PCB Repair Logs Q*bert
Q*Bert
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| Pin Out | Reserved |
Repairer: Arcade King
Forum Thread: Q*Bert PCB Repair
All you get when you fire the board up is scrolling horizontal lines. No sync.
I had to make a simple H/Vsync to csync adapter so I could work on the PCB on my test rig.
PCB has battery corrosion around the bottom left hand corner that covers about 1/4 of the bottom of the board about 2/3's the way across and about 1/4 of the way up along the edge connector. Removed the battery and sprayed the board with isopropyl alcohol to prevent further damage.
General probing.
Other bad IC's 74ls157 D2 through to D10. Replaced all 9 IC's. some were dead others were on the way out so best to replace the lot. El Salvador dated 8136
74ls374 @ D11 pin 16 stuck high 74ls244 @ D12 pin 3 was stuck low. 74ls86 @ D16, E15 and F17 74ls273 @ E16 These IC's have to do with the background generation. I put in sockets because they were in the battery acid damaged area. After removing the IC's I cleaned the plated through holes the best I could using a fibre glass pen then dropped a socket in.
Replaced 4118 rams @ E7 and E10-11 for Hitachi 4116's, the legs were basically about to fall off. 4118's are 1kx8 while 4116's are 2kx8. pin 10 (A10) is already pulled High so a simple drop in replacement. Also replaced 2 of the program roms for Hitachi ones to match the other 2 that were already on the board.
At this point I can see data there on my CRO but its just looping.. OK note to self Qbert has to have the test pin grounded for the game to run Game is running great except all the character graphics are squished up. (see pic)
Problem turned out to be a 74s161 timer @ H5 I used a 74ls161 in its place. Those 74S161's get far too hot for my liking. I'm going to replace the lot with LS which work just fine. (The bootlegs use LS)
Game board now 100% but the sound board is another matter, the board uses some funky voltages. I attached a step down transformer to the cab yesterday so I could test the soundboard but unfortunately all I got out of it was garbage sound. I've just ordered a pair of SC-01-A Speech Chips from Kevin at www.GameRoomRepair.com so I can eliminate the speech chip before I start tearing apart the sound board. It could very well be a voltage problem also but its always a good idea to have some of these rare IC's on hand. lets face it the sound is what makes Q*bert so special. I'll update the thread on the soundboard once I've received the IC's
First pic is of the GFX fault the rest are of the game running 100% The distortion on the left is just a monitor sync issue. I cant adjust the sync on my C1084s without pulling the case off.
