Porchy

Double Dragon repair log #4

Mar 122011

The sound circuits on these DD boards really were bad!
Another one with dodgy sound, music was intermittent and half the SFX were really really low.
Did a full capacitor replace on this board for the sound, half the caps had started to leak. This brought back the music.
The sound effects were a little confusing. Like the last board I could see the data going into the M5205 chips but on IC80 there was nothing coming out of pin 10. I replaced the chip but this time there was no change. The board has had the op amps replaced at some point and there was a little rework done on them. Pin 5 (input) of the op amp at IC97 was shorted to pins 6 and 7 (output) effectively bypassing the op amp altogether, this explained why the sound was really low. Removing the short fixed the sound.
Another one destined for eBay.

Backer 32

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Mar 062011

My friend often regaled me with tales of Backer from his misspent youth. The idea of backing up files and information from your PC to a video tape always struck me as too ridiculous to be true but after many years he has gone and found one and purchased it for nothing but nostalgic purposes.
I asked him to send me some pictures over and that he did.

The idea of being able to store 4 gig of data on a single video must have been quite appealing but I’m not sure I would have wanted to place my trust in it.
We really need to try this beast out.

Rainbow Islands repair log #1

PCB Repair Logs, Repair Logs Comments Off

Mar 052011

Got hold of a very poorly Rainbow Islands Extra board.
This board had some repair work done previously. There are a few burned out tracks and some dodgy looking wire links.

On power up it just showed a black screen, time to break out the Fluke 9010a.
The Fluke showed I had active interrupt lines. The 68000 CPU has 3 interrupts, IPL0, IPL1 and IPL2. IPL1 and 2 are tied to +5v (they are active low therefore unused here). IPL2 was stuck low.
I traced the line to a nearby 74ALS74 chip and then back to a 74LS273 (IC32). Regardless what the inputs were doing, the outputs were all stuck low. I replaced this and tested, still a blank screen. I check the 74ALS74 again and although all the inputs were now present and correct, its output to IPL2 was still stuck low. I piggybacked a new IC onto it and the game came to life. Replaced the IC.

Now the game booted up I could see that the colours of the character sprites were wrong, mainly black.

This caused me a lot of headache as the colours came good when I put the logic probe on different pins of different IC’s. I determined which IC was partially responsible for sprite colours by interrupting lines on various logic chips. I found that if I toggled pin 9 of IC35 (74LS157) the colours came good more regular. I removed this chip and tested it in my logic tester, it passed but if I put it on a loop it would intermittently fail. Replaced this and the colours were now back to normal.

There is also a problem when the sprites are facing left where it shows a broken character but still facing right. The pictures below shows the broken up boss sprite and broken rainbows when fired to the left.

This ended up being a short on pin 15 @ IC38 (74LS153). This pin was shorted very slightly to an exposed track running next to it. Removing this short fixed the graphics completely and the game is now 100%.
Very pleased.

Street Fighter Zero 2 repair log #1

PCB Repair Logs, Repair Logs Comments Off

Mar 022011

Got this for repair today. Was under the impression it had suicided but this had jailbars on all screens starting from the Q sound screen.

On opening the case it was obvious what the cause may be.
One of the gfx maskroms was only half fitted.

Refitting the Rom fixed the problem.

X-Men Children of the Atom Phoenix error

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Mar 022011

I got 2 CPS2 boards today for repair.
One of them was a Children of the Atom game that had suicided, simple enough.
I erased ROMs 3 and 4 and burned the bootleg code. The game booted up to the copyright screen then bombed me out with an error.

After a bit of playing about it turns out that the installed ROMs were from the Japanese version of this game and this is different from the Euro version (which is what the Phoenix ROMs are based on) so I had to erase ROMs 5 – 10 and reprogram them with the Euro version.

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