Cinematronics Blowing Breakers (frying Resistors)

SteveJ

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Just rebuilt a Cinematronics display board, using this parts list: (www.biltronix.com/arcade_electcomp_01.html#Star_Castle_Monitor_Board)

The Circuit breaker is tripping after a few seconds, but only if the display is connected.
Game plays fine blind.

I smoked a few resistors after the breaker tripped (in the R123 - R129 row: R125, R127, R128). It didn't trip breakers before I replaced all the parts
-- Obviously my error. Should I disconnect the HV, CRT, & Yoke before troubleshooting the board? I'm afraid keeping turning it on will only smoke more parts.

So here's a dumb question -- in general, what causes the breakers to trip? I know the circuit pulls too much current, but what causes that? Is it usually shorts? I'm trying to pull together the troubleshooting tips from the various sources

Does this ring a bell with anyone? I'm going through the troubleshooting tips in the various FAQs. any help is appreciated.

Steve
 
Did you change the transistors on the heat sinks on the side of the chassis ? Also, if one of those is or was bad, then one of the small transistors at q102, q103, q104 etc could be bad. First replace the smoked resistors and and chassis transistors and then you can either shotgun the smaller transistors or meter them and compare them to their corresponding transistor at Q202, q203 etc and look for any differences if you dont want to take them out of circuit to meter them. It's not the most accurate way to find the bad one but it worked for me.
 
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