ABI CMOS/TTL etc tester / Coutant RL 150/100 SMPS

: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 :oscillator 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.

magic

the

unlikely,

years. I

electro

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

I put sone w/w Rs on the outputs and monitored voltages, a few tenths of volts + on + and - on -, except one of the 5V, not even a mV, so perhaps a duff C on board of SM that is obscured by heatsinks etc. Just with the 10 or so pings a second of drive, that drops back to 1 a second with half mains, the voltage supply over the 3842 stays constant at 13.6V so supplying itself , not just startup supply. I'll have to start dismantling to trace that 5 V section but other people's repairs take presedence for the moment.