> -----Original Message----- > From: cctalk [mailto:[email protected]] 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 > > > > > -----Original Message----- > > From: cctalk [mailto:[email protected]] 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 <[email protected]>: > > > > > > > > > > > > > > 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. > > > > > > > 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. > > > > > 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 > > > > > >
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
