hoping to see if the person that acquired the computer was interested 
in restoring it to operational status. Bob and I have accumulated a significant 
amount of both hardware and software for this computer.
I am also quite good at trouble shooting this design as I original brought my 
NIC-80 back to life without schematics (we now have a schematic set, thanks to 
a fellow in Australia that had a set of manuals ).
The person that bought it would have been relatively close in Wisconsin, as it 
was a pick up local item.
Thanks
Dwight

Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

Toby Thain via cctalk wrote:

On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:


Given the normal usage that has evolved for the terms DC and AC rather than
their dictionary definitions, I would suggest that the current that gets
passed by a rectifier has both a DC component and an AC component.  When



It does not, due to unidirectionality.



Consider the current through the rectifier as the sum of a "DC" current plus
an "AC" current.  The "DC" current has a steady positive value and the "AC"
current varies above and below zero with a magnitude less than or equal to
that of the "DC" current.

When the two are summed, the result is a varying current which does not go
below zero.  This is what I mean by it having a DC component and an AC
component.

This sort of analysis often used in electronic engineering to break down
more complex entities into simpler ones which can be analysed separately
with greater ease.  Didn't somebody have a theorem or an axiom or something
that says this is a valid way to do it? I forget who.  It was a long time
ago.  Kirchoff maybe? No, it wasn't him, maybe he was the one that said
the sum of currents into and out of nodes is zero and stuff like that...
  
It is a particularly suitable strategy for the case in hand because a

transformer will not pass "DC" from primary to secondary so the effect of
this component can be ignored (except that it could cause the transformer
core to saturate which must be allowed for.  This is only relevant to the
designer of the power supply but if I don't mention it, someone will
surely tell me that I should have.)

(I am starting to regret making the effort to accurately describe this
unusual and confusing (to me anyway) circuit for the benefit of others who
might find themselves struggling with this power supply as I was and might
find some hints on how it operates to be helpful.)

Regards,
Peter Coghlan.

Re: DEC H7822 power supply

[Maciej W. Rozycki via cctalk]

On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:

> I replaced the capacitor in question with a blue Nichicon SE of the same
> value scavanged from another H7821 until I order some spares.  I now have
> 8.7V available on the 9V supply, a little less than I hoped for but it is
> enough to make the internal thinwire tranceiver happy.  Now there is just
> the seized fan to deal with.

 Tolerance is 5% on this line, so you're well within.

> Thanks again to you and Tony for leading me in the direction of the likely
> source of this fault.  I would never have thought of looking in the power
> supply to find it.

 You are welcome!  I wish I had the skills to actually diagnose a faulty 
PSU myself like you do.

 Experience has taught me to look into the PSU first for all kinds of odd 
phenomena.  For example I had a WiFi+5-port 100BASE-TX Ethernet bridge 
which stopped talking to one particular device, a 10BASE-T to 10BASE2 
media converter/repeater regardless of the port it was wired to; IIRC 
frame reception worked, but transmission did not make it through.

 It cost me a lot of hair pulling to sort it, including actually buying a 
brand new identical media converter, the first suspect, as it was the only 
device that caused the bridge to exhibit its odd behaviour.  Which did not 
help of course and the new device triggered exactly the same symptoms.

 Eventually it has turned out to be the bridge's PSU being on its way out. 
It was one of those nasty plug top PSUs that are not worth even looking 
inside, and just replacing it with a new one (which of course cost more 
than the bridge combined with its PSU originally did!) cured the problem.  
Out of 4 such bridges I bought ~15 years ago 3 are still in service, but 
all their PSUs had to be replaced.  At least they had a standard connector 
for the power plug (the newer replacement devices don't anymore, sigh).

 The 4th bridge, the same that caused problems, started having more issues 
with its wired ports later on if more than 2 devices were plugged IIRC, 
with no clear reason except for suspision of a power deficit, so I put it 
aside with a plan to recap it and see whether it helps (this discussion 
just reminded me about it, so maybe I'll try doing it over the coming 
weekend as I have since got the parts required).

