Power Macintosh 5260/100 arcing

[techknight]

Someone gave me 2 of these machines that he had in his attic since about 2001. they came from a local school district and has all the school programs on them.

Well, i fired one of them up, and the machine ran, however the HV was arcing every once in awhile with a jerk in the picture each time. it eventually stopped, but are these flybacks known for failure? dont think ive seen any of them arc like this.

 

[Trash80toHP_Mini]

Sounds like you shouldn't fire them up again until one of our resident flyback gurus passes judgment! :-/

 

[techknight]

Luckily, it hasnt done it again, but i am not going to plug the other one in for safe measures.

However, i noticed when you turn the power on to the unit, it bongs and starts right up. even if you shut down, it will turn off then back on and start up. without pressing the power button. Reasons?

 

[Dennis Nedry]

However, i noticed when you turn the power on to the unit, it bongs and starts right up. even if you shut down, it will turn off then back on and start up. without pressing the power button. Reasons?

This is a problem located on the logic board. It's more than likely caused by a bad capacitor or two.

Notice that if you remove the logic board from a 5260, 5500, etc, the shell auto-magically turns on and fires up the display. The logic board actively pulls some signal low (presumably) to keep the Mac turned off if it's working properly. They do it this way so that if the soft power circuit fails, it will just always turn on by default. Many Macs with soft power exhibit this behavior with age as capacitors begin to fail.

 

[Dennis Nedry]

This is a problem located on the logic board.

After further thought, there is also a slight possibility that the problem does lie in the shell or dirty logic board edge connector, but very unlikely. The only way to know for sure would be to swap logic boards.

 

[techknight]

i put a PCI based logic board in there and it works fine. only the original logic board does it. even after capacitor replacement. dunno. oh well. I have another logic board of the same type from the second 5260 that just loudly chirps.