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PowerBook 520c PSU to repair or not?

croissantking

Well-known member
I just received my parts-only PowerBook 520c from eBay. Confirmed with a multimeter that the problem is with the PSU - I opened it up and found the 3.15A fuse was blown, so I soldered in a replacement. When I plugged it in, it made an almighty pop/flash and took out some 16R and 8R2 resistors in the below image. The resistors are connected to the 'source' pin of a MOSFET, which I desoldered in order to test and it looks like it's not working properly.

I am interested in repairing this for the sake of having an authentic setup, but not sure it is worth it vs. getting a third party 16V PSU off eBay and splicing in the connector.

Is it worth buying a new MOSFET and seeing what happens?

Can failing caps cause the power supply to short out in the way it did?


Screenshot 2022-05-26 at 15.17.24.png
 

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Johnnya101

Well-known member
Someone on here did a hack with I think it was the 1xx series adapters, and stuffed a modern PSU board inside the original case, and used the original cord and everything. You could do that too.
 

croissantking

Well-known member
Whilst I think what to do, here's an ensemble of the machines I now have: a 145, 520c and 1400cs.

The 1400cs is rock solid reliable and a pleasure to use – but it has a passive matrix LCD, no CD-ROM and cacheless CPU. So it's a low-end example. I'd love to at least get an active matrix LCD.

Now, whereas 145 feels positively ancient, the 520 feels ahead of its time - sleek and smooth, and almost experimental with its dual colour plastics. It feels good quality and as though it represents the pinnacle of Apple portable design at the time. In terms of look and feel the 1400 seems like a direct evolution of the 520 design philosophy, but more cheaply constructed and not blessed with as much pride taken by its engineers (things like the lack of an LED on the caps lock button indicate cheapness to me, as well as the messy back panel/ports as compared to the 520's elegant and symmetrical layout). However, at least the plastics are not brittle on the 1400 so they got something right there.

The 520c has already blessed me with a working 250MB IBM SCSI drive, so I am using it in the 145 now, since its own Quantum GoDrive is toast.



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croissantking

Well-known member
Someone on here did a hack with I think it was the 1xx series adapters, and stuffed a modern PSU board inside the original case, and used the original cord and everything. You could do that too.
I see you have a Personal Laserwriter NT in your collection. I used to have one of these and I'd very much recommend the upgrade to an NTR board if you can find one. It halved the time it took to print.
 

croissantking

Well-known member
I haven't even gotten to it yet, don't even know if it works! I really only use my IIg.
Hmm, may not be worth the effort then! I successfully replaced some kind of motor inside it but then I believe the caps went bad and it was outside the realm of my abilities at the time to tackle. I got fed up and chucked it.

The IIg is a real showpiece, I'm sure.
 

croissantking

Well-known member
Well, I got the power adapter working, sort of.

I replaced the MOSFET and the blown resistors, and put in a new fuse. It didn't blow upon plugging in this time, so I proceeded to test the voltages on the pins. On VBATT I get around 16.5V, which is correct, but on VMAIN, I only get around 2.5V. As expected, it won't boot the laptop.

I created a makeshift 'harness' to swap over VBATT and VMAIN and like this the PowerBook started up first time!

I'm suspecting bad caps at this point. If that doesn't work I may just swap over VBATT and VMAIN at the power adapter side and be done with it, since I won't be charging any batteries on this thing anyways.
 

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croissantking

Well-known member
Quick update on this one. Running off VBATT works well but I’ve found that if I turn up the screen brightness to max and the CPU/hard disk are working hard it powers off. So I’d really like to get VMAIN working properly.

I’ll start by doing a recap. Of course it’s possible I used the wrong MOSFET to repair, but I’m not sure.
 

iomac

New member
I’m trying to recap a M1893 which looks very similar, but with a massive soldered-on heat sink on the bottom that’s preventing access to the underside of the board — and the bugger doesn’t want to budge. There are apparent solder points on the underside of the board, but solder wick hasn’t quite done the trick and I feel like I‘m scorching the board just trying to get the solder to flow…

Any recommendations for how best to remove the heat sink?

60BB8D5D-6370-49C5-B7A5-F2A9C5725EA7.jpeg
 

Iesca

Well-known member
Gotta just turn up the temp on your iron, it's definitely possible to get it off. You shouldn't be scorching the board, the heat is going into the plate (plus there's the plastic separator). If you have it, use a beveled edge tip, and add some flux. The pin is a hook, so that will be a little difficult, but it will come up!
 

croissantking

Well-known member
I have this metal plate. I desoldered the one point you see in the middle without much trouble and then hinged the thing out of the way.

My new caps are on the way. I’ve gone for brand name components from Panasonic/Nichicon/Vishay etc. Here in the UK, Mouser is too expensive because of international shipping, so I’ve used a company called Farnell which is a local equivalent.
 

croissantking

Well-known member
I’m trying to recap a M1893 which looks very similar, but with a massive soldered-on heat sink on the bottom that’s preventing access to the underside of the board — and the bugger doesn’t want to budge. There are apparent solder points on the underside of the board, but solder wick hasn’t quite done the trick and I feel like I‘m scorching the board just trying to get the solder to flow…

Any recommendations for how best to remove the heat sink?

View attachment 43914
Nice job @iomac on cracking open the casing btw. I plan to close mine up with a few dabs of hot glue (I LOVE hot glue).

Is your PSU dead, or are you replacing the capacitors as a matter of course?
 

iomac

New member
Thanks @croissantking , I followed the strategy in this video:
(Basically using a flat-bladed screw driver, smacking, and working around the case. Not the prettiest, but it did work.)

Also, thanks for the pointer above. I was able to get the shield out of the way -- was surprising to find that pin under there:
shield.jpegopen.jpeg

And yeah, the AC adapter is dead. Checking the voltages, I was getting effectively zero V on all of the output pins -- hence this little adventure.

Now that I have some access I need to do some probing before order new parts. The little probing I was able to do from the top side suggests the problem is on the high-voltage side -- I expect it will be the caps.
 

croissantking

Well-known member
Thanks @croissantking , I followed the strategy in this video:
(Basically using a flat-bladed screw driver, smacking, and working around the case. Not the prettiest, but it did work.)

Also, thanks for the pointer above. I was able to get the shield out of the way -- was surprising to find that pin under there:
View attachment 44003View attachment 44004

And yeah, the AC adapter is dead. Checking the voltages, I was getting effectively zero V on all of the output pins -- hence this little adventure.

Now that I have some access I need to do some probing before order new parts. The little probing I was able to do from the top side suggests the problem is on the high-voltage side -- I expect it will be the caps.
Did you also check if the 3.15A fuse is blown, as mine initially was?

I’ve just won an AAUI twisted-pair transceiver on eBay, so I’ll be able to hook this thing up to the internet once I fix the PSU. Exciting…!
 

croissantking

Well-known member
OK, I’ve just completed the re-capping.

C37AE880-CCCC-4A1A-B9AC-2EF524E1B735.jpeg

I’m rather disappointed and surprised that it hasn’t fixed the problem! Still get 2.1V on the VMAIN side. I suppose there is a faulty component somewhere — I’m willing to put in the time to troubleshoot and get this fully fixed, but I don’t really know where to start. Is it a case of ‘any of the dozens of components could be bad’ or can we narrow it down? I’d really appreciate any kind of pointers.

I’ve swapped over the red and orange wires for the time being, so I can use my 520c. But it’s limited to 1A on the VBATT circuit, so I can’t push it too hard.
 
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