Yet Another LC PSU thread - How to test with a multi-meter?

[reallyrandy]

I have a TDK and an Astec PSU for my 2 LCIIs. Both are completely dead. I could just re-cap and hope for the best but Id' like some guidance on testing voltages with a multi-meter. How can I tell what the voltages are coming out of the PSU?

Also, I have lots of hardware reference books but none go in-depth with the LCII, are there any out there?

 

[Nixontheknight]

It should say which voltages are supposed to come out of which pins on the logic board, hook it up to a known working LC logic board that you don't care about, flick on the supply, and check the voltages, comparing to what they are marked as on the board.

 

[joshc]

LC II hardware reference notes: https://cdn.preterhuman.net/texts/computing/apple_hardware_devnotes/Mac LC II.pdf

Measuring PSU voltages is just a case of using your multi-meter to measure the voltages at the pins on the power cable on the logic board side.

The LC power pinout is here:

Mac LC/II/III/III+/475 Quadra 605 Performa 475/476 power supply pinout and wiring @ old.pinouts.ru

Let us know how you get on.

 

[reallyrandy]

It should say which voltages are supposed to come out of which pins on the logic board, hook it up to a known working LC logic board that you don't care about, flick on the supply, and check the voltages, comparing to what they are marked as on the board.

Unfortunately, I care about all of them. Is there no way to test directly from the pins on the psu molex?

 

[cheesestraws]

You should be able to get an idea whether anything is dangerously over without the PSU plugged into a board. Note that its outputs will be a bit off without a load, but you'll probably be able to tell if it's way off.

 

[reallyrandy]

You should be able to get an idea whether anything is dangerously over without the PSU plugged into a board. Note that its outputs will be a bit off without a load, but you'll probably be able to tell if it's way off.

How can I tell that? What I'm after is what pins should I put the multimeter on?

 

[cheesestraws]

How can I tell that? What I'm after is what pins should I put the multimeter on?

@joshc linked this information above but I think it got lost. Which voltages are on which pin are on this pinout:

Mac LC/II/III/III+/475 Quadra 605 Performa 475/476 power supply pinout and wiring @ old.pinouts.ru

Put the ground probe on one of the ground pins and measure pins 4, 5 and 7

 

[reallyrandy]

@joshc linked this information above but I think it got lost. Which voltages are on which pin are on this pinout:

Mac LC/II/III/III+/475 Quadra 605 Performa 475/476 power supply pinout and wiring @ old.pinouts.ru

Put the ground probe on one of the ground pins and measure pins 4, 5 and 7

Thank you, that's what I was looking for.

 

[Snial]

Thank you, that's what I was looking for.

Hi, I've just noticed this is a very similar post. Did you manage to test your LC PSU without having to plug it into the board?

 

[Phipli]

Hi, I've just noticed this is a very similar post. Did you manage to test your LC PSU without having to plug it into the board?

The best way to get meaningful results is to artificially load the PSU, for example with some high power resistors. What have you tried? What are you hoping for?

Some PSUs won't start withought a load, others give significantly different voltages to real use. You sort of end up in a... trust issues situation even if you get a reading.

 

[pl212]

Just a note that my freshly-recapped TDK 699-0153 was almost exactly on point (+5, +12, -12) even with no load present. Hardest part was getting the probes to touch the pins through the narrow openings in the plastic cable shroud.