Macintosh SE works fine then completely dead an hour later.

[fergycool]

Just got myself a Macintosh SE yesterday (finally!). I bought it on eBay and there was a risk in shipping (which I was OK with). However, when it arrived it turned on fine (although the internal SCSI drive is dead). It boots fine from a 700k System 6.0.8 floppy. So I was very happy.
However, after shutting it down, then powering back on an hour later it is dead. No lights or sound at all.
I opened up the case (after making myself one of those discharge tools).
I disconnected the SCSI drive from both the SCSI bus and the Molex connector. I removed the logic board. The battery looked fine, but I still snapped its legs and removed it. There is no corrosion on the board. In fact it looks quite clean!
I tested the power from the drive Molex connector and neither the 5v or 12v sides give any reading at all. Not suprising as the PSU fan does not kick at all when powered on.
From reading on here I guess that the PSU was on its last legs and is now dead. So it will need recapping or replacing.

Thank you.

 

[joshc]

It certainly sounds like the power supply could be the culprit, yes. Is it a Sony or Astec unit?

 

[fergycool]

It certainly sounds like the power supply could be the culprit, yes. Is it a Sony or Astec unit?

Thanks. It's a Sony CR-44.

 

[joshc]

These tend to be good units but are worth a recap at this point - they also have a voltage adjuster inside the unit as well, but a recap is where I would start.

There are alternatives available, new power supplies that are compatible, but it all depends on how much you want to invest in it.

 

[fergycool]

These tend to be good units but are worth a recap at this point - they also have a voltage adjuster inside the unit as well, but a recap is where I would start.

There are alternatives available, new power supplies that are compatible, but it all depends on how much you want to invest in it.

Thanks a lot. I guess a recap of the PSU is on the cards. A shame I only got to use my nice "new" Macintosh SE for just 30 mins First time I've used a compact Mac in well over three decades!

 

[finkmac]

could also be a flaky AC socket / power switch. i've come across that before.

 

[superjer2000]

could also be a flaky AC socket / power switch. i've come across that before.

I was just going to suggest the power switch as well. I have had a couple of Sony PSU power switches fail with the same symptoms and it's a known issue.

I was able to repair them by taking the switch apart (be careful to not lose the small ball bearing balls) cleaning it all with deoxit and putting it back together.

 

[chiptripper]

And check the solder joints on the back of the analog board, particularly at plug connectors. I’d be surprised if there aren’t at least a couple that are cracked.

 

[fergycool]

Thanks a lot for all those suggestions. I will check them all. To my naive thoughts they do sound a more plausible cause than the PSU failing. There were no symptoms during those 30 mins until it was completely dead (it had been turned off for an hour or two before powering back on).

 

[cheesestraws]

Yes, I have twice lost whole days to tracking down things that turned out to be blown fuses in the socket. Oops.

At risk of stating the obvious, and not at all meaning to sound patronising, you have checked the fuse in the plug hasn't gone, right?

[Not that I've ever spent ages trying to debug that one, either, grief]

 

[fergycool]

Yes, I have twice lost whole days to tracking down things that turned out to be blown fuses in the socket. Oops.

At risk of stating the obvious, and not at all meaning to sound patronising, you have checked the fuse in the plug hasn't gone, right?

[Not that I've ever spent ages trying to debug that one, either, grief]

Not at all patronising as I've done the same! Fairly recently I lost most of a morning checking a battery charger that would not turn on, without checking the fuse in the extension lead plug. What's worst is that the extension lead had been left outside and the plug was slightly damp so it really, really should have been obvious! For this Mac I checked the fuse, I tried a second power lead AND a completely different plug socket!

 

[MacintoshSE1987]

Have you checked the caps?

 

[fergycool]

Yes it was the fuse in the PSU. I spent 10 mins testing the socket and switch before noticing the very obviously blown fuse! Unfortunately I only have a 5A version of those glass fuses. Plus until I know what caused the fuse to blow not sure I want to put one back in. However, it has been quite cold in the UK recently and this sat in a cold courier van for three days. I guess it's conceiveable that the PSU was cold and caused some moisture to condense on it and caused a short?

 

[cheesestraws]

Hmmmm, difficult to tell. Do you have a DC load or some chunky power resistors or anything? It might be worth testing the PSU in isolation once you replace the fuse...

 

[fergycool]

Hmmmm, difficult to tell. Do you have a DC load or some chunky power resistors or anything? It might be worth testing the PSU in isolation once you replace the fuse...

I'm sure I can come up with something to test it.

 

[fergycool]

I replaced the fuse and tested. The voltages are all over the place. The 12v pins are giving 0.5v and the 5v is 0.2v. I guess the caps are gone! Time for plan B!

 

[joshc]

I replaced the fuse and tested. The voltages are all over the place. The 12v pins are giving 0.5v and the 5v is 0.2v. I guess the caps are gone! Time for plan B!

Tested with the logicboard and analog board plugged in, or standalone with nothing else plugged into it? Sorry if the question seems daft, it's just that I fell into this trap after my first time recapping an SE/30 power supply and not realising that it wouldn't do much without a load.

 

[fergycool]

Tested with the logicboard and analog board plugged in, or standalone with nothing else plugged into it? Sorry if the question seems daft, it's just that I fell into this trap after my first time recapping an SE/30 power supply and not realising that it wouldn't do much without a load.

Ahh! I did not realise that! This was not under load at all. So if I plug in a 12v bulb to simulate a load I should get a more accurate reading?

 

[fergycool]

Hmm. I added a few LEDS to the socket (from a breadboard). They all lit up and I took 5.3v and 10.45v. But then I heard a "zzzz" and the fuse blew again. So I guess there is short somewhere in the PSU on the 230v side and it was not condensation.

 

[chiptripper]

Electrolytics fail open, so a dried up cap might plausibly cause a short.