Re: Atari PSU with collapsing 5V rail

[Adrian Graham via cctalk]

> On 20 Aug 2017, at 23:20, Chuck Guzis via cctalk  
> wrote:
> 
> On 08/20/2017 12:12 PM, Brent Hilpert via cctalk wrote:
> 
>> If the transformer were faulty and heating up internally, it would seem 
>> unlikely that it would cool off that quickly to recover, IME it takes some 
>> time for a transformer to cool off.
> 
> I have an open-frame linear PSU that started behaving that way.  Turned
> out to be a current-sense resistor with a bad internal connection.  As
> things warmed up, the resistance would rise until the current overload
> IC kicked it and shut things down.   It was pretty frustrating because
> the entire time, the output looked pretty stable.

Dammit. Spoke too soon. The machine ran for over an hour happily Bubble 
Bobbling so I swapped the disk for Super Sprint and 5V started disappearing on 
me. I turned it off for a minute and it came back to life and ran for another 
few minutes steady at 5.4V again. 

Back to jury-rigging I guess.

—
Adrian/Witchy
Binary Dinosaurs - Celebrating Computing History from 1972 onwards

Re: Atari PSU with collapsing 5V rail

[Adrian Graham via cctalk]

> On 20 Aug 2017, at 23:20, Chuck Guzis via cctalk  
> wrote:
> 
> On 08/20/2017 12:12 PM, Brent Hilpert via cctalk wrote:
> 
>> If the transformer were faulty and heating up internally, it would seem 
>> unlikely that it would cool off that quickly to recover, IME it takes some 
>> time for a transformer to cool off.
> 
> I have an open-frame linear PSU that started behaving that way.  Turned
> out to be a current-sense resistor with a bad internal connection.  As
> things warmed up, the resistance would rise until the current overload
> IC kicked it and shut things down.   It was pretty frustrating because
> the entire time, the output looked pretty stable.

Chuck wins some 16-bit air, or I suppose technically 16/32 bit air. I changed 
the reference resistors to the NE5561N and the PSU is now stable, no picture 
drift on the monitor and the 5V rail doesn’t move from 5.4V. If I could send an 
e-beer I would :)

http://www.binarydinosaurs.co.uk/atariSTPSUfixed.jpg

(dodgy disk in the A drive there, it’s currently running Bubble Bobble)


—
Adrian/Witchy
Binary Dinosaurs - Celebrating Computing History from 1972 onwards

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

[Brent Hilpert via cctalk]

On 2017-Aug-21, at 8:46 AM, Dominique Carlier via cctalk wrote:

