Re: Resistor/Fuse replacement (DEC H7104-D)

[Mattis Lind]

2016-03-22 20:47 GMT+01:00 Noel Chiappa :

> > From: Josh Dersch
>
> > I have no excuse, I just get nervous working on these things.
>
> I should hope you do get nervous! Anytime one is working around equipment
> that
> contains lethal voltages, one _should_ be nervous! It helps with...
>

Don't work with lethal voltages! Use a insulation transformer. Then it is
not as likely to kill you unless you brake the rule and put both your hands
in the supply. Then use a variac. My experience is that you can observe the
behaviour at a much lower voltage when the load is small. This supply if I
remember correctly will work fine from 60 VDC at the input caps.

I do this all the time. I am not nervous when putting the scope-probe on
anything in there.

One more thing regarding the H7104. The circuit that enables the relay will
also enable the signal to the main chopper transistors. Thus there will be
no switching at all unless the input voltage is above 250VDC or so. I
disabled this circuit for testing purposes. As long as the load is small
this should not cause any problems. (And since I tested I know it didn't)

>
> > I suppose eventually I'll get used to it.
>
> Don't get too used to it, one wants to always be aware and cautious!
>
> (I myself am missing half a nail - and I'm lucky that's all that's missing
> -
> because I got too "used to" working with my table saw...)
>
> Noel
>

/Mattis

Re: Resistor/Fuse replacement (DEC H7104-D)

[Noel Chiappa]

> From: Josh Dersch

> I have no excuse, I just get nervous working on these things.

I should hope you do get nervous! Anytime one is working around equipment that
contains lethal voltages, one _should_ be nervous! It helps with...

> I suppose eventually I'll get used to it.

Don't get too used to it, one wants to always be aware and cautious!

(I myself am missing half a nail - and I'm lucky that's all that's missing -
because I got too "used to" working with my table saw...)

Noel

Re: Resistor/Fuse replacement (DEC H7104-D)

[Josh Dersch]

On Tue, Mar 22, 2016 at 12:29 AM, Mattis Lind  wrote:

> >>> Good news - mine worked so fingers crossed for yours too. I now have a
> >> functioning PSU again though I've not tried it back in the chassis
> yet...
> >>
> >> Nice!  My replacements arrived today and unfortunately I did not have
> > such good luck.  No smoke or fire, but now I get nothing at all out of
> the
> > supply.  The whine is gone, but there's nothing output at all.  The
> > fuse/resistor didn't blow (it's still got continuity across it) and the
> > transistor I replaced is still fine, but there must be something else in
> > the supply that's causing issues...
> >
> > Blargh.  I hate working on power supplies.
>
>
> In this case you have an excellent technical manual and a good schematic
> which should help a lot. Working with big SMPSU without schematics or
> technical manuals is a not fun.
>

Yeah, I have actual original copies of the printsets, too.  I have no
excuse, I just get nervous working on these things.  I suppose eventually
I'll get used to it.


>
> So here is my piece of advice directly from my head.
>
> 1. The PSU has really two AC inputs wired together in the input harness.
> You can separate the startup supply part from the SMPSU part. Connect the
> startup PSU to a separate AC input and the SMPSU part to a insulation
> transformer, a variac and lightbulb in series.

2. Check that the startup PSU, that uses a normal 50/60 Hz transformer
> gives the correct voltage. +11 if I remember correctly.
> 3. There is a circuit that monitors the input rectified 300VDC voltage and
> enables the relay when it has reached a proper voltage. It is a soft start.
> Disable it for temporarily. Good idea to check that is working though. If
> not the soft start resistors will become overheated when trying to run it
> at full load.
>

The relay (and the circuit driving it) appears to be working -- I hear it
click on at power-up (faintly, over the roar of the fans) and click again
after power-down.  I'll hopefully have some time this week to play around
some more, thanks for the suggestions!

I'll note that my earlier statement that I was getting "nothing" out of the
supply turns out to be slightly inaccurate -- with a load, I get nothing
(well, 0.07v) out of the 5V supply; without a load the voltage slowly
increases (maybe 0.5V per second).  Didn't let it run long enough to see
where it ends up ;).

