Robotron infinite rug pattern

Qesmann

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I'm trying to restore a Robotron, but I've run into a roadblock. This is my first time working on a game so I don't know many tricks and I don't have spare working parts for testing.

The problem is that the game is stuck in rug pattern mode when the power is turned on. The pattern sweeps onto the screen, and then about ten seconds later it starts over. After a while it may play a sound while the rug pattern is drawn. On the ROM board, it flashes the 1-3-1 error code.

I know that code may mean that the RAM at that position is bad or that the power to the RAM is bad. I think I've eliminated those possibilities by using new 4116 RAM chips, rebuilding the power supply, and verifying all the power connections. The motherboard is definitely getting 12v, 5v, and -5v. The voltages at every RAM chip are 12v, 4.95v, and -5.02v. Also I put in a new 40-pin cable between the motherboard and ROM board and tested each pin for a connection. Replacing the cable fixed a problem where the error code would sometimes show garbage. Now it's a consistent 1-3-1.

I think I've covered the basics, but that's the limit of what I'm able to do on my own. Maybe there are bad chips somewhere on the motherboard, but I don't know how to do tests to find them.

Is there anything else I can try before sending the boards out for repair? (or maybe finding someone near Seattle who can repair it)

Thanks
 
It sounds like one of three or four common chip level issues. Each of them will involve using a logic probe or oscilloscope to diagnose and will involve unsoldering and resoldering one or more chips on the board. If you are not comfortable with that, then send the boards out.

If you PM Saltbreez, he is out your way and is a wiz at fixing Williams boards. He can give you some suggestions or depending on what he has going on, he may be able to fix or replace your boards for a reasonable price.

ken
 
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It sounds like one of three or four common chip level issues. Each of them will involve using a logic probe or oscilloscope to diagnose and will involve unsoldering and resoldering one or more chips on the board. If you are not comfortable with that, then send the boards out.

While I'm comfortable with soldering, I don't have a a logic probe or oscilloscope. Rather than spend money on that, I'll look into getting help.
 
While I'm comfortable with soldering, I don't have a a logic probe or oscilloscope. Rather than spend money on that, I'll look into getting help.

Qesmann,

I'm up herein Bellingham, WA, and I can help with your board, either by exchange with a working board or by directly fixing your PCB.

PM me: Saltbreez
 
The 74153 chip at position 3D on the motherboard needed to be replaced.

Saltbreez easily solved the problem after seeing that the rug pattern was actually a vertical blind pattern. Had I seen many rug patterns before, I would've pointed out that it appeared in vertical stripes.

Now the game works great. The monitor could use a tune-up, but for being the original monitor, it looks decent.
 
+1 on Saltbreez working on Williams boards. I just wish he was closer. Mailing boards back and forth is a pain (and draining to the wallet).

ken
 
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