Funhouse71
Active member
Bought this board off Dan (frothmeister) with known ram issues, images of issue with this Nemesis board can be found in this thread:-
Dan's (frothmeister) konami-gx400-nemesis-konami-gt-conversion-with-issues thread
Test screen displays multiple ram failures and in game upper half of screen just displays a white band with no sprites whatsoever, plus it had a broken sound pot.
RAM failures reported:-
CHARACTER RAM - BAD
SCROLL RAM - BAD
VRAM 1 - BAD
VRAM 2 - BAD
OBJ RAM - BAD
First thing I noticed was board was running some electrically erasable EEPROMS (27512's) for all locations, this meant the rom images were either doubled up for the 256 image Eproms @ locations at E-1 - E08 and quadrupled up for the 128 image eprom @ location B09, not ideal if you wanted to test the rom images for comparison against the MAME ones. The legs on these particualr type of eproms are very thin and flimsy, one broke off when extracting it from the socket plus Konami roms sockets are well known to be especially flaky at the best of times, especially after 40 years, not a good combination, but more on this later.
I tackled the missing game sounds, it was very obvious with a broken sound pot there would be no volume at all so this needed replacing to see if game sounds are present. I borrowed a volume pot from another Konami game which restored the sounds, a nice easy fix.
As Dan mentioned the game booted but had the ram issues previously mentioned above.
I swapped in a known working bottom board and the white band on upper half of screen had gone but still had ram issues as before so multiple issues with ram obviously was on top board and white band and missing sprites issues were on bottom board.
Looking for a quick fix for some of the ram issues I looked at the schematics and the LS138 @ 6J was a possible culprit after reading some other Nemesis repair logs about multiple ram issues, I thought I would swap this out first but this changed nothing.
Next I startied probing around all chips, especially the buffer chips, nothing seemed untoward over the whole board until I reached the very far left hand corner of the board. The LS245 @ 18A looked like it had seen a very hard life, the pins were black and looked to have got hot at some point. I started checking the outputs down one side of the chip and when I reached Pin 11 I came across a dead output. I removed the chip and stuck it in my ABI and it failed on 3 output pins in a row, outputs 11-13.
After replacing this chip and with the working bottom board still installed all rams finally passed their tests, basically this one chip had stopped all that ram from being accessed.
I now had a completely working game but I wanted to fix the broken bottom board, however whilst doing numerous boot tests I noticed occasionally I had the odd ROM error. I re-seated the roms several times and occasionally it would boot cleanly, other times not.
After closer inspection of the EPROM sockets I noticed some crusty black contacts so with a magnifying eye piece I scraped the contacts clean with a jewellers screwdriver and while I was at it I re-burnt all the roms with some normal correct sized EPROMs that had thicker contact legs. After several reboots of the game I had no more ROM errors appearing.
Now top board was fixed I turned my attention to the bottom board. Looking at the bottom board section of schematics I checked in the sprite ram section of the board. Going through each chip I didn't see anything too suspect and was puzzled for a long while as I was concentrating all my efforts trying to locate an issue in this section for missing sprites until I spotted a lone LS273 buried in the middle of the schematics @ 18G which I had completely missed. Checking the outputs every single output seemed to be reporting as dead, surely not?
This was yet another Fujitsu chip, after removing and testing in the ABI, sure enough showed all output pins were kaput
I put in a fresh chip and white band had disappeared and sprites were all back, game looked finally fixed...but not quite
Something wasn't quite correct with the scoreboard horoscope emblems, plus when in game the ship's multiple orbs were strangely jagged looking.
This was a sprite issue, so back to schematics and I went over the sprite section yet again, especially around the ram chips themselves and finally found a stuck data out, (pin 14) on the 4164 ram at 8G.
Replacing this restored the orbs and high score emblems to their former glory. Obviously I wasn't able to see this issue or check the sprites were ok until they even displayed so this ram fault may have arose during repair as this repair took me about a month on and off.
Interestingly, no sprite ram issues were reported either on boot up so I wouldn't trust the in game ram tests!.
As final finish to this repair aesthetically I noticed that a few of the resistors on the top board were very rusty, one 12k resistor in particular after cleaning the legs up, was reading 13k out of circuit.
Some chips were crudded up with dirt so I washed and dried both boards and went round and cleaned the pins on the all the chips that still remained dirty looking.
The TPL-4 chips for controls had all been socketed previously with turned pin sockets some time ago but started to looking tarnished so these were replaced with some fresh quality Harwin turned pin sockets.
The metal PCB feet were polished and all the screws replaced and the piece of flappy kapton tape over the steering header connector was removed in order to tidy up the board to complete the repair.
