Powerbook 520 odd behaviour

weckart · Mar 14, 2015

I recently acquired a Powerbook 520. It has a 160MB HDD and just the onboard 4MB of RAM. I managed to find a power supply for it and it booted up just fine. I got the flashing folder so wasn't sure whether the HD was dead, wiped clean or otherwise corrupted.

While I went looking for a Sys 7 floppy to check, the PB switched itself off. I couldn't get it to start again. I stripped the machne and checked for damage or loose connections. Everything seemed fine but it still wouldn't boot or even chime.

Fast forward a week and I was about to put it away as a bad job and gave it one more try. It booted up and this time the HD started up. It had an installation of Sys 7.1, Word, WordPerfect and a couple more applications. After about five more minutes it switched itself off again and I could not get it to restart. No chime or chimes of death. Nada.

Not really sure how to troubleshoot this one. Clearly, the logic board and psu are relatively ok as the PB would never have booted otherwise. The heatsink over the cpu daughterboard seems to be fitting correctly, so I don't think the unit is overheating. I dunno.

PerformaGuy · Mar 14, 2015

Is the power supply you found one that just fits/plugs in or is it the right power adapter from another 520?

Maybe the voltage/amperage is under or over what it needs.
Also, how does the 520 keep system time, is there a pram battery that needs to be replaced or is it in the main battery?

MacTech68 · Mar 14, 2015

When it fails, you might want to quickly check the AC adapter voltage, without disconnecting the AC mains cable.

https://support.apple.com/kb/TA32851?locale=en_US&viewlocale=en_US

The external power supply may be overheating, and a thermal cut-out switches it off to protect itself. It should reset once disconnected from the mains for a short period of time.

You might want to remove the batteries from the PB500, as that would be putting extra load on the power supply if it's trying to charge the battery.

Another tidbit I found with the 4 pin connector on the motherboard. The pins would push back thru the connector, and as a result, they would no longer make reliable contact with the AC adapter. You can push them back out a couple of millimeters, but that requires disassembling the main machine.

Why they didn't make the connector solid in the rear to prevent the pins from moving is beyond me.

weckart · Mar 15, 2015

PerformaGuy said:
Is the power supply you found one that just fits/plugs in or is it the right power adapter from another 520?

M1893 is the model number. A one size fits all 5xx Powerbooks, I believe.

MacTech68 said:
When it fails, you might want to quickly check the AC adapter voltage, without disconnecting the AC mains cable.

https://support.apple.com/kb/TA32851?locale=en_US&viewlocale=en_US

The external power supply may be overheating, and a thermal cut-out switches it off to protect itself. It should reset once disconnected from the mains for a short period of time.

You might want to remove the batteries from the PB500, as that would be putting extra load on the power supply if it's trying to charge the battery.

Another tidbit I found with the 4 pin connector on the motherboard. The pins would push back thru the connector, and as a result, they would no longer make reliable contact with the AC adapter. You can push them back out a couple of millimeters, but that requires disassembling the main machine.

Why they didn't make the connector solid in the rear to prevent the pins from moving is beyond me.

Thanks. This looks likely. I powered it up just now. It booted to the desktop and switched itself off almost immediately. It looks to be a power issue of some sort. Now I need to dig out my multimeter and hope the probe points can squeeze into the small holes on the psu jack.

MacTech68 · Mar 15, 2015

weckart said:
...Now I need to dig out my multimeter and hope the probe points can squeeze into the small holes on the psu jack.

A paperclip might help.

weckart · Apr 7, 2015

I finally located my mulitmeter and measured the voltages out of the adapter. I could only make out the number four on the jack with the hole bottom left if looking at the face of the jack with the triangle notch on the bottom. The top two holes as per the photo below registered 16.5V approx with the bottom two showing 0V. I assume this is how it should be. The only thing I noted was that hole 4 seems to be lacking an inner sleeve but as it isn't meant to be providing power, I am not sure that is even an issue.

The 520 still boots and switches off shortly after the desktop has settled down. The charger is barely lukewarm, so I am not sure about overheating. I opened up the notebook and make sure the power port pins inside were even and protruding sufficiently to ensure contact with the psu jack.

On the basis of this, the psu actually seems to be in order. Any other suggestions for things I might have overlooked?

MacTech68 · Apr 7, 2015

Some other possibilities that I can think of.

