John's Arcade Forum - Classic Arcade and Pinball Collecting and Restoring Discussion Forum - RETRO MAME - Nintendo Vs Forum

   While fixing a "hum" on my asteroids, I was desoldering  an LM324 (audio amp IC) on the pcb. but being a newbie I messed it up (maybe shorted something and/or ruined the chip) . when I went to power up the whole game was dead, except the marquee. wouldn't play blind, and the p1,p2 lights just steadily lit.
   Now upon power up I get neckglow for a second and then quickly almost no glow (is this the spot killer kicking in?)
   At the edge connector im getting just 8vac at pin 20, while the manual shows I should be getting 36vac. also im only getting 5 and 10vac at pins 7 and 10 of the molex connector feeding the monitor, when I should be getting 30vac. and  im not showing any voltage at the X and Y outs of the pcb.
   I am getting the proper 5 and 10.3vdc on the AR board, and I am getting 5vdc at pin 2 of the pcb edge connector.  Ive recapped the whole game including big blue, and replaced the bottlecap transistors on the chassis, and all fuses are good.  I really hope someone can point a newbie in the right direction. thanks for any help

well first reinspect all of your work. you probably are still shorting something out.

The monitor is in spot killer so you are fine there.

thanks for the suggestion Ian, ill do that. I don't know how something as simple as an audio amp chip would kill the whole game. I did discover a small 3- leg transistor that had been "twisted" so the legs were shorting against themselves. ill be so happy if I can bring that game back to life.

if you managed to short the power rails to a pin you might be drawing too much current and killing off the supply.

I am showing 20vdc on the two LM324N chips located on the main pcb. (boy that seems like a lot of voltage). but at least theres power there.
these are quad op amps that are notorious for causing a hum.