>> As is typical for power supplies of this type and era, this power supply 
>> includes current limiting circuitry.
>> 
>> The current-limiting circuitry will throttle down the output voltage (not 
>> shut it off completely) as the output current draw goes above a design limit.
>> This would appear to fit the symptoms you describe.
>> 
>> The current-limiting circuitry works by placing a small-value resistor in 
>> the current path after the main regulator transistor(s) (aka pass 
>> transistors) but prior to the voltage-regulation sense point.
>> A transistor senses the voltage across this R.
>> As the output current increases, the voltage across the current-sense R 
>> increases, at some point the transistor starts to turn on, and the 
>> transistor is connected in such a way that as it turns on it reduces the 
>> drive to the pass transistors, throttling down the output voltage.
>> 
>> Arbitrarily using the "A2" heatsink half of the two +5 supplies in this 
>> power supply for component references, the current-sense R is comprised of a 
>> series-parallel circuit formed by the BE junctions of the 2 pass transistors 
>> (A2.Q1, A2.Q2), the two 0.1ohm Rs on the emitters of the pass transistors 
>> (A3.R10,A3.R11), the 47ohm Rs between B of those transistors, A3.R23, 
>> A3A1A1.R8, 376.R9, along with additional influence by 376.R8 and A3A1A1.R10.
>> The current sense transistor is inside the LM376 (see internal schematic), 
>> 376.Q16 between pins 1 & 8, controlling the 1st-stage driver transistor 
>> 376.Q14.
>> 
>> There are various things that could go wrong on this circuitry.
>> Anything that upsets the current-sense resistance network to cause the net R 
>> to increase will lower the output current that can be drawn (that is, the 
>> current limiting circuitry will start kicking in too 'early').
>> 
>> A likely scenario is one of the pass transistors has failed open.
>> This would take out a parallel leg of the current-sense resistance.
>> All current would  be forced through the good pass transistor and it's 
>> emitter resistor, raising the current-sense voltage for a given output 
>> current.
>> The current-limiting circuitry would kick in at a lower current than the 
>> design intention.
>> This is beneficial inasmuch as it would work to save the good pass 
>> transistor.
>> 
>> The 0.1 ohm 9W emitter resistors are critical, although they're probably 
>> wirewound and fairly reliable unless quite overstressed.
>> One of these resistors being open would result in the same operation as an 
>> open pass transistor.
>> You'll have difficulty measuring them with accuracy but you could do some 
>> sanity checks for continuity around both the pass transistor circuit legs,
>> as well as checking the pass transistor BC/BE junctions.
>> 
>> (In principle, the 'proper' thing to do in this area is look at what the 
>> current-sense voltage is doing, but that requires knowing what the target V 
>> is. Could compare with the other half of the supply.)
>> 
>> None of this is to suggest this area is necessarily at fault, or rule out 
>> other areas of the supply.
>> 
>> Another possible fault that would fit the symptom (decreasing voltage as 
>> current draw increases, if that's what's going on) is inadequate (partially 
>> failed) drive to the pass transistors.
>> In short, anything reducing the power gain of the regulator error amplifier 
>> could produce this symptom.
>> 

> 
> Also following the suggestions of Curious Marc, I focus now on the comparison 
> between the two almost identical circuits that deliver the regulated + 5V on 
> G2.
> 
> Following your explanations, I started by checking the transistors and 
> resistors on the heatsinks A1 and A2, and also checking the resistors of 0.1 
> Ω (R10 to R13)
> 
> http://www.zeltrax.com/classiccmp_forum/psu_g2_test/cheked.jpg
> 
> But first I see on the schematic that these transistors are supposed to be 
> "2N6254", but I see on A1 and A2 that the 4 transistors are "7540" (full 
> name: POWER PHYSICS 001554 7540), I do not find The datasheet of this model.
> 
> http://www.zeltrax.com/classiccmp_forum/psu_g2_test/serie_pass_transistor.jpg
> 
> The results of the test on the pass transistors:
> By doing the various checks between B E C for NPN transistor, no problems. No 
> unwanted open or closed circuit at wrong place.
> However if I measure the value between B and E, on all the transistors I read 
> + - 0.510 except for one where it is + -0.440, it is Q2 on A1 which is 
> precisely the board that delivers the + 5V which collapse. Is this transistor 
> defective?
> 
> The small resistances which are between the bases and collectors of each 
> transistors all show + -50 Ω (they are supposed to be 47 Ω but I imagine it's 
> OK like that)
> But about R10, R11, R12 and R13, these resistors are supposed to be have a 
> value of 0.1 Ω , right?
> Because for these 4 resistors I read values 

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

[Dominique Carlier via cctalk]

Because I had removed every wires to test transistors on A1 and A2, and 
since I have to buy 4 new 0.1ohm resistors and an equivalent of 2N6254, 
in the meantime because they are identical I decided to interchange A1 
and A2, I was hoping note a +5V collapsed on the other output but no, it 
is always the same output which is in default, the one that is 
associated with A1. It is therefore possible that the problem is not at 
the level of these series pass transistors.


Maybe Q2 on the regulator board ?


On 20/08/2017 09:25, Brent Hilpert via cctalk wrote:

On 2017-Aug-20, at 12:08 AM, Brent Hilpert via cctalk wrote:

On 2017-Aug, at 12:10 PM, Dominique Carlier via cctalk wrote:

Question: a faulty voltage regulator can behave in this way? I always thought 
it worked or it did not work, but not between the two states depending on the 
charge.

(In answer to the question, yes, a faulty regulator can produce 'in-between' 
output voltage.)


