W/G 27K7502 comes on/off at random

SilverDuck

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I have a 27K7502 that I just got back from Chad at Arcade Cup. The monitor only comes on after I connect/disconnect the AC power about 10 times, and then....it goes off at random times. When I turn the game on, I get nothing on the monitor, so I have to unplug the AC connector that feeds the monitor, and reconnect, disconnect, reconnect, etc etc until finally it will come on. When it does not come on, I do get a click on the chassis somewhere, but no fizzle with neckglow. When it does come on, the picture is nice, but it shuts off at random times.

Most likely culprit?
 
wells

You dont say what the problem was before you sent it to chad and what he all did to it but when i have that problem i start at the 1uf cap by uc3842 ic and also the 22uf in the power section.
Check 100uf 200v cap and 33uf 250v cap also.
Check your 10k resistor in the power section and see if that is still in value.
 
I sent him a parts chassis and he got it running. I bought the chassis from Modesitt after he stripped all the parts off of it, and Chad repopulated it to get it running.
 
Could be something as simple as the B+ being borderline high causing it to shutdown.
Seems the 7400/7500 are very touchy on this, so always a good idea to check it in the cab it will call home. And your AC source may be a couple volts higher too, which may be enough to top it over. (hence Chad sets it on his bench, but it may be higher in your cab)
Just worth checking and setting.
 
The pins inside the AC power connector on the monitor board are known problems with them spreading too far open allowing poor/intermittent connection.
 
The pins inside the AC power connector on the monitor board are known problems with them spreading too far open allowing poor/intermittent connection.

Good point Ken..... I had a 7401 totally kick my tail because of that, finally just removed the onboard connector and put a pigtail on it with new pins and housings.
 
Good point Ken..... I had a 7401 totally kick my tail because of that, finally just removed the onboard connector and put a pigtail on it with new pins and housings.

That's exactly what needs to be done with all the U2000/U5000 and K7400/K7500 series chassis.
 
I had this problem last week, try turning the Screen down on the flyback some and see if it continues to not power up.

this could be a B+ thing or it could be the HV shutdown.

other users urged me to re-cap my 7500 because that could contribute to the problem, but you just got caps put in.

strange.
 
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