Opinion - Repairing linear PSU with pcb damage - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: September 10, 2021, 05:20:09 am
content: I took a chance on some non-working stuff on eBay to try a chance at repairing it. The power supply board is a linear power supply which is pretty straight forward. The transformer sends a few different AC voltages to rectifier diodes and fuses then to voltage regulators and filter capacitors, DC comes out. Simple enough.Whether it is by physical impact or careless "repair", two of the power supply filter capacitors are ripped off the board - held in with one leg loosely, and the other leg has a big chunk of PCB on it. Lifted pads, definitely.Now these filter capacitors are connected to pretty thick tracks on top of the PCB, but it seems like there is nothing going on the bottom layer, it must be a middle layer that was destroyed.Assuming no other traces were destroyed because of it, I was thinking of taking new capacitors and wire wrapping both leads and connect them to where the tracks lead to, according to the schematic. It seems like for these two damaged ones, I will either be directly connecting to other filter capacitors in the circuit or going to or from a rectifier diode.I don't know terribly much about linear power supplies, so I don't know if there is something I need to be aware of before wiring a capacitor directly to the destination of the PCB trace when it is a power supply. I was thinking, since the pads are gone, i would hold the capacitor to the PCB with hot glue.Unfortunately, i already looked around but I can not purchase a replacement for this linear power supply, since it's quite old (1989), so I'm really hoping the wire wrap trick will work.

author: bob91343
author_rank: Super Contributor
timestamp: September 10, 2021, 05:55:12 am
content: Do you have a schematic diagram?

author: Ian.M
author_rank: Super Contributor
timestamp: September 10, 2021, 06:32:10 am
content: Pictures please. Both sides of the board, before and after removing the offending capacitors.I wouldn't use hot-glue. It can loose adhesion unpredictably unless the surface is absolutely clean and preheated before application, and of course softens due to heat, which is far from ideal in a linear PSU!

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 10, 2021, 09:21:17 am
content: middle way, no waythose pcb's are 2 layer maxvery simple to repair what you describe, patience and multimeter in diode-test-mode, you also may have some broken tracks when the savage tech miss-treated the boardbig track>>big copper conductor (like those 2.5mm2 conductors or maybe less) anf you're ok

author: Jwillis
author_rank: Super Contributor
timestamp: September 10, 2021, 02:50:04 pm
content: On a severely damaged PCB , If there is enough trace left to surface solder wire and enough space to add stand offs you could daughter board the filter caps. For very large caps you can chassis mount them like ebastler suggested. The extra length of wire won't effect the performance of the supply . Leaving components loose will inevitably led to problems latter . I wouldn't suggest hot glue as a good mounting practice because of the low softening temperature . Hot glue working temperature is between 65C and 180C .