tron 90412 power supply help!

karatechamp999

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hi guys, so my tron bit the dust, started resetting randomly then now its just garbage on the screen. i started checking voltages around the boards and found it to be really low in the 5volt circuit (3v). the 12v is fine. the 5volt pot on the power supply doesn't do anything. so i checked for corrosion its all good, i put an off board battery in it when i first got the machine. while checking around i noticed that the transistors on the heat sink were not behaving correctly when measured with a dmm, so i pulled them from the board and tested them today, and they checked out fine while out of the pcb, put them back in and they aren't testing right. so my question is does this mean something else in the circuit making these not test right while soldered in, or is this normal behaviour for transistors while in the circuit? thanks in advance
 
yes something else is causing it then. you may have one of the lm305 bad. i would check for cold solder joints on the pcb and caps too if they are original. if you want to do a major rebuild i do make a kit with everything including connectors.
 
does this mean something else in the circuit

I replace all the capacitors on there and then reinstall and test
hit all the cold solder joints too that you can see

when the capacitors dry out, all kinds of screwy stuff can happen
each out of specification component changes the mathematical equation
yes, some components need to be removed from circuit to test
the kicker is some components can test good out of circuit but when a "load" is placed on them, they fail. total bitch when that

when out in the field bidding on a game, one has to take into account that the monitor chassis and the power supply could probably use a cap kit/rebuild on them both. it's just been so many decades that they all need it almost
 
okay, made some headway for those who might be experiencing similar issues. start testing voltages from the MCR suitcase into the power supply with the output connectors unconnected, got a good stable 6v (don't forget this is unloaded voltage, it will drop when the load is applied and when all is working can be adjusted) next start tracing voltage from here. plugged the outputs back into the power supply and disconnected the ssio/video pcbs, it dropped back to 3v (always measuring voltage at the 5v cap on the power supply next to the output connectors) while thinking that there must be a short somewhere in the output connectors or the wiring to the main game pcbs i noticed that some of the wiring from the output connectors was going up to the front of the cab (coin door and control panel) meticulously unplugging, then measuring the voltage between each connector throughout the front end of the cab, i traced back to a connector going into the spinner wheel under the control panel, which when unplugged got me my 6v back at the power supply. i then plugged the audio amp back in (leaving the spinner wheel unconnected) still got 6v, so far so good, but then when i plugged the main game pcbs back in (just the power and video connector, as illustrated by todd from TNT amusements video on youtube) she dropped to the 3v at the power supply. sooo, it looks like i have a malfunction/ short on the game board AND at the spinner wheel?! I've already reseated many of the chips on the board, still get a flashing yellow LED at top of ssio board which i heard indicates a bad ROM, i'll go ahead and reseat the rest and replace the caps on the ssio/video pcbs. When this TRON started going bad it was losing sounds and would make popping noises, then it started just to reset on its own, so i'm thinking caps
 
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