Power Supply / Wiring Problem?

steve8091

Member
Joined
Jan 5, 2012
Messages
284
Reaction score
5
Location
Menasha, Wisconsin
I'm troubleshooting a new dead cabinet I bought, and finding a lot wrong along the way. The latest - the switching power supply seems to be putting out adequate voltage, but as soon as I plug a PCB into the JAMMA harness, the voltages drop off significantly. The +5V, for example, drops from a solid 5.0V to about 1.8V, and the LED on the supply even goes out.

Is this an issue with grounding, or with the power supply being overtaxed, or both? Any suggestions would be appreciated.
 
I'm troubleshooting a new dead cabinet I bought, and finding a lot wrong along the way. The latest - the switching power supply seems to be putting out adequate voltage, but as soon as I plug a PCB into the JAMMA harness, the voltages drop off significantly. The +5V, for example, drops from a solid 5.0V to about 1.8V, and the LED on the supply even goes out.

Is this an issue with grounding, or with the power supply being overtaxed, or both? Any suggestions would be appreciated.

It is something wrong with the wiring. Start by using the ohm meter and see what you get when you ohm out the +5 to ground with ALL power off and pcb connected. If it is real low there is a short or wiring problems.
 
There could be one of two problems: short circuit/overload causing the power supply to shut down or a bad power supply.
 
There could be one of two problems: short circuit/overload causing the power supply to shut down or a bad power supply.

+1

You could be overloading the supply. I have one where if the voltages gets below 4.85 it will shut down until you unplug it for about 45 seconds. It would be nice if it did the same when the voltage get above +5.25 but it doesn't. I have tried with a 6.3 volt light bulb and got it up to 6.1 volts.
 
It is something wrong with the wiring. Start by using the ohm meter and see what you get when you ohm out the +5 to ground with ALL power off and pcb connected. If it is real low there is a short or wiring problems.

Are you saying that I should ohm between the terminals on the PS, or to another ground point? On the PS, the resistance between +5V and ground is about 80 ohms. I'm not sure what qualifies as low.

I didn't mention it, but there is also a slight buzzing coming from the PS. I can pull a PS from another machine to check it, but I was worried that I might damage that one if it is a wiring issue. Do I need to be worried?
 
If you have a different JAMMA board, try plugging it in. If the voltage behaves the same, replace the power supply.

If you are trying to test the +5V to ground path, you need to take the switcher out of the loop. Pull the +5V lines off the switcher and retest.

ken
 
Back
Top Bottom