Omega Race Repair

musicman282

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Well I've decided to attempt to repair the board in my Omega Race and am going to document the process in this thread. Any help or suggestions are appreciated greatly.

First a little history. I purchased this Omega Race last year in non working condition off of Ebay. I got a really good deal on it and was planning on attempting the repair the board in it. Well I purchased some test equipment and went to town trying to repair the board. I spent hours and hours trying to repair it and was unsuccessful. I finally decided to send it to ElektronForge for repair. They took forever repairing the board but did fix it and for a reasonable price. The game worked for about 3 or 4 months and then one day I turned it on and it didn't work :sad:

So I've decided to attempt to repair it again. I figure since it worked a few months ago I just have to located 1 faulty component to get it working again. I've already gone ahead and rebuilt the power supply using the kit from Bob Roberts to ensure that I have proper voltages. I was having an issue where the power supply was maxing out at 4.9 volts and I suspected that it was causing my issue.


Picture of the game:
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I do not have a test bench for vector games so I just took some of the wiring brackets off of the harness in the game so I could set the board in a position to make it easier to test components while it is running.
PCB in position for testing:
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I do not own some of the fancy test equipment that others have, but I'm hoping what I have is adequate.

I plan on using a logic probe, oscilloscope, logic comparator, multimeter, and eeprom programmer. I also have a logic analyzer, but it's such a pain in the butt to set up I hope I don't have to use it. I'm thinking for this board repair it shouldn't be necessary.

Tech arsenal:
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I've read through Omegaman's posts on his repair threads and I've decided to take a similar approach.

I've read the atari asteroids schematic on the DVG and have marked up the Omega Race schematics so i have a basic understanding of how it works.

Another note is that this board has zero acid damage which is a rarity.

Symptoms:
Game does nothing - the monitor powers up and the spot killer is on. I have good voltages from the rebuilt power supply. I've probed the Z80 and there is life in the circuit. When coined up the coin meter clicks, but there are no error codes flashing on the start buttons and I do not get any error tones out of the speakers.

Plan of attack:

Remove all 2114 rams and see if I get any error codes
Swap out Z80 with Z80 on daughterboard to see if that does anything.

That's all I have so far, after I do those two things I'll update the thread with the results and my next step.
 

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So I reseated the daughterboard and powered up the game to double check the symptoms. The game is actually playing blind now. I think that it wasn't running the game code before because the daughter board needed reseated. I didn't remove the ram yet, but I probed the DVG section of the board and I think the DVG keeps resetting. I checked the X and Y output sections and they keep slowly pulse from high to low on the output pins of the 74374 which are the data latches that feed into the DAC to display the image on the screen. These should be pulsing really quickly if the DVG were working correctly.

I'm going to check the state machine area of the DVG next.
 
I think I'm making progress.

I used my logic probe and comparator to check out the DVG state machine and noticed that one of the outputs on pin 14 of the 74138 decoder wasn't pulsing like I expected it to. I put my logic comparator on it and it is showing pin 14 as being bad.

I'm going to replace it and hopefully the game will be up and running again.

Pointing to the bad chip in the DVG state machine circuit:
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Logic comparator showing a bad chip:
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GREAT SUCCESS!! (well almost)

Replaced the chip and now the DVG has sprung to life. I'm still not getting anything on the monitor but I can tell the DVG is working. I've got data all the way to the DACs. Next step is going to be breaking out the oscilloscope and checking the analog output section of the DVG to see if I can find out where my signal to the monitor is dying.
 
I traced the problem to the 4016 chips in the analog vector section of the DVG. One of the chips was bad. I swapped the two chips to verify and the problem moved from the x section to the Y section. Unfortunately I do not have any of these chips on hand and am going to have to find a source. If anyone has one to sell me please send me a PM.


Thanks.
 
Boardset works now!!

Well I'm getting an output on the XYZ channels from the board, but of course, the monitor is blowing fuse F600. This thing must've gotten struck by lightning. I don't get how the board can lose two chips and the monitor blows all at once. I have really shitty luck. I replaced the chasis power transistors because they tested bad and F600 still blows. I'm getting a funky reading on the Q606 transistor compared to the Q706 so I think somewhere around there might be my problem. I'm going to have to pull all the transistors to test them individually. I don't mind cause I don't have any on hand and I'm also out of 2A fuses. I'm too tired to do it now, but I'll get to the root of the problem tomorrow and update.

Knowing my luck at this point, once I get the monitor up and running it is going to be displaying garbage vectors due to some kind of a board problem. I'm nervous to hook my scope up the outputs and even check it at this point.
 
Check the fuses in your power brick...there should be 2 for the monitor..if one blows that will cause fuses in the monitor to blow. Or could just be bad fuse/connection. Also check the pins in the monitor molex to make sure non have slid out.
 
PS if you do scope the outputs, you could either:

A. Use the scope as a test x-y monitor (in xy mode) THEN deal with the monitor

B. Scope the outputs, you should get jagged/zigzag signals. If they're anything but that description, might not be good yet.
 
PS if you do scope the outputs, you could either:

A. Use the scope as a test x-y monitor (in xy mode) THEN deal with the monitor

B. Scope the outputs, you should get jagged/zigzag signals. If they're anything but that description, might not be good yet.

They appear to be zig zags when i scope the x and y outputs and the z looks good also.





Check the fuses in your power brick...there should be 2 for the monitor..if one blows that will cause fuses in the monitor to blow. Or could just be bad fuse/connection. Also check the pins in the monitor molex to make sure non have slid out.

I tested all the fuses in the power brick and they are OK. Ill check the 30v AC at the deflection board tonight. I've got to pick up some more 2a fuses first from the radioshack.
 
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