Robotron 1-3-8 Error

dahnz

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Having fixed my power supply issues (RAM is now getting +4.9, -4.9, and 12.2), I'm trying to pin down the 1-3-8 message I keep getting on this board. I've tried swapping RAM chips, replacing the socket, and checking continuity. I thought I'd found the problem when I found the D37 trace was broken between 3R and 4H but fixing it didn't get rid of the error. I've also socketed and replaced the 74LS374s and the 74153s.

Any suggestions?
 
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So, swapping the 38 with the 28 doesn't change the error? Try wiggling the power connector on that CPU board, or flexing the ribbon cable between it and the ROM board to see if that changes things...
 
Having fixed my power supply issues (RAM is now getting +4.9, - 4.9, and 12.2), I'm trying to pin down the 1-3-8 message I keep getting on this board. I've tried swapping RAM chips, replacing the socket, and checking continuity. I thought I'd found the problem when I found the D37 trace was broken between 3R and 4H but fixing it didn't get rid of the error. I've also socketed and replaced the 74LS374s and the 74153s.

Any suggestions?

Got copy of the Williams Robotron/Stargate logic probe debugging guide?

Saltbreez
 
So, swapping the 38 with the 28 doesn't change the error? Try wiggling the power connector on that CPU board, or flexing the ribbon cable between it and the ROM board to see if that changes things...

Nope, swapping the RAM chips makes no difference. I've reflowed the power connectors, rebuilt the power supply, and verified the voltages at the RAM are stable and good. I've also wiggled the ribbon cable between the CPU and ROM boards and later replaced the ribbon cable just in case.

Got copy of the Williams Robotron/Stargate logic probe debugging guide?

Yep, I have a copy and I have a logic probe, and I'm working my way through it, but I was hoping someone might have seen this before and offer a shortcut. The board was booting up in my Stargate (though still with the 1-3-8 error), but it won't get past the rug test in my Robotron. It does one pass through the rug test, then shows a screen of vertical lines, then goes back to the rug test, then keeps cycling through those two screens. The ROM board just keeps repeating the 1-3-8 message.

Ken suspected the special chips on the ROM board were causing me problems. I have two other ROM boards but no way to know if they're okay (one was okay before it was posted here but could have died in the mail). Neither gives a better result.
 
I have a Robotron board that has a similar issue. I've done everything you have (except needing to fix a trace) and still haven't fixed it. I have been talking with Andy about this and if you look at the Sinistar manual (Rev D MPU board) it uses 74LS373s instead of 374s. One is edge triggered the other is level triggered. The other difference at the board level is that Rev B boards have a 0.1 mfd capacitor soldered from pin 1 to pin 10. This would seem to indicate that there is some timing difference that may have some effect on the addressing of the RAM chips. I am not an electrical engineer so exactly why the differences matter. My gut feeling is that there is some other chip on the bus that is causing the issue rather than the addressing chips, but I have not found which one.

One of the things Andy & I had talked about, since the chips are socketed, why not try 373s in place of the 374s. I have not yet gotten to that yet. If you have time (and the chips), give it a try and let us know.

ken
 
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