25 Jun
2023
25 Jun
'23
4:32 p.m.
-----Original Message-----
From: Jon Elson via cctalk <cctalk(a)classiccmp.org>
Sent: 25 June 2023 16:24
To: Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
Cc: Jon Elson <elson(a)pico-systems.com>
Subject: [cctalk] Re: Rainbow H7842 PSU Fault
On 6/25/23 07:36, Rob Jarratt via cctalk wrote:
Well, apply current-limited 12 V DC to the
output of the bridge rectifier and
see what current it draws.
Could be a failed capacitor or regulator, or something downstream of the
regulator that has failed.
If you mean the 7812 on PSU Sheet 1 then I believe it is fine as I have already tested it
with a bench PSU supplying it with 15VDC and it works fine.
This made me suspect that the startup transformer
may have been
damaged. So I checked the output of the startup transformer. On the
bad PSU this was about 2.4VAC, while on the working one it was about
12VAC. I lifted all 4 of the diodes connected to the startup transformer and
they
all tested OK.
(Maybe you have already checked this.)
Jon