Working on two 603TCFL mobos. Running Windows XP-Pro. Pentium 1.0 GHz processors. Both boards originally had many bad capacitors, which were replaced. After repair, both worked OK. Late last year they both started failing -- would not come up, or came up and 'froze,' or kept resetting. Found that the system temperature had to reach approximately 80 degrees F. for the boards to work. If they both reached that temp, they would run OK indefinitely.

If they were not running, putting a hair dryer on the boards for a few seconds would bring them up. After they came up, applied Radio Shack component cooler to ALL components, including memory, and boards continued to function. Checked all board for bad solder joints, broken land patterns on reverse of board, and all seemed OK.

Does this appear to be a heat sensitive capacitor? Any suggestions on how to continue checking out this problem?

Thanks in advance.

Charlie Jackson

Is your motherboard battery ok?
Batteries, when almost dead, can be induced to give of their last by warming them.

Sylvander:

Good suggestion! However, I have seen battery problems before and replaced both batteries. Whatever is heat sensitive is not on the component side of the board. Almost impossible to use the coolant on the land-pattern side, since the boards are mounted in the machines. I've had both boards under a magnifier and can't find any bad solder joints or broken lands, though there may be some. Maybe I'll try removing the boards and connecting only the power, keyboard, mouse and monitor, allowing me to spray the land-pattern side.

Thank you.


Charlie Jackson

My opinion:
It`s not worth the trouble to repair a damaged motherboard...

R53S:

You're right about that - but I'm a retired EE with plenty of time and hate to have an electronic problem I can't solve. It's a challenge!

CFj

Well, in that case, be sure the specs of your capacitors are
the same specs of the factory ones...

r53s:

Capacitors aren't that difficult to replace, as long as you can get the proper uF values. The voltage can be higher, I'm sure if you have a history in electronics you already know that. I've repaired at least 40 motherboards with bad capacitors, one of them yesterday, I've only run across 3 that still refused to boot after replacing the bad ones.

OK on with the problem at hand...

Most of the time the capacitors used in computers are 105C temp range, which is a lot hotter than a computer should normally get, long before it gets there the machine would either shut down, fry the CPU or give you an error messsage. I can't see any reason heat would be required for a motherboard [or capacitor for that matter] to run. You can put the computer in a refrigerated room such as a meat cooler and it should still boot up and run. huge vaccuum tube based early machines like ENIAC had colossal air conditioning units to keep them cooled as well as possible. (ENIAC'S unit took up an entire floor of the building) Some people use liquid nitrogen for CPU cooling and the entire case will usually be freezing or close to it, the computer will still run fine.

If you are having to heat the thing to get it to run, something really strange is going on, usually you have to fight to cool it enough...Have you tried a different power supply? Since heat causes expansion, I could understand a slight bad contact being solved by heating up, but on two boards? That's stretching it...I'm stumped really, but trying to bounce some ideas around, maybe something will click...Have you tried reseating video and RAM?

Weeeeeeeell...
next time i`m going to think twice before
throwing a motherboard...

Hehe..as long as I can find the right capacitors, I make $40 a pop for about a half hour of soldering. Would be a lot quicker, but it's a pain to get the things out. I have 3 or 4 boards here now that I can't do because I can't find the right uF values in 8mm diameter. For example I can find 6.3V 1000uF in 10mm all day long, nobody has the 8mm size, but they've been used in tons of motherboards...same for 1200 and 1500, and one oddball board with 6.3V 3300uF in 10mm that I can't find...and it really sucks to have to tell a customer they have to buy a new motherboard, close to $100, when the only reason I can't fix it is I can't find $3 worth of capacitors...