Shadow Lord
Veteran Member
Quick recap: I picked up a nice looking but problematic Compaq Portable 486c - most of the issues have been resolved. My last remaining issue is that I can not adjust brightness on the screen at all. It is on full max blast all the time. Initially I had thought the pot controlling the brightness had gone bad. However, after taking the pot out of circuit and testing it it turned out to be fine.
I worked (fumbled around really) on the circuit some more and looking at the four transistors on it one of them appears shorted open.
You can see pictures of the board here (with the offending transistor already removed):
and the transistor here:
.
Checking the two outer legs of the transistor shows a short. I took the transistor out of the circuit and it continues to show a short along the two outer legs. As I understand it that should not happen. Would that be a correct assessment? If it is shorted open would it explain the light being on at full force? I found a replacement for the transistor but it will take a month to get here from China. Anything else that a trained eye sees that I should check on? The cap looks OK visually but I am going to check it with an ESR meter to be sure. TIA.
I worked (fumbled around really) on the circuit some more and looking at the four transistors on it one of them appears shorted open.
You can see pictures of the board here (with the offending transistor already removed):
and the transistor here:
Checking the two outer legs of the transistor shows a short. I took the transistor out of the circuit and it continues to show a short along the two outer legs. As I understand it that should not happen. Would that be a correct assessment? If it is shorted open would it explain the light being on at full force? I found a replacement for the transistor but it will take a month to get here from China. Anything else that a trained eye sees that I should check on? The cap looks OK visually but I am going to check it with an ESR meter to be sure. TIA.