 And it was just one of many incidents I had with PSUs playing tricks, so 
the PSU is now my first and primary suspect if a device misbehaves in a 
way that cannot be clearly attributed to a software bug (which is by far 
the most common case nowadays, a clear sign of a generation change to me).

  Maciej

Re: DEC H7822 power supply

[Maciej W. Rozycki via cctalk]

On Wed, 11 May 2022, Paul Koning wrote:

> > I guess especially for standard capacitors factories ordered whatever was 
> > readily available whereas with the high-ripple low-impedance/ESR parts the 
> > choice was much more limited.
> 
> I wonder if nowadays a good replacement for the case where low ESR is 
> needed would be a big ceramic capacitor.  Unlike the old days those now 
> can be had in many-µF capacitances.

 Possibly, in the lower capacitance range, if not for the horrendous 
price, e.g. $50/£40 each for a 470µF/25V part: 



(at least you get free shipping for just one piece).  There's still little 
choice for the higher range parts found in DEC PSUs, such as 1800µF/25V, 
4700µF/10V or 6800µF/20V even.  With aluminium organic polymer capacitors 
rated voltage also quickly drops for higher capacitances, so you won't get 
any of these as replacements either.  I don't know offhand to what extent 
these limitations come from current technology vs the laws of physics.

  Maciej

Re: DEC H7822 power supply

[Toby Thain via cctalk]

On 2022-05-12 4:40 a.m., Christian Corti via cctalk wrote:

On Thu, 12 May 2022, Peter Coghlan wrote:
about it?  Maybe it would be more accurate to use terms like steady 
voltage

and alternating voltage? Alternating doesn't seem like that good a term


In German it's exactly like you suggest it. We say "Gleichspannung" (= 
constant/steady voltage) and "Wechselspannung" (=alternating voltage)


I also hate the English/American expression "inverter" for voltage 
converters, because really nothing is being inverted in any way.




Generating AC from DC _does_ always involve generation of "inverted" 
voltages relative to the input DC (AC has positive and negative cycles), 
so the term isn't really strange?



But hey, they still have inches and feet and ounzes (be they fluid or 
solid) and gallons, so what can I expect? ;-


Christian

Re: DEC H7822 power supply

[Toby Thain via cctalk]

On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:

It's hard to come up with suitable terms for this sort of stuff that
convey the meaning of what is going on.  I struggled with it for a while
and that was what I ended up with.

With the strict meaning of DC and AC being direct current and alternating
current and given that we are often talking about voltages rather than
currents, meanings are already getting stretched.  Besides, what's direct
about it?  Maybe it would be more accurate to use terms like steady voltage


Many textbooks (and wikipedia) define DC as "in one direction", which is 
accurate. There is no need to refer to voltage; DC is indeed descriptive 
of the _current_ not voltage. "Constant voltage" is not a synonym for 
"DC", although it is a subset of DC we frequently encounter.



and alternating voltage? Alternating doesn't seem like that good a term
either.  To me it suggests some sort of square wave switching very rapidly
between one extreme and another, not a nice lazy sine wave which is the
normally accepted meaning.


Likewise, alternating means "alternating direction".



Given the normal usage that has evolved for the terms DC and AC rather than
their dictionary definitions, I would suggest that the current that gets
passed by a rectifier has both a DC component and an AC component.  When


It does not, due to unidirectionality.


this mixture is fed into a transformer primary as in this case, the DC
component does not pass through from the primary to the secondary but the
AC component does.  Transformers only work on AC, right?

Or maybe it could equally be said that a transformer can be used to convert
pulsed DC to AC?
...
Regards,
Peter Coghlan.


Sent from my DEC Alphaserver 800

Wayne S wrote:


“ The ripple on the rectified 5V and 12V supplies gets transformed into an
isolated AC source for the 9V supply.  ”
Shouldn’t that be “pulsed DC” instead of “AC” as rectification
changes AC to DC ?


Sent from my iPhone


On May 11, 2022, at 01:36, Peter Coghlan via cctalk  
wrote:

The ripple on the rectified 5V and 12V supplies gets transformed into an
isolated AC source for the 9V supply.

