Midway T2 PCB Repair

[panpar227]

I've got a Midway Terminator 2 PCB A-14818-40009 sat in front of me currently.

When I first received it, it would power up but showed ROM errors on the test screen. The thing was caked in dirt so I stripped everything, gave it a good clean with a toothbrush and some pcb cleaner and re-assembled. Now i'm getting nothing at all from the board

When I power up the screen does change slightly as if it detecting a signal but their is no picture. I have checked that my voltages are good at the edge connector and they are good.

I am getting a red LED1 lit solid but the manual doesn't give me any indication of what this means.

I do not have any of the Video ROMS installed but I am assuming that even without these the board should boot.

Anyone any ideas what my next move should be?

panpar2272014-05-10 21:05:03

 

[silverfox0786]

how long did you leave it to dry and did you remove an many chips and any batteries if any off the board before clean.

its possible there is still water under the chips and one problem if there is a battery is 3.6v is enough to kill the board if its attached when water hits it

what I would do is first hit it both sides with a hair dryer and hope its still ok after being powered on wet (it it was wet that is)

once you don't that then we can be sure its not the washing that the problem and look into the board functions

 

[panpar227]

The board was cleaned weeks ago, was hit with the compressor, then the hair-dryer and has been in the airing cupboard ever since so I'm 99% certain there is no PCB cleaner left. Plus PCB cleaner is mostly alcohol or similar isn't it?

There was no battery in place when I received the board and there is still no battery.

 

[adebov]

Was is a nylon toothbrush (static issues with all that scrubbing???).

I wonder how much of the video circuit will work (e.g. the test screen) without any video ROMs in place?

 

[panpar227]

It was a nylon one, I'm hoping that's not my issue. First ever repair attempt might be over before it's begun!

I've been round the board with the multimeter and all of the ICs, video Ram, ROMs etc.. all appear to have the correct voltage going to them.

I have put all of the Video ROMs back in place now and the Red LED is no longer lit.

 

[jonhughes]

The board will need ROMs to boot. I can only draw on what I know from my Mortal Kombat boards. Remove either U89 & U105 (the revision roms) and you'll be presented with a black screen. Replace the ROMs and try again.

Did you remove the PLCC chip and every other socketed chip? - that could well be your problem.

jonhughes2014-05-10 22:26:01

 

[panpar227]

I've put all of the roms back on the board, reseated the PLCC chip and powered on. Initially I got nothing as usual but after a few power cycles I was presented with this....

Not sure what I have done but it seems to be a step in the right direction at least.

 

[jonhughes]

Did you clean the socket and the PLCC chip contacts? I've found the smallest things can stop these boards from booting up.

 

[panpar227]

I've cleaned all of the contacts on every chip including the plcc.

I take it U99 on these boards is the CPU?

 

[panpar227]

I have been round the board and checked voltage on all of the chips and all seems ok, everything is getting power.

Is there a way, using my logic probe, that I can check for activity on the Roms? Just trying to narrow down my search.

They are 27c040 chips

 

[jonhughes]

I'm not sure, it's sounds like you have a problem between contacts. I've never had a board not reboot (that had booted to the test screen) after cleaning it. I've put chips back in the wrong way around, accidentally missed the socket with a pin and bent the leg under the chip or bent the pins on the reverse while putting the chips back in their sockets while on a hard surface. It's hard to say but what was happening before cleaning should also be happening after.