RE: H7861 PSU issues

[Rob Jarratt via cctalk]

I rather cut the story short, I did repair the damage and had the PSU
working again very briefly, but something else failed somewhere and it just
does not work correctly.

Regards

Rob 

> -Original Message-
> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Noel
> Chiappa via cctalk
> Sent: 02 November 2017 16:24
> To: cctalk@classiccmp.org
> Cc: j...@mercury.lcs.mit.edu
> Subject: Re: H7861 PSU issues
> 
> > From: Rob Jarratt
> 
> > when I replaced it and powered on there was a big bang
> 
> What went 'bang'? (I assume if there was a loud noise, it mus have left
visible
> damage somewhere.)
> 
>   Noel

Re: H7861 PSU issues

[Noel Chiappa via cctalk]

> From: Rob Jarratt

> when I replaced it and powered on there was a big bang

What went 'bang'? (I assume if there was a loud noise, it mus have left
visible damage somewhere.)

Noel

RE: H7861 PSU issues

[Rob Jarratt via cctalk]

In my case the PSU where I had this still does not work. It is a H7140 from
a PDP-11/24. I found the failed 555 after help from a list member, but when
I replaced it and powered on there was a big bang (I should have told you
that!). I have never been able to repair this PSU and I need someone who
really knows what they are doing to repair it as I think it is beyond me.

Regards

Rob

> -Original Message-
> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Aaron
> Jackson via cctalk
> Sent: 02 November 2017 14:23
> To: cctalk@classiccmp.org
> Cc: j...@mercury.lcs.mit.edu
> Subject: Re: H7861 PSU issues
> 
> Thanks! It was very satisfying and not the worst thing to go wrong for a
> beginner.
> 
> I was also quite surprised that such a simple component would die, and
what I
> find more confusing is that it died while I was using the machine.
> 
> Aaron.
> 
> Noel Chiappa via cctalk <cctalk@classiccmp.org> wrote:
> 
> > > From: Aaron Jackson
> >
> > > Picked up a few 555s and sockets and now it works!
> >
> > Congratulations!
> >
> > It's odd that a 555 failed, but sometimes there's no rhyme or reason
> > to what fails. E.g. I was fixing some broken M7859's (KY11-LB
> > Programmer's Console), and on one of them a 7493 (4-bit counter) had
> > died. That's not one of the 'problem' 74xx chips, like ISTR the 7474
being?
> >
> > Noel

Re: H7861 PSU issues

[Adrian Graham via cctalk]

>I was also quite surprised that such a simple component would die,
>and what I find more confusing is that it died while I was using
>the machine.

A 555 can also take a Commodore PET down because it's solely in charge of
the RESET circuit, and no RESET == no PET.

On 2 November 2017 at 14:22, Aaron Jackson via cctalk  wrote:

> Thanks! It was very satisfying and not the worst thing to go wrong
> for a beginner.
>
> I was also quite surprised that such a simple component would die,
> and what I find more confusing is that it died while I was using
> the machine.
>
> Aaron.
>
> Noel Chiappa via cctalk  wrote:
>
> > > From: Aaron Jackson
> >
> > > Picked up a few 555s and sockets and now it works!
> >
> > Congratulations!
> >
> > It's odd that a 555 failed, but sometimes there's no rhyme or reason to
> what
> > fails. E.g. I was fixing some broken M7859's (KY11-LB Programmer's
> Console),
> > and on one of them a 7493 (4-bit counter) had died. That's not one of the
> > 'problem' 74xx chips, like ISTR the 7474 being?
> >
> >   Noel
>



-- 
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk

Re: H7861 PSU issues

[Aaron Jackson via cctalk]

Thanks! It was very satisfying and not the worst thing to go wrong
for a beginner. 

I was also quite surprised that such a simple component would die,
and what I find more confusing is that it died while I was using
the machine.

Aaron.

Noel Chiappa via cctalk  wrote:

> > From: Aaron Jackson
> 
> > Picked up a few 555s and sockets and now it works!
> 
> Congratulations!
> 
> It's odd that a 555 failed, but sometimes there's no rhyme or reason to what
> fails. E.g. I was fixing some broken M7859's (KY11-LB Programmer's Console),
> and on one of them a 7493 (4-bit counter) had died. That's not one of the
> 'problem' 74xx chips, like ISTR the 7474 being?
> 
>   Noel

Re: H7861 PSU issues

[Noel Chiappa via cctalk]

> From: Aaron Jackson

> Picked up a few 555s and sockets and now it works!

