Repair Log

1942

I promised Guddler I’d fix this for him, and the first thing I managed to do was pop one of the Z80’s by accident! Oops! After replacing the (luckily socketed) Z80, I discovered that the not booting problem was caused when the PCB doesn’t receive enough voltage (quite a common problem). Instead of booting and playing (like it used to), it was crashing with a coloured screen (I forget which colour…) After a quick feel around with my fingers, I noticed that one of the 2016 RAMs was extremely hot. I checked it with a logic probe, and it didn’t look too healthy. So I piggybacked a known good RAM and the game booted and worked albeit corrupt (because the bad RAM fights the good one, so this trick should only be performed VERY temporarily). On replacing the RAM the game plays fine.

Asteroids #1

Well I’ll freely admit to having no knowledge whatsoever of exactly how these boards work… So I asked Mark at Leopardcats to help me out with these faults. Here’s the run down:

Game plays but all objects are only a few ‘pixels’ wide (game still plays in full screen though and ‘sprites’ are all full height) - FIX - 7497 @ J8 proved to be faulty, on replacing game appears to be fine but test screen shows RAM error… Replaced RAM at P4 and test screen is now fine, can’t actually see any change in the behaviour of the game though (maybe the 2114 was fine, could have been that the solder joints were bad). Anyway, now found following fault:

After warming up for a good five minutes, the ship (and nothing else) becomes corrupt, also the cross hatch on the test screen is affected - fine at first and then after warming up it becomes unstable. FIX - After much scratching my head and swapping those 7497’s around which are all socketed on this board, I came to the conclusion that maybe its not the chips now that are faulty, as the same problem manifests with whatever combination I insert the ICs in. But I do get a stable kind of picture occasionally, so I replaced one of the sockets and now the PCB plays absolutely fine.

Asteroids #2

This is a strange one, spot killer lights and (obviously) screen is blank but activating the test switch doesn’t create the expected tones to denote faulty RAM, instead I get a ’tick, tick, tick…’ first thoughts are that the board is constantly resetting and doesn’t get as far as emitting a full tone for the test facility - but this doesn’t appear to be the case, and I’m now perplexed… FIX - working on it now…

Bombjack #1

Having two of these already, have to admit I didn’t exactly test this after I bought it… I knew that it has (and still does) a RAM fault on the test/boot screen but the game plays absolutely fine. Well, having decided to sell some of the stuff I can do without it was time to test this board fully. The buyer knows of the RAM fault already so this isn’t a priority especially as I’ve said it works 100% anyway (could well be a fault with the testing routine?? Possibly??) Anyway… I tested it LOADS and nuts I found a fault… There’s intermittent graphics corruption, what happens is that you play the game and all of a sudden the background is corrupt and upside down, not only that but the sprites react to the ’new’ background, strange… After a second or two the display reverts back to normal only to occur again at random. I assumed this to be a cocktail switch problem owing to the fact the background is upside down, so I attempt to troubleshoot this area. After about two hours of deciding maybe I’m wrong, I decide to clean all the socketed chips - which is what should be done first anyway… Well stupidly enough, it didn’t take much finding “ROM 6,” which stores the BACKGROUNDS has a pin that is bent up and not making contact with the socket, DOH!!! When the pin is straightened the problem disappears… Temporarily… Pressing down on “ROM 6” appears to make the problem go away completely - solution: Re-solder the socket and the game is now fine! Some notes here: The RAM error is “RAM 4”, and replacing the 2114’s on the top board makes no difference to this. I’m wondering whether the RAM check is referring to the 2128’s on the bottom board, but I can’t find any information on the board… I would swap in new ones, but I don’t have any spare, and they aren’t socketed. Lesson learnt here, the backgrounds were inverted NOTHING ELSE WAS THOUGH. This screams that the ROM holding the background information was playing up, inexperience is my excuse for wasting time checking the cocktail switch. I assume that if it was a problem with the cocktail switch then ALL the graphics would be upside down not just the backgrounds. Also, the ‘gravity’ of the character would be impaired, but Bombjack just carried on playing the ‘right’ way up.

