Tempest Board Playing Blind Help

QuartrArcade

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This one is close to working, but I'm stumped at this point. Board plays blind, it is definitely the board.

Every once and a I'll get almost a complete game image (usually inverted or distorted) to appear for a few seconds and then it disappears. Appears to be rather random. I was thinking it is something in vector generator section and have replaced the 312 DACs and TL082s to no avail.

Any tips on where else to look?

Thanks,
Anthony
 
More info, pots were also replaced. Finally thought to put in back test mode and here's what I get on the screen now.

Anthony
 

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This is where an oscilloscope comes in handy. You can use it to track down the voltages/signals as it goes through the output sections of the board and see exactly where it is failing.
 
Yes, +/- 15.12 VDC on the board at the test lugs and voltage regulators.

Anthony
 
That's what I'm thinking, I pulled the scope out and the output on the Tl082 at A11 is bad. Already replaced that so I'm thinking the LF13201N at B11 is the problem. Going to dig through my parts board as I don't have one handy.

Anthony
 
Problem solved: LF13201N at B11 was bad. Grabbed one from a Space Duel parts board and Tempest is all better.

Thanks for the help,
Anthony
 
Good to know, fixed a Space Duel board as well today, that one had a bunch of data lines stuck low going into a DAC. A 74LS194 IC was the problem (forget which location), but all if its outputs were dead, inputs were good.

Having fun fixing these vector boards now that I know a bit about board repair. Have some more Tempest boards to tackle next week.

Anthony
 
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