Dead pcb and monitor - where to start?

delroy666

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When I picked up my Pac cab, it was almost complete except for the PCB. The monitor shows some signs of life - I can see a glow in the neck, and a flash of light on the screen when I turn it off. So, I bought a 'working' Pac board from a fellow KLOV member hoping I could use it to troubleshoot the monitor and eventually get everything working. When I connect it to the monitor and power up, I get nothing on the screen - not surprising, since I don't even know if the monitor completely works.

However, I can't even get the board to play blind. I get a constant buzzing noise from the speaker, and two 'beep' sounds after powering it up or resetting. Adjusting the volume pot on the board has no effect on the loudness of the buzz or beeps. I've ruled out cabinet's switcher, fuses and harness by connecting a lab power supply directly to the board on a test bench. It doesn't respond to 'coin up' or '1p start' control signals with the DIPs in play mode or test mode.

It's a chicken and egg situation, so where should I start troubleshooting? Buy the cheapest Jamma board I can find and use it to troubleshoot the monitor first? Is there anything I can try on the Pac board to get it playing blind? I can probably gain access to an oscilloscope. I'd appreciate any advice.
 
If you have another cab you can swap in this monitor to verify it works. A cheap Jamma board will not do you any good if you don't have a Jamma harness, and it doesn't sound like you do.
 
I do have another cab, but the monitor in that one is totally dead. However, I was going to just 48-in-1 that machine when I'm finished restoring the Pac anyways, so I guess I'll order a 48 or 60-in-1 board now to help me get this monitor going.
 
Have you replaced fuse blocks yet? If they are original, I'd replace them first, they are known to cause problems. If you have the original filter board, lose that too, its not needed and is also known to be problematic. Also, I'd scrub the edge connector really good, or if you have the means, replace it.
 
+1 on the fuse blocks. You can get replacements at your local Radio Shack store. At least I think they still have those in the Great White North.

If you can't, you can take the fuses out and clean the corrosion out of the cheap ones that are in there then crimp 'em back a bit so they hold tight to the fuse when you put it back in. You should be able to get that to work well enough for testing until you can get new fuse holders.

Oh, and it goes without saying - UNPLUG IT before you mess with the fuses and the fuse holder. ;)
 
Thanks for the suggestions. I've taken the fuse block and edge connector out of the equation by connecting the board to an adjustable linear lab power supply (borrowed from work), with the wires soldered directly to the PCB traces. The board does the same thing as when connected to the harness, arcade switcher, etc. The cab didn't come with a filter board.

As for the 2nd monitor, I'm using the same iso and cleaned-up fuse block that work to power up the first monitor.

Are the two beeps I'm hearing part of the normal boot up process for a Pac-man? Are they associated with a particular error message, or is it just something screwed up on my board? With the DIPs set to factory default, I figured I should be able to momentarily ground the 'coin 1' and '1p start' signals and hear the associated sound effects, but I get nothing.

The Canadian Radio Shacks were owned by Tandy, the same parent company as the US Radio Shacks, but was later spun off as InterTAN. A couple of years ago, Circuit City acquired InterTAN and rebranded all the stores to "The Source by Circuit City". They don't carry the same inventory of electronics parts as they use to, although you can still get basic stuff like cables and fuse holders. Thank goodness we have Digi-Key in Canada.
 
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