If the rest of these suggestions fail to get you closer to a diagnosis, then it may be old capacitors on the motherboard. You could try warming the board with a hairdryer for a minute or so, before powering on.

I wonder, since it appears to fail just after the desktop loads, if it is actually going into sleep mode. There is an LED on the top edge of the display housing which should blink if that's the case.

Secondly, try booting with extensions off (hold down the shift key whilst booting).

Third, try getting the machine into SCSI Disk mode. This requires the use of a PowerBook SCSI adapter that has all 30 pins present. There are third party adapters that have a switch for normal and SCSI Disk Mode.

Lastly, minimize it's configuration. You should be able to remove the following.

Floppy drive
Keyboard (you'll need an external ADB keyboard to power up)
Trackpad - I'm guessing
Internal Backup Battery (underside of the main top housing next to the trackpad)
Display - not sure about this, but if you have a powerbook display adapter and a suitable external display it might work.
Hard drive - if you have a powerbook SCSI adapter, and can duplicate a system on an external drive, this would work.

In all cases, make sure the shield is replaced over the CPU daughter card - this has the heatsink attached to it.

weckart · Apr 10, 2015

Thanks for all the suggestions. Plenty to work from. The PB is not sleeping, it dies suddenly as if the power has been pulled. Once that happens, I have to leave it for a day before it will power up again. The last boot (with extensions off) did not even make it to the desktop before it died. It may yet be a psu issue, I am not sure why.

I have stripped it down to the logic board and as far as I can make out, all the caps look fine. Nothing internally has leaked or looks otherwise worn or shorted. I have booted from a Disk Tools floppy before, so I know that the floppy is OK. Booting without the battery still results in a power cut before too long.

I don't have an ADB keyboard to try (hoping to get one before too long) and had already detached the PRAM battery. The only thing left that I can see from the Service Manual is something about a logic board fuse. Not sure if that makes much difference since the the PB should not even boot if that is blown. Might try another psu if I can find one cheap.

MacTech68 · Apr 10, 2015

It's a good one, that's for sure.

The fact that it takes a day before it powers on again does seem to be PSU related, but which, on board or external. Have you tried disconnecting the backlight inverter, and/or the display?

You might be able to rig a generic AC adapter to power it up (preferably without cutting the original AC Adapter's cable

Though that is up to you).

From what I understand, the machine can run (without a battery) on anything from 12v to 17v - though Apple quotes a range of 16.4v to 16.6v
Together, VBatt and VMain could deliver as much as 2.5Amp

Note that at the bottom of this article Apple also says this:

The PowerBook 500 series AC adapter has two separate outputs, VBatt and Vmain. The VBatt supply is used for charging the batteries while the VMain supply provides power for the PowerBook. Power from VBatt is automatically diverted to power the PowerBook if additional power is needed.

EDIT: Just to mention, IIRC, power on can be achieved by momentarily shorting Pin 2 (PSW) on the ADB connector to ground. See http://en.wikipedia.org/wiki/Apple_Desktop_Bus for the pinout diagram.

PB500 Series AC Adapter Plug & Socket trim annot comp 75.jpg

1stworldview · Apr 11, 2015

i would really love to get this stuff.

weckart · Apr 12, 2015

MacTech68 said:
It's a good one, that's for sure.

The fact that it takes a day before it powers on again does seem to be PSU related, but which, on board or external. Have you tried disconnecting the backlight inverter, and/or the display?

You might be able to rig a generic AC adapter to power it up (preferably without cutting the original AC Adapter's cable Though that is up to you).

I am giving the jerry built adapter a go. I have a Kensington multi-doodah that should do the trick. Booting without the display attached isn't going to give me much info. It is just the one cable.

Thanks for all your help, btw!

1stworldview said:
i would really love to get this stuff.

Knock yourself out but be quick.

http://m.ebay.co.uk/itm/141628480179

MacTech68 · Oct 14, 2016

Just wanted to add to this resource.

I discovered that Lind used to make an Auto-Air DC-DC adapter that actually had a PowerBook 500 Series DC connector.

Archive.org Lind product page

The product part number is PB-5 - It boggles my mind as to where Lind got the 4 pin connectors.

There doesn't seem to be any others by the usual outlets (VST & NUPower).

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Powerbook 520 odd behaviour

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