Congratulations!

It's odd that a 555 failed, but sometimes there's no rhyme or reason to what
fails. E.g. I was fixing some broken M7859's (KY11-LB Programmer's Console),
and on one of them a 7493 (4-bit counter) had died. That's not one of the
'problem' 74xx chips, like ISTR the 7474 being?

Noel

RE: H7861 PSU issues

[Rob Jarratt via cctalk]

Great news, congratulations! I am about to see if my H7826 works tonight
after cleaning it up and replacing a few electrolytic capacitors.

Regards

Rob

> -Original Message-
> From: Aaron Jackson [mailto:aa...@aaronsplace.co.uk]
> Sent: 01 November 2017 18:25
> To: r...@jarratt.me.uk
> Cc: 'General Discussion: On-Topic Posts' <cct...@classiccmp.org>
> Subject: Re: H7861 PSU issues
> 
> Picked up a few 555s and sockets and now it works! I am very happy. Going
> from not knowing how switch mode power supplies work, to watching some
> YouTube videos, and then finally being able to debug the problem and fix
it was
> a lot of fun.
> 
> I wonder what will die next.
> 
> Thanks,
> 
> Aaron.
> 
> 
> Rob Jarratt writes:
> 
> > I had a dead 555 on a completely different PSU, so it could be worth
> > checking. I socketed it when I replaced it so it was easy to replace
again.
> >
> > Also, just because a capacitor doesn't appear swollen or show signs of
> > leakage, it seems that this doesn't necessarily mean that it doesn't
> > need replacing. In yet another PSU that I repaired recently, replacing
> > the capacitors fixed it, although in the end I think the one that
> > really fixed it was showing signs of leakage. On a lot of caps that I
> > replace they show no leakage signs, but I do see a bit of a deposit on
> > the negative terminal, I am not sure if this is a sign of any kind of
problem.
> >
> > Regards
> >
> > Rob
> >
> >> -Original Message-
> >> From: cctech [mailto:cctech-boun...@classiccmp.org] On Behalf Of
> >> Aaron Jackson via cctech
> >> Sent: 31 October 2017 21:26
> >> To: cct...@classiccmp.org
> >> Subject: Re: H7861 PSU issues
> >>
> >> Just had another look after watching a video about how switch mode
> >> power supplies work On the small control board connecting to J4,
> >> there are
> > two
> >> D44Q1 transistors. As expected, there is about 65KHz going into the
> >> base
> > of the
> >> transistor for the 5V side. However, there is no signal going into
> >> the
> > base of the
> >> transistor for the 12V side, from pin 3 of the 555. So, it looks like
> >> the
> > problem is
> >> coming from around here. I measured the suspicious components around
> >> the
> >> 555 and they seem fine.
> >>
> >> How likely is it that the 555 is dead? There is 10v going into pin 8,
> > which I
> >> believe is correct.
> >>
> >> Thanks,
> >>
> >> Aaron.
> >>
> >>
> >>
> >>
> >>
> >> Aaron Jackson writes:
> >>
> >> > Hi everyone,
> >> >
> >> > I've been trying to figure out what is wrong with the 12V rail on
> >> > my
> >> > H7861 (BA11-S) power supply. It's showing about 4.2V. The 5V rail
> >> > is spot on.
> >> >
> >> > Page 39 of the following schematics is the main part board of the
PSU.
> >> > http://bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf
> >> >
> >> > Going into the collector of Q3 is about 80V coming straight from T2
> >> > (I think I measured it at about 100Hz), but the emitter is putting
> >> > out the 4.2V, which is the same as the base voltage and output
> >> > voltage. I tried replacing this transistor because the hFE was
> >> > about 80 and a good one was about 120. Unfortunately it didn't do
> anything.
> >> >
> >> > None of the capacitors look swollen and I don't see any leakage.
> >> > There is a smaller board which I think goes into J4. The 12V side
> >> > seems to have a 555 timer and adjusting the pot doesn't change the
> >> > voltage at all.
> >> >
> >> > My understanding of switchmode power supplies is very poor. Does
> >> > anyone have some pointers on what to check or what might be the
> >> > possible
> >> cause?
> >> >
> >> > Hopefully I can get my PDP up and running again... Only got about
> >> > 20 minutes use out of it.
> >> >
> >> > Thanks!
> >> >
> >> > Aaron.
> >>
> >>
> >> --
> >> Aaron Jackson
> >> PhD Student, Computer Vision Laboratory, Uni of Nottingham
> >> http://aaronsplace.co.uk
> 
> 
> --
> Aaron Jackson
> PhD Student, Computer Vision Laboratory, Uni of Nottingham
> http://aaronsplace.co.uk

