Omega Race graphics error - SOLVED

wolfeel

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***SOLVED - D110 reversed and R261 wrong value***

Awhile ago I built a couple Omega Race boards using KLOVer douglasgb's brand new boards. The first one I built worked 100% out of the gate. The next one I built is having an issue. Both boards have sockets for every IC which has been a help for testing chips as I can swap suspected chips on the known working board to verify if they work or not. Obviously I could have an issue with a socket on the faulty board, but I am going to assume they were installed correctly... at least for now.

The monitor is a known working monitor. Spot killer is off. Game plays.

IC Chips that I have tested by swapping to the known working board:

Both TL082 and both TL081, both 4016 in X&Y area, both 561J, both 74LS374 in X&Y, 74LS157 in column 4 from A to F, 74LS191 in column 3 from A to F, ICs in column 6 from D to M, column 2 from A to E, column 1 from A to D, IC at F8 and E8, IC at 9H, 9J and 9K.

Attached is a video of the faulty board while in test mode (sound board not attached). When in game mode I can play the game and hear that everything works.

Any advise as to where I can zero in at would be appreciated. Thanks!

 
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In addition I just swapped out and verified the following ICs:

H4 and G4, J-M3, J-M4, J-M5, PN6, P8, T7 and S7. I also verified all ROMS and RAM at H-N1.
 
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I set the working board next to the faulty board and found a few differences around the transistors in column 1 around A to C... the two 2n3904 and the 2n3906. I replaced all three yet I am still getting faulty measurements in comparison to the known working board.

In circuit, the 2n3906 red to the middle leg and black to each outer leg on the good board I am getting a junction drop of 1.6 and 1.5...on the faulty board I am getting 1.6 on the upper leg but .0L on the lower leg. This leg is tied to the .001uf capacitor at C210 and then the resistor directly below. Swapped the capacitors between each board and still the same. The resistor tests good in circuit. Replaced the 2n3906 with no change.

I am also getting differences on the legs of the two 2N3904s directly below. I replaced those two with no change.
 
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I think I found my bone head move that has caused my problem...I will report back tonight.

Yep...confirmed bone head! I found R261 had the wrong resistor value and the biggest culprit...D110 was installed backwards. Quality control was lacking the day I first built this. Glad I have another one of these beautiful boards built!
 
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