Thanks again,
Josh




> 4. Now you need to have the SMPSU section connected to AC inlet. On one of
> the daughter boards there is a switching bias supply. Check that it
> generates the +/-12 V and +5V.
> 5. Is the main SMPSU switching logic making a nice square wave signal
> output. The control board is yet another daughter board.
> 6. I disconnected the output terminals from the H-bridge to the transformer
> and connected a dummy load to be able to have a look at the output
> waveform.
> 7. Reconnect the transformer. The main switch produces +5V and +38V. The
> 38V is then used on the daughterboards to create all the other voltages,
> +/- 12V, +/- 15V, +12V SB, +5VSB (depending on which supply). Is there 38V
> here?
> 8. There is a crowbar circuit on the +5V output terminals. Check that it is
> not tripping.
>
>
> Please note that when working with the +2.5V supply it gets the bias
> voltages from the +5V supply. So either get that one working first or
> supply bias voltage from a regular PC supply.
>
> /Mattis
>
>
> >
> >
> > - Josh
> >
> >
>

Re: Resistor/Fuse replacement (DEC H7104-D)

[Vincent Slyngstad]

From: drlegendre: Monday, March 21, 2016 6:50 PM

I don't quite get what makes this DigiKey part suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".


I take "UL1412 recognised fusing" (sic) on the first line of the data sheet
to mean that they do market them that way.


One reason I question it, is the fact that the fusing ratings are only
plotted for like 40X or 50X expected current. Can the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?


I read a little over 1000 seconds to fuse at 10W, which is only a 
few times the 2W rating.  Admittedly, 20 minutes at 5X load 
amounts to a pretty slow fuse.  I can only assume their concern 
is fire prevention, rather than circuitry protection.


With regard to the suggestion of a fuse and a resistor, you'd 
need more room (likely not a problem), and a flameproof 
version of the resistor.  I don't know anything about UL 
ratings, so I don't know if that could be made OK there or 
not.


   Vince 

Re: Resistor/Fuse replacement (DEC H7104-D)

[Mattis Lind]

>>> Good news - mine worked so fingers crossed for yours too. I now have a
>> functioning PSU again though I've not tried it back in the chassis yet...
>>
>> Nice!  My replacements arrived today and unfortunately I did not have
> such good luck.  No smoke or fire, but now I get nothing at all out of the
> supply.  The whine is gone, but there's nothing output at all.  The
> fuse/resistor didn't blow (it's still got continuity across it) and the
> transistor I replaced is still fine, but there must be something else in
> the supply that's causing issues...
>
> Blargh.  I hate working on power supplies.


In this case you have an excellent technical manual and a good schematic
which should help a lot. Working with big SMPSU without schematics or
technical manuals is a not fun.

So here is my piece of advice directly from my head.

1. The PSU has really two AC inputs wired together in the input harness.
You can separate the startup supply part from the SMPSU part. Connect the
startup PSU to a separate AC input and the SMPSU part to a insulation
transformer, a variac and lightbulb in series.
2. Check that the startup PSU, that uses a normal 50/60 Hz transformer
gives the correct voltage. +11 if I remember correctly.
3. There is a circuit that monitors the input rectified 300VDC voltage and
enables the relay when it has reached a proper voltage. It is a soft start.
Disable it for temporarily. Good idea to check that is working though. If
not the soft start resistors will become overheated when trying to run it
at full load.
4. Now you need to have the SMPSU section connected to AC inlet. On one of
the daughter boards there is a switching bias supply. Check that it
generates the +/-12 V and +5V.
5. Is the main SMPSU switching logic making a nice square wave signal
output. The control board is yet another daughter board.
6. I disconnected the output terminals from the H-bridge to the transformer
and connected a dummy load to be able to have a look at the output waveform.
7. Reconnect the transformer. The main switch produces +5V and +38V. The
38V is then used on the daughterboards to create all the other voltages,
+/- 12V, +/- 15V, +12V SB, +5VSB (depending on which supply). Is there 38V
here?
8. There is a crowbar circuit on the +5V output terminals. Check that it is
not tripping.


Please note that when working with the +2.5V supply it gets the bias
voltages from the +5V supply. So either get that one working first or
supply bias voltage from a regular PC supply.