Should modify that answer a little: a regulator like this can, not just if 
faulty, but also by design intention, produce an 'in-between' output voltage, 
as per the functioning of the current-limit circuitry.

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

[Dominique Carlier via cctalk]

Hello,

Yes, it is a "Fluke 73" maybe not enough accurate for that kind of 
measurements ?



On 21/08/2017 18:53, Anders Nelson via cctalk wrote:

Hi Dominique,

Are you using a standard DMM to make your resistance measurements? If not,
you may have more consistent results by using a laboratory DMM that is
rated to measure milliohms.

On Mon, Aug 21, 2017 at 11:47 AM Dominique Carlier via cctalk <
cctalk@classiccmp.org> wrote:


Thank you very much for these valuable detailed information! :-)

Also following the suggestions of Curious Marc, I focus now on the
comparison between the two almost identical circuits that deliver the
regulated + 5V on G2.

Following your explanations, I started by checking the transistors and
resistors on the heatsinks A1 and A2, and also checking the resistors of
0.1 Ω (R10 to R13)

http://www.zeltrax.com/classiccmp_forum/psu_g2_test/cheked.jpg

But first I see on the schematic that these transistors are supposed to
be "2N6254", but I see on A1 and A2 that the 4 transistors are "7540"
(full name: POWER PHYSICS 001554 7540), I do not find The datasheet of
this model.


http://www.zeltrax.com/classiccmp_forum/psu_g2_test/serie_pass_transistor.jpg

The results of the test on the pass transistors:
By doing the various checks between B E C for NPN transistor, no
problems. No unwanted open or closed circuit at wrong place.
However if I measure the value between B and E, on all the transistors I
read + - 0.510 except for one where it is + -0.440, it is Q2 on A1 which
is precisely the board that delivers the + 5V which collapse. Is this
transistor defective?

The small resistances which are between the bases and collectors of each
transistors all show + -50 Ω (they are supposed to be 47 Ω but I imagine
it's OK like that)
But about R10, R11, R12 and R13, these resistors are supposed to be have
a value of 0.1 Ω , right?
Because for these 4 resistors I read values ​​ranging from 0.2 to 0.4 Ω!

http://www.zeltrax.com/classiccmp_forum/psu_g2_test/resistor_check.jpg

Strange thing, today I take the measurements again (with two different
multi-meters to be sure) and the values ​​today are different, located
between 0.8 and 1 Ω !! I do not understand this variation, I had
unwrapped only one leg, I removed both now, same type of result: 0.9 Ω !

Unfortunately because these 4 resistors are in the same state, these are
probably not the cause of the collapsed +5V only on the side of A1, What
is your opinion about that?
Anyway, I'm going to change those resistors for sure. I will also change
the transistor which only passes 0.44 instead of 0.52, I intend to put
an equivalent of 2N6254 hoping that the actual 7540 are also an
equivalent of the 2N6254 mentioned in the schematics.

Thanks a lot for your help !

Dominique

On 20/08/2017 09:08, Brent Hilpert wrote:

On 2017-Aug-19, at 12:10 PM, Dominique Carlier via cctalk wrote:

Maybe it's better to give us all the useful information these power

supplies, moreover it might be useful to other people with the same
computer.

An overall bloc diagram of the D-116 power supply including G1 and G2.
http://www.zeltrax.com/classiccmp_forum/psu_overall_bloc_diagram.jpg

The complete schematics of the part of the power supply named G2.
http://www.zeltrax.com/classiccmp_forum/g2_schematics.jpg

A drawing of the regulation board of the power supply G2 with the

physical locations of the components.

http://www.zeltrax.com/classiccmp_forum/g2_regulator_board.jpg

The schematics of this regulation board.


http://www.zeltrax.com/classiccmp_forum/g2_regulator_board_schematics.jpg

And a bit of literature concerning the principle of operation about the

regulation with this PSU (you will understand better why I am a little bit
lost ;-) This principle of regulation with a panoply of verification and
Protection systems everywhere is unusual for me)

http://www.zeltrax.com/classiccmp_forum/psu_regulation_principe.jpg

I have already tried without the CPU board: same symptoms. Next step,

try to check the capacitors in operation.

