Ross Herbert wrote in message
...
On Sat, 10 Oct 2009 11:11:08 +0100, "N_Cook" wrote:

:Went to use it this week , first time for ages and not a dickybird, no
magic
:smoke/ ominous noises. Just single cycle slow repeat ping/clicks from
the
:inverter transformer. Was working fine last time of use.
:Anyone happen to have schematic of the ABI DDS-40XP Digital Diagnostic
:System or more pressingly the SMPS, I only have the ABI user manual
:I may be able to get away with 2 SMPS replacement fitted in there, the
:Coutant (maybe type number B91510 ) from 1988 uses a lot of early days SM
,
:seems very high power, I suppose for the situation if all 118 relays are
:active at the same time plus CRT plus floppy drive.
:-12V,1A
:+12V, 3A
:+5V,12A
:and a separate +5V,5A
:I'll have to confirm this ps does not require a load to start up,
unlikely,
:but not done so yet , no obvious fuses on main board .
:So far cold checked the smps and nothing amiss on Rs,Cs or large active
:Uses UC3842 supervisor, plenty of data, so should be able to confirm the
scillator part of things easy enough.
:


Have had similar symptoms form older SMPS which have lain dormant for
years. I
would look for faulty components around the 3842. Usual things such as
electro
caps and you may find a high value startup resistor open circuit.

If I find time this week my plan of action is to start around there.
Optoisolator seems to work 0.05V change on cold double DVM diode test
I've traced the dropper from mains to the 3842 starter supply is.
Will pwer via variac to find point of extinction , temporary drop that
dropper in value to run even lower, then temporary putting a couple of 10
ohms in the primary side of the inverter Tr.
Then if the oscillator seems to function correctly with error amp defeated
will then be able , hopefully, see which area of the low voltage side is
causing an error to feed-forward