/Mattis


>
>
> - Josh
>
>

Re: Resistor/Fuse replacement (DEC H7104-D)

[Chuck Guzis]

On 03/21/2016 07:34 PM, dwight wrote:

Maybe a real fuse in series with a real resistor.


I'd asked that, but reconsidered in that fusible resistors all seem to 
have a strong positive temperature coefficient and then a point at which 
they will fuse.


IOW, the things degrade gradually before going ka-pow; something not 
realized with a resistor+fuse combination.


See, for example:

http://www.vishay.com/docs/28737/nfr25.pdf

--Chuck

Re: Resistor/Fuse replacement (DEC H7104-D)

[dwight]

Maybe a real fuse in series with a real resistor.
Dwight



From: cctalk <cctalk-boun...@classiccmp.org> on behalf of drlegendre . 
<drlegen...@gmail.com>
Sent: Monday, March 21, 2016 6:50 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Resistor/Fuse replacement (DEC H7104-D)

I don't quite get what makes this DigiKey part suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".

One reason I question it, is the fact that the fusing ratings are only
plotted for like 40X or 50X expected current. Can the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?

Always trying to learn..

On Mon, Mar 21, 2016 at 2:53 PM, Adrian Graham <wit...@binarydinosaurs.co.uk
> wrote:

> On 18/03/2016 02:11, "Josh Dersch" <dersc...@gmail.com> wrote:
>
> >> Onecall are education-only suppliers but the same part numbers work with
> >> Farnell/Element14. Part# is 1692450.
> >>
> >
> > Thanks!  Yes, that looks very similar except mine has a tolerance rating
> > of 10%.  Vincent helpfully pointed me at:
> >
> >
> http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/989-
> > 1272-1-ND/4215463
> >
> > which look like they should do the job, and I ordered a handful just in
> > case I ever need a few more.
>
> Good news - mine worked so fingers crossed for yours too. I now have a
> functioning PSU again though I've not tried it back in the chassis yet...
>
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>
>
>

Re: Resistor/Fuse replacement (DEC H7104-D)

[drlegendre .]

I don't quite get what makes this DigiKey part suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".

One reason I question it, is the fact that the fusing ratings are only
plotted for like 40X or 50X expected current. Can the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?

Always trying to learn..

On Mon, Mar 21, 2016 at 2:53 PM, Adrian Graham  wrote:

> On 18/03/2016 02:11, "Josh Dersch"  wrote:
>
> >> Onecall are education-only suppliers but the same part numbers work with
> >> Farnell/Element14. Part# is 1692450.
> >>
> >
> > Thanks!  Yes, that looks very similar except mine has a tolerance rating
> > of 10%.  Vincent helpfully pointed me at:
> >
> >
> http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/989-
> > 1272-1-ND/4215463
> >
> > which look like they should do the job, and I ordered a handful just in
> > case I ever need a few more.
>
> Good news - mine worked so fingers crossed for yours too. I now have a
> functioning PSU again though I've not tried it back in the chassis yet...
>
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>
>
>

Re: Resistor/Fuse replacement (DEC H7104-D)

[Adrian Graham]

On 18/03/2016 02:11, "Josh Dersch"  wrote:

>> Onecall are education-only suppliers but the same part numbers work with
>> Farnell/Element14. Part# is 1692450.
>> 
> 
> Thanks!  Yes, that looks very similar except mine has a tolerance rating
> of 10%.  Vincent helpfully pointed me at:
> 
> http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/989-
> 1272-1-ND/4215463
> 
> which look like they should do the job, and I ordered a handful just in
> case I ever need a few more.

Good news - mine worked so fingers crossed for yours too. I now have a
functioning PSU again though I've not tried it back in the chassis yet...

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?

Re: Resistor/Fuse replacement (DEC H7104-D)

[Adrian Graham]

On 18/03/2016 02:11, "Josh Dersch"  wrote:

>> However the only ones they sell are 5% tolerance, ie brown-black-gold-gold
>> not brown-black-gold-silver + blue, but the technical chap I spoke to seemed
>> certain these would be ok. I bought 5 just in case.
>> 
>> Onecall are education-only suppliers but the same part numbers work with
>> Farnell/Element14. Part# is 1692450.
>> 
> 
> Thanks!  Yes, that looks very similar except mine has a tolerance rating
> of 10%.  Vincent helpfully pointed me at:
> 
> http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/989-
> 1272-1-ND/4215463
> 
> which look like they should do the job, and I ordered a handful just in
> case I ever need a few more.

