Williams power supply - 12v missing

Tweeg

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I've got a Joust that's not working, and giving the 1-3-1 RAM error. The 12V is out on the power supply... or at least, it's out when the boards are all plugged up. When I remove the load from it, the 12V line goes up to about 28V, but under load it measures roughly zero. I've replaced the 2N3055. I don't think the bridge rectifier for that line is bad, because I'm measuring about 29VDC at its + terminal. I'm suspecting the 723 voltage regulator now, but wanted to see if anyone else had ideas... thanks in advance.
 
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That sounds like the caps may have gone bad. It probably needs a complete working over to bring it back into spec.

You can order the parts and do it yourself, or there are a few of us that rebuild the power supply boards for fairly reasonable rates if you don't want to do it yourself.

ken
 
It has been my experience that either your LM723 is bad or the socket if it is socketed is bad. Lately I have been running into a lot of defective single wipe sockets installed on these power supplies.

I also agree with Ken, that it is most likely time to recap that sucker too.
 
The bridge rectifier tests out OK. I'll probably just order the repair kit from Bob, it's only $12 including new Molex connectors. Before I order, I think I'll hook up a PC power supply to the CPU board and see if I can get it to boot, just to make sure I don't need to order RAM also.
 
Crap. I put good clean 12V power to the CPU board, now instead of a blank yellow screen I get a rug pattern alternating every few seconds with a screen full of vertical yellow lines, and still the 1-3-1 error flashing. Maybe the RAM has gone bye-bye, but... is there anything else that uses the 12v regulated output? Why would I get different results with or without the 12v if the RAM is fried anyway?
 
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Assuming you are using a separate 12V power supply plus the original power supply for the other voltages, have you tied the grounds of the two power supplies together? If not, they you are supplying a floating voltage to the +12V lead.

ken
 
Assuming you are using a separate 12V power supply plus the original power supply for the other voltages, have you tied the grounds of the two power supplies together? If not, they you are supplying a floating voltage to the +12V lead.

ken

Ken you have the patience of a saint, I just sat here shaking my head after reading it. My hat is off to you, Brother.
 
Assuming you are using a separate 12V power supply plus the original power supply for the other voltages, have you tied the grounds of the two power supplies together? If not, they you are supplying a floating voltage to the +12V lead.

Yep, I did tie the grounds together, and I measured the 12V at the CPU board. Good call though, I can easily imagine myself having failed to do that.

I'm going to assume the RAM is toast, and that the machine just behaves differently with RAM that's powered up but malfunctioning than it does with RAM that's getting no power. At any rate I'd rather order the RAM and end up not needing them than to not order them and end up having to pay another shipping charge and wait around on them.
 
Just a quick update, I got the repair kit from Bob. I only replaced the one LM723 that regulates the 12V, and the capacitors. I had already replaced the 2N3055, and I didn't want to fool with the other LM723 since it was working properly. The power supply is fixed now, and I'm pretty sure it was the LM723 that was bad since it was actually physically disintegrating as I removed it... the legs were horribly corroded.

Turns out the RAM was definitely fried as well, so I'm glad I ordered replacements. While I had the CPU board out for that, I also installed a lithium battery upgrade. The AA battery holder was falling apart and the memory wasn't being held. That's fixed too. With Joust back up and running, I now have no non-working games, I guess that means it's time to buy something!

P.S. Anyone else noticed that these Williams boards are a huge pain when it comes to soldering / desoldering anything on a ground trace? They seem to have a nearly infinite capacity to suck heat away from the solder joint.

P.P.S. Thanks to everyone who chimed in on this!
 
P.S. Anyone else noticed that these Williams boards are a huge pain when it comes to soldering / desoldering anything on a ground trace? They seem to have a nearly infinite capacity to suck heat away from the solder joint.
+100000. Every time I have to desolder something on one of those big pads (the bridges, the negative end of the big cap, the input headers, etc.) I am tempted to go get the Bernzomatic torch. They are a serious pain.

ken
 
Resurrecting this thread as I'm dealing with the same issue after rebuilding my supply with the deluxe Bob Roberts kit.

No +12v or -5v from the supply. I replaced pretty much everything except the header pins on the board including socketed new ICs, all caps, transistors on heat sink, BR, fuses and voltage regulators.

I have neither LED #1 or #2 lit, I get 1.3.1 RAM errors at the diagnostic. Game was working perfectly fine when I brought it home, played for about 45 mins and then blew a fuse on the power board and has since been dead.
 
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Even if you're a beginner, look at the schematic, focusing on the circuit for whatever voltage you're missing, and start checking for continuity. I did a rebuild kit on one, was missing a voltage, and it turned out the big radial cap somehow wasn't making contact to the top layer of the board, as if the through hole was broken.
 
Yep I'm looking over the schematics, one of my main concerns was that harness between the transformer and the power board was burned up and hacked to shit and I had to try and reassemble it with new female pins and connector, I'm just hoping they are correct now.

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You MUST replace the male header pins on the PCB as well, not just the connector/female side. With the plating burned on those pins, they'll act like resistors, heat up, burn what you just replaced.
 
You MUST replace the male header pins on the PCB as well, not just the connector/female side. With the plating burned on those pins, they'll act like resistors, heat up, burn what you just replaced.

Yeah I hear ya, getting them off without damaging everything is proving a challenge.
 
You also need to replace the header going to the transistor array on the heat sink. In your pictures, those headers look burned as well.

ken
 
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