Star Castle Audio board pop breaker

sushko

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Hi my Star Castle Audio board works fine and sometimes not. What happens is the q17 and q18 get piping-hot and eventually blows the breaker #1. I have two boards and they both do the same thing. I have replaced all electrolytic capacitors on both boards and transistors q17, q18 ,power transistors ic4, ic5. I was thinking the next step would you go for the op amp.

This seems to be an intermittent problem as sometimes the machine works perfectly with no heat and other times it heats up and shuts down right away. Makes it more fun for troubleshooting.

Any way any help would be appreciated

Rich
 
Are you getting proper power to the audio board?
 

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I will check it out. I see the monitor looks like it shares all power sources and if I leave the audio board unplugged the machine will run indefinitely. Never pops breaker. Maybe their monitors more lenient I will go over it. Thanks
 
Okay finally had a chance to go over this powers everything looks good got 30 volts to 5 volts got the plus-minus decided to check the speaker to check to see if it was 8omh. All looks good. Of course this Moment In Time the amplifier is a cool too. I have to check it when the thing starts acting up.
 
I have both of my Star Castles set to 5.04.....Why 5.04? Because the first one worked at that value, so I adjusted the other one to be the same.

Breaker 1 is for the +25V... But 5.2 seems too high. Hopefully it fixes your problem.
 
Wow 5.04 that sounds like this board set is very finicky. I changed the big caps on the power supply a while back maybe I forgot to adjust to 5 volts at that time. So far so good though. More testing needed because this was always an intermittent problem.
 
While the +5V supply is used on the audio board to operate the TTL logic, it is not used by the power amplifiers at all. The transistors are not piping hot over small variances in the +5V.

How loud are you playing the game? Cine/VB audio boards will certainly heat up their transistors if they are cranked up. It sounds too me like one of the transistors eventually gets so hot that it goes into thermal runaway and cannot shut off and that is causing the surge in current that is popping the breaker.

Try running a small fan over the audio power amp section of the board to keep the transistors cool. Also, remove the heatsinks, clean off the old dried up thermal grease, put on some new grease, and re-install the heatsinks. It might help.

If you are not running it loud and it is still heating up like that then there's likely a bad part on the audio board. It could be a leaky disc cap (C45,C46) in the power amp section or the final stage TL081 (IC25) might be flaky.

Maybe after the speaker coil warms up then it shorts. Temporarily try another speaker or install an in-line fuse.

How positive are you that the breaker pops due to audio? Did you play with the audio power plug disconnected for a while to see if things were stable with just the game and monitor working? Just wondering.

Good luck,

Bill B.
 
I wasn't having any problems with audio board disconnected till the other day. The breaker popped without audio board pulled in. I was playing around with testing cpu board and led is now suck on. I have a second board so I put that in and it has been fine so far. Maybe cup board would lock up and cause this problem. I am going to bench test it with 5v. See if I have clock and some other stuff. At least at this point it's not an intermittent problem. LOL
 
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