PCB Repair Logs – Page 116

Golden Axe repair log #1

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

PCB Repair Logs, Repair Logs Comments Off

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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