; 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&
> 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
cmp.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 u
>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, Aar
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
> 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)
t.me.uk
> Cc: 'General Discussion: On-Topic Posts'
> 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
ech
>> 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
>&g
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 ar
minal,
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
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 th
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
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