Hi everyone I’m a newbie looking for some help with an old ac/dc switched mode psu.
This https://www.us.lambda.tdk.com/products/legacy-products/pdf/wa_fall94.pdf

Original failure was overheating 5v output load resistor and failed electrolytic nearby. Replaced the resistor (100R) and around 9 other low voltage caps serving the 24/5/15v outputs.

Issue now is that the auxiliary outputs 24, 15 etc are all correct voltage but can’t deliver any current when loaded. The main 5v output is also ~3.5v.

I’m assuming something wrong with feedback loop but not sure where to start without diagrams. No components such as resistors look too be hot or faulty.

Whilst testing I realised the external sense terminals were not connected and assumed that to be the issue but since bridging them to the output there was not noticeable change in voltage. Is this a significant clue?

Any help is appreciated!

 

Hi. Does anyone have any suggestions?

I’ve since worked out it’s a flyback design and what appears to be 1:1 transformer isolation for the feedback loop. There are no off the shelf smps IC’s used - instead T393 (Voltage comparator) and 555’s etc. I’ve gone over all of the components and pcbs to check for dry joints, corrosion, overheating or any other damage and can’t see a thing.
I’ll start measuring voltages on the ICs to check for good Ground and Vcc…