I'll be adding mine tonight or tomorrow so if the smoke escapes I'll get
some of those, why they didn't come up on my search for 'fusible resistor'
I'll never know.

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?

Resistor/Fuse replacement (DEC H7104-D)

[Josh Dersch]

Hi all --

Yesterday I replaced the dead 2N6547 transistor in the H7104 and fired 
'er up again.  Same exact results.  (The timbre of the power supply 
whine may have changed slightly, it's hard to tell).  So, back to the 
drawing board.  I tested the replacement transistor after power-up and 
it was still good, so at least it wasn't a casualty.


On closer inspection, I found what appears to be a large-ish (maybe 
2.5-3mm in diameter) resistor with a hairline crack down the middle.  
Testing reveals it to be open-circuit, and looking at the print set 
reveals it to be connected to a leg of the transistor I just replaced, 
so that seems suspect.  I noted no smoke or odor during any of the times 
I've powered this thing up (the resistor is on the outside edge of the 
supply and I was watching pretty closely at all times) so I assume it 
was dead long before I got ahold of this machine and I just overlooked it.


It's listed in the print set as a 1 Ohm, 2 Watt resistor, with a "FUSE" 
designation.  I'm not entirely sure what I should be searching for for a 
replacement; clearly the "fuse" part of the designation is important but 
I'm not sure what a modern equivalent is.  I've browsed around Mouser 
for awhile and I'm not seeing anything obvious.  I'm sure this is 
obvious to anyone with experience -- can you point me in the right 
direction?


Thanks,
Josh

Re: Resistor/Fuse replacement (DEC H7104-D)

[drlegendre .]

Glad this came back up.

Was any consensus achieved, regarding the use of `flameproof` resistor
types as direct substitutes for designated "fusible resistors"?

On Thu, Mar 17, 2016 at 7:44 PM, Adrian Graham  wrote:

> On 17/03/2016 22:46, "Vincent Slyngstad"  wrote:
>
> > From: Josh Dersch: Thursday, March 17, 2016 3:34 PM
> >> It's listed in the print set as a 1 Ohm, 2 Watt resistor, with a "FUSE"
> >> designation.  I'm not entirely sure what I should be searching for for a
> >> replacement; clearly the "fuse" part of the designation is important but
> >> I'm not sure what a modern equivalent is.  I've browsed around Mouser
> >> for awhile and I'm not seeing anything obvious.  I'm sure this is
> >> obvious to anyone with experience -- can you point me in the right
> >> direction?
> >
> > There was a recent discussion here about a similar component in
> > a VT100 supply.  I think a suitable replacement was eventually found
> > at Farnell/Newark.
>
> Yep, that was me looking for the same part. Does yours look like this?
>
> http://f0p.co.uk/r22.jpg
>
> According to Onecall Farnell 'a blue band at position 5 indicates 20%
> tolerance' which would make it a tolerance multiplier of 2.
>
> However the only ones they sell are 5% tolerance, ie brown-black-gold-gold
> not brown-black-gold-silver + blue, but the technical chap I spoke to
> seemed
> certain these would be ok. I bought 5 just in case.
>
> Onecall are education-only suppliers but the same part numbers work with
> Farnell/Element14. Part# is 1692450.
>
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>
>
>

Re: Resistor/Fuse replacement (DEC H7104-D)

[Vincent Slyngstad]

From: Josh Dersch: Thursday, March 17, 2016 3:34 PM
It's listed in the print set as a 1 Ohm, 2 Watt resistor, with a "FUSE" 
designation.  I'm not entirely sure what I should be searching for for a 
replacement; clearly the "fuse" part of the designation is important but 
I'm not sure what a modern equivalent is.  I've browsed around Mouser 
for awhile and I'm not seeing anything obvious.  I'm sure this is 
obvious to anyone with experience -- can you point me in the right 
direction?


There was a recent discussion here about a similar component in 
a VT100 supply.  I think a suitable replacement was eventually found 
at Farnell/Newark.


   Vince