Results of the observations:
- This is definitely the regulated +5V of the G2 power supply. More I

add boards more the + 5v level goes down. +5v, +4.8v, +3.6v, +2.9v. It
remains stable however with just the CPU and the three core memory boards,
it becomes difficult for the power supply when I add boards in addition to
these.

- This is definitely not a problem at the level of the Power Fail

circuit.

- The big capacitors are not in fault (I rechecked twice).
- So this maybe a problem at the level of the regulation itself, the

+5V balancing system ?

Question: a faulty voltage regulator can behave in this way? I always

thought it worked or it did not work, but not between the two states
depending on the charge.

(In answer to the question, yes, a faulty regulator can produce

'in-between' output voltage.)

As is typical for power supplies of this type and era, this power supply

includes current limiting circuitry.

The current-limiting 

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

[Anders Nelson via cctalk]

Hi Dominique,

Are you using a standard DMM to make your resistance measurements? If not,
you may have more consistent results by using a laboratory DMM that is
rated to measure milliohms.

On Mon, Aug 21, 2017 at 11:47 AM Dominique Carlier via cctalk <
cctalk@classiccmp.org> wrote:

>
> Thank you very much for these valuable detailed information! :-)
>
> Also following the suggestions of Curious Marc, I focus now on the
> comparison between the two almost identical circuits that deliver the
> regulated + 5V on G2.
>
> Following your explanations, I started by checking the transistors and
> resistors on the heatsinks A1 and A2, and also checking the resistors of
> 0.1 Ω (R10 to R13)
>
> http://www.zeltrax.com/classiccmp_forum/psu_g2_test/cheked.jpg
>
> But first I see on the schematic that these transistors are supposed to
> be "2N6254", but I see on A1 and A2 that the 4 transistors are "7540"
> (full name: POWER PHYSICS 001554 7540), I do not find The datasheet of
> this model.
>
>
> http://www.zeltrax.com/classiccmp_forum/psu_g2_test/serie_pass_transistor.jpg
>
> The results of the test on the pass transistors:
> By doing the various checks between B E C for NPN transistor, no
> problems. No unwanted open or closed circuit at wrong place.
> However if I measure the value between B and E, on all the transistors I
> read + - 0.510 except for one where it is + -0.440, it is Q2 on A1 which
> is precisely the board that delivers the + 5V which collapse. Is this
> transistor defective?
>
> The small resistances which are between the bases and collectors of each
> transistors all show + -50 Ω (they are supposed to be 47 Ω but I imagine
> it's OK like that)
> But about R10, R11, R12 and R13, these resistors are supposed to be have
> a value of 0.1 Ω , right?
> Because for these 4 resistors I read values ​​ranging from 0.2 to 0.4 Ω!
>
> http://www.zeltrax.com/classiccmp_forum/psu_g2_test/resistor_check.jpg
>
> Strange thing, today I take the measurements again (with two different
> multi-meters to be sure) and the values ​​today are different, located
> between 0.8 and 1 Ω !! I do not understand this variation, I had
> unwrapped only one leg, I removed both now, same type of result: 0.9 Ω !
>
> Unfortunately because these 4 resistors are in the same state, these are
> probably not the cause of the collapsed +5V only on the side of A1, What
> is your opinion about that?
> Anyway, I'm going to change those resistors for sure. I will also change
> the transistor which only passes 0.44 instead of 0.52, I intend to put
> an equivalent of 2N6254 hoping that the actual 7540 are also an
> equivalent of the 2N6254 mentioned in the schematics.
>
> Thanks a lot for your help !
>
> Dominique
>
> On 20/08/2017 09:08, Brent Hilpert wrote:
> > On 2017-Aug-19, at 12:10 PM, Dominique Carlier via cctalk wrote:
> >> Maybe it's better to give us all the useful information these power
> supplies, moreover it might be useful to other people with the same
> computer.
> >>
> >> An overall bloc diagram of the D-116 power supply including G1 and G2.
> >> http://www.zeltrax.com/classiccmp_forum/psu_overall_bloc_diagram.jpg
> >>
> >> The complete schematics of the part of the power supply named G2.
> >> http://www.zeltrax.com/classiccmp_forum/g2_schematics.jpg
> >>
> >> A drawing of the regulation board of the power supply G2 with the
> physical locations of the components.
> >> http://www.zeltrax.com/classiccmp_forum/g2_regulator_board.jpg
> >>
> >> The schematics of this regulation board.
> >>
> http://www.zeltrax.com/classiccmp_forum/g2_regulator_board_schematics.jpg
> >>
> >> And a bit of literature concerning the principle of operation about the
> regulation with this PSU (you will understand better why I am a little bit
> lost ;-) This principle of regulation with a panoply of verification and
> Protection systems everywhere is unusual for me)
> >> http://www.zeltrax.com/classiccmp_forum/psu_regulation_principe.jpg
> >>
> >> I have already tried without the CPU board: same symptoms. Next step,
> try to check the capacitors in operation.
> >>> Results of the observations:
> >>> - This is definitely the regulated +5V of the G2 power supply. More I
> add boards more the + 5v level goes down. +5v, +4.8v, +3.6v, +2.9v. It
> remains stable however with just the CPU and the three core memory boards,
> it becomes difficult for the power supply when I add boards in addition to
> these.
> >>> - This is definitely not a problem at the level of the Power Fail
> circuit.
> >>> - The big capacitors are not in fault (I rechecked twice).
> >>> - So this maybe a problem at the level of the regulation itself, the
> +5V balancing system ?
> >>>
> >>> Question: a faulty voltage regulator can behave in this way? I always
> thought it worked or it did not work, but not between the two states
> depending on the charge.
> > (In answer to the question, yes, a faulty regulator can produce
> 'in-between' output voltage.)
> >
> > As is typical for power 

