IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

[guyjim]

Hi guys,

I have an IBM ThinkCentre in reasonable shape. The problem with it is that when Windows XP (or any other operating system i.e. Linux on a CD/DVD etc) starts to load, the system reboots.

You can sit around in the BIOS all day long and it will run just fine.

Issue is definitely down to the motherboard, troubleshooted all the other hardware i.e. checked that it wasn't a fan issue, replaced the PSU, checked the RAM, swapped the hard drive, reset the BIOS etc.

Desoldered a few large caps near the CPU and a couple of smaller ones, tested them with a Peak Electronics ESR meter, readings given as follows;

KZJ (ChemiCon) 16v 1800uF 105 deg C
1836uF 0.0 ohm ESR
1829uF 0.0 ohm ESR
1822uF 0.0 ohm ESR
1829uF 0.0 ohm ESR

Not sure what brand the smaller caps are, poss Sanyo?, not sure of value? possibly 820uF? markings printed on them as follows; 428 SEPC 820 2.5

872.5uF 0.0 ohm ESR
867.6uF 0.0 ohm ESR

Also checked all of these with my digital multimeter set to 2M ohms, each capacitor slowly charges until I get a reading of 0.0.

Cannot see any leaks, nothing really looks amiss but from what I have read on here the ChemiCon capacitors can go and still look OK.

Bad or not?

Thanks in advance, GJ.

[bigbeark]

Re: IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

I believe from my reading on this site the KZJ and KZG are suspect.

These are hot-running boards, especially if fitted with Prescott CPU. Heat shortens cap life. Many of these boards have all poly(solid) caps around the CPU, Any 'lytics in that location are likely to be cooked, especially KZJ.

Symptoms sure sound like tired caps to me, but check the power supply as well, or try another known good power supply and see what happens.

Make sure the extra 4-pin power connector is attached - easy to miss.

I just recapped one of these successfully, but I have had difficulty with others.

You will need to apply new solder to the cap "legs", then re-apply the iron to get the caps off the board. Be very careful, the cap legs should come free without any yanking.
Also make sure you have the board mounted on a sturdy jig. Do NOT press on the cap legs with the iron thinking you will budge the cap. Very easy to slip with the iron and tear a trace.

Replace any of the 85C caps with 105, they are prbably cooked too.
Good Luck. When they work right, they are nice enough boards.

[guyjim]

Re: IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

Hi bigbeark,

Thanks for the informative response!

I don't think the CPU is a Prescott, but as you've said it probably does run pretty hot in there, especially with the case design having just the one extremely powerful Delta fan at the front (the case is one of the midi tower designs..) I think it may be a Northwood.

Again you're right about the caps around the CPU, they are all solid Aluminium caps; I think they may be of Sanyo manufacture.

Three out of the four KZJ 16v 1800uF 105 C deg C I've removed are situated right near to the CPU heatsink.

I definitely did check the PSU, and the 4-pin power connector was attached.

The other caps on the board are as follows;

Chemicon KZJ 10v 1500uF 105 deg C x 3
Chemicon KZG 6.3v 1500uF 85 deg C x 2
Chemicon KZG 6.3v 1000uF 85 deg C x 4
Rubycon YK 25v 100uF 85 deg C x 7
Rubycon YK 25v 10uF 85 deg C x 12
Rubycon YK 16v 470uF 85 deg C x 6
Rubycon YK 16v 220uF 85 deg C x 4
Rubycon YK 10v 330uF 85 deg C x 4
Panasonic 10v 33uF 85 deg C x 1
Rubycon MBZ 6.3v 1000uF 105 deg C x 3

I can replace any and all caps relatively easily using my rework station

I'm thinking from what you siad I should definitely try and replace all of the KZJ and KZG, but what about the other caps, most of them are 85 deg C but is it really necessary to replace all of them?

The trouble is, most of the Rubycon caps that I would probably buy either are not stocked by national electronics suppliers, or they are very (probably prohibitively so) expensive to buy.

I can buy a few on eBay at a fairly OK price, I don't know of anywhere else in the UK that sells high quality capacitors at a cheap price however.

Your thoughts please?

Thanks in advance, GJ.

[bigbeark]

Re: IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

I would replace ALL the Chemi-cons as a start.

See if that gets it going. In my case I had a mix of polys and lytics around to the heatsink. I had the 2200uf 6.3v caps in quantity, and these were what was used near the heatsink. I just left the solid caps alone.

The board I just serviced was an 8926 in a desktop case. I replaced all the KZG/KZJ plus the caps between the PCI slots, which I think were 470uf 16v.

That machine has a 2.4Ghz Celeron with 128MB cache - a real dog.

I sustituted a 2.8Ghz Prescott with 1GB cache. Performs way better!

PS: What are the diameters of the KZG & KZJ?


PPS: Run MEMTEST to make sure no RAM problem. It's on your Linux Live CD. Let it run for an a couple of hours. Could be a memory problem.

[guyjim]

Re: IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

Hi bigbeark,

Ok, good advice there.

Diameters you requested as follows;

Chemicon KZJ 16v 1800uF 105 deg C x 4 (12mm)
Chemicon KZJ 10v 1500uF 105 deg C x 3 (8mm)
Chemicon KZG 6.3v 1500uF 85 deg C x 2 (8mm)
Chemicon KZG 6.3v 1000uF 85 deg C x 4 (8mm)

I think I alredy ran memtest86, and possibly changed the RAM anyway, I can't really remember because I've had this base unit for a while now.

Will get some replacement Rubycon MCZ caps ordered.

Cheers! GJ

[guyjim]

Re: IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

Hi,

Sorry the KZJ 16v 1800uF 105 deg C x 4 is actually 10mm.

Cheers, GJ

[bigbeark]

Re: IBM ThinkCentre Motherboard - Start to load OS - Reboots - Bad Caps?

So you can use the same caps for #2 & #3. It's OK to go from 6.3v to 10v.

I thought I might have some of the caps you needed, but alas, no. There seems to be a lot of variants of these M50 boards - everyone I see is different.