Replacing capacitors in an old laptop

I expect some of you to laugh when you read this but it's a hobby to me so I don't care. :pac: I didn't know whether to post this in Electronics or Gadgets, however.

I have a very old laptop computer, a Compaq SLT/286. It's not like your typical modern laptop, it's absolutely huge and weighs 6.5kg! Judging by the components on the motherboard it dates from mid-to-late 1989. I got hold of it in 2004 when I was scrapping old computers from a business in Limerick and decided to keep it as an oddity. It was working perfectly up until recently; the only bit of physical maintenance I had to do was to replace the RTC chip on the motherboard as its internal battery had depleted. Even the main Ni-Cad battery held a charge up until about 6 months ago; pretty impressive.

However, it's now showing some signs of what I suspect are capacitor issues. On some occasions when you power it down, it won't come back up until you unplug it from the PSU and let it sit for a while. I don't know how long exactly, but it would be within 15 minutes anyway. Also, last night it did something it never did before. When you power it up, it goes through the POST sequence and performs a memory test. After the memory test, it spins up the hard drive. Last night, I had it on for a few hours when it spontaneously rebooted itself and the hard disk spun down. At the stage of the POST where it would normally spin up the hard drive, I could hear the drive starting to spin up, but then it rebooted again and spun down the disk. I powered it off in order to avoid damaging the drive.

The latter sounds to me like there's not enough power being provided to spin up the hard drive. Due to the age of the system, I'm suspecting that the electrolytic capacitors are drying out; I intend to get a capacitance meter to test this as my regular multimeter won't cut the mustard. I've done up an inventory of the caps in the main PSU as well as the secondary PSU inside the system. There's no electrolytics on the motherboard itself, they're all confined to the two PSU boards.

TL;DR - If I confirm a capacitor issue, can anyone recommend where I could get some good quality caps to replace what's in there? I'd like to go for the likes of Rubycon or Panasonic if possible, assuming it won't break the bank really.

Radionics, Farnell, Ebay.

You want an ESR meter that also reads capacitance. Not a capacitance meter...that in itself will not tell you if they need replacing or not.

Kalman

Karsini wrote: »

I expect some of you to laugh when you read this but it's a hobby to me so I don't care. :pac: I didn't know whether to post this in Electronics or Gadgets, however.

I have a very old laptop computer, a Compaq SLT/286. It's not like your typical modern laptop, it's absolutely huge and weighs 6.5kg! Judging by the components on the motherboard it dates from mid-to-late 1989. I got hold of it in 2004 when I was scrapping old computers from a business in Limerick and decided to keep it as an oddity. It was working perfectly up until recently; the only bit of physical maintenance I had to do was to replace the RTC chip on the motherboard as its internal battery had depleted. Even the main Ni-Cad battery held a charge up until about 6 months ago; pretty impressive.

However, it's now showing some signs of what I suspect are capacitor issues. On some occasions when you power it down, it won't come back up until you unplug it from the PSU and let it sit for a while. I don't know how long exactly, but it would be within 15 minutes anyway. Also, last night it did something it never did before. When you power it up, it goes through the POST sequence and performs a memory test. After the memory test, it spins up the hard drive. Last night, I had it on for a few hours when it spontaneously rebooted itself and the hard disk spun down. At the stage of the POST where it would normally spin up the hard drive, I could hear the drive starting to spin up, but then it rebooted again and spun down the disk. I powered it off in order to avoid damaging the drive.

The latter sounds to me like there's not enough power being provided to spin up the hard drive. Due to the age of the system, I'm suspecting that the electrolytic capacitors are drying out; I intend to get a capacitance meter to test this as my regular multimeter won't cut the mustard. I've done up an inventory of the caps in the main PSU as well as the secondary PSU inside the system. There's no electrolytics on the motherboard itself, they're all confined to the two PSU boards.

TL;DR - If I confirm a capacitor issue, can anyone recommend where I could get some good quality caps to replace what's in there? I'd like to go for the likes of Rubycon or Panasonic if possible, assuming it won't break the bank really.

