Monday 3 July 2017

Wei-Ya switching PSU repair

Quick repair from the weekend just gone... I needed you use my Jamma test rig for a new board I'm repairing, and being the cautious type I always like to check my PSU voltages before plugging a board in. Well it was a good thing I did, my Wei-Ya PSU, a clone of an original by all accounts was out putting 10Vdc on the 5V line! Yikes... The voltage adjuster did nothing, I was stuck with 10Vdc on the 5v line. I checked the other voltages; +12Vdc & -5Vdc and to my surprise they were sitting at +24v and -10v respectively. I very nearly decided to bin the thing, but my tech head got the better of me and I decided to crack the case open to see if I could spot anything obvious.

Well as you can see below, there was a hairline crack (highlighted) in the PCB, when I used my meter to test continuity the outside and middle track of the three were broken and contact could be made by flexing the PCB.

I scraped away the solder mask around the affected area.

I then made some links using some old wire and soldered them across the traces. 

Once reassembled, the PSU was working to the correct spec and the adjuster controlled the 5v line perfectly. I could have finished this off by applying some lacquer (Or the wife nail varnish!) over the bare traces, but really its not required for how I'm using it, if it was in a cab I may have done so but not for my test rig, the solder side of the PCB does have a sheet of insulating material between the traces and the metal case and for me that will do for now.

I can only imagine this was a manufacturing defect that was worsened by me moving my test rig around...

Cheers, Mart.