trashedcabs
Grand Master
I need high res photos of the back of the PCB here. Solder side of U50. The component side would be nice too but I don't think there are any traces I'm missing that actually go anywhere.
Here's the story: I picked up this Fever SOS board from China for next to nothing. The description quite literally translated to "found a cave substrate on the street" with a picture of it in a dirty alleyway.
When it arrived the program ROMs were both missing, so after burning some new ones there was no output at all and the CPU was resetting constantly. I noticed some CPU address lines were stuck high--I pulled the CPU, socketed it, and replaced it with a Motorola one and the game was appearing to get to the copyright screen before resetting. Obviously, there was still no output, but I could gather this is where it was crashing from looking at how it behaves in MAME.
VERY sporadically (one in maybe 100 reboots), I would get SOME very garbled sound output. One single time, the game actually started and appeared to run with sound! I walked away to look something up and heard "PRESENTED BY CAVE" and ran back. This was short lived, as it never did that again, and a few reboots later I left it on for a couple minutes to probe stuff with my scope and suddenly without touching anything the cap at A26 started smoking. I replaced the cap but have not had any sound since then.
I really wanted to get any video output at all. I pulled all the remaining graphics ROMs and they all verified good. Some pins on the customs were corroded but the only actually missing pins I could verify were a ground pin and a VCC pin, both of which had continuity to other pins internally, so I left them missing for now. I reflowed all the customs as some pins had popped up. The two 74HC04s at UA1 and UB1 and both had stuck outputs, so I replaced both and I had some video output finally, though it was just a blue blocky pattern.
I was thinking about a RAM issue, so I decided to shotgun all the SRAM since I had them already and they have been a failure on other boards for me. The pattern changed to scrolling lines when I replaced U37 and U38. The DRAM activity seemed erratic when I looked at them with my scope so I replaced both DRAM chips. Occasionally, I can see activity on the IO and RAS pins of U36 but not U35, and that's when scrolling lines show up on the screen. It seems to come and go. I'm worried the 9838EX002 custom is dead, which would basically make this thing not worth fixing since the only donor would be from another very expensive PCB.
Any thoughts of where I should go next? I'm not super experienced with game board repair, but I'm trying to learn.
Here's the story: I picked up this Fever SOS board from China for next to nothing. The description quite literally translated to "found a cave substrate on the street" with a picture of it in a dirty alleyway.
When it arrived the program ROMs were both missing, so after burning some new ones there was no output at all and the CPU was resetting constantly. I noticed some CPU address lines were stuck high--I pulled the CPU, socketed it, and replaced it with a Motorola one and the game was appearing to get to the copyright screen before resetting. Obviously, there was still no output, but I could gather this is where it was crashing from looking at how it behaves in MAME.
VERY sporadically (one in maybe 100 reboots), I would get SOME very garbled sound output. One single time, the game actually started and appeared to run with sound! I walked away to look something up and heard "PRESENTED BY CAVE" and ran back. This was short lived, as it never did that again, and a few reboots later I left it on for a couple minutes to probe stuff with my scope and suddenly without touching anything the cap at A26 started smoking. I replaced the cap but have not had any sound since then.
I really wanted to get any video output at all. I pulled all the remaining graphics ROMs and they all verified good. Some pins on the customs were corroded but the only actually missing pins I could verify were a ground pin and a VCC pin, both of which had continuity to other pins internally, so I left them missing for now. I reflowed all the customs as some pins had popped up. The two 74HC04s at UA1 and UB1 and both had stuck outputs, so I replaced both and I had some video output finally, though it was just a blue blocky pattern.
I was thinking about a RAM issue, so I decided to shotgun all the SRAM since I had them already and they have been a failure on other boards for me. The pattern changed to scrolling lines when I replaced U37 and U38. The DRAM activity seemed erratic when I looked at them with my scope so I replaced both DRAM chips. Occasionally, I can see activity on the IO and RAS pins of U36 but not U35, and that's when scrolling lines show up on the screen. It seems to come and go. I'm worried the 9838EX002 custom is dead, which would basically make this thing not worth fixing since the only donor would be from another very expensive PCB.
Any thoughts of where I should go next? I'm not super experienced with game board repair, but I'm trying to learn.
