Williams Stargate no display or Rom bd segment display

bluestreak

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Williams Stargate no display or Rom bd segment display

I'm about to dig into this a lot deeper, or as deep as I can, but wanted to check here if anyone knows a common resolution to the issue I'm having.

No CRT display but have filaments glowing and high voltage, no 7-segment display on ROM bd on power-up, Sound bd diagnostics seem to work by pressing diag switch on bd, voltages off of power supply correct with no AC leakage, no reponse from "reset" switch on CPU bd.
I've swapped out the main boards mounted on rear door from another unknown if working Stargate, but no change. This did not include the sound bd.
Is there anything anyone knows of that I may be missing that should be obvious before I spend a ton of time tracing supply voltages?
Thanks
 
Well, it's hard when you don't have at least one set working to narrow it down. First off is to check what the +5 is reading at the board connectors (CPU and ROM) as well as the chips on the boards. Then check the ribbon cable between the ROM board and the CPU. Flex it to see if it comes up or gives anything on the LED display. Try reseating or swapping chips between the two boards to see if you can get one set to work...
 
I've tried the cable flexing already. Next I guess I just have to begin checking voltages across board connectors. Just weird it's the same issue with both board sets, unless it's a common faulting board or component and both sets have the same issue.
I'm going in.......
 
Check the voltages at the MPU board and then at the 4 corners of the RAM chips. The voltages should be 0V, +5V, +12V and -5V, unless the 4164 mod had been done.

Also check the voltages at the ROM card.

If you have the original linear power supply, you should see 3 lit LEDs on it.

ken
 
Ok, a follow up to what the problem was. PS was all good on voltages but one of the LED's (+5) was burnt out.
So luckily, even though all metered out ok, I began to trace this voltage and found a bad connection on the power feed to the ROM board. All is good now and working great except for me.
Realized I need a bunch of practice to get back into a good game on this one. :).
Lots of buttons.
 
The LED may not be burned out, they take a lot of abuse for some reason and one of the legs may have broken off. I see that all the time. If you replace it (I recommend that you do), be careful of getting the super bright LEDs. They really look odd if you have just one. Either find the regular red LEDs or replace all 3.

ken
 
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