Bombjack #2

The fault is that the blue output on the screen is about one millimeter out of line with the rest of the colours and it ‘fuzzes’ a bit (hmmm… better word required!) The resistor pack at RA10 had an incorrect value on it, so I swapped a correct one into it… Of course, that didn’t make ANY difference at all but you have to try these things… I then traced the blue output to the 2114 RAMs which come up OK on the test/boot up screen so I’ve never suspected them before (I’ve had this board for quite some time now…) Anyhow, one of the RAMs is a different make to the rest (maybe its a different speed slightly?! It certainly has a different number after 2114-…) Swapped in another, so they’re three of the same and BINGO problem fixed!

Commando

I bought this board as working, so I guessed there couldn’t be much wrong with it… After extensive cleaning (there was even a dead spider between the boards) I removed the ribbon cables, cleaned them and the connectors and replaced them. Now the board works absolutely fine.

Moon Cresta

Well first up, I knew this was obviously a bootleg so I found the pinouts for myself which turned out to be Galaxian pinouts. Looking at the board after I found this out I recognized it to be a bootleg cocktail Galaxians board with a Moon Cresta hack applied to it. Actually I keep saying its Moon Cresta, but when I finally got it to work turns out its a Star Fighter, which is a copy of Eagle, which is a copy of Moon Cresta! Anyhow, the fix… The game played after replacing the processor but had thick red vertical lines going across the screen. Turns out to be a slightly broken trace under a socket, looks like someone’s been too heavy-handed removing an EPROM with a screwdriver! Anyhow, little bit more solder completes the connection and its fine. I may even convert this back into a Galaxians if I can get hold of the parts.

Mortal Kombat II

Game arrived without a sound board, but fortunately after reseating the ROMs the game played okay (guess they don’t travel very well, got LOADS of faults on the diagnostics screen!) Anyway… Managed to buy a sound board but it didn’t come with any cables, so asked on UKVAC and found out that the power leads use the same kind of molex connectors as the Williams boards - so not a problem there as I have some already. The parallel cable can be substituted with a normal PC floppy cable! Obviously it only uses half the connections, but it all works just fine! One fully working board with sound!

Pac-Man

Nothing at all on either the original AC power supply or via a JAMMA rig. Replaced the processor which gave a trace of life. Couldn’t test the PROMs as my programmer can’t read them - they really didn’t look too healthy… So, I bought a complete ROM-set! I changed ALL the PROMs with the known good set, and now I got a changing graphic on the screen… Guessing that this is probably a RAM fault, I set about changing in a spare set of 2114’s to see if there was any difference. The very first one I changed gave me a fully working Pacman board (via JAMMA anyway…) Once the game was working correctly I swapped back in the original ROMs one by one, turns out two of them are faulty. Unfortunately though, it still didn’t work in the original cab with the AC PSU… I measured the resistor at R52 which was OPEN! And bingo! When replaced, one fully working Pacman! It should also be noted that the two large capacitors were both dry and cracked, I assumed they were the problem - but they held a charge just fine! They will still be replaced though, as they look AWFUL and probably/definitely will be the cause of a problem in the very near future.

Which leads me on to the next fault… Noticed that the monitor had started to ’tick’, almost like it was losing sync for a second and jumping but not enough to do anything serious. Anyway, replaced those caps because I suspected a power supply problem and now the game is just fine again.

Pleiads

Okay, not strictly my repair but it is one of my boards and it was repaired 😄 Well anyway… It had a screen of garbage when powered on, and no amount of ’tender’ flexing, pressing or fingertip probing seemed to make any difference. Using a logic probe I SWEAR I checked all the Data/ Address/ Control lines on EVERYTHING! Absolutely flummoxed! Sent it back to the shop that I bought it from (well, it was bought as working!) and it turned out to be a faulty ROM socket. I’d love to know how he diagnosed that one….!

Street Fighter II’ - Champion Edition

Bought this board as faulty/dead from a shop in London, didn’t boot or something. On the train home I detached the ROM board and one of the connectors came off and was stuck to the motherboard. That’s when I noticed the connector wasn’t aligned properly - the last two pins weren’t ‘inside’ the housing! I realigned it, but thought “That can’t be it…!” When I got home I plugged the “dead” board in and it booted and played fine! The only problem was the sound, but on reflowing the solder on the amp (it just looked odd) that fixed that too! Now fully working 100%