Unthawing a Frozen Computer

Computers can be really tricky. I'd like to share an anecdote which shows how tricky a μP can be.

In the mid '90s I was working with some control application based on a PC. The application had been working fine so far, but at certain point someone decided to change the computer we were using by another PC. The new PC had been used as an administrative workstation for more than one year, having performed flawlessly.

Nobody's going to be surprised if I say that the new combination of tested software and "reliable" computer didn't work. The curious thing was why. First, we noticed that the software would run fine for about 10-20 minutes, and then hang up, no matter the task being performed. As ten or twenty minutes are consistent with a thermal time constant playing some role, we decided to cool the μP. Applying some compressed air on the chip succeeded in unfreezing the PC. Obviously, that PC was not suitable, but what was still puzzling us was how that problem never had happened before.

After some debugging, it turned out that the problem started when the μP was above 70-80°C (which is not very hot), and a "RET n" instruction was executed. That instruction was the only one, out of the full set, that seemed to fail. The explanation was that our software, written in Assembler with some sections in Basic, relied heavily on that instruction (which pops the stack prior to returning control), while all the administrative applications previously run had been developed in C. C handles the stack quite differently; it uses consistently an alternative, plain form of RET instead.

Summarizing: A critical flaw, thermally triggered at relatively low temperatures, and affecting only one specific instruction, went unnoticed during more than a year of perfect performance.

70 - 80 deg C is extremely hot. I've had cpu's lockup at 60.

Sounds like a microfracture in one of the SMD solder pads. You might have just melted the solder enough to form a bridge.

Applying a blowtorch to electronics just doesn't sound right to me though

Hello Jonas,

Check out "Florida Motherboard Specialists" down in Miami FL area. They probably can replace any bad component on your dead MB. They're quite inexpensive and are superb technicians!!! If they cannot fix the MB, then all you do is pay for the postage of shipping (the MB only) to and from their shop. They will not charge you for the looksee...well, that's what I experienced with them last summer. Check 'em out!

They fixed my HP laptop......replacing a dead Video chip that normally cannot be replaced by most electronics shops and it only cost my around $130 for the repair and shipping total! They saved me over $800 (the replacement MB from HP plus labor and shipping costs)!!!

You can find them in Ebay or do a Google search. I highly recommend them and will be sending them another dead laptop this next week that my stepdaughter dropped onto the floor by accident!

Good luck fixing the Dell!!!! Have a great sunny day!

i m really happy to hear that ur comp started n its working fine...i am thinking of buying a laptop..perhaps after ur description i will go for dell rather than hp...

if u got video of that..go to dell..i hope u will get a good fortune..

best of luck buddy..

n to add..to ur happiness..god must have given this as a nice christmas present way before 25th december..

best wishes from manish in india