Repair Logs – Page 115 – JAMMArcade.net

Ultimate Mortal Kombat 3 repair log

May 192012

PC18 from Jamma+ forum dropped me 2 UMK3 boards around a while back in the hope we could get one of them working.
Both had sound issues.

The first board failed its self test flagging the ROM U2 as bad, when one fails none of the others are checked and the game boots.
The second board just had a feedback sound playing all the time and no game sounds were there even though all self tests pass.

I check the ROM’s out first and they were all fine
Checked the voltages on both boards and they were all fine.

Probing around at the sound ROM’s on the first board I could see that none of the chip select lines were ever being activated. I traced this back to the protected GAL22V10 chip, fortunately I had another GAL from the second board but got the very same fault. Refusing to believe that both chips were bad and in the same way I started looking elsewhere.
The ADSP-2105 chip is the sound processor on this board and could see that all the address and data lines were completely dead.
At this point I wrote the board off and focused my attention on getting the second board running.

I know that if the -5v is missing then the you will get the very noise that I was getting with this one. Only trouble is all the voltage levels were fine to all points I could trace.
These boards have A LOT of small surface mounted capacitors and resistors which makes tracing things out a huge task and as there are no schematics available I was getting a bit frustrated.

Out of frustration I decided to probe the sound processor on the board and found that on start up all the address and data lines are in fact tri-stated just like the first one so it got me thinking that the other board was maybe OK.

Looking around on the underside of the board I found this

This actual mark was tiny until I starting prodding at it and missed it on my initial inspection but there was no continuity between the 2 ends of it so it was cut all the way through. Even better news was it did go to that GAL chip so probably would affect the sound circuit.

I patched the trace with some kynar

Fired the game up and was greeted with a 1 tone sound which actually means the sound hardware is OK, previously I had 2 tones which means there is a fault.

Due to the reason mentioned above I’m not going to try fixing the other board up but I have confirmed that all the processors and stuff are working so there are spares should he need them.

Game Gear repair log

May 192012

Not much to say here. Usual Game Gear faults of low sound and hardly any brightness on the screen. Always down to poor grade/leaky caps.
I had 2 of these to do so ordered up a bunch of capacitors and just changed the lot out.
Both of these were my mates but said I could have one of them if his one worked.

I never took any pictures of the internals as I wasn’t originally going to log this but as I’ve not got much else at the moment I thought why not.
All the original capacitors were surface mounted ones but the replacement ones I used were radial ones and there is plenty of room internally to allow the case to be closed up again, plus it makes it easier to solder them in.

Anyway, the sound is back nice and loud and the screen brightness is pretty decent. Shame the actual screens in these things were poor to begin with.

Silent Scope 2 repair log

PCB Repair Logs, Repair Logs 2 Responses »

May 022012

Picked up a pedestal and rifle from Silent Scope the other day and also got with it Silent Scope 1 and 2.

Silent Scope 1 had already had its NVRAM replaced and was working.

SS2 had unfortunately already suicided. I burned a new M48T58Y RTC RAM and fitted it but it didn’t initially work. It turned out that one of my solder points wasn’t good enough and simply re-flowing sorted it out but not before I delved into the contents of the RAM chip itself.

My initial thought was that the dump in MAME was for a different region but I don’t think this is the case. The contents of this RAM chip consist of some text 14 bytes long followed by a 2 byte checksum. The game code copies the contents of this RAM and its checksum into memory, works out the checksum again and compares it to the one in the chip, if it matches it goes ahead and boots. I proved this by writing a small program to calculate the sum and writing my own replacement.
The contents of this chip do not affect any on screen text.

All up and running…………..until
Playing SS1 the game froze and gave me a BACKUP RAM fault and rebooted. I first check the power supply which was a spliced ATX PSU and found the voltage to be around 4.6v. I replaced this power supply and no more errors regardless of how much i played.

Now it really is all up and running and I’m quite happy with it.

Teenage Mutant Hero Turtles repair log #2

PCB Repair Logs, Repair Logs 3 Responses »

Apr 232012

Got this from a Jamma+ forum member.
Sold as having graphics problems that went away when touching one of the MASKROMs.
On testing it had lines running vertical down the screen and the fault did appear to go away when touching K27 MASKROM. This however was not dry joint, it was a floating output meaning the MASK was knackered.

I removed the MASKROM and programmed a replacement 27C400 EPROM.
Game now works fine and all self tests pass.

The game does appear really washed out on my test bench but plays fine in a cab. Not sure why this is but I cant actually see anything wrong with the output signals so ill ignore it for now.

UPDATE:
This board also had another fault where button 2 for players 1, 2 and 3 didn’t work.
Turtles actually has an IO test within its test menu so it was easy to check all inputs.

I traced the signal through a resistor network and could see the state toggling with a button press. Traced it back a bit further to a 74LS253 chip at location C26. Replaced this chip now all working again.

Vectrex repair log

Console Repair Logs, Repair Logs 2 Responses »

Apr 162012

I grabbed this little fella from eBay not too long ago for very nice price although it was sold as having vertical collapse on the screen.
As it happens this was a complete lie but it is eBay so I should have known better.

On powering up I was greeted with nothing. No ‘Vectrex buzz’, no noises of any sort, nothing!
Getting the easy stuff out the way first I checked the plug fuse. All OK in there.

Time to open it up and see what we can see.
I saw dust, and lots of it.

Let me take a moment to explain a little something about the Vectrex. The picture above shows the logic board in its housing. In the Vectrex it is not just a matter of removing a couple of screws and taking out the board. Everything is connected to everything and sometimes not by means of plugs either, they are soldered in there so removing the logic board took a long time and a lot of pictures were taken of various wire locations and a lot of tiny screws were removed.

I checked voltages at the transformer and got 240v. I checked the output of the transformer and got nothing. Problem #1 found.
The transformer is a standard 9-0-9 VAC type and I bought a replacement from Maplin (thanks to Mesmeric_G from UKVAC for pointing me in the right direction).

In the mean time I set about cleaning this logic board down.

Whilst the board was out I tested the on/off/volume pot, this checked out OK (but more on that later).

So a few days later the transformer arrived and I went about fitting it. Once everything was in position to test I fired it up and…….nothing!
Turns out my on/off/volume pot is a little temperamental on one of the power lines and will occasionally give a poor connection causing the voltage to drop to around 4v. As a temporary fix Ive hardwired the line in the ON position and am using the plug as a means of turning it on and off. As Im unable to find a suitable replacement for this switch I will probably add a DTSP switch at some point in the future to control the ON/OFF function.

So now Ive got a booting Vectrex with sound.
Another problem now. It boots straight into the Mine Storm game that’s built in.

I know for a fact that there is a Vectrex boot screen that should appear first. The game also doesn’t respond to any of the controls and it locks up when it displays “PLAYER 1”

Looking at the schematics that are floating around it looked like the sound chip is also responsible for dealing with the controls.
The chip in question is an AY-3-8912. This chip is socketed so removed it and fired it up.

The Vectrex logo is back but I have no replacement chip to use in this yet so that’s where this log will end for now.
I’m positive that’s the only problem left now so will try find a replacement chip somewhere.

Thanks to Phu from the RetroComputerMuseum for his advice. His knowledge on the Vectrex is unsurpassed.

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