Various Software and Documentation for shipping + donations (round 8)

[Tapley, Mark via cctalk]

All,
More of the stack. if any of this interests you please contact me via 
Private (not list) email at mtap...@swri.edu.

If you do want something, send me your shipping address and exactly 
what you want. I'll get back to you with estimated shipping costs (USPS media 
rate where possible) as soon as I can. You send me payment (any method is 
acceptable; USPS does not recommend cash in the mail) and I will ship when 
payment arrives. If you want Fed-Ex or something different from USPS media let 
me know at your first contact and I will price that for you. If you can afford 
to send slightly more than costs, I'll collect up the surplus for Cindy and get 
it to her.
If more than one person wants the same thing, it goes to the person 
sending me the earliest time-tagged email. 
If Al K. wants anything for Bitsavers, he gets priority (even if his is 
not the first email) up until it leaves my hands.

There will be multiple sets of email from me, hopefully at a faster 
cadence, each with a short list of things, unless/until someone asks me to 
quit. 

Thanks for your attention!

- Mark

———

Cheyenne Bitware for Windows version 3.3 fax/data/voice (2 3.5" disks)
User's Guide and disks in a ziplock bag

185x(L) soundcard driver for Win NT 4.0 Version 2.00.03 (3.5" disk)

DesignCAD 2D Demo (3.5" disk)
(to install, enter A:INSTALL, indicates DOS)

Microsoft Works Word Processing Conversion program and supplemental Setup 3 
(1987-89) (3.5" disk)

S3 Trio64V+ version 3.1 (2 3.5" disks)
installation diskette for Windows, DOS
OS/2 driver

Mediamatics MPEG Arcade player (3.5" disk)

Toshiba America information systems technical notes for ATAPI CD-ROM (Oct 1996)
leaflet only

US English Medical Dictionary for use with Spellfinder 7.51.13 for windows 
(1993) (5.25" disk)

Radio Shack 5.25" disk (5 disks)

Timeworks Personal Computer Software Data Manager 2 with Report Writer 
(Commodore 64/128, 5.25" disks)
Miscellaneous paperwork
Data diskette 
No manual?

