[rescue] SUN IPC PSU - still not working after recap

[Patrik Schindler]

Hello, Jan,

Am 06.06.2025 um 14:42 schrieb Jan Liška via rescue <rescue at sunhelp.org>:

> Hello,
>  I’ve started recapping my IPCs using locally sourced low-ESR capacitors. However, both PSUs I’ve recapped so far exhibit the same issue:
>  They power on for a very brief moment (about 0.1 seconds), the 5V rail voltage rises to 2–3V, and then the unit shuts down. I checked the units for cold solder joints and significant corrosion damage on trails but found none.
>  I’ve been advised that either one of the TLP634 optocouplers may be faulty, or the capacitors I used might not be truly low-ESR as claimed by the seller. 
>  I doublechecked the capacitors and they seem to be OK - I used mostly Panasonic low-ESR capacitors like CE 3300uF 16V EEUFR1C332L. I replaced all capacitors except for the largest 400V one.
>  Before I proceed with replacing more components, I would greatly appreciate any advice.

I have no experience with your specific PSU, but the behavior you are describing sounds generally like a) overcurrent protection kicks in, or b) overtension (voltage) protection kicks in. The latter is usually part of the normal feedback circuit to achieve stable output tension. I admit, I can't recall how overcurrent protection is established.

Usually, only one rail (5V) is monitored for correct tension, while 12V automatically "inherits" its value with nominal load through transformer design (turns ratio from primary to secondary).

I'd check for shorts e. b. by applying 5V and 12V from an external source. Other measures heavily depend on specific design. Sometimes, an IC is used to provide necessary functions, maybe this is at fault?

Just general advice, sorry.

:wq! PoC