Looking for a needle in a stack of needles...

[Frankie]

I have a 1200xl that has a loose connection somewhere. I know it's just going to take time to find it but where else can I whine about it and have someone understand me. My wife just looks at me like I'm nuts.

 

If I press down just slightly on the center of the board it boots fine. Leave it alone.. and black. .... arrrggggggg

[ACML]

Probably one of the following:

 

1) less likely: try re-seating the IC's. One of them may have intermittent continuity on one pin due to oxidation.

2) more likely: a semi-cold solder joint has developed. One solder pad has de-bonded from a pin, resistor or capacitor which is causing an open. This can be very difficult to track down.

3) quick try: Blow compressed air over the motherboard especially under the sockets. A tiny piece of tin solder may have been liberated and is resting between two pins causing a short. The air may free the debris ( a long shot, but will only take a few minutes).

4) probably won't work, but maybe it will. Assuming you still have the RF shielding, insert some non conductive material in the center of the PCB and trap it between the PCB and RF shield. This will apply pressure to the center of the PCB (like your finger pushing down, cause the board to flex slightly and restore function). I've done something similar to this with success on an 8086 MOBO that I damaged pushing in RAM DIMMs too many times or with too much force. This is the "last resort" if you've given up all hope.

 

Just thinking out loud.

Edited November 30, 2013 by ACML

[+Larry]

If you press to one side or the other or top/bottom, does it boot?

 

Re-seating chips is always a good idea.

 

Had a similar problem with a 130XE -- sound came and went. Pushed on the board, it stayed. I ended up "touching up" every solder joint that I could find on the left half of the board (50/50 chance). Got it, so I only had to do half the board!

 

-Larry

[Shawn Jefferson]

1. Take a magnifying glass and look at all the solder joints in the section of the board where you think the problem is, look for cracks/lines on the solder.

 

2.Start resoldering in that section... pick likely suspects and start working. Might take a bit, but you'll find it eventually.

[Rybags]

I'd leave the soldering for a bit...

 

Just prize slightly up then reseat the main (larger) ICs. If no good then do all the smaller ones too.

[Bryan]

Check the voltage regulators on the heatsink and reflow their pins. The heatsink is long and much less flexible than the circuit board and can stress the solder joints.