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Double Dragon repair log #1

Aug 012010

Got a broken DD board off Ebay. Original fault was the picture was white with black blocks.

The board had many repairs done in the past, some bad some good, so I started by removing them all and checking them through. One of them was a length of kynar replacing a lifted track but was going to the wrong place! fixed that but made no difference at all.
Some of the RAM had been socketed but had used badly cut down sockets, replaced these also.

After a long time inspecting the underneath of the boards and fixing a LOT of broken tracks I noticed a few chips on the CPU board had a lot of flux around the solder points but no sockets had been fitted here. They were all 74LS273 chips and one was a Fujitsu! Put the probe of the Fujitsu chip and most of the pins were dead. Desoldered to find a lot more broken tracks. Tested the old chip, it failed miserably. Put a socket in, pulled the schematics for the CPU board and repaired all the tracks that were broken. New chip inserted and fired it up, all back to normal.

Super Contra repair log #1

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Aug 012010

This baffled me for a long time but ended up being really simple.

When the player died and the Continue countdown came up, it would only count down to 7 then returned to the title screen. Logic suggests that this shouldnt be the case and checking in MAME proved it.
The problem ended up being button 1 for player 2 was stuck on.
Traced the stuck low signal through resistor array CRA3 and to a 74LS253 IC @ D19. Pulled and replaced the IC now all is happy.

Pitfall II repair log #1

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Jul 252010

I wired up the non jamma board I recently got, its a SEGA board marked up as Pitfall II but at some point the ROMs had been swapped out for Wonderboy ones. I already have a Wonderboy board and prefer them to be original so I burned a new set of Pitfall unencrypted roms and swapped them over.
I noticed the the game also had a fault where the left side of the screen was repeated on the right side. After a little tracing out I found a 74LS283 with a floating pin, I swapped this for a spare and fault fixed.
Not a fan of this game, will probably sell it.

Golden Axe repair log #1

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Jul 242010

I have decided to take a look at the Golden Axe problem today.
The problems with it are:
1. None of the inputs register
2. There is no sound

Normally faulty inputs are easy but not with the System 16 board. The inputs are controlled and isolated by 8 NEC2501 chips. I couldnt find a single bit of info on these chips but as luck would have it when I removed the chip from the board there is an alternative printed on silkscreen of TLP521-4. The datasheet for these is readily available and its description is a photo transistor. I wasnt prepared to believe that all 8 of these chips had gone so I traced the pinout back to the edge connector. It turns out that pin 4 on the solder side of the edge connector NEEDS to be connected to its own +5v as this supplies the voltage to the photo transistors and in my haste to get an adapter up and running I never wired all the points in. Lesson learnt. All inputs have now been tested working.
Next job, sound. I have dumped the 2 ROMs associated with the sound and checked them against MAME, both are good.
NOTE: The SEGA branded MPR- maskroms can be read as a 27c301 with a slight wiring mod.

There is a Z80 on the board which is the processor for the sound, this was dead. Replaced the processor and full sound is there.

Very happy to have this one up and running.

1942 repair log #1

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Jul 182010

I bought this 1942 board some time ago for very little as it needed repaired.

This was my second board repair so took me a bit longer than what it probably should have.

The symptoms of the fault were the character planes moved from its starting position right to the top of the screen and appeared again at the bottom, this cycle just repeated. Also the backgrounds were all messed up and at a certain point in the rolling demo, the game would freeze.

Now for the other problems. When things are in the wrong place or not behaving as expected then RAMs are a good place to start probing. Its worth mentioning now that MAME is an excellent tool for seeing how things should be.

I checked the address lines on RAM (TMM2016) @ N10 + N11 with a scope, very weak signals on several lines. I desoldered the RAM and checked it in my ABI Chipmaster, came up as “Out of spec”. Replaced this with a known good one from a scrap board and all working nicely again.

Now I don’t have a setup capable of housing a vertically orientated monitor nor do I have any plans ever to get one so this board is going to be sold.

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