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Troubleshooting a TOEI CM-B14N that blows the F3 1A fuse, potential short.
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Puyo:
Greetings! I'm new here, and new to arcade repairs, and could use some help. I know a bit about electronics, and I do alright with a desoldering pump, an iron, and a multimeter.
I have a "Pac-1 Pac-2" bootleg board, with Ms. Pacman ROMs installed, in what I think is an old TAITO / HOEI Space Bird or Space Battle cocktail cabinet, with a TOEI CM-B14N monitor.
The monitor blows the F3 (1A) fuse on power up with no other noise or signs of life (the game plays, but nothing from the monitor). The service manual:
https://usermanual.wiki/Document/TaitoTVMonitorServiceManualToeiCMR20andCMR14.647713656/view
suggests that I should check for a short in B+, the horizontal output and HV circuits being likely culprits.
So far so good, though I'm not sure where to check B+ voltage, or where the high voltage or horizontal output circuits are (I can't find Q202! Q32 is top center, but no Q202).
Safety wise, I know general electronics safety precautions, about discharging caps, and the flyback at the tube (though I doubt any of that has gotten charged in a while), and running the monitor through the isolation transformer exclusively. Any other safety recommendations are most welcome, I've never worked on CRT tubes, or with high voltages.
When I first pulled out the monitor and did a visual inspection, I found a small cap that had obviously expired, and replaced it. I also replaced 2 larger ones (not the big filter cap though), because it looked like they had leaked, but in retrospect it was probably just glue residue. I also dusted the board because it was covered in nasty sticky black sooty dust, I only mention in case it's a meaningful symptom. I've also disconnected the video inputs to pull the monitor out.
Some pointers would be most appreciated.
Thanks!
Puyo:
I poked around some more, did another visual. Tried looking for pins that are grounded but maybe shouldn't be in the area of the AC connector. One thing that strikes me as potentially weird is the 4-pin "PT" (Power Transformer?) connector next to the AC connector, is just 2 jumper wire going from one pair of pins to the other. See photo.
The service manual also refers to power transformer T3 which I cannot find. T1 and T2 are right there, no T3.
I looked at the trace side of the PCB, and it's not super obvious where the B+ territory is, vs the high voltage. It's not as obviously secluded as other boards I'm seeing in YT videos.
I inspected T2 with my multimeter. There's a side with 2 pins and one with 3 pins. The side with 3 pins has only 0.2 Ohm across any of the 3 pins, which seems suspiciously low to me. Could this be the short I'm looking for?
The side with 2 pins has a more normal sounding 65 Ohm of resistance.
There's also continuity between one side and the other: from one pin of the 2-pin side to any of the top 3 pins I get 35 Ohm, and 99 Ohm (35 + 65) from the other. As far as I know, and I do know very little, I shouldn't have continuity across the 2 sides of a normal transformer. I am testing it while it's still on the board though, which could be the wrong way to do it since continuity might be going around, but then shouldn't the resistance across both sides of an otherwise isolated transformer be a little more... resistive than 35 Ohm if it goes around the transformer?
Is it worth pulling it out for proper testing? This is where my lack of experience really shines 8)
Cheers!
princess prin prin:
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