Re: Help with dead lisa 2

>Hello, I have a lisa 2 that only tries to power up 1 out of 100 tries with
>the switch.

If it turns on sometimes, it would seem the power supply might be ok.

The Lisa power supply is turned on and off by the COPS421 on the I/O board.

Clean the I/O board contacts and check the motherboard connector.

If you have some test equipment, see if the COPS421 has power on pin 9 and the oscillator is running (pin 2 or 3, but the oscillator will be affected by a low impedance instrument); to do this, you will need to defeat the back panel interlock (eg. jam some cardboard into the switch on the back of the power supply.)

Pin 14 of U7F on the I/O board should have about +5 volts with the power off; if so, try briefly touching pin 12 to pin 14; this should turn on the power supply.

Good luck!

James

James MacPhail                   "Think not of engineering as art,
uo957_at_email.domain.hidden                 but of art as engineering"
Sigma Seven Systems Ltd.
james_at_email.domain.hidden        <http://SigmaSevenSystems.com>

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