Tecmo Knight repair log #1

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Aug 252010
 




Game looked fine initially but when starting the game and on one of the intro scenes, the sprites had jailbars in them.

After a couple of frustrating hours figuring out what to read the maskroms as and if they were in the right places I settled on reading them as 27C040.
Three of the masks on the B board dumped fine but one of them gave random junk out at every read so it looked ok on the logic probe but the eprom reader told a different story.
Hunted out an 27c040 eproms and burned a new chip from the MAME set, the game now runs and plays 100%.

Street Fighter II Hyper Fighting repair log

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Aug 232010
 

Got this board off ebay, sold as having graphics corruption. There was slight corruption on the title screen and a fair bit in-game, shadows were the worst part but the Ryu character suffered really badly too.
As I have a spare board set for CPS1 games I started by swapping the B board over from a champion edition board. The fault disappeared
I swapped the 3 eproms over from the Champion Edition board to the Hyper Fighting board (these are the only difference between the 2 games) and the fault came back.

I know the first picture is from a Champion Edition, I had the CE ROMs fitted at the time of taking a picture

There is not much to the B boards so took a wild guess that the problem was with one of the 42 pin maskroms. I systematically swapped them over one at a time tested the board after each swap. Turns out that the very last maskrom has one of its address lines stuck, swapped this one for the one off the donor board and all fixed. Replaced the 3 eproms for Hyper Fighting and all the faults are now cleared up.

Bubble Bobble repair log #1

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Aug 012010
 

This game was completely DOA. Checked the clock signal, all fine. Checked /RESET line of Z80, stuck low.
I replaced resistor R30 (330ohm) which is part of the Z80 reset circuit, it fell in half on removal.
The /RESET was now HIGH but all the address line were stuck.
I pulled both the Main and Sub Z80’s, both failed tests.
Also found 2 dead EPROMs. Burned 2 x 27256 eproms( a78-07 and a78-08)

All seemed to be firing up after that.

X Multiply repair log #1

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Aug 012010
 

Started off as a physical problem with corroded legs on MASKROM’s giving corrupt graphics on sprites.

Three legs were corroded on MASKROM T44.00, which is an NEC 23C1000. After a little asking about, I was told the EPROM equivalent was a 27C301 (non JEDEC).
I obtained a 27C301 eprom and burned a T44.00 from MAME. Pretty much all the graphics were back but there were some white blocks around the ship sprite and certain enemy bullet sprites. Found a broken track from pin 20 (chip enable). Repaired this and the white boxes are now gone from the ship sprite. There were still white boxes around the projectiles. I have now confirmed that with an original ROM the game works fine.

I took a closer look at the pinouts from a 23C1000 MASK ROM and a 27C301 EPROM. MASKROM’s have less pins than their EPROM equivalent mainly due to not have programming pins but also this ones only has one enable pin (pin 20) and the EPROM has separate /OE and /CE pins. I lifted pin 2 and soldered a wire from this to pin 22 on the EPROM and fired the game up, all the graphics are now 100% working. I initially thought this corruption was down to the speed of the EPROM but now I know otherwise.

Graphics fault


Fixed



Bomb Jack repair log

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Aug 012010
 

Received an “untested” Bomb Jack board from eBay.
It appears to be a bootleg/original hybrid. The A board was a bootleg, the one with only 2 x AY-3-8910’s on it and the B board is from an original.

The game was missing the green and blue colours and sound was stuck in a constant repeating loop from power up.
The RGB, sync and video ground go to a 5 pin header on this bootleg, not a 6 pin header, the previous owner was clearly not had an adapter or plug for anything on this board and had soldered the wires directly on, had also melted all the plastic supporting these 5 pins so a couple were shorting to ground, easy fix. The sound had a corrupt EPROM, I erased and burnt a new one, still no change. The RAM had already been socketed so I tested it and it came up clear. Checked the Z80 with the logic probe and found the address lines were all high except for a couple that were pulsing. De-soldered it and tested it, it failed on pretty much everything, replaced it and now the sound was working but seemed to be lagging behind when compared to MAME. I put in a new RAM and the fault was fixed. Swapped the RAM back and fault returned. This RAM works fine in my other boards so am putting it down to RAM speed.

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