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MAC IIvx turns on automatically, won't turn off. #noegrets

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Hi there

 

I've got a Macintosh IIvx that I'm repairing. I replaced the battery and all the caps, can't see any PCB damage. It turns on as soon as it gets mains power, and if you try to shut it down, it boots right back up again. Machine works perfectly fine in every other way except for the automatic turning on. Pin 26 of the EGRET chip that goes to the PSU ON wire on the power supply. That seems to always be high and looks like it's the reason the power supply is always on.

 

EGRET chip has (Motorola logo) 341S0851 (c) 1990 APPLE 0C25TLLNG9230 on it.

 

Things I have done (with testing between steps):

- replaced all caps and battery and cleaned up motherboard with 99.9% ispropyl

- cleaned in distilled soapy water (and dried with compressed and and heat gun)

- removed EGRET chip, cleaned underneath and reinstalled (with leg 26 lifted/disconnected for testing)

 

Things I have tested:

- computer turns itself on with and without keyboard/mouse connected to ADB ports

- computer turns itself on with and without new battery

- power supply doesn't turn itself on when not connected to motherboard

- shorting pin 26 of EGRET chip to ground turns computer off, ungrounding turns it back on

 

After lifting leg 26 of EGRET chip, it no longer turns itself on, but the lifted leg is still high. Shorting the leg to the pad it's supposed to be soldered to turns the computer on, removing short turns it off again.

 

I can't find schematics for the IIvx or any spec sheet or pinout for the EGRET chip.

 

Any suggestions? Thanks.

egret_chip.jpg

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At the risk of stating the obvious, you don't have the rear power button in the always on position, do you? There is a button with a little slot in the ps at the rear of the machine that could be set to be always on, presumably for servers.

 

Button at the lower left (on a Q650, but this is the same thing ps-wise):

 

23.jpg.39ef0abc8464b7f6c27ef9c79f556154.jpg

 

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Its probably what the poster said above.. it could also be the psu is just messed up. The mac iivx and vi were known for having some issues I think.

Edited by Papichulo

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I have a similar issue. Though my IIvx doesn't power on for ages when plugged in, it only powers on after being left plugged in for some time. But like yours, it witches on all by itself seemingly randomly.

 

Not that it's ideal, but would it not be easier to just buy/use a random standard 'kettle' style power lead that it uses and wire in a switch like a lamp has? It won't fix the problem but it will guarantee it won't turn in by itself.

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You can always turn the button on the PSU by 90º to see if it was in the "always on" position. This was done as a failsafe on these machines in case they were used as servers and power was interrupted.

 

Of course, it could just be a wonky PSU or even something on the board. I have a IIci with the exact same issue, although the power-up isn't immediate. The board was re-capped and it's been problematic since, which I think is just the result of cursory work.

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This was solved by the first reply - turney power switch on the back was set to keep it on. I followed traces all over the board and hopefully I would have found that power switch at the back sooner rather than later, but thank you for saving me time. Good luck to everyone else with their similarish problems. 

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