FIXED!...one of my favourite games I remember playing as a kid
Dan's (frothmeister) konami-gx400-nemesis-konami-gt-conversion-with-issues thread
Test screen displays multiple ram failures and in game upper half of screen just displays a white band with no sprites whatsoever, plus it had a broken sound pot.
RAM failures reported:-
CHARACTER RAM - BAD
SCROLL RAM - BAD
VRAM 1 - BAD
VRAM 2 - BAD
OBJ RAM - BAD
First thing I noticed was board was running some electrically erasable EEPROMS (27512's) for all locations, this meant the rom images were either doubled up for the 256 image Eproms @ locations at E-1 - E08 and quadrupled up for the 128 image eprom @ location B09, not ideal if you wanted to test the rom images for comparison against the MAME ones. The legs on these particualr type of eproms are very thin and flimsy, one broke off when extracting it from the socket plus Konami roms sockets are well known to be especially flaky at the best of times, especially after 40 years, not a good combination, but more on this later.
I tackled the missing game sounds, it was very obvious with a broken sound pot there would be no volume at all so this needed replacing to see if game sounds are present. I borrowed a volume pot from another Konami game which restored the sounds, a nice easy fix.
As Dan mentioned the game booted but had the ram issues previously mentioned above.
I swapped in a known working bottom board and the white band on upper half of screen had gone but still had ram issues as before so multiple issues with ram obviously was on top board and white band and missing sprites issues were on bottom board.
Looking for a quick fix for some of the ram issues I looked at the schematics and the LS138 @ 6J was a possible culprit after reading some other Nemesis repair logs about multiple ram issues, I thought I would swap this out first but this changed nothing.
Next I startied probing around all chips, especially the buffer chips, nothing seemed untoward over the whole board until I reached the very far left hand corner of the board. The LS245 @ 18A looked like it had seen a very hard life, the pins were black and looked to have got hot at some point. I started checking the outputs down one side of the chip and when I reached Pin 11 I came across a dead output. I removed the chip and stuck it in my ABI and it failed on 3 output pins in a row, outputs 11-13.
After replacing this chip and with the working bottom board still installed all rams finally passed their tests, basically this one chip had stopped all that ram from being accessed.
I now had a completely working game but I wanted to fix the broken bottom board, however whilst doing numerous boot tests I noticed occasionally I had the odd ROM error. I re-seated the roms several times and occasionally it would boot cleanly, other times not.
After closer inspection of the EPROM sockets I noticed some crusty black contacts so with a magnifying eye piece I scraped the contacts clean with a jewellers screwdriver and while I was at it I re-burnt all the roms with some normal correct sized EPROMs that had thicker contact legs. After several reboots of the game I had no more ROM errors appearing.
Now top board was fixed I turned my attention to the bottom board. Looking at the bottom board section of schematics I checked in the sprite ram section of the board. Going through each chip I didn't see anything too suspect and was puzzled for a long while as I was concentrating all my efforts trying to locate an issue in this section for missing sprites until I spotted a lone LS273 buried in the middle of the schematics @ 18G which I had completely missed. Checking the outputs every single output seemed to be reporting as dead, surely not?
This was yet another Fujitsu chip, after removing and testing in the ABI, sure enough showed all output pins were kaput
I put in a fresh chip and white band had disappeared and sprites were all back, game looked finally fixed...but not quite
Something wasn't quite correct with the scoreboard horoscope emblems, plus when in game the ship's multiple orbs were strangely jagged looking.
This was a sprite issue, so back to schematics and I went over the sprite section yet again, especially around the ram chips themselves and finally found a stuck data out, (pin 14) on the 4164 ram at 8G.
Replacing this restored the orbs and high score emblems to their former glory. Obviously I wasn't able to see this issue or check the sprites were ok until they even displayed so this ram fault may have arose during repair as this repair took me about a month on and off.
Interestingly, no sprite ram issues were reported either on boot up so I wouldn't trust the in game ram tests!.
As final finish to this repair aesthetically I noticed that a few of the resistors on the top board were very rusty, one 12k resistor in particular after cleaning the legs up, was reading 13k out of circuit.
Some chips were crudded up with dirt so I washed and dried both boards and went round and cleaned the pins on the all the chips that still remained dirty looking.
The TPL-4 chips for controls had all been socketed previously with turned pin sockets some time ago but started to looking tarnished so these were replaced with some fresh quality Harwin turned pin sockets.
The metal PCB feet were polished and all the screws replaced and the piece of flappy kapton tape over the steering header connector was removed in order to tidy up the board to complete the repair.
FIXED!...one of my favourite games I remember playing as a kid
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