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Author Topic: No startup - Lisa Power Supply Unit?  (Read 4295 times)

Ona Beach

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No startup - Lisa Power Supply Unit?
« on: April 22, 2024, 10:16:48 pm »

My Lisa 2/10 no longer powers up. No response anywhere when power button is depressed. Is it ok to power up the PS on the bench without anything connected (no load) to it?
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sigma7

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Re: No startup - Lisa Power Supply Unit?
« Reply #1 on: April 23, 2024, 03:22:10 pm »

My Lisa 2/10 no longer powers up. No response anywhere when power button is depressed. Is it ok to power up the PS on the bench without anything connected (no load) to it?

No response may be due to problems other than the PSU.

Try removing the I/O Board and reassembling (without it); most Lisa's will power up immediately if power is connected and the I/O board is missing. If it does power up, then the problem is likely on the I/O Board. If it does not, then checking the PSU outside the Lisa would be a good step.

But, the PSU won't just start up outside the Lisa when plugged in.

If you plug it in with nothing connected, you should be able to measure 5.6V or so at the +5 Standby pin. If it isn't there, then I'd guess the fuse is blown, and you may be able to see some obviously damaged parts inside.

To get the PSU to start up, you'll need a test fixture that:
  • Connects +5 Sense to +5.
  • Has a modest load from +12 to Ground
  • Has a modest load from +5 to Ground
  • Has a switch or jumper to connect +5 Standby to ON (connect to turn on, disconnect to turn off)
Some terminal connections (double check against one of the PSU schematics, eg: Lisa PSU - improved Rev J Schematic). One side of the connector is numeric, the other alphabetic which skips some letters such as I and O.
  • +5 Sense = N
  • +5V = M,11, 12.
  • +12V =  K,L,9,10
  • Ground = 13,14,15,16,17,18,P,R,S,T,U,V
  • +5 Standby = 20
  • ON = X

One of the test fixtures I have used has a 1 ohm @ 50W load on +5 and a 15 ohms @ 15 watts load on +12. These are certainly more of a load than is necessary to just power it up, but a minimum load may conceal the ripple that can result from bad filter caps.

HTH
« Last Edit: April 23, 2024, 08:15:31 pm by sigma7 »
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Lisa2

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Re: No startup - Lisa Power Supply Unit?
« Reply #2 on: April 24, 2024, 01:02:55 pm »

This problem could be as simple as the covers not being fully closed and the interlocks are not closed.
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andrew

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Re: No startup - Lisa Power Supply Unit?
« Reply #3 on: April 24, 2024, 10:26:47 pm »

This problem could be as simple as the covers not being fully closed and the interlocks are not closed.
I've had this happen more times than I care to admit...
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AlexTheCat123

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Re: No startup - Lisa Power Supply Unit?
« Reply #4 on: April 24, 2024, 10:43:24 pm »

Quote
I've had this happen more times than I care to admit...

Same here. I eventually got so tired of it that I just bridged the pins of both switches with a piece of wire and now there's nothing to worry about!
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