RE: DEC H7822 power supply

[Peter Coghlan via cctalk]

>
> Wayne: AC DC  terminology has been well documented since the 1800's. 
> Don't try to reinvent the terms or no one will know what you are talking 
> about.
> I answered a few things below...
> 

They didn't have switch mode power supplies in the 1800s.  Terms like AC and
DC as understood back then can be used to describe what goes in to and comes
out of this power supply but they are not ideal for describing what's going
on in the middle of it.

It seems like an unusual sort of design to me.  I haven't come across the
idea of extracting ripple from one output and using it to create another
output before.  It took me a long time to figure out what was going on.
Maybe it is a common thing to do and I haven't seen it because of my
lack of experience with this sort of thing?  Could anyone who is more
familiar with switch mode power supplies comment?  Anyway, I was just
trying to describe what I've seen. 

>
> Wayne: Alternating Current  is a continuously varying sine wave. The polarity
> does reverse over time.  Perhaps Alternating Current isn't a good term and
> should be Alternating voltage instead but AC is the terminology and it
> describes the form of the wave. Is basically says that there is a zero to
> positive component and a zero to negative component of the voltage as 
> measured over time in 2 half waves
>

Ok. I doubt we will find many true sine waves inside this power supply though.

>
> Wayne:  There is no AC component.  The output from a rectifier is pulsed DC,
> either half wave or full wave. An additional circuit after the rectifier
> provides the smoothing to provide nearly pure DC. Nearly pure meaning the
> voltage remains constant and does not drop much when measured over time.
> The most pure DC source is a battery.  Transformers work on AC or Pulsed DC.
>

It depends on your definition of AC component.  How about we say the output
of a rectifier consists of a steady component plus a varying component?
I guess you could call it pulsed DC if you want.  Whatever it is, when you
put it through a transformer, what you get out the other side will have a
varying component and no steady component.  The output of the transformer
is probably vaguely sinusoidal because the performance of the core is likely
to fall off as frequency rises.  It could be described as AC.  It could not
be described as pulsed DC.  

>
> Wayne: There is no negative component of Pulsed DC so no AC.
>

As before, how about we call it a steady component plus a varying component?

>
> Wayne.  Lotta good text on this out there. Basically a variable current
> induced through a wire generates a magnetic field. Any wire placed next
> to it, has that field induced in it as well.  The catch is that the field
> has to pulse or alternate to keep generating the field and being induced
> into the other wire. It's the movement IE the up and down motion of the 
> voltage that causes the field to be induced in the other wire.
>

In a transformer, it is the variation of the current in one wire which
creates a varying magnetic field which induces a current in the other wire.

>
> Wayne:  I just got an Dec AlphaStation 200. Look like its running NT though. 
>

It's probably ok but check the power supply for leaky capacitors!
Have a look around for batteries that might leak while it was/is in
storage too!

>
> >
> > “ The ripple on the rectified 5V and 12V supplies gets transformed 
> > into an isolated AC source for the 9V supply.  ”
> > Shouldn’t that be “pulsed DC” instead of “AC” as rectification
> > changes AC to DC ?
>

No, it shouldn't.  What goes into the transformer could be described as
pulsed DC.  What comes out of the transformer cannot be described as pulsed DC.
It has a varying component and no steady component, therefore I described it
as AC.

Regards,
Peter Coghlan.

Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

Maciej W. Rozycki wrote:
> On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:
> 
>>  Anyway, the good news is that I think I have found the source of the
>> problem.  One of the capacitors used to filter the (DC?, pulsed DC?,
>> rippled DC?, biased AC?) supply to the 9V regulator is marked 330uF/25V.
>> It reads 6uF on the capacitance range on my multimeter.  This can't be
>> helping the cause.  It's not showing any signs of leakage but it's got
>> a brown sleeve and the same logo as the nasty, leaky SXF capacitors but
>> it is marked KME.  (I said there was only one capacitor in the filter
>> in a previous posting.  Originally I managed to spot a little 10uF/100V
>> capacitor but somehow failed to notice the chubbier 330uF/25V capacitor
>> completing a PI filter with a small choke...)
>
>  Likely just a general purpose capacitor.  I only have 2 330uF/25V 85°C 
> Nichicon SE parts listed for the H7821 (and I have a note about one PSU of 
> this kind having a 220uF/35V part in place of one of those too).  Also no 
> 100V parts at all, but 4 10uF/35V 105°C parts, either Teapo SE or Daewoo 
> RS.  Teapo SE and Chemi-con KME series are standard general purpose parts 
> and given the low temperature rating Nichicon SE are likely such as well.
> 
>  I guess especially for standard capacitors factories ordered whatever was 
> readily available whereas with the high-ripple low-impedance/ESR parts the 
> choice was much more limited.
> 

Hi Maciej,

I replaced the capacitor in question with a blue Nichicon SE of the same
value scavanged from another H7821 until I order some spares.  I now have
8.7V available on the 9V supply, a little less than I hoped for but it is
enough to make the internal thinwire tranceiver happy.  Now there is just
the seized fan to deal with.

Thanks again to you and Tony for leading me in the direction of the likely
source of this fault.  I would never have thought of looking in the power
supply to find it.

Regards,
Peter.

>
>   Maciej
>

Re: Who/what is Molecular Electronics Branch Electronic Technology Division

[ED SHARPE via cctalk]

YEP THAT IS  PART OF  TE PICTURE THX   ED#

In a message dated 5/12/2022 3:22:23 AM US Mountain Standard Time, 
cctalk@classiccmp.org writes: 
https://archive.computerhistory.org/resources/access/text/2018/11/102740473-05-01-acc.pdf

??

On Wed, May 11, 2022 at 3:08 AM ED SHARPE via cctalk
 wrote:
>
> Were did you find that reference. Gavin?
>
> Sent from the all new AOL app for Android
>
>  On Tue, May 10, 2022 at 5:02 PM, Gavin Scott wrote:  
>Perhaps: "Molecular Electronics Branch, Electronic Technology
> Division, Air Force Avionics Laboratory, Wright-Patterson Air Force
> Base, Ohio."
>
> On Tue, May 10, 2022 at 5:31 PM ED SHARPE via cctalk
>  wrote:
> >
> > Who/what is Molecular Electronics Branch Electronic Technology Division 
> > thanks Ed#
> >
> > Sent from the all new AOL app for Android
>


-- 
-Jon
+44 7792 149029 

Re: Who/what is Molecular Electronics Branch Electronic Technology Division

[Jonathan Katz via cctalk]

https://archive.computerhistory.org/resources/access/text/2018/11/102740473-05-01-acc.pdf

??

On Wed, May 11, 2022 at 3:08 AM ED SHARPE via cctalk
 wrote:
>
> Were did you find that reference. Gavin?
>
> Sent from the all new AOL app for Android
>
>   On Tue, May 10, 2022 at 5:02 PM, Gavin Scott wrote:   
> Perhaps: "Molecular Electronics Branch, Electronic Technology
> Division, Air Force Avionics Laboratory, Wright-Patterson Air Force
> Base, Ohio."
>
> On Tue, May 10, 2022 at 5:31 PM ED SHARPE via cctalk
>  wrote:
> >
> > Who/what is Molecular Electronics Branch Electronic Technology Division 
> > thanks Ed#
> >
> > Sent from the all new AOL app for Android
>


-- 
-Jon
+44 7792 149029

Re: DEC H7822 power supply

[Christian Corti via cctalk]

On Thu, 12 May 2022, Peter Coghlan wrote:

about it?  Maybe it would be more accurate to use terms like steady voltage
and alternating voltage? Alternating doesn't seem like that good a term


In German it's exactly like you suggest it. We say "Gleichspannung" (= 
constant/steady voltage) and "Wechselspannung" (=alternating voltage)


I also hate the English/American expression "inverter" for voltage 
converters, because really nothing is being inverted in any way.


But hey, they still have inches and feet and ounzes (be they fluid or 
solid) and gallons, so what can I expect? ;-


Christian