StarGate Mini

dhawk

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My Stargate works, however blue seems to be missing. (I have recapped the monitor & replaced some transistors)
Also, the mountains come and go…

When I run the tests it says: All systems indicate go and COLOR RAM TEST VERTICAL BARS INDICATE ERROR. I am assuming this may mean some video ram chips might need replaced??

Also, in test mode, there is no Blue bar, just Red and Green.

I looked a the manual, it says replace CPU/VIDEO board....

Any ideas?
 
if you look near the video header you'll find a column of 3 little transistors, Q1 Q2 and Q3. (consult the Stargate drawing set for the part numbers and locations on the MPU) Q3 should be the one that drives blue. you can try swapping Q1 or Q2 with Q3 to see if red/green disappears but blue comes back. the part number is 2N4403.

if blue is still missing after replacing the transistor I would suspect something a little deeper, they'll run to an IC in the circuit -- haven't dealt with this problem myself (yet)
 
if you look near the video header you'll find a column of 3 little transistors, Q1 Q2 and Q3. (consult the Stargate drawing set for the part numbers and locations on the MPU) Q3 should be the one that drives blue. you can try swapping Q1 or Q2 with Q3 to see if red/green disappears but blue comes back. the part number is 2N4403.

if blue is still missing after replacing the transistor I would suspect something a little deeper, they'll run to an IC in the circuit -- haven't dealt with this problem myself (yet)


Yeah, I replaced that transistor....
 
check 2B (7489) and 2C (74LS257) next.

Q1 and Q2 should be connected to 1B and Q3 only going to 2B -- they then combine at 2C.
 
Could be a cold solder joint at the video connector on the board.

I didn't have that problem. After I rebuilt my PS, I re-landed the video cable one pin off. I lost my red. I did a WTHDID and looked, and found my mistake. Perhaps you are a pin off in the other direction?
 
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