Fixing up a ProFile after a PSU failure, analogue board pulling down voltages? from Adrian Graham on 2016-09-25 (lisalist1)

From: Adrian Graham <binarydinosaurs_at_email.domain.hidden>
Date: Sun, 25 Sep 2016 13:30:31 -0700 (PDT)

Hi folks,

I've been pointed over here from the Vintage Computer Forum so first, hi! Adrian/Witchy here, owner of Binary Dinosaurs in the UK and a pair of Lisae - 2/10 with ProFile that I'm sure James McPhail has helped me with in the past and a MacXL that doesn't power up.

After a panic earlier this year about the batteries on the I/O board of my working machine I was testing everything after removing them and cleaning up when the ProFile did what seemed to be a capacitor-death based power down.

Rather than retype everything here's my original question:

My main Lisa ProFile went pop recently, though not literally. It seemed like a graceful death while the drive span down. Looking in the PSU one of the low voltage caps had burst messily so yesterday I recapped the whole unit and cleaned up the mess. It's now putting out correct voltages, with 'correct' here meaning 'same as my Apple/// ProFile PSU' (6v, 15v, -15v with no load)

Trouble is the ST506 won't spin up with the electronics board connected to the ProFile controller in either ProFile box. If I disconnect the ribbon cable and just leave power the drive will spin up happily. Measuring the 5V line on the ProFile controller board shows that with the drive connected it's pulled down to +1V on one PSU and 0.8V on the other so clearly something on the drive electronics module has popped too, but what?

I know the controller and PSU in both boxes are ok as with my one remaining good ST506 my Lisa will see it.

Things I've done so far:

tested power rails on the controller board on its own, seems OK tested +5V on the analogue board on its own, it pulls ~850mA and nothing gets hot
tested +12V on the analogue board on its own, pulls ~100mA which seems low but if there's nothing connected....
checked all diodes on the analogue board, OK. Checked drive mechanism on its own, ie no analogue board, seems OK. Brake works as it should and motor spins up.

Any hints appreciated!

Cheers

Adrian

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