clh333
Active member
Working on a Mac SE (same as was referenced in PSU issue post earlier). After substituting a known-good PSU I assembled the computer and powered on, with the back shell removed for observation. Observed the following: No chime, black screen and a hissing, crackling sound. Immediately shut down. Checked all connections tight.
Crackling seemed to have come from the rear of the chassis but needed a second brief power-up to locate the source: from inside the neck of the CRT; small arcs visible. Not good: I have no idea how serious this is or what can happen if it is allowed to recur but I assume this could fry something expensive.
Referring to Pina's Dead Mac Scrolls, this condition is described on P 147 as an analog board problem, with shorted barrel-rectifier diode CR2 ( GI854, 600V 3A) the likely fault.
While the unit was apart I refreshed the solder on the board; it's possible that I caused the breakdown of the diode. I can test this of course but other questions occur to me as well:
In order to work on the analog board I disconnected the HT lead from the flyback to the CRT. When I reassembled I was careful to reseat it, but might I have missed something there; got it wrong? Also: in the course of disassembly I did not remove the CRT board from the CRT or inspect its pins for tarnish or signs of a poor connection. Should I have done that automatically? Could that contribute to this problem?
I'm pretty sure the ground wire from the CRT board to the CRT chassis / frame is in the same position (upper left lug) and making good contact. Beyond that I'm not sure of anything.
Any suggestions or help with diagnosis would be greatly appreciated. Thanks for your replies.
-CH-
Crackling seemed to have come from the rear of the chassis but needed a second brief power-up to locate the source: from inside the neck of the CRT; small arcs visible. Not good: I have no idea how serious this is or what can happen if it is allowed to recur but I assume this could fry something expensive.
Referring to Pina's Dead Mac Scrolls, this condition is described on P 147 as an analog board problem, with shorted barrel-rectifier diode CR2 ( GI854, 600V 3A) the likely fault.
While the unit was apart I refreshed the solder on the board; it's possible that I caused the breakdown of the diode. I can test this of course but other questions occur to me as well:
In order to work on the analog board I disconnected the HT lead from the flyback to the CRT. When I reassembled I was careful to reseat it, but might I have missed something there; got it wrong? Also: in the course of disassembly I did not remove the CRT board from the CRT or inspect its pins for tarnish or signs of a poor connection. Should I have done that automatically? Could that contribute to this problem?
I'm pretty sure the ground wire from the CRT board to the CRT chassis / frame is in the same position (upper left lug) and making good contact. Beyond that I'm not sure of anything.
Any suggestions or help with diagnosis would be greatly appreciated. Thanks for your replies.
-CH-
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