You have two main problems there, the first is a leaky battery like you mentioned, but that wasnt what caused the bad smell and smoke, you also have a blown Tantalum capacitor , I would replace the Cap, and then scrub the entire board with Kontak PCB Cleaner 😀 , and then asses the board for PCB damage , you might have some broken tracks and looking at the pics there is definitely a bad surface mount resistor.

The Tantalum caps tend to fail epically especially when they get moist (could have been from the battery acid)

FaSMaN wrote:

You have two main problems there, the first is a leaky battery like you mentioned, but that wasnt what caused the bad smell and smoke, you also have a blown Tantalum capacitor , I would replace the Cap, and then scrub the entire board with Kontak PCB Cleaner 😀 , and then asses the board for PCB damage , you might have some broken tracks and looking at the pics there is definitely a bad surface mount resistor.

The Tantalum caps tend to fail epically especially when they get moist (could have been from the battery acid)

Thanks for your reply.

I don't think the capacitor burning out has anything to do with the battery, because they're pretty far from each other (see sixth image).
As to me breaking some tracks 😵, is there any way to fix them?
Also, could you please clarify on the bad resistor? In which photo do you see it?

Regarding the PCB cleaner you're referring to, from what I see, those are usually made to remove flux from PCBs, will it still be good for my needs?
I've managed to find it on RS, but it's 30 euros (including shipping, which is 12eur alone) 😲. Are there any alternatives?

Munwele wrote:

Thanks for your reply. […]
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Thanks for your reply.

I don't think the capacitor burning out has anything to do with the battery, because they're pretty far from each other (see sixth image).
As to me breaking some tracks 😵, is there any way to fix them?
Also, could you please clarify on the bad resistor? In which photo do you see it?

Regarding the PCB cleaner you're referring to, from what I see, those are usually made to remove flux from PCBs, will it still be good for my needs?
I've managed to find it on RS, but it's 30 euros (including shipping, which is 12eur alone) 😲. Are there any alternatives?

It might not have been related, but will need replacing as they normally fail and create a short,when they fail it makes a lot of smoke when blowing and matches your description 😀

Its not your fault if any are broken, the acid in the battery would eat at the copper and eventually break them , I use a good magnifying glass to visually follow each track and check for damage, then a multimeter to check continuity and finally use some wrapping wire to solder to the opposite ends of the track to create a bridge, or scrape away at the damage track and use the exposed copper to solder the wrapping wire to.

Second last photo, second smd cap or resistor counting from right to left, you will notice its allmost black.

PCB clean is a multi purpose circuit board cleaner, I found it works the best, many users on the forum also use a combination of vinegar and lemon juice , and then afterwords clean it with isopropyl alcohol, Ive tested that in the past and while it does work, its not as good as the PCB cleaner that allows you to clean everything in one go.

Edit: your case isnt that bad and should be fixable , I did a video a while ago of a extremely bad one that need scraping and soldering: https://www.youtube.com/watch?v=TSq3rTp4ub8

Jesus, I just watched some of the video and skipped through it (for now, we'll watch all of it, it will be of great help when we're about to start the repair), and that's totally awesome.
I'll buy a PCB cleaner ASAP and see what we can do with it.
I'll keep you informed.

Also, if you don't mind me asking, can you give me the list of tools you used in the video? I see that you're using some items, but I have no idea what they're called.
Thanks 😀

That video is a worst case scenario, where the battery acid started eating away at the fibre glass , looking at yours its nowhere near as bad and if your lucky just needs a very good clean and that cap replaced.

before you buy it try the vinigar method first , like I said its not that bad and you already have some isopro-alcohol

All you will need:

Fibre Glass pen
PCB Clean
Toothbrush

to fix track:
Soldering iron
solder
30awg wrapping wire
multimeter
Fiber pen to scrap away the solder mask
optional: craft knife

Don't waste your time with trying to brush that stuff off, you will never get everything. Use the vinegar method. And for a test (after cleaning and drying), you can power up the board without that capacitor.

h-a-l-9000 wrote:

Don't waste your time with trying to brush that stuff off, you will never get everything. Use the vinegar method. And for a test (after cleaning and drying), you can power up the board without that capacitor.

Thanks for your reply.
Okay, so I will try the vinegar + alcohol method first. We have to get some vinegar because we don't have any! 😁
I'll keep you updated.

I honestly don't think it's going to work with that blown capacitor. When it shorted, the computer turned off immediately . Our reaction was to quickly disconnect the PSU from the mains.
Also, I'm a little hesitant to turn it on like that, more damage might be done, what do you think?

The blown cap should be removed, but it might be able to run without replacing it. Before you disturb it, try to read the markings if possible and write them down. Otherwise, you'll just have to assume it's the same as the others near it which are the same size. Also make note of the polarity, although in this case you already have a picture that clearly shows it. 😀 On tantalum caps the stripe is positive - the opposite of how electrolytics are marked. If you toss an electrolytic in it's place (people sometimes do this) then keep this in mind.

Since the power supply turned itself off it must have been overloaded. Hopefully it detected the overload and turned off intentionally to protect itself, in which case it's probably still okay, but it's possible the power supply could have been damaged. Either way this means there's a short somewhere, presumably that cap. If you have a multimeter then you could measure the resistance across the failed cap. This is effectively measuring the resistance between the positive voltage rail (whichever rail that cap is on) and ground. Normally you'd expect to see it gradually climb to a high value, although exactly how high varies a lot between boards. If it's 0 ohms then there's a short somewhere, most likely the blown cap.
After removing the cap check the resistance across the solder pads and see if the resistance has changed.