Disk Guard Complete Hard Disk Protection for Mac OS 7.5.3 or higher by ASD 
(3.5" disk)
not opened

Concentric Data Systems R Report Writer for DOS, XBase edition (1992) (2 x 
3.5" disks, 2 x 5.25" disks)
unopened disks
Getting Started manual, shrink-wrapped
Using R Version 5.0 (2 copies)

Re: Atari PSU with collapsing 5V rail

[Jules Richardson via cctalk]

On 08/21/2017 10:06 AM, Chuck Guzis via cctalk wrote:

Well, to throw some kerosene on the fire, this from Wikipedia:


:-)


"According to etymologist Jan Freeman, the story that duct tape was
originally called duck tape is "quack etymology" that has spread "due to
the reach of the Internet and the appeal of a good story" but "remains a
statement of faith, not fact."  She notes that duct tape is not made from
duck cloth and there is no known primary-source evidence that it was
originally referred to as duck tape. Her research does not show any use
of the phrase "duck tape" in World War II, and indicates that the
earliest documented name for the adhesive product was "duct tape" in
1960.


This kind of stuff is fascinating. I wonder what was used for sealing ducts 
prior to WWII? Despite a lack of written evidence I do think it's 
reasonable to assume that there were people during WWII calling an 
adhesive-covered duck cloth product "duck tape" though - and that "duct 
tape" as a term didn't come into use until much later (and yes, that at 
that point it wasn't a cloth-based product at all)



I prefer gaffer's tape to duct tape for most dry repairs.  Doesn't leave
a gooey mess behind when removed--and it's much stronger.


I agree about the gooey mess (although for actual duckwork the aluminum 
foil tape seems to work well) - although it does seem to be one of those 
cases where expensive duct tape is much better quality than the cheap stuff.


As an aside, I'm wondering if there's a difference between gaffer tape and 
hockey tape - they seem pretty much interchangeable to me, but maybe "good 
gaffer tape" is significantly stronger or something.


cheers

Jules

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

[Dominique Carlier via cctalk]

Thank you very much for these valuable detailed information! :-)

Also following the suggestions of Curious Marc, I focus now on the 
comparison between the two almost identical circuits that deliver the 
regulated + 5V on G2.


Following your explanations, I started by checking the transistors and 
resistors on the heatsinks A1 and A2, and also checking the resistors of 
0.1 Ω (R10 to R13)


http://www.zeltrax.com/classiccmp_forum/psu_g2_test/cheked.jpg

But first I see on the schematic that these transistors are supposed to 
be "2N6254", but I see on A1 and A2 that the 4 transistors are "7540" 
(full name: POWER PHYSICS 001554 7540), I do not find The datasheet of 
this model.


http://www.zeltrax.com/classiccmp_forum/psu_g2_test/serie_pass_transistor.jpg

The results of the test on the pass transistors:
By doing the various checks between B E C for NPN transistor, no 
problems. No unwanted open or closed circuit at wrong place.
However if I measure the value between B and E, on all the transistors I 
read + - 0.510 except for one where it is + -0.440, it is Q2 on A1 which 
is precisely the board that delivers the + 5V which collapse. Is this 
transistor defective?


The small resistances which are between the bases and collectors of each 
transistors all show + -50 Ω (they are supposed to be 47 Ω but I imagine 
it's OK like that)
But about R10, R11, R12 and R13, these resistors are supposed to be have 
a value of 0.1 Ω , right?

Because for these 4 resistors I read values ​​ranging from 0.2 to 0.4 Ω!

http://www.zeltrax.com/classiccmp_forum/psu_g2_test/resistor_check.jpg

Strange thing, today I take the measurements again (with two different 
multi-meters to be sure) and the values ​​today are different, located 
between 0.8 and 1 Ω !! I do not understand this variation, I had 
unwrapped only one leg, I removed both now, same type of result: 0.9 Ω !


Unfortunately because these 4 resistors are in the same state, these are 
probably not the cause of the collapsed +5V only on the side of A1, What 
is your opinion about that?
Anyway, I'm going to change those resistors for sure. I will also change 
the transistor which only passes 0.44 instead of 0.52, I intend to put 
an equivalent of 2N6254 hoping that the actual 7540 are also an 
equivalent of the 2N6254 mentioned in the schematics.


