| Arcade Collecting > Restorations & repair |
| Arcade PCB Repairs - New to the game... |
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| bperkins01:
This update will be the SELF INFLICTED WOUNDS update.. the moral of the story at the end... Continuing from my last update... Ran the board over night and tested - the ROM socket is definitely flaky. Overnight burn in also caused the 555 timer chip in the high score retention circuit to fail. I'm going to run this board for 4-5 days to make sure the remaining chips are cooperative before calling success. This board is putting up a fight: Replaced the ROM socket at F7 - this cleared up the image instability. The shooter showed a new odd symptom, intermittently upon game start - the shooter would move either all the way to the right, or up, or up and to the right. Once you moved the trackball - the game played normally. If the shooter does the self movement and I don't touch anything - it will make the exact same motion through all three shooters during game play.. I first replaced the 74LS74 at D11. It is a common to both the X and Y direction of the trackball and maybe it was weak. No change. Next I replaced the 74LS157 at D/E11 - It is the next chip common to the inputs and its closer to the trackball in the circuit. No change. Last real chip (closest) to the trackball is the 4585B at E/F11. It is a comparator chip that I need to read up on to determine if it can start in some weird state and cause the issue. I have one green board and one red board in the track ball? Could it be some weird mismatch? Need to keep digging into this one.. The vertical and horizontal counters chips (C11, B11) are on separate 74LS191's. It would not be likely that they both failed in the exact same way (moving the shooter w/o input) either. I'm pretty sure they are doing what they are being told. I'll have to figure out what line is telling them the wrong thing. During all of this - the high score circuit lost retention. -30V was still there. So the new 555 timer was still working, and score loss was also intermittent. It would retain for a while, then go away. I popped in a spare ER-2055 to see if it retains. Monitoring continues. Next - the LM324 chip failed. Audio went half out.. Replaced it and audio is back to normal. Is this board really that tired? Maybe the power is not clean at the board level? (I was on the right track here..) My other 3 boards work perfectly. There are a couple of capacitors on the input side at the board level that I will re-check to make sure they are doing their jobs. Outstanding items: - Continue to monitor the high score retention circuit - Determine root cause of trackball/shooter movement at startup. This particular board has been educational to say the least.. After messing with it and doing some testing with my new oscilloscope, I was as a loss to explain the odd shooter behavior. So I sent a video to a MikeA and he said "static?" After thinking about it for a few minutes, it explained everything. SELF INFLICTED WOUNDS!!! The first 3 boards I tested using an LCD. When I let them run overnight to burn in, I'd just unplug the 12v power cord from the monitor. Since then I got a new monitor. It is a pristine K7203 that is essentially brand new. I've been unplugging the molex power connector from the back when I let boards burn in over night. The plugging and unplugging has been creating electrical noise that has caused a couple of these chips to blow as well as causing me to chase ghosts. The board had legitimate issues when I started working on it, the last few repairs I will add to the getting experience bucket. All future board tests will be on the LCD when checking for stability overnight. Moral of the story: Electrical noise is real and causes crazy stuff to happen. Board works. |
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