2 Nov
2015
2 Nov
'15
1:05 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Robert
Jarratt
Sent: 02 November 2015 20:36
To: 'General Discussion: On-Topic and Off-Topic Posts'
Subject: RE: Testing H7864 (MicroVAX II) PSU With No Load
I have just uploaded all the corrections. So the connector names on the risers should now
correspond. I have also corrected the area on the primary control module around C403 and
R407.
Regards
Rob
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of
Mattis Lind
Sent: 02 November 2015 13:20
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Testing H7864 (MicroVAX II) PSU With No Load
2015-11-01 17:35 GMT+01:00 Robert Jarratt <robert.jarratt at ntlworld.com>:
I took a quick look at the schematics and I had hard times following
the schematics, but I guess I asked for it.
I did warn you! :-) :-), but thanks for looking and trying to make sense of them.
> > Maybe you can publish your schematic
somwhere. It is much
> > easier to come
> up
> > with ideas to pin point problems if we all view the same schematic.
> > I
> think it
> > would be possible to identify the problem without comparing
> > the two PSUs
> at
> > least in this case where there is some kind of fundamental problem.
>
> I do intend to publish the schematics, but right now I am pretty
> sure they
> are:
>
> a) full of mistakes
> b) not drawn logically
> c) there are a couple of areas I couldn't trace without major
> surgery on the board.
>
Well. I guess that anything is better than nothing.
Here is a link to what I have now http://1drv.ms/1KQkTBp
There are Eagle sch files, and PNG files for those who do not have Eagle.
Anyway. I think that the signal is produced somewhere behind the
transformer
T301 and then passes through a number of driver stages (Q405 and Q408)
until it gets to the Q301. You could check the signal on T301 and
onwards. The designation for the connector of the small boards are all
X1 while there X1, X2, X3 mentioned on one schematic so I am a little
bit confused. Then there are four small boards which presumably have
Xn connectors but I can only find three in your schematics. But this
is maybe a result of the fact the schematics are incomplete or me
misunderstanding something.
Yes, I wasn't very disciplined with the labelling. Basically on the big schematic,
called Secondary I have drawn the connectors for each of the riser boards. The
text near the connector identifies which riser board it is the connector for and
the connector schematic only has one connector, but it will always be called X1,
I didn't make it correspond to the Secondary schematic. I will fix this. Note also
that the small riser on the primary side is included in the Primary Control
schematic, I didn't do a separate schematic, which was a mistake I think.
The circuitry C403 and R407 doesn't make
sense to me. It has to be a
drawing mistake.
Thanks, I will check this. I have found lots of mistakes, I am sure this is another
one.
Maybe it is a good idea to to focus on one area and to make that part
of the schematic complete. Like the part surrounding the main switch
transistor. Then try to follow the signal back through T301 and trace that part
out.
Yes, I agree, the Primary Control is the one where the incorrect operation
seems to be happening, Q301 does not appear to be switching. I think this
schematic is as complete as I can make it, although it could still have
mistakes....
Some time ago I got a scope on Q301, and I could see the b-e never went high
enough to switch it on. There were some very short and very low pulses every
40us, but that was all. When I compared this to the working one, I could see a
signal, still every 40us, but definitely switching the transistor on during the
cycle.
>
> If the PWM signal is produced on the secondary side then there has to
> be some small PSU providing power to this circuitry at startup so that
> the PSU can bootstrap. But I cannot see where this is.
>
> Good Luck!
>
> /Mattis
>
>
>
> >
> > Regards
> >
> > Rob
> >
> >