Re: H7861 PSU issues

[Aaron Jackson via cctalk]

Picked up a few 555s and sockets and now it works! I am very
happy. Going from not knowing how switch mode power supplies work, to
watching some YouTube videos, and then finally being able to debug the
problem and fix it was a lot of fun.

I wonder what will die next.

Thanks,

Aaron.


Rob Jarratt writes:

> I had a dead 555 on a completely different PSU, so it could be worth
> checking. I socketed it when I replaced it so it was easy to replace again.
>
> Also, just because a capacitor doesn't appear swollen or show signs of
> leakage, it seems that this doesn't necessarily mean that it doesn't need
> replacing. In yet another PSU that I repaired recently, replacing the
> capacitors fixed it, although in the end I think the one that really fixed
> it was showing signs of leakage. On a lot of caps that I replace they show
> no leakage signs, but I do see a bit of a deposit on the negative terminal,
> I am not sure if this is a sign of any kind of problem.
>
> Regards
>
> Rob
>
>> -Original Message-
>> From: cctech [mailto:cctech-boun...@classiccmp.org] On Behalf Of Aaron
>> Jackson via cctech
>> Sent: 31 October 2017 21:26
>> To: cct...@classiccmp.org
>> Subject: Re: H7861 PSU issues
>>
>> Just had another look after watching a video about how switch mode power
>> supplies work On the small control board connecting to J4, there are
> two
>> D44Q1 transistors. As expected, there is about 65KHz going into the base
> of the
>> transistor for the 5V side. However, there is no signal going into the
> base of the
>> transistor for the 12V side, from pin 3 of the 555. So, it looks like the
> problem is
>> coming from around here. I measured the suspicious components around the
>> 555 and they seem fine.
>>
>> How likely is it that the 555 is dead? There is 10v going into pin 8,
> which I
>> believe is correct.
>>
>> Thanks,
>>
>> Aaron.
>>
>>
>>
>>
>>
>> Aaron Jackson writes:
>>
>> > Hi everyone,
>> >
>> > I've been trying to figure out what is wrong with the 12V rail on my
>> > H7861 (BA11-S) power supply. It's showing about 4.2V. The 5V rail is
>> > spot on.
>> >
>> > Page 39 of the following schematics is the main part board of the PSU.
>> > http://bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf
>> >
>> > Going into the collector of Q3 is about 80V coming straight from T2 (I
>> > think I measured it at about 100Hz), but the emitter is putting out
>> > the 4.2V, which is the same as the base voltage and output voltage. I
>> > tried replacing this transistor because the hFE was about 80 and a
>> > good one was about 120. Unfortunately it didn't do anything.
>> >
>> > None of the capacitors look swollen and I don't see any leakage. There
>> > is a smaller board which I think goes into J4. The 12V side seems to
>> > have a 555 timer and adjusting the pot doesn't change the voltage at
>> > all.
>> >
>> > My understanding of switchmode power supplies is very poor. Does
>> > anyone have some pointers on what to check or what might be the possible
>> cause?
>> >
>> > Hopefully I can get my PDP up and running again... Only got about 20
>> > minutes use out of it.
>> >
>> > Thanks!
>> >
>> > Aaron.
>>
>>
>> --
>> Aaron Jackson
>> PhD Student, Computer Vision Laboratory, Uni of Nottingham
>> http://aaronsplace.co.uk


--
Aaron Jackson
PhD Student, Computer Vision Laboratory, Uni of Nottingham
http://aaronsplace.co.uk

Re: H7861 PSU issues

[Aaron Jackson via cctalk]

That's good to know. I'll head over to Maplin after work and pick up
some timers and sockets.

I removed one of the suspicious ceramic caps and tested it and it came
out fine. The other cap is shared with the other oscillator so I assume
it is fine. 

Thanks!

Aaron.