Thanks a lot for your help !

Dominique

On 20/08/2017 09:08, Brent Hilpert wrote:

On 2017-Aug-19, at 12:10 PM, Dominique Carlier via cctalk wrote:

Maybe it's better to give us all the useful information these power supplies, 
moreover it might be useful to other people with the same computer.

An overall bloc diagram of the D-116 power supply including G1 and G2.
http://www.zeltrax.com/classiccmp_forum/psu_overall_bloc_diagram.jpg

The complete schematics of the part of the power supply named G2.
http://www.zeltrax.com/classiccmp_forum/g2_schematics.jpg

A drawing of the regulation board of the power supply G2 with the physical 
locations of the components.
http://www.zeltrax.com/classiccmp_forum/g2_regulator_board.jpg

The schematics of this regulation board.
http://www.zeltrax.com/classiccmp_forum/g2_regulator_board_schematics.jpg

And a bit of literature concerning the principle of operation about the 
regulation with this PSU (you will understand better why I am a little bit lost 
;-) This principle of regulation with a panoply of verification and Protection 
systems everywhere is unusual for me)
http://www.zeltrax.com/classiccmp_forum/psu_regulation_principe.jpg

I have already tried without the CPU board: same symptoms. Next step, try to 
check the capacitors in operation.

Results of the observations:
- This is definitely the regulated +5V of the G2 power supply. More I add 
boards more the + 5v level goes down. +5v, +4.8v, +3.6v, +2.9v. It remains 
stable however with just the CPU and the three core memory boards, it becomes 
difficult for the power supply when I add boards in addition to these.
- This is definitely not a problem at the level of the Power Fail circuit.
- The big capacitors are not in fault (I rechecked twice).
- So this maybe a problem at the level of the regulation itself, the +5V 
balancing system ?

Question: a faulty voltage regulator can behave in this way? I always thought 
it worked or it did not work, but not between the two states depending on the 
charge.

(In answer to the question, yes, a faulty regulator can produce 'in-between' 
output voltage.)

As is typical for power supplies of this type and era, this power supply 
includes current limiting circuitry.

The current-limiting circuitry will throttle down the output voltage (not shut 
it off completely) as the output current draw goes above a design limit.
This would appear to fit the symptoms you describe.

The current-limiting circuitry works by placing a small-value resistor in the 
current path after the main regulator transistor(s) (aka pass transistors) but 
prior to the voltage-regulation sense point.
A transistor senses 

Re: Atari PSU with collapsing 5V rail

[Chuck Guzis via cctalk]

On 08/21/2017 07:32 AM, Jules Richardson via cctalk wrote:

> And if we're talking WWII, wasn't it duck tape? Duck cloth with an
> adhesive layer. "Duct tape" came later...
> 
> I wonder if we're being messed with ;-)

Well, to throw some kerosene on the fire, this from Wikipedia:

"According to etymologist Jan Freeman, the story that duct tape was
originally called duck tape is "quack etymology" that has spread "due to
the reach of the Internet and the appeal of a good story" but "remains a
statement of faith, not fact." She notes that duct tape is not made from
duck cloth and there is no known primary-source evidence that it was
originally referred to as duck tape. Her research does not show any use
of the phrase "duck tape" in World War II, and indicates that the
earliest documented name for the adhesive product was "duct tape" in
1960. The phrase "duck tape" to refer to an adhesive product does not
appear until the 1970s and was not popularized until the 1980s, after
the Duck brand became successful and after the New York Times referred
to and defined the product under the name "duct tape" in 1973"

I prefer gaffer's tape to duct tape for most dry repairs.  Doesn't leave
a gooey mess behind when removed--and it's much stronger.

--Chuck

Re: Atari PSU with collapsing 5V rail

[Jules Richardson via cctalk]

On 08/20/2017 01:57 PM, Mike Stein via cctalk wrote:

Well, if we're going to nitpick it's _baling_ wire as in tying up bales
of hay; bailing is for leaky boats.


And if we're talking WWII, wasn't it duck tape? Duck cloth with an adhesive 
layer. "Duct tape" came later...