Closely examine the caps on the power panel [ using a magnifying glass] and look for any that are showing signs of bulging. These caps, when leaky, can cause bizarre faults.

It should be quite cheap, to replace all the caps on the power panel . I use the 'hot and cold' method to induce any faults in that area.

Cheers guys.

Haven't gone near it since, haven't really had the time, but I'll get hold of an ESR meter and see what I find in there.

Got my mits on an ESR meter today so I got to work.

Here is the power board from inside the laptop:
https://dl.dropboxusercontent.com/u/23270031/boards.ie/IMG_0490.JPG

I think I might have found something, here's the ESR values:

C510: 0.042Ω (1500 uF 25V)
C503: 0.075Ω (100 uF 25V)
C504: 0.073Ω (100 uF 25V)
C500: 2.54Ω (3300 uF 6.3V)
C511: 3.60Ω (1800 uF 16V)

C500 and C511 seem very high. There's not much identification on the caps, just the code 678D, and from a bit of googling it seems that the ESR should be 0.055Ω and 0.057Ω respectively.

Yurp they look dried up. Depending on the meter you may have to take them out of circuit to test them accurately.

I haven't been looking at this lately as I've been busy with other things but I had another look this morning.

I recently got my mits on another one of these, the Compaq SLT 386s/20 - identical except for the 386 motherboard. I tried swapping the internal power boards and the problem was reversed, the 386 was rebooting and the 286 was perfectly fine. So I've narrowed down the problem at least.

I took apart the 386 PSU and noticed that it's slightly different. C510 is another 3 leg cap. Looking at the 286 PCB I can see that it has the pinout for a 3 leg cap but just isn't used. So that makes me wonder if I could just replace those with 2 leg caps?

I might just try it and order some caps when I have some time to look at it.

You'd be best replacing like with like or checking the component datasheet for a similar component. A three leg cap is two capacitors with a common ground or a bodge non-polarising...not compatible with a single 2 leg.

whizbang

I have seen caps where the third leg is only a mounting pin. Much like large 4 pin caps, there is no connection to the capacitance pins, but they usually must be isolated from any other connection.

Doge

Sir Liamalot wrote: »

Radionics, Farnell, Ebay.

You want an ESR meter that also reads capacitance. Not a capacitance meter...that in itself will not tell you if they need replacing or not.

Damn, i just spent €33 on a Multimeter with capacitance for the intended use of testing bad capacitors , i wish i read this beforehand. I guess it will be a useful upgrade on my cheapo €5 multimeter at least.

Karsini wrote: »

Got my mits on an ESR meter today so I got to work.

Which ESR meter did you get? Or can anyone else recommend a cheap one that does the job?

Doge

Ended up buying a MS
ESR-100 V2 from MIB instruments in the end with an accepted offer of $50 so I got a nice little discount:

http://pages.ebay.com/link/?nav=item.view&id=390609552907&alt=web

Ships from their UK store too I think.

There's a few video reviews and teardowns of it on YouTube and its a nice little unit apart from the cheap plastic case.

ShRT

Doge wrote: »

Ended up buying a MS
ESR-100 V2 from MIB instruments in the end with an accepted offer of $50 so I got a nice little discount:

http://pages.ebay.com/link/?nav=item.view&id=390609552907&alt=web

Ships from their UK store too I think.

There's a few video reviews and teardowns of it on YouTube and its a nice little unit apart from the cheap plastic case.

Have one of these, haven't used it too much but works well. Compared against one of the cheaper ESR metres (a diy kit from China) and got same kind of results. Only downside is the chart on the front had very wide ranges and it doesn't tell you the capacitance of what you are testing

Doge

ShRT wrote: »

Have one of these, haven't used it too much but works well. Compared against one of the cheaper ESR metres (a diy kit from China) and got same kind of results. Only downside is the chart on the front had very wide ranges and it doesn't tell you the capacitance of what you are testing

I saw a diy Kit from china on ebay alright and I was tempted.

The lack of in circuit testing and probes put me off it though. Thanks for the feedback!