Omega Race PCB repair

Malice95 said:
Microdoctor? Got a link? How is it better then a fluke? I'm thinking about picking up a fluke.
Click to expand...

Better than a fluke? No it's not as flexible. It's designed around z80 based systems. There was meant to be other Roms released for different CPU's but I have never seen one. Where would you get one? I've never seen or found any info on one, probably only a couple in existence.
Very easy to use, you remove the z80, plug in
The pod then choose a pre programmed test...ram/rom/address-data line check/disassemble/checksum/ io read/ io write/ auto memory map/ plus more. You enter a start address and finish address on
Most tests unless you ask it to auto map the board.
You can print memory contents in hex/bin/ASCII or assembly language .

Sorry for the poor layout....bloody iPhone :)


IMG_0723.jpg
 
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I'm watching this very closely.

I hope to learn by osmosis. ;)

Thank you so very much for showing your skillset. Even though I can't do it, I love to watch.
 
omegaman said:
Another thing to remember is not to try and scratch the crud off the board, the traces are very thin at points between the solder pads and easily damaged. Use a toothbrush and chemical cleaner, .
Click to expand...

What type of chemical cleaner do you use?
 
I use a mixture of lime scale remover / strong surface cleaner and a toothbrush.....just make sure you keep an eye on it and give it a good wash afterwards, If you stick it in the dishwasher remove the IC in sockets and de-solder the X and Y pots, or add switch cleaner to them afterwards.
You really need to remove any areas of the green mask that has lifted.
 
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Right, time to run a few tests.

I should see this when running a shorts test

IMG_0802.jpg


Unfortunately I get this

IMG_0801-1.jpg


This means data line 0 and data line 5 are shorted to ground, if it had shown a "1" that would mean shorted to Vcc.


IMG_0800.jpg
 
I took a look at the schematics, the program rom's and rams are tested good so the only thing left on the data bus was the 74245 at S1....this is the buffer for the video ram and rom. I removed the chip and the game now boots but obviously reporting bad video ram and rom.

I should get time to fit a new 245 tomorrow. fingers crossed!!

http://www.youtube.com/watch?v=HbK1sFjkh18
 
So you didnt have to fix any of the traces? How about the thick traces
running around the outside of the board that looked bubbled. Was that just solder mask?
 
Just one trace so far, on row 2 right between 2 legs of an IC where the trace goes very slim. I noticed it when I was inspecting the board over a bright light.
Yes the bubbles were just the mask lifting.
 
Update for today. It's nearly there now. I had a problem with an address line on the video Ram/Rom being shorted to +5. from looking at the board I could tell it wasn't any of the Ram sockets as the trace from that pin didn't run past the +5v line. It did run past pin 21 of the Rom socket though. I lifted one side and held it up to the light...Bingo!!!

IMG_0814.jpg

if you look at the 4th pin back from the right you can see a bridge to the address line.

The next problem was a missing data line to the Ram, again holding the board to the light showed me where the problem was.

IMG_0815.jpg


not a very good photo but you can see the break on the 3rd trace down on the right of the photo.



Now I get video!!!

IMG_0817.jpg


I just need to figure out the Ram issue now, the chip is good so I guess there maybe an issue with the solder on that socket.
 
"I had a problem with an address line on the video Ram/Rom being shorted to
+5. from looking at the board I could tell it wasn't any of the Ram sockets as
the trace from that pin didn't run past the +5v line. It did run past pin 21 of
the Rom socket though."

So how could you tell the short was there to begin with?
I am assuming the Micro doctor told you. How could you tell without it?

How does a short like that develop beside some stray solder?

I see you are testing the board without the smaller PCB portion. Does the
board not need that for testing? Just sound and IO correct?

I just picked up another Omega Race boardset so I am going to try to
cleanup and do socket/chip replacement myself. This one still has the
battery on it as well but appears to have a lot less acid damage.
Its confined to right near the battery. Are there any custom chips or hard to
find chips that need to be replaced on an Omega race board?

What are you sources for TTL chips these days?

Hopefully I'll be able to figure it out, if not I'll punt to you.
 
Good question :)

I knew the address line was stuck high by using a logic probe, there should have been activity on all the lines but 1 was static. I checked with a multi meter and sure enough it was shorted to Vcc. The video address lines emanate from a few 74157's so I removed the chip in question and tested it....it was fine so I knew it had to be a problem with one of the sockets as the video address lines only run to the Ram and Rom.

I guess it was a bit of solder or corrosion I missed on the clean up.

You can check the main board using the Microdoctor if its resetting (can't read rom contents)

You need the sound board plugged in if you are testing in the game as the control lines connect to the sound board (test switch, lights)

Custom chips? only a prom and a couple of chips in between the cpu and the data bus....I've never seen them fail though.

The DAC's are the same as the ones used in Asteroids....In fact Omega race vector section is a duplicate of Asteroids....it just runs on a Z80 instead of a 6502. I forget what the DMAGO line is on Omega race but you can isolate the vector side of things the same way as you can with asteroids.

TTL chips? I have so many I hardly ever buy any :)

Ebay for Ram and PCB cleaner/ flux removal spray.

Dental tools (picks) are great for clearing bridges on traces like the one in the photo.
 
Can you talk about the test bed you are using to test all this?

Do you just have a cabinet worth of boards, harness, Power brick attached to
a wooden board with a spare monitor or are you using a full cabinet?
Pictures?

I just got my otther boardset in the mail.. thankfully the damage is only in
about a 5"x 3" area. I also picked up a spare working moitor so now I need
to build a test bed.
 
Malice95 said:
Can you talk about the test bed you are using to test all this?

Do you just have a cabinet worth of boards, harness, Power brick attached to
a wooden board with a spare monitor or are you using a full cabinet?
Pictures?

I just got my otther boardset in the mail.. thankfully the damage is only in
about a 5"x 3" area. I also picked up a spare working moitor so now I need
to build a test bed.
Click to expand...

I have an OR upright I can plug the board into and a Kurz Kasch test unit for working on the bench, monitor wise I use an oscilloscope with XY mode. It's not as good as a proper vector monitor but it gives you an idea what is going on. You wouldn't pick up on some of the small graphics problems on the scope.

I will post some pics and a video clip of the test unit.
 
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