> -----Original Message----- > From: cctalk <cctalk-boun...@classiccmp.org> On Behalf Of Rob Jarratt via > cctalk > Sent: 09 April 2020 19:52 > To: 'Matt Burke' <m...@9track.net>; 'Mattis Lind' <mattisl...@gmail.com>; > 'General Discussion: On-Topic and Off-Topic Posts' <cctalk@classiccmp.org> > Subject: RE: VAXmate PSU > > > > > -----Original Message----- > > From: cctalk <cctalk-boun...@classiccmp.org> On Behalf Of Matt Burke > > via cctalk > > Sent: 09 April 2020 09:40 > > To: cctalk@classiccmp.org > > Subject: Re: VAXmate PSU > > > > On 08/04/2020 22:24, Rob Jarratt via cctalk wrote: > > > I will look at all the suggestions, particularly of a failure on the > > > secondary > > side. Something must have burned up, because there was a distinct > > burning smell after the initial failure, although I have never been > > able to see any physical damage to anything, despite looking many times. > > > > > > > > > > > > But the thing that really puzzles me is that, after correcting the > > > probes to > > include the D19 anode, there doesn’t seem to be anything that would > > cause > > D19 to trigger. Am I reading the trace wrong? > > > > > > > The only paths to ground for VCC are C12, E3 and D19. The fact that > > VCC is stable for a period of time and then drops suddenly suggests it > > must be D19. It looks like there could be a pulse on D19 gate but it > > is in the order of 1-2 uS before VCC drops. There are more pulses > > prior to that but I wonder if some of that is just induced noise? > > > Here is a trace taken using a 5us timebase. > > https://rjarratt.files.wordpress.com/2020/04/primary-side-shutdown-detail- > high-resolution.png > > As a reminder the probes are connected as follows: > > Ch1. 555 timer. > Ch2. D19 Anode > Ch3. D19 Gate. > Ch4. Q1 Source. > > It doesn't look like there are any glitches on the D19 gate. I don't think it > is > clear why D19 is triggering, because all the previous oscillations are about > the > same. > > > > > It will be interesting to see what's happening on the secondary side, > > particularly with Q2. I guess you have already checked the obvious > > things like a short circuit on one of the outputs? Also worth checking > > the rectifier diodes D11, D12, D22 and D23 (I think). > > I did check Q2 before, but perhaps I should check again. I have checked for > shorts on the actual outputs, but there don't seem to be any. I have checked > one of those rectifiers, I think one of my next tasks is to desolder all of > them > and check them.
I have put probes on Q2 with the probes connected as follows: Ch1. D19 anode (for triggering) Ch2. D19 gate Ch3. Q2 anode Ch4. Q2 gate The result is here: https://rjarratt.files.wordpress.com/2020/04/primary-side-shutdown-secondary-scr-detail.png It doesn't look like Q2 is being triggered. > > > > > Matt
