Strange Williams PS Issue

[YellowDog]

I have two Williams power supply boards that are acting the same way. These are the newere Joust & later style with teh separate heat sink.

When it is plugged in without the output power cable (i.e. no load) the +5V is right on. When the CPU & ROM boards are plugged in (i.e. under load) the +5V goes to 1.26V. So far I have
1) replaced all the capacitors in the 5 Volt section including C10 (the 18,000uF)
2) I have replaced BR1
3) I made sure all the fuses were the correct size and that they have continuity.
4) I replaced IC2 (the 5 V voltage regulator
5) Pulled Q1 (the SCR) and replaced it
6) Reflowed all the headers
7) Cleaned the corrosion out of the fuse holders
8) Run a diode test on D2 & D3
9) Swapped a different set of outboard power transistors (the ones on the big heat sink)

Before I just start shotgunning parts (even more than I already have) has anybody ever seen this before & what did you do to fix it?

Thanks,

ken

EDIT: Yes I have tried a different PS board and everything works with the other board.

 

[Dokert]

I have found this problem to be crappy solder joints on the trans for the 2N6057.

 

[copious]

Or switch to a switcher PS

 

[Dokert]

Or switch to a switcher PS

These boards are NOT in a game.

 

[YellowDog]

I have found this problem to be crappy solder joints on the trans for the 2N6057.

I had thought about that, but I reflowed the header pins for the transistor just as a normal part of the rebuild. I also tried two other transistor blocks with exactly the same results every time.

I'll play with it a little more tomorrow.

ken

 

[modessitt]

I fixed one of these not long ago for a Joust that did the same thing. Disconnect the power connector to the CPU and the +5 is fine. Connect it and the +5 drops to about one volt.

The boards where in the cab of a friend collector who isn't as experienced as you, so I'm sure you're not having the exact problem, but it might help you find your problem.

First thing I did was test the CPU board in my game, as I figured the problem was there. I did find one bad RAM and replaced it, and the CPU worked fine, but I got the same problem once I put it into his game.

I then checked and found BR1 was shorted. I replaced it, but still had the problem.

I eventually figured out that my friend had replace connector J4, but put the key in backwards (2nd from right instead of 2nd from left as normal) so the connector from the heat sink was being plugged in backwards. Fixed the connector and the problem was fixed.

I'm sure you aren't experiencing the same thing, but it may be enough to know a signal crossing in that area causes that problem, and you may have a part in that area that might be making something similar happen...

 

[YellowDog]

Thanks Steve. The connector is in good shape, so I'll play with it more tomorrow after I get back from the auction. I don't think I will be buying anything (famous last words) but it will be good to get a chance to meet up with some folks.

ken

 

[modessitt]

just goes to show - didn't even know there was an auction tomorrow.

If you see a Hydro Thunder (complete) for $100 or less, buy it and I'll come get it in Houston. or send it down with any Austin peeps who know me...

 

[YellowDog]

just goes to show - didn't even know there was an auction tomorrow.

If you see a Hydro Thunder (complete) for $100 or less, buy it and I'll come get it in Houston. or send it down with any Austin peeps who know me...

Sorry Steve, I didn't get your message until just now. I had to get up at 5am to get my butt out the dorr in time to meet up with Pat up there. I don't recall seeing any Hydro Thunders. There was a Jetski game in the big game row. I don't remember the name, but it went for $400 or so IIRC.

I didn't know about an auction until earlier in the week when I dropped into the 'auction and CL forum' here and there was a message about it. It seemed very last minutish.

ken

 

[YellowDog]

Ha! I win! I got it finally!

After replacing practically everthing else in the +5V circuit (add a new LM723 socket, Q4 and Z1 to the list of items replaced), I started testing the resistors. I got a strange reading off of R20 so I unsoldered one leg so I could test it out of circuit and it was broken in half. The leg I had unsoldered was spinning freely with half the resistor attached. I didn't have any 1.5K resistors so I stuck a 2K one in for a quick check and it works perfectly.

I just got back from Fry's where I picked up some 1.5K resistors and I'll swap that temporary one out for the correct resistor and test it again. Once the football game is over.

This is one for the books. Now I will have to test all the resistors in the other one that was acting up in case it was the same thing. At least I have a place to start.

Whew...it was a tough fight, but, I win...

ken