Rob Jarratt via cctech <cct...@classiccmp.org> wrote:

> I had a dead 555 on a completely different PSU, so it could be worth
> checking. I socketed it when I replaced it so it was easy to replace again.
> 
> Also, just because a capacitor doesn't appear swollen or show signs of
> leakage, it seems that this doesn't necessarily mean that it doesn't need
> replacing. In yet another PSU that I repaired recently, replacing the
> capacitors fixed it, although in the end I think the one that really fixed
> it was showing signs of leakage. On a lot of caps that I replace they show
> no leakage signs, but I do see a bit of a deposit on the negative terminal,
> I am not sure if this is a sign of any kind of problem.
> 
> Regards
> 
> Rob
> 
> > -Original Message-
> > From: cctech [mailto:cctech-boun...@classiccmp.org] On Behalf Of Aaron
> > Jackson via cctech
> > Sent: 31 October 2017 21:26
> > To: cct...@classiccmp.org
> > Subject: Re: H7861 PSU issues
> > 
> > Just had another look after watching a video about how switch mode power
> > supplies work On the small control board connecting to J4, there are
> two
> > D44Q1 transistors. As expected, there is about 65KHz going into the base
> of the
> > transistor for the 5V side. However, there is no signal going into the
> base of the
> > transistor for the 12V side, from pin 3 of the 555. So, it looks like the
> problem is
> > coming from around here. I measured the suspicious components around the
> > 555 and they seem fine.
> > 
> > How likely is it that the 555 is dead? There is 10v going into pin 8,
> which I
> > believe is correct.
> > 
> > Thanks,
> > 
> > Aaron.
> > 
> > 
> > 
> > 
> > 
> > Aaron Jackson writes:
> > 
> > > Hi everyone,
> > >
> > > I've been trying to figure out what is wrong with the 12V rail on my
> > > H7861 (BA11-S) power supply. It's showing about 4.2V. The 5V rail is
> > > spot on.
> > >
> > > Page 39 of the following schematics is the main part board of the PSU.
> > > http://bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf
> > >
> > > Going into the collector of Q3 is about 80V coming straight from T2 (I
> > > think I measured it at about 100Hz), but the emitter is putting out
> > > the 4.2V, which is the same as the base voltage and output voltage. I
> > > tried replacing this transistor because the hFE was about 80 and a
> > > good one was about 120. Unfortunately it didn't do anything.
> > >
> > > None of the capacitors look swollen and I don't see any leakage. There
> > > is a smaller board which I think goes into J4. The 12V side seems to
> > > have a 555 timer and adjusting the pot doesn't change the voltage at
> > > all.
> > >
> > > My understanding of switchmode power supplies is very poor. Does
> > > anyone have some pointers on what to check or what might be the possible
> > cause?
> > >
> > > Hopefully I can get my PDP up and running again... Only got about 20
> > > minutes use out of it.
> > >
> > > Thanks!
> > >
> > > Aaron.
> > 
> > 
> > --
> > Aaron Jackson
> > PhD Student, Computer Vision Laboratory, Uni of Nottingham
> > http://aaronsplace.co.uk

RE: H7861 PSU issues

[Rob Jarratt via cctalk]

I had a dead 555 on a completely different PSU, so it could be worth
checking. I socketed it when I replaced it so it was easy to replace again.

Also, just because a capacitor doesn't appear swollen or show signs of
leakage, it seems that this doesn't necessarily mean that it doesn't need
replacing. In yet another PSU that I repaired recently, replacing the
capacitors fixed it, although in the end I think the one that really fixed
it was showing signs of leakage. On a lot of caps that I replace they show
no leakage signs, but I do see a bit of a deposit on the negative terminal,
I am not sure if this is a sign of any kind of problem.

