Electronics > Repair

'Historic' Motherboard with 'Bad Caps' repaired

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Dr. Frank:
Hi,

I got a failing, 'historic' PC to repair.
The MoBo is from DFI, an absolutely no-name brand from Taiwan.
It's got ridicluous 500MHz, 256MB, and still runs on Windows 98 (w/o internet connection, of course).

But I still need it urgently, because it still has ISA slots, which support an old GPIB card, and my acquisition program under Turbo Pascal is still running.
I did all those nice measurements with this PC, which are on display on the EEVBLOG forum, e.g. LTZ1000, 3458A, 5442A, VHP202Z stability.


The PC won't start up from cold, or only after several retries.

I checked the ATX PSU, but that was ok.

Inspecting the board itself, many of the 1000µF/6V electrolytics were blown, or their case were bulged out.
That is a very obvious visual root cause, I think.
The capacity of the caps also were reduced greatly.
I have no ESR meter at hand, but I assume that they are high ohmic now.

So I got  replacement caps; 1000µF/16V, 105°C, automotive grade from FROLYT (small German manufacturer).
They are bigger, and also have a different pitch.
But anyhow, their ESR should be lower, due to the higher nominal voltage.

The dis-assembly was very difficult, due to multilayer PCB with big ground areas. See photo of the not-yet-cleaned solder junctions..

I needed 2 strong solder irons, one soldering pump iron from one side of the PCB, and from the other side a 300°C iron, to disassemble the Bad Caps and clean the vias.

The assembly of the new caps was also quite difficult, as the soldering temperature was partly too low, that the vias would suck the new solder into themselves.

But anyhow, the repair was successful, the board now starts without any problems.


Afterwards, I re-discovered the old site http://www.badcaps.net/forum/showthread.php?t=425, which described exactly that problem.

So, in the beginning of the 2000s, several Asian manufacturers were hooked on a bad electrolyte technology, which was presumably "stolen" from another company but with the wrong recipe.

So I looked closer on the failing cap, manufacturer was TAYEH, which is on the list of companies, which produced those failing caps.
And the MoBo is from 2001, or so.. Bingo!

A very interesting industrial story also, I think.

Frank

wraper:
Frankly saying those capacitors were not too bad if managed to survive 13 years.

XOIIO:
Agreed 13 years isn't bad.

But, if it's a no name motherboard how is it historic in any way?

Dr. Frank:

--- Quote from: XOIIO on July 22, 2014, 01:27:36 pm ---Agreed 13 years isn't bad.

But, if it's a no name motherboard how is it historic in any way?

--- End quote ---

13 years old- W98 - 500MHz.. if you don't call THAT historic in the fast progressing PC business..

Forgot to mention, that in this PC I still have 5 1/4" and 3 1/2" floppy drives running, for the case that I ever have to access those old formats again. (Perish the thought!)


Well, 13 years endurance for 105°C electrolyte capacitors is not that good either, especially as they obviously fail systematically (9 off 13).
And we've got a real root cause for that failure..
 
I have old instruments here from HP and Fluke, with electrolyte caps ok after 20... 35 years.

Frank

XOIIO:

--- Quote from: Dr. Frank on July 22, 2014, 01:41:13 pm ---
--- Quote from: XOIIO on July 22, 2014, 01:27:36 pm ---Agreed 13 years isn't bad.

But, if it's a no name motherboard how is it historic in any way?

--- End quote ---

13 years old- W98 - 500MHz.. if you don't call THAT historic in the fast progressing PC business..

Forgot to mention, that in this PC I still have 5 1/4" and 3 1/2" floppy drives running, for the case that I ever have to access those old formats again. (Perish the thought!)


Well, 13 years endurance for 105°C electrolyte capacitors is not that good either, especially as they obviously fail systematically (9 off 13).
And we've got a real root cause for that failure..
 
I have old instruments here from HP and Fluke, with electrolyte caps ok after 20... 35 years.

Frank

--- End quote ---

Historic implies it had some sort of meaningful purpose, or something noteworthy. I have an 88 or so year old typewriter but it isn't historic. If it had written some important document maybe, but that's doubtful.

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