Repair Logs – Page 112 – JAMMArcade.net

Rainbow Islands repair log #2

Jul 192013

Nearly 12 months ago my Rainbow Islands went a bit crazy and kept giving me random crashes like the following

I thought I had sorted it with a simple ROM change but after a lengthy gaming session recently I discovered that this was not the case.

I couldn’t find anything wrong with this board. Sometimes I could play it for hours, sometimes it crashed at startup, sometimes it wouldn’t even start up at all.

Whilst I never gave up hope that I would find the fault I just didn’t know where to start.
My goal here is to document all the code with comments, create a decent set of schematics for the PCB and basically note any points of interest within the code and hardware.

Tonight I feel confident in saying that I have fixed my board.
While I has adding to my schematic, trying to find where a trace ultimately ended up, I found that pin 9 of IC57 (74LS138) was tied to VCC (kind of anyway, it had a resistance of 38 ohms).
The pin does in fact go to pin 19 of a 74LS244 at location IC79.

I removed the chip and it failed all tests, the connection to VCC also disappeared. I’ve replaced this chip and all seems to be well in my world once again.

For all those people that have asked me in the past “how long does a repair normally take?”. Although this kind of fault is quite rare, it has literally been 12 months of chipping away at different things. Had this been any other game then I would likely have given up on it a long time ago.

Snow Bros repair log #1

Apr 272013

Ive decided its time to make a start on the huge back log of repairs that I need to get finished.
Today Snow Bros was on the cards. It was a fairly recent purchase but as I really like the game it was first on my list.

Board boots up and passes its self tests but had big graphics problems.

Cant tell from the pictures but the screen is also flashing.

This board is tiny so I started looking for RAMs that weren’t program or sound related and shorting a couple of data lines together. There is a bank of 4 41464 RAM chips in the bottom left corner that would appear to be screen RAM.

First off I found the /OE on the left hand 2 were shorted to ground so I desoldered them. At some point a track had burnt out and was shorting against the ground pin above it. Removing this short gave me this

Much better, the colours are now sorted but the screen was still flashing and the graphics on the title screen left trails of the image. I checked the RAM chips I had removed and found a dead one.
I just went ahead and desoldered the other 2 RAM chips. Again, one was good and one was bad. I replaced these chips with an 81464 from a scrap board.

All working now. Ill have a game on this later.

Spectrum+ repair log

Computer Repair Logs, Repair Logs 2 Responses »

Mar 312013

My mate bought a Spectrum+ off eBay recently and it didn’t work.
All we got on powering up was this

First thing I did was check the voltages. They all seemed fine so on with the next test.
The ULA was the only chip that was socketed so I quickly replaced it with a known good one. Still the same fault.

To save myself some time I thought I would desolder the Z80 CPU in order to use the Fluke 9010. Turns out the CPU was at fault and on fitting a new one we got this (bad picture, I know)

Anyway, I carried out the very simple composite mod and this is pretty much all done. Another Spectrum saved

SEGA Tetris repair log

PCB Repair Logs, Repair Logs Comments Off

Feb 022013

Got a Tetris that was sold as faulty.
As with pretty much any PCB I buy, a visual check was carried out and straight away I found this capacitor.

The board came with an adapter but looked a mess and the wire was far too thin on the power lines so I swapped it out.
I also found a couple of pins touching in one of the unused connectors

And finally I found the sound pot was no soldered in at all and was missing its ground pin.

I took a pot from an old scrap board and fitted it.

Now it was boot up time.

All looks ok so far, but…..

I initially thought it was a dodgy EPROM but they checked out fine. Then I realised that the EPROM at location B1 on the ROM board was missing.

I burned a new one from the Jap set and now we have this.

Everything seems to be working fine.
This board still has its battery installed in the FD1094 and surely will be coming to the end of its life by now. I don’t trust myself with a battery change but I think I have desuicided ROM’s so will just wait until it dies completely or I will sell it on as I cant imagine wanting to play this in my cab.

Pac-Man repair log #1

PCB Repair Logs, Repair Logs 5 Responses »

Jan 202013

Quite a few weeks ago I took part in a charity event which saw me win a personalised copy of Pac Manic Miner Man written by Jim Bagley and runs on original Pac-Man hardware.
My good friend Equites from the J+ forums hooked me up with an original Pac-Man board and after making up a jamma adapter it was clear some repairs were needed.

The board has 2 daughter boards for the custom chips, one of them being a 3rd party one.

A quick inspection revealed this

I reseated the the sub board and the game booted to random garbage on screen

The boards watchdog was also “barking” so I check the 4 program ROMs, all of which were recognised by MAME.
This was the ideal time to hook up the Fluke 9010 and see what was going on.
First off it showed me that the RESET line was active so I told the Fluke to ignore it.
I carried out BUS and ROM checks. All of which returned OK. I tried to carry out RAM tests and DIP switch tests but I couldnt read anything back other that “F7”.
Something was wrong at address line 14 and it pointed towards the 3rd party sync bus PCB. Equites confirmed that the previous owner of the board had this module plugged in backwards so that confirmed my suspicions.
Andyman from the J+ forum also showed me a picture of what his look like without the Sync Bus PCB attached and it was identical.

I spent quite a bit of time wondering the best way to tackle this. I could buy another 3rd party module, or, as the schematics for a TTL version are available I could build my own. My saviour came in the form of the fantastic reprogrammable device from FPGAARCADE.COM.
I have a spare here that is currently programmed with the Commodore 64 PLA replacement but I do have the tools required to reprogram it. What I didnt have was the code to program it with. A quick email to Mike, the owner of FPGAARCADE and he sent me the file required.
Once I had the chip reprogrammed (took ages as my current programmer didnt want to bother working) I fitted the device and….

As all the RAM chips are socketed I pulled them and tested them. The 2114 RAM at position 4R can back as failed. I have some spares of these so fitted a new one and fired the board up again.

SUCCESS!
This game will sometimes be running Jim Bagleys Pac Manic Miner Man so now was an ideal time to try the ROMs out on the actual hardware.

Very happy to get this running.

Thanks to:
Equites for the PCB
Mike at FPGAARCADE for the Sync Bus program file
Andyman for help diagnosing
Jim Bagley for creating PMMM

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