(Topic ID: 217879)

Sys80 lamp driver failing on multiple boards

By zacaj

5 years ago

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Latest reply 5 years ago by srcdube
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Black Hole Gottlieb, 1981

Working on a black hole, originally with ni-wumpf boards. When I got it I replaced all the burnt out lamps, and they all worked. A bit later I noticed the top middle lane (L42) had stopped working, so I went to replace it again, but the bulb was still fine. Tracing back I found out that the transistor for this bulb had failed, so I replaced it. Lamp worked again for a while, and then the transistor failed again. And again. I figured it might be the ic driving the transistor and just ignored it.

Then I swapped in an original sys80 driver board, with all tested transistors. Lamp worked again for a few minutes and then the transistor on this board blew as well. So it must be something external to the board. Nothing is shorted against that socket or anything that i can see

OP
Quoted from zacaj:
Working on a black hole, originally with ni-wumpf boards. When I got it I replaced all the burnt out lamps, and they all worked. A bit later I noticed the top middle lane (L42) had stopped working, so I went to replace it again, but the bulb was still fine. Tracing back I found out that the transistor for this bulb had failed, so I replaced it. Lamp worked again for a while, and then the transistor failed again. And again. I figured it might be the ic driving the transistor and just ignored it.
Then I swapped in an original sys80 driver board, with all tested transistors. Lamp worked again for a few minutes and then the transistor on this board blew as well. So it must be something external to the board. Nothing is shorted against that socket or anything that i can
see

Harness wire short?
With power off, Remove the connector and check the resistance to ground for that signal (on the harness) and other similar lamps on the connector... any difference?

Voltage levels too high to board?
Check 5v voltage levels to the driver board (although if it's too high you'd expect to see failures on other pins too)

Transistors before the driver are faulty?
With power off, Check the resistances to power and ground for any transistors further back in the path that are driving you output transistor... compare with other similar transistors on good paths.

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