Wei-Ya switching PSU repair

[smarty]

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.

smarty2017-07-03 13:25:00

 

[Hurray Banana]

the money shots missing Martin

 

[dj_yt]

Nice stuff. But why would a cracked trace, cause the voltage to double?

 

[smarty]

Ha! The money shot is now there

No idea on this one Chris, one for the PSU guys, lol. This 100% fixed the issue, but yes when I checked the +12 and -5 i though it was very odd they had essentially all doubled in value, something the PSU's small onboard transformer could have taken care of?

smarty2017-07-03 13:28:49

 

[dj_yt]

Curious. Yes, I guess it depends on what those cracked traces connected to. Maybe a component was being taken out of circuit as a result.

 

[Bods]

That is interesting you say the voltages are higher. I have a PSU that was in a Crane machine, like Jamma type but one with big Heatsink one side and wire mesh the other, from Deith Leisure Spares Model:E0502 but the insides are from a USA Crane Machine so must of been added

I worked out in the end that this was only being used to power the 12v for the Credit board, the display for the credits is stuffed, only has a couple of lines lit. I thought it's a shame to use it when it's got +12v -5V and +5V with adjuster. So I can save this to use in a cab like some Atari's that have a switcher basically for the +5v instead of a full Jamma psu, so I've connected up a Standard 12V adaptor from say a LCD Monitor, must of got that for free, probably from the tip and it seemed ok, had just under 12V output, but when I hooked to the Credit Board, the Crane only registered the odd coin

Turned out the PSU, (after altering the input connection with cable instead of kettle socket, other end was chopped off which was good as It had connector block before) was faulty, when connected to Credit pcb it was only outputting around 9V, so I reconnected this original PSU only to find that was outputting I think 26v on the 12V line and about 12V on the 5V one

amazingly it hadn't damaged the Credit PCB, not investigated that one yet so i'll have to check this one out sometime

I did have a look at the 12V adaptor though having set it all up to go in the machine, it was pulsing the output, I plugged a 12V led spotlight on it and the lights were pulsing, so I thought I'd start with the Cap on Primary side which usually causes them to not start up, and that was it, so the start up cap was causing that pulsing, after it was replaced I connected it up and coin mech accepted every coin dropped in, which it wasn't before with the 26v's going to it either