I wonder if we're being messed with ;-)

RE: DEC VT125 on Schpock in Birmingham, UK

[Rob Jarratt via cctalk]

> -Original Message-
> From: hollo...@gmail.com [mailto:hollo...@gmail.com] On Behalf Of Pete
> Hollobon
> Sent: 21 August 2017 12:52
> To: r...@jarratt.me.uk
> Cc: General Discussion: On-Topic and Off-Topic Posts ;
> Paul Anderson 
> Subject: Re: DEC VT125 on Schpock in Birmingham, UK
> 
> On 20 August 2017 at 19:45, Rob Jarratt  wrote:
> >> -Original Message-
> >> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Rob
> >> Jarratt via cctalk
> >> Sent: 19 August 2017 23:33
> >> To: 'Paul Anderson' ; 'General Discussion:
> >> On-Topic and Off-Topic Posts' ; 'Pete Hollobon'
> >> 
> >> Subject: RE: DEC VT125 on Schpock in Birmingham, UK
> >>
> > Well, that didn't go too well.
> >
> > I made the offer of the asking price. I got no reply, no acknowledgement, no
> acceptance or rejection. Then today someone else made an offer which seems
> to have been accepted. When I asked why I had not even had a response I was
> told he wasn't prepared to wait for several weeks (I had said I might not be
> able to collect for a week or two), and I had not been given any opportunity 
> to
> discuss it. I could see he had accepted someone else's offer, and he then
> promptly asked me if I would beat his highest offer.
> >
> > After accepting someone's offer it doesn't seem too right to then ask if
> someone else will beat it. Perhaps not the kind of seller to deal with I 
> think.
> >
> > So, although I have wanted a VT125 for a long time, it looks like I am
> > not going to get one :-(
> >
> 
> Ugh. Sorry to hear that.
> 
> I've some success buying things with Schpock, but it is more like making a 
> best
> offer on a buy-it-now on eBay: until the other side accepts, it is just an 
> offer.
> There isn't an equivalent of a straight buy-it-now, any offer (even of asking
> price) is up for approval by the seller.
> 
> It looks like that guy sold it to someone else off Schpock anyway, presumably
> for more than the £55 he quoted you.
> 


I get the bit about the offers, but then he got to the point of saying he 
accepted the offer. *After* accepting the offer he asked me if I would beat the 
offer. That is the bit I found unacceptable.

Regards

Rob

Re: DEC VT125 on Schpock in Birmingham, UK

[Pete Hollobon via cctalk]

On 20 August 2017 at 19:45, Rob Jarratt  wrote:
>> -Original Message-
>> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Rob Jarratt
>> via cctalk
>> Sent: 19 August 2017 23:33
>> To: 'Paul Anderson' ; 'General Discussion: On-Topic and
>> Off-Topic Posts' ; 'Pete Hollobon'
>> 
>> Subject: RE: DEC VT125 on Schpock in Birmingham, UK
>>
> Well, that didn't go too well.
>
> I made the offer of the asking price. I got no reply, no acknowledgement, no 
> acceptance or rejection. Then today someone else made an offer which seems to 
> have been accepted. When I asked why I had not even had a response I was told 
> he wasn't prepared to wait for several weeks (I had said I might not be able 
> to collect for a week or two), and I had not been given any opportunity to 
> discuss it. I could see he had accepted someone else's offer, and he then 
> promptly asked me if I would beat his highest offer.
>
> After accepting someone's offer it doesn't seem too right to then ask if 
> someone else will beat it. Perhaps not the kind of seller to deal with I 
> think.
>
> So, although I have wanted a VT125 for a long time, it looks like I am not 
> going to get one :-(
>

Ugh. Sorry to hear that.

I've some success buying things with Schpock, but it is more like
making a best offer on a buy-it-now on eBay: until the other side
accepts, it is just an offer. There isn't an equivalent of a straight
buy-it-now, any offer (even of asking price) is up for approval by the
seller.

It looks like that guy sold it to someone else off Schpock anyway,
presumably for more than the £55 he quoted you.

Pete.