I have a small 13.8V 10A PSU which has decided to be a 9V PSU. To save me reverse engineering the PCB does anyone have the circuit for a PSU sold as a Maplin XM19 or RPS1012A?
It will be one of the 2N3055’s on the back I reckon, usually is…
The voltage reference / control circuit is usually symmetrical around them so its easy enough to compare voltages across both sides.
My 30A Maplin supply has suffered a similar fault when a battery was reversed across its o/p posts (I was younger then).
That’s messy to test with how they are wired in physically. It was working FB 6years back when last used. I use it to charge car batteries in-situ, but not today. With it being 13.8V you can connect across a car with the battery still connected and it wont gub the car electronics which an unregulated charger can do.
I only found out in the rain this morning investigating the shipment of fail delivered to Mrs. FMF’s car battery overnight. A new Bosch job from the local factors sorted that out and yes, I checked the car was charging. (12.6V engine off, 14.1V engine idling)
I’ll have a butcher’s tomorrow at the 2n3055 pass transistors (2 off) and also check the 2SD880 that drives them. Thanks for the suggestion. I did discover it’s an LM324 quad opamp and not a uA723 after much head scratching!