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Vintage laptop PSU repair

C

codyw1996

Member
Joined
Nov 12, 2016
Messages
27
My 286 laptop's PSU died after I accidentally left the laptop running overnight.
It was working fine when I fell asleep, and then dead when I woke up.
I don't see any obvious damage and it doesn't smell burnt.
It's putting out less than 1 volt. It's rated for 17 volts.
I tested the fuse in the PSU and it's fine, so i'm guessing it just needs a new capacitor.
The LED in the PSU is pulsating, which is abnormal.
When plugged into the laptop, the power indicator LED blinks along with the PSU's which isn't normal.
I'm pretty sure the PSU is the problem, but I'll send the laptop as well.
The PSU's label has a pinout diagram.

Here's a video: https://www.dropbox.com/s/yzzq5c37p6hxab0/VIDEO0033[1].mp4

Looking for someone with the experience and equipment to fix it.
You can name your price, i'll send it to you first so you can figure out the cost of components.
I'll pay return shipping, as well.
 
Why do you suspect the PSU and not the laptop itself? Looks to me like a power rail short that could be due to a bad cap or other component in the laptop itself.
 
Just a hunch really. Tested the external PSU with a multimeter and it was outputting like 0.2 - 0.6 volts. Maybe it only outputs the full 17 volts when plugged into the laptop. Didn't think to check that, so maybe it is the PSU in the laptop. It's a small form factor AT-like PSU. In any case, i'm not equipped or experienced enough to check or repair capacitors. So I'd still need help.
 
The pulsing leads me to suspect that it is a feedback issue, as it is trying to power up the LED but the voltage collapses and it retries to gain power. Completely possible by an internally shorted capacitor. Check the wall wattage.
 
0.6V could well be an overvoltage crowbar in the PSU--most are designed to function with a load. You could probably check that by putting a load that draws about 1/2 the nameplate current.

Just pointing out that there's a considerable amount of difference in labor working on a PSU in a nice box and working on a laptop. In a laptop, it might not even be the main board that's at issue--could be a disk drive, backlight inverter, etc.
 
I did try removing the add-on cards, drives, display, co-processor, and CMOS battery. I'm pretty sure one of the of the PSUs just has a bad component. The main motherboard only has integrated circuits on it.
 
I'm sure the mainboard also has capacitors. :)

Let's calculate a dummy load for your PSU for testing. Suppose it can support your laptop drawing 2A, so the effective load resistance would be 17/2 = 8.5 ohms. A 100W incandescent 120V lamp has a cold resistance of about 9.5 ohms, so close enough. Put one across the output of your PSU and measure the output voltage. If you still get 0.6V, I'll agree that it's at fault.
 
What's the make & model no. of the computer?

And what kind of connector is on the 'brick'? Just the 'normal' one pin in the middle, or more than one?

m
 
It's working now.
I have no idea what the issue was, but now I can't reproduce the problem.
Something is definitely dying, but it seems fine now.

IMAG0073[1].jpg

Guess this thread can be closed.

It's a Halikan LA-30A.
The brick has two 17 volt pins, two ground pins, and one NC pin. It outputs 17v at 3.42 amps.

It looks like the old pre PS/2 keyboard connector.
 
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Unplugged the charging brick from the wall and laptop for a few hours and it stopped working again.
Left it plugged into the laptop for a few minutes while the laptop's power switch was off (don't think i've purposely tried this before) and it started working.
Maybe it needs to charge the CMOS battery a bit?
The battery still works. The laptop's RTC has only lost a few minutes after months of being in storage.
Tried wiggling the charger connector while the laptop was running and nothing happened.
Maybe a capacitor (in the laptop, or the brick) is just taking a while to build a charge. I don't know.


After inspecting the capacitors in the brick more closely, I noticed that the one closest to the power input has some black gunk beneath it.
I'm not sure if this stuff is leaking out of the cap, or if it's just some glue or other compound breaking down with age.
That whole area of the brick's circuitry is the part that smells most like popped capacitor, but it's still pretty faint.

IMAG0076[1].jpg
 
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codyw1996 said:
Maybe it needs to charge the CMOS battery a bit?
Click to expand...
Not likely.

codyw1996 said:
The battery still works. The laptop's RTC has only lost a few minutes after months of being in storage.
Click to expand...
I'm not convinced. The battery that runs the computer does not power the RTC.

Try running it... without the battery. If the battery is hosed it could be the problem.
 
Oops, I meant that the CMOS battery still works. I removed the main battery the day I received the laptop, because it only held a charge for like 25 seconds, and I didn't want it to start leaking. As a side note, I think this is one of the earlier clam shell laptops to actually have a battery (released in 1989). According to an old review, it lasted like 45 minutes, but took forever to charge.

Anyway, the CMOS battery is attached to the ISA riser card, and I used the computer for a long stretch of time (a couple months) without the riser card installed. I had to reconfigure the BIOS every time I unplugged the laptop for longer than an hour. So, I know it'll boot with cleared, or corrupted RTC RAM.

I'm also willing to sell it. I was thinking like 50 bucks plus shipping since it needs repairs.
It's missing an internal screw or two (nothing structurally integral) and the ISA slot covers.
I'll throw in the SVGA card (2mb Trident card), and the much-too-new plug and play sound blaster that I use for adlib games.
 
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That's not my exact machine. It's probably the same internally, but my laptop is missing the brand logo sticker on top, and my LED indicator cover doesn't have any writing on it. Why is it listed in the "Tapes and Data cartridge" sub-category? Talk about a fail.
Not sure which technology the battery was based on, I remember the model number was LAP-82. I threw the battery away.

That one on eBay is in much better cosmetic condition than mine. I'll probably buy it for parts if the bid+shipping stays below 80 bucks, assuming I still have mine.
 
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codyw1996 said:
It's working now.
I have no idea what the issue was, but now I can't reproduce the problem.
Something is definitely dying, but it seems fine now.

View attachment 45251

Guess this thread can be closed.

It's a Halikan LA-30A.
The brick has two 17 volt pins, two ground pins, and one NC pin. It outputs 17v at 3.42 amps.

It looks like the old pre PS/2 keyboard connector.
Click to expand...

I've got a scrap LA-22 but unfortunately the power brick is quite a bit different.
 
codyw1996 said:
After inspecting the capacitors in the brick more closely, I noticed that the one closest to the power input has some black gunk beneath it.
I'm not sure if this stuff is leaking out of the cap, or if it's just some glue or other compound breaking down with age.
That whole area of the brick's circuitry is the part that smells most like popped capacitor, but it's still pretty faint.

View attachment 45259
Click to expand...

Yep, that's capacitor electrolyte, and it looks like its corroding the inductor next to it as there's copper corrosion on one of the legs.

I would recap the whole supply not only because of that cap, but for age as well. Capacitors don't last forever and will degrade even if they're not used.
 
Almost all of the solder joints are corroded, regardless of whether they're near a capacitor or not.

I'll probably just use it till it dies, then build a proper 286 desktop with more expansion slots. This laptop seems to run games much slower than other 286's on Youtube anyway, but then again i've only tested it with the one Trident card. ISA SVGA cards are stupidly expensive on eBay, even though they're not rare.
 
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