Regards

Rob

> -Original Message-
> From: cctech [mailto:cctech-boun...@classiccmp.org] On Behalf Of Aaron
> Jackson via cctech
> Sent: 31 October 2017 21:26
> To: cct...@classiccmp.org
> Subject: Re: H7861 PSU issues
> 
> Just had another look after watching a video about how switch mode power
> supplies work On the small control board connecting to J4, there are
two
> D44Q1 transistors. As expected, there is about 65KHz going into the base
of the
> transistor for the 5V side. However, there is no signal going into the
base of the
> transistor for the 12V side, from pin 3 of the 555. So, it looks like the
problem is
> coming from around here. I measured the suspicious components around the
> 555 and they seem fine.
> 
> How likely is it that the 555 is dead? There is 10v going into pin 8,
which I
> believe is correct.
> 
> Thanks,
> 
> Aaron.
> 
> 
> 
> 
> 
> Aaron Jackson writes:
> 
> > Hi everyone,
> >
> > I've been trying to figure out what is wrong with the 12V rail on my
> > H7861 (BA11-S) power supply. It's showing about 4.2V. The 5V rail is
> > spot on.
> >
> > Page 39 of the following schematics is the main part board of the PSU.
> > http://bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf
> >
> > Going into the collector of Q3 is about 80V coming straight from T2 (I
> > think I measured it at about 100Hz), but the emitter is putting out
> > the 4.2V, which is the same as the base voltage and output voltage. I
> > tried replacing this transistor because the hFE was about 80 and a
> > good one was about 120. Unfortunately it didn't do anything.
> >
> > None of the capacitors look swollen and I don't see any leakage. There
> > is a smaller board which I think goes into J4. The 12V side seems to
> > have a 555 timer and adjusting the pot doesn't change the voltage at
> > all.
> >
> > My understanding of switchmode power supplies is very poor. Does
> > anyone have some pointers on what to check or what might be the possible
> cause?
> >
> > Hopefully I can get my PDP up and running again... Only got about 20
> > minutes use out of it.
> >
> > Thanks!
> >
> > Aaron.
> 
> 
> --
> Aaron Jackson
> PhD Student, Computer Vision Laboratory, Uni of Nottingham
> http://aaronsplace.co.uk

Re: H7861 PSU issues

[Aaron Jackson via cctalk]

Just had another look after watching a video about how switch mode power
supplies work On the small control board connecting to J4, there are
two D44Q1 transistors. As expected, there is about 65KHz going into the
base of the transistor for the 5V side. However, there is no signal
going into the base of the transistor for the 12V side, from pin 3 of
the 555. So, it looks like the problem is coming from around here. I
measured the suspicious components around the 555 and they seem fine.

How likely is it that the 555 is dead? There is 10v going into pin 8,
which I believe is correct.

Thanks,

Aaron.





Aaron Jackson writes:

> Hi everyone,
>
> I've been trying to figure out what is wrong with the 12V rail on my
> H7861 (BA11-S) power supply. It's showing about 4.2V. The 5V rail is
> spot on.
>
> Page 39 of the following schematics is the main part board of the PSU.
> http://bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf
>
> Going into the collector of Q3 is about 80V coming straight from T2 (I
> think I measured it at about 100Hz), but the emitter is putting out the
> 4.2V, which is the same as the base voltage and output voltage. I tried
> replacing this transistor because the hFE was about 80 and a good one
> was about 120. Unfortunately it didn't do anything.
>
> None of the capacitors look swollen and I don't see any leakage. There
> is a smaller board which I think goes into J4. The 12V side seems to
> have a 555 timer and adjusting the pot doesn't change the voltage at
> all.
>
> My understanding of switchmode power supplies is very poor. Does anyone
> have some pointers on what to check or what might be the possible cause?
>
> Hopefully I can get my PDP up and running again... Only got about 20
> minutes use out of it.
>
> Thanks!
>
> Aaron.


--
Aaron Jackson
PhD Student, Computer Vision Laboratory, Uni of Nottingham
http://aaronsplace.co.uk

H7861 PSU issues

[Aaron Jackson via cctalk]

Hi everyone,

I've been trying to figure out what is wrong with the 12V rail on my
H7861 (BA11-S) power supply. It's showing about 4.2V. The 5V rail is
spot on.

Page 39 of the following schematics is the main part board of the PSU.
http://bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf

Going into the collector of Q3 is about 80V coming straight from T2 (I
think I measured it at about 100Hz), but the emitter is putting out the
4.2V, which is the same as the base voltage and output voltage. I tried
replacing this transistor because the hFE was about 80 and a good one
was about 120. Unfortunately it didn't do anything.

None of the capacitors look swollen and I don't see any leakage. There
is a smaller board which I think goes into J4. The 12V side seems to
have a 555 timer and adjusting the pot doesn't change the voltage at
all.

My understanding of switchmode power supplies is very poor. Does anyone
have some pointers on what to check or what might be the possible cause?

Hopefully I can get my PDP up and running again... Only got about 20
minutes use out of it.

Thanks!

Aaron.