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Old Chicony laptop - can it be saved?

R

Rymdljus

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Jul 1, 2012
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I bought this 1991 laptop on a whim for almost nothing at a flea market. The model is a Chicony NB8620 and at startup it said it was a 486SLC notebook with 5670 kb RAM. About a minute after I turned it on it started to smell oddly and then I noticed a very thin wisp of smoke coming from within. I pulled the plug on it before anything else happened, and as far as I can tell the computer might be fine except for the part that burned, but I don't have any experience with burnt out components.

This is the part that burned:

DSC00262 copy.jpg

Is there a way to save this computer? I know smoke must be a very bad sign, but I'm hoping I might have pulled the plug in time...? ^^;
 
That's just a power resistor and not hard to replace. If you get a replacement, get several, because I have a feeling that the resistor is reacting to a too-high load of some sort (ie.g. a shorted capacitor somewhere).
 
Yep, that's a resistor, on some sort of power supply/ regulator board. If I'm seeing it correctly, it's a 27ohm, 1% tolerance, and probably 2 watt. The 1% tolerance might be a bit tricky to find, but I think you could use a 5% with no ill effects (it may even be a 5%, I can't tell for sure if the last band is brown or gold), and you should be able to get one of those for less than 50 cents from any decent electronics component supplier.

But as Chuck mentioned, resistors don't usually burn out without some external influence... there's a pretty good chance something else has gone bad. If that's the case, then it'd still probably be fairly easy to fix, but it'd be difficult to talk someone with no electronics knowledge through the diagnostic process. Got any techie friends/relatives you could take it to?
 
Thanks for the quick replies! That sounds hopeful then, at least. The thing is I've never soldered anything (since elementary school), but I've been wanting to learn because of things like this. I think I'll read up on it to see if I'll be able to do it. I am a bit concerned about the size of the board. It looks very cramped.

Here's another picture of the board:

DSC00281.jpg

The resistor's last band is indeed gold. Does that make it a 1% or 5%?

I'm unfortunately the most techie person in my family and among my friends (I'm the person people go to with computer related problems :p), so I'm not sure about the diagnostic thing, but I guess it's best to tackle one problem at the time. Perhaps a friend of a friend might be able to help. Are there some things that are more likely than others to be the problem in cases like this? I'm thinking the huge power brick, which might be hard to replace...
 
Is it possible to see the reverse side of the board? I'm curious as to the application of the resistor.

OT must have better eyes than mine--or a better computer monitor. I see red-black-black-silver?-gold which would make this a 2.0 ohm, 5% resistor. If OT sees violet as the second band, then it's 2.7 ohms. If there's no silver 4th band, then it's 27 ohms. An ohmmeter (as on a multimeter) should solve that one.

That, being a power resistor, will normally run fairly hot--and power resistors do age ungracefully. There may well be nothing wrong with your PSU other than an aging resistor.
 
To me it looks like red, gray, black, gold. Or perhaps red, black, black, gold. It's hard to tell since the resistor is burned. :/ I don't think the two middle ones are supposed to be the same color, but they are similar, and I'm not sure what to expect either.

Here's the back side of the board:

DSC00283.jpg
 
Hmmm, is that black widget on the backside connected to the same pads as the toasty resistor on the front? Any discernible markings on it?
 
Chuck: I thought it was, but then I took a closer look and I noticed that there is another black widget underneath the burnt resistor, as seen here:

DSC00284.jpg

The black thing on the backside is connected to that, but it might be connected to both of them, since they look kind of soldered together on the backside:

DSC00285.jpg

There are markings, but I can barely make them out on the black thing on the back because they're facing the board, but it says "MQ 125V" on the one on the top side, and I think it does on the thing on the back as well.

(There's even another tiny widget underneath the black one on the top side, but I don't think that is connected to the others.)

Wow, I'm learning stuff as I go along here. :) I really appreciate the help!
 
Ok, the resistor does appear to be red-black-black-gold, which would be 20 ohms, 5% (and still probably 2W, which is just an educated guess based on its size). From the angle of the first picture, it looked more like red-violet-black-brown. A 20 ohm resistor is a bit of an odd value, but it shouldn't be too hard to get... but if you can't find one anywhere, you can probably get away with a 22 ohm, which is much more common. There's usually a bit of leeway in the value of a power resistor anyway.

I'm guessing maybe the black things are fuses, perhaps the ones denoted by F1 and F2 on the label.
 
Yup, those are bel fuses. There should be additional markings as to their rating, such as "2A". The $64 question is "Is one of those fuses connected to the same pads as the resistor?". If so, then the fuse is probably blown and the whole load is flowing through the resistor, making things very toasty indeed.

I know it's silly, but I've seen resistor-protected fuses before.
 
Okay, so the resistor is probably 20 ohms 5%, and 22 ohms might work. What does this fuse situation mean exactly? Will it be harder to fix if the fuse is connected to the resistor? I can't find any additional markings. "MQ 125V" is all there is. But, as shown in the last picture, the label on the connector in front of the resistor does say "F1 3A/125V" and "F2 5A/125V". Does that help?
 
I don't know where you're located, so I can't specify a store, but there are inexpensive Chinese-made multimeters that can be had here in the US for somewhere around $5 at Harbor Freight stores. They're perfectly adequate for what you need.
 
I live in Sweden, actually! Maybe I should have said so ^^ But that's okay, I can get a hold of a multimeter for that price easily, if my googling hasn't failed me. If a cheap one is enough, I'll get a cheap one and take it from there. This'll be interesting regardless the outcome. :)
 
Volts (AC and DC) Ohms and Current (amps) are a minimum. An audible continuity test is very convenient (allows you to keep your eyes on the work, not on the meter). Capacitance, frequency, etc. are bonuses, but not strictly necessary.
 
Yeah, capacitance and frequency aren't terribly important, but I would recommend getting something with a diode test function, if you can. I think some of the cheap ones have the feature. Being able to check diodes and (also do basic checks on transistors) is quite handy in troubleshooting power supply issues.
 
So now I have a multimeter (it's a UNI-T UT20B), and I don't know how to use it, hehe. ^^;;; I've started reading up a bit on electrics, but it might take a while before I get the hang of it...

I'm really a newbie at this. I'm supposed to check if the fuses are still working, right? Do I need to get the fuses off the board first? I don't have any equipment to do that either, yet. Or is it enough that no electricity is going through the board?

I think I need to set the selector on the multimeter to somewhere on the "ohms" side, but I don't know which setting, since it goes from 2000k to 200. I don't know how to connect it either...
 
Okay, for resistances (and fuses) set the range to 200. Touch the tips of the leads together. See how the display goes from a leftmost "1" (signifying out of range) to nearly 0.00? That signifies that there is low-resistance continuity between the tips. And now you know how to check a fuse--with the power off, place the tip of each probe on the wire leads coming out of a fuse. You should see a reading of nearly 0.00. Anything much about 0.10 may be a problem.

Now check the 2 fuses.
 
That wasn't so complicated. Thanks :)

I get 00.4 (it only shows one decimal) on both the fuses, but then again, that's what I get when I touch the tips together as well.

On the resistor itself I get about 27.5-27.6. It's hard to keep this thing still!
 
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