Joust original power supply issues

TrevEB

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I have a new powerboard and all of the voltages from the original main transformer have been tested and verified within acceptable ranges.

Heatsink with 2 power transistors.
Transistor tn6057 which makes the +5vdc's work was burned out.
Replaced with an NTE247

Now, everything powers up, but fuse #3 blows out.

Yes, we have heard this one before.

However, if I remove the heatsink from the sheetmetal panel that it and the power board and sound board are mounted to, then everything is fine.

I found +30vdc coming from from the heatsink fins.

I have tried isolating the power board, heatsink and main transformer from each other and the grounding wire that runs throughout the cabinet.

No difference.

I have remounted the power transistors using the original (heat transfer plastic, or rubber?) thinking maybe these transistors needed isolation from each other?

No difference.

It cannot be normal for 30 volts to be running through the fins.

Further, I found +16vdc at the four corners of the powerboard, (the screw holes)

So when the power board and the heatsink come into contact with each other via the sheetmetal panel. ZAP!

Where is all this excess electricity coming from????

All tests are done without anything else attached to the powerboard.

I also disconnected the monitor, coin door and lighting.
 
Do you have new insulators? I would put new ones on if you have them. And if there is a thermal paste on there, clean it all off in case someone used something conductive by mistake.

Get your meter out and start doing continuity checks between the different parts and the heat sink. Try to find something that is shorting to it. Also do the same with the wires to the connector, as you may have some broken insulation there that it grounding to the heatsink.

Do you have 16vdc at the four corners if the heat sink isn't installed and plugged in? If so, do the same thing for that, looking for a short somewhere. You might want to check the ground braid to the plate coming from the power supply, too...
 
Sounds like you have solder bridges on the headers where there shouldn't be solder bridges. Let's see a pic of the back of the power supply.
 
So I took a break from Joust and went to the Big Sur to calm down and refocus. Plus I now have a Ms PacMan which the wife would rather see working than Joust. Typical.

I managed to get everything up and running with the original power supply and no strange voltages coming from the heat sync fins or the PS board.

What is killing me now is the Power Transistor 2N6059 for 5vdc on the heat sync dies 3 minutes after powerup. It usually kills a ram chip with it. NICE.

I have tried again and again to make absolutely sure everything is isolated properly. The result. 3 dead power transistors.

My next test before shipping this all out for repair is to test the main power transformer for 5 minutes on each output to see if I see a spike in power or some other weird occurrence on my meter.

I've also ordered 10 more 2N6059s so I can go on a transistor killing spree.

Any other suggestions?
 
Long Beach! I ain'd driving down there. :)
Thanks for the offer! Would you ship them. Yeah, they are heavy but so are backup batteries.

In other news:
Here are the voltages from the power supply
1&3 = 121.4
9&10 = 130.2
15&16 = 10.6
16&17 = 10.6
11&12 = 26.8
13&14 = 9.4
19&20 = 6.8

On the board; Pins 1-7 to the power transistors
1 = 1.74vdc
2= 6.5vdc
3 = 15.00vdc sustained without power
4 = 1.53vdc sustained without power
5 = key
6 = 2.41vdc sustained without power
7 = 36.6vdc drops off slowly when power is cut.

I videoed 5 minutes of each and reviewed.
The power supply:
Lugs 9-10 climbed to 131.8
Lugs 11&12 jumps to 27.3vdc

On the power board, pin 7 jumps to 37.0vdc

Tests to the powerboard were done with the heatsync disconnected.
 
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