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ShootTheCore

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Some folks have expressed interest in seeing a short writeup on the arcade repairs and console repairs / mods that I do in my spare time, so I'll post a little Repair Diary here when I do one.
Some quick notes:

1) I don't do this kind of work for hire - only for myself and one or two friends.
2) I'm all self-taught based off of what I learn from blogs, forums, YouTube videos, and the advice of some friends that do electronics rework professionally.
3) I'm leaving out details of the HOURS of continuity testing, logic testing, Googling, forum posts, etc that it takes to diagnose these boards.

OK, with that said, here's Repair Diary #1. I purchased this Forgotten Worlds conversion board with a background problem - the character sprites would appear, but the background would only display scrolling vertical lines.
IMG_3369.JPG

The culprit was the PAL chip at location 1A on the secondary B Board - this chip "engages" the background ROM chips. It was burning hot to the touch after the board had been left on for a moment, so it was the obvious culprit. I replaced the chip with a programmable GAL chip using the data from the equivalent MAME ROM set, and all was well.
IMG_3370.JPG
IMG_3359.JPG
 
Great review! Keep'em coming!

One question, how did you troubleshoot the PCBs normally? Can you shed some light, like i.e.

1) Visual examination looking for missing chips or scratches
2) thermal test touching chips and checking with cooling spray any improvements
3a) If black screen, check CLK, RST, Address bus, etc.
3b) If specific problem check schematics for source of background chip, etc.

Once again thumbs up :thumbup:
 
CPS1 system is notorious for failures on two IC's : CPS-A-01 and CPS-B-21 (depending on the game).
These IC's had a high failure rate, especially CPS-A-01, so you should consider yourself a lucky guy !
The PAL@1A selects all ROM's (tiles & sprites) inteleaved , and it is possibble that only one output to one
/CS of some rom's to be bad.Also, PAL@1A is hot under normal operation, not burning, remember, PAL16L .... are bipolar in nature , not CMOS, so heat output is normal.

Have a good day, Dragos.

P.S. : looking more careful at your pics, i can tell that your PAL@1A = S9263B is from a SF2CE game, so it seems that the pal is just fine ! :thumbup:
 
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Both of you guys are WAY smarter about these things than me. I am but a humble padawan that still has a lot to learn. :D

@mr3xtraball I agree that I got lucky with this board. It helps that it was purchased as an inexpensive conversion board from Street Fighter 2 CE. Maybe the 1A PAL hadn't failed after all, and replacing it with the programmed GAL for Forgotten Worlds was the real problem all along. But the PAL that was in there got WAY hotter than the replacement-it was sizzling hot!

@Darksoft I didn't have to do any in-depth digging with this board - I got lucky with the obvious sizzling hot PAL. On other boards though, yes I do a visual examination of the board under a microscope to look for broken traces, touch the chips by hand to see if any are unusually hot, pull any socketed ROMs and compare the checksums to MAME.

I'm working on a glitching Simpsons board now that is my first dive into interpreting schematics and using a logic probe and oscilloscope to analyze the memory chips and the logic gates that control the memory addressing. When I get that board sorted out, I'll include details on the analysis in my write up here.
 
The PAL@1A is normat to get hot, again - its bipolar technology, as long it does its job on a SF2CE board,
leave it alone and move on.From my head, GAL16V/20V/22V uses mixed tech bipolar&CMOS, so its temp is lower, but not much.

About Simpsons pcb, plz take some (good quality) photos and i will help you.I have some experience with "evil" Konami, in fact you can say that i an a konami addict.Also you can contact "Caius", he is a professional repairer.

If you are going to continue repairing boards, you will a decent scope, analog/digital, preferably with dual trace(VERY useful vhen troubleshooting triggered/long delay/multiple signals), decent soldering iron (both A/C powered , and gas powered), better soldering station with solder suction - option, hot air gun, misc. tools etc...

Have a good night, Dragos.
 
I'll start a new thread on the Simpsons PCB project. I think I have it narrowed down to a faulty RAM chip - I'll know for sure when the replacement chip arrives.

I'm doing fairly well so far on the equipment side - I have an AmScope LED microscope, Hakko FK888D soldering station, a Hakko FR300 solder sucker, and a Wellon VP-390 EPROM programmer. A better oscilloscope will be my next equipment upgrade - I currently have a DSO Seed single-probe digital scope that gets the job done for now, but I agree that a dual-trace scope would definitely be more useful. I haven't needed a hot air gun yet, but I'm sure that day will come... one tool at a time, one project at a time. :D
 
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