For curiosity's sake, you can also use the multimeter to find which other caps are in parallel on the same rail. If you find caps of equal size that are in parallel then it increases the likelihood that they were the same. It also gives a sense of how significant or insignificant that one cap is - if you're missing 1 out of 7 caps it's not as big a deal as if you're missing 1 out of 2.

shamino wrote:

The blown cap should be removed, but it might be able to run without replacing it. Before you disturb it, try to read the marki […]
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The blown cap should be removed, but it might be able to run without replacing it. Before you disturb it, try to read the markings if possible and write them down. Otherwise, you'll just have to assume it's the same as the others near it which are the same size. Also make note of the polarity, although in this case you already have a picture that clearly shows it. 😀 On tantalum caps the stripe is positive - the opposite of how electrolytics are marked. If you toss an electrolytic in it's place (people sometimes do this) then keep this in mind.

Since the power supply turned itself off it must have been overloaded. Hopefully it detected the overload and turned off intentionally to protect itself, in which case it's probably still okay, but it's possible the power supply could have been damaged. Either way this means there's a short somewhere, presumably that cap. If you have a multimeter then you could measure the resistance across the failed cap. This is effectively measuring the resistance between the positive voltage rail (whichever rail that cap is on) and ground. Normally you'd expect to see it gradually climb to a high value, although exactly how high varies a lot between boards. If it's 0 ohms then there's a short somewhere, most likely the blown cap.
After removing the cap check the resistance across the solder pads and see if the resistance has changed.

For curiosity's sake, you can also use the multimeter to find which other caps are in parallel on the same rail. If you find caps of equal size that are in parallel then it increases the likelihood that they were the same. It also gives a sense of how significant or insignificant that one cap is - if you're missing 1 out of 7 caps it's not as big a deal as if you're missing 1 out of 2.

Thanks for your reply.
Yes, there's a high possibility that we'll be replacing the tantalum capacitor with a normal electrolytic one.
I, too, think the capacitor is to blame for the computer turning off. But if you're saying that the PSU could be damaged, it would be safe to put it in another system and test it, right?
The 4 capacitors that can be seen in the picture, including the burnt one, are of the same value. The print on the burnt capacitor can still be read, with some effort 😉.
Today, I'll be buying vinegar and hopefully, we'll also be starting the "operation". Also, is there a possibility for the vinegar to do more damage to the motherboard?

UPDATE:
I just did the vinegar + alcohol method. I'll leave it up to you to decide whether I've done a good job or not, I personally think I haven't.

Here are the images, could you please explain what the hell is going on?
http://imgur.com/a/EcQY4

I just tried turning it on, same thing as before but this time, nothing burnt out or shorted. Power and HDD LEDs turned on for a split second but nothing happened. We'll try replacing the capacitor today.

That doesn't look so bad. The green stuff has been mostly neutralized. You can clean the remainders with the alcohol and a toothbrush.
I assume you have washed the vinegar with fresh water? Have you pulled the jumper to see how good the contacts are? Have you cleaned the pins of the ROM chips?

The traces runnung around the battery don't look good. You should try with a continuity check of a multimeter.

h-a-l-9000 wrote:

That doesn't look so bad. The green stuff has been mostly neutralized. You can clean the remainders with the alcohol and a toothbrush.
I assume you have washed the vinegar with fresh water? Have you pulled the jumper to see how good the contacts are? Have you cleaned the pins of the ROM chips?

The traces runnung around the battery don't look good. You should try with a continuity check of a multimeter.

No, I have not used fresh water and yes, I cleaned the rom chips. Apart from alcohol, what else should I use now?
Thanks.

uh - vinegar needs to be washed off completely or it will start its own corrosion. Best done in the sink under fresh water. Use the chance and brush off the dirt together with soap, both sides. No need for alcohol then. After that, swing it around to get rid of larger spots of water and the dry, best at highler temperatures like 80-100°C.

Have no fear with the water - I've washed multiple boards that way. Just make sure it's dry before powering on.

Just did what you told me to do. I'm drying it at the moment.

Sorry this is an old post, but I had to point out something interesting.

I recently acquired a Prolinea 3/25 that was listed as "not working" and stated perhaps it was the power supply. Nope, the same capacitor was blown as in your photos. Powered right up when I removed the cap. Based on what was on the HDD, I believe this may have occurred at least 25 years ago when the computer was only a few years old.

I also acquired a better motherboard for the computer that didn't have such extensive battery leakage damage. The 4 tantalums near the power connector are a different color than the original motherboard, but all were intact when I received the board. I powered up that board half expecting the same tantalum to blow. Sure enough, same capacitor released the magic smoke.

I wonder just what percentage of the 3/25 models had the same fate. It had to be very high. I supposed that's what you expect when a 16V rated tantalum is used on a 12V rail. I will be replacing these with 25V parts.

BTW this is my first retro machine after eBay window shopping for many years, but always reasoning that it was pointless to get involved with some old computer. I lusted after these in the early 90s because some local computer store sold them despite the Prolinea 386 being everything I later was against: proprietary, no extra drive bays, integrated peripherals. Such a cute little computer though.