Pr3tty F1y
Student
I have a T-Unit (NBA Jam) that I'm trying to fix up. After swapping in known good ROMs, PALs, CPU, and FPGA chip I got it to boot but the graphics are fuzzy/crunchy looking. It looks like a RAM issue to me from other boards I've dealt with RAM issues on, but I'm pretty sure the video DRAM is not the issue.
UA12/UB12 and UA14/UB14 show as bad in the self-test but I removed the original chips and swapped in known good chips and nothing changed. Still got the crunchy/fuzzy graphics (with a bit of a waterfall effect of the distortion running down the screen).
The game is playable through the garbage graphics, so I know at least some of it is running. I'm just not an expert at all and reading through the schematics to figure out the data and address lines is not getting me any where. I'm thinking it may be some of the LS logic chips but I wasn't sure if anyone had any pointers.
From prior work repairing a MK II board, I do vaguely remember if something was wrong with either the A or B DRAM, it would cause the corresponding other video RAM to test bad. That was mostly me shorting the pins of the DRAM on that board as I was using solder paste and hadn't gotten a good technique down yet for the SOJ package chips. Things went MUCH faster today with it only taking 30 minutes or so to remove the original chips, clean up the pads, and apply just enough solder paste and use a low enough hot air flow to not move the chip but also get the paste to suction onto the legs. I did do a good bit of testing with my multi-meter (I don't have a logic probe) and I'm fairly certain that everything is good/back to the way it was with the video DRAM.
Everything else looks clean on the board. I checked the under side for bent/cross-talking pins but the minor corrections I made (which I'm really not 100% sure they were touching or not, but I bent back the suspect ones regardless) had no effect.
I just wasn't sure if someone with more experience than me would know what chips/set of chips could induce failures on UA12/UB12 and UA14/UB14 as the other ram chips test good.
UA12/UB12 and UA14/UB14 show as bad in the self-test but I removed the original chips and swapped in known good chips and nothing changed. Still got the crunchy/fuzzy graphics (with a bit of a waterfall effect of the distortion running down the screen).
The game is playable through the garbage graphics, so I know at least some of it is running. I'm just not an expert at all and reading through the schematics to figure out the data and address lines is not getting me any where. I'm thinking it may be some of the LS logic chips but I wasn't sure if anyone had any pointers.
From prior work repairing a MK II board, I do vaguely remember if something was wrong with either the A or B DRAM, it would cause the corresponding other video RAM to test bad. That was mostly me shorting the pins of the DRAM on that board as I was using solder paste and hadn't gotten a good technique down yet for the SOJ package chips. Things went MUCH faster today with it only taking 30 minutes or so to remove the original chips, clean up the pads, and apply just enough solder paste and use a low enough hot air flow to not move the chip but also get the paste to suction onto the legs. I did do a good bit of testing with my multi-meter (I don't have a logic probe) and I'm fairly certain that everything is good/back to the way it was with the video DRAM.
Everything else looks clean on the board. I checked the under side for bent/cross-talking pins but the minor corrections I made (which I'm really not 100% sure they were touching or not, but I bent back the suspect ones regardless) had no effect.
I just wasn't sure if someone with more experience than me would know what chips/set of chips could induce failures on UA12/UB12 and UA14/UB14 as the other ram chips test good.
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