performa 580CD wont start until logic board removed

[danc]

Hi

Have a performa 580CD here that wont start - no fans, no chime, no hard drive noise etc. Reccaped it, made no difference.

However, if the logic board is removed the fan will start up (obviously not a lot else happens).

Anyone came across this before? Been collecting macs for a while and have fixed a few along the way but I dont know where to start with this one.

Thanks

 

[Bunsen]

Sounds like the power supply is not putting out enough juice.  Or you could try replacing the motherboard battery.

 

[danc]

Will they not run at all without a battery? I have removed it - it didn't run with it plugged in either though and is probably long dead. Would you suggest re capping the psu board too then? Caps all look good but who knows.

Computers not really worth anything but I like to tinker.

 

[Bunsen]

A quick test to see if the battery is the problem is the old double-boot:

Power it up, attempt to start, and leave it (not) running for a while (five minutes say).  Then quickly flick the power switch off-on.  If it boots on the second power-on, then yes it just requires a new battery.  The idea is that leaving the power connected will get some juice into the PRAM circuit, enough for it to boot if it's not switched off for long enough to drain the charge.

If five minutes doesn't work, try an hour and if that doesn't work try overnight.