Bally -49 rectifier board TP5 voltage high

ripondan

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I will start from the beginning. I haven't had a SS project in a while so I picked up a Future Spa project and started in on it. All connectors were hooked up and I powered it up. MPU only had 2 flashes. Ordered and installed a new 5101 chip and powered it up again. MPU flashes 7 times and she is up and running. Had a couple display issues due to the connectors, but after reseating them they all worked and looked good. I decided to play a quick game before starting to clean it up to check the functionality. Everything was working good and then there was no more solenoid power. I thought I had blown a fuse but after visual and ohm checking the fuses all looked good. I restarted the game to check the MPU flashes. Now I am getting 6. I then began to check the voltages at the test points on the rectifier board. They all were in spec except TP5 which is at 67 vdc which is supposed to be 43 vdc. The rectifier board appears to have one of the bridges replaced at some point and due to a different size they are not attached to the heat sink. Would a failed bridge cause the voltage to go high or should I be looking elsewhere?
 
That's a weird problem. Any time I start seeing weird voltages like that the first thing I do is check with another meter to verify. Could be a near dead battery in the meter throwing you off. Just to be sure.

Then I would check the input and output voltages at the bridge rectifier for the solenoid voltage. Check the input AC and output DC. If there is a problem at the bridge it should be obvious when checked right at the bridge. If the input and output voltage are both high then there is a problem with the transformer. If only the output voltage is higher then there's a problem with the bridge rectifier.
 
Got it. The 600 ohm 10 watt power resistor was bad. For some reason I overlooked it on the schematic. I was visually following the traces on the board and checked my voltages at various points. I had 65 vdc before the resistor and "0" after it. I replaced the bridges anyway to eliminate future issues.
 
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