[NTLK] Notephone and OMP/MP100 issues

[Joel M. Sciamma]

Frank,

> Fact is that the problem lies on the base station mainboard. If you remove
> it, put it in the fridge, leave it there for an hour, take it out again,
> connect it to the handset and to a phone line FAST, you'll normally get a
> dial tone.

This sounds very much like a micro-fracture of a solder joint or a PCB trace, something like that. When the PCB is cold, the tiny contraction brings the edges of the crack together just enough to make contact but any heating pulls them apart again. Sometimes, flexing the board finds it but that's not a great idea with multilayer boards unless a very gentle deflection does the trick. Surface mount components can also fail this way at the junction between the termination and the body of the part.

I have had a few of these and the only way I found them was to methodically examine the PCB under a microscope, prioritising those areas close to the circuit that is giving the trouble. As luck will have it, the fault could also be far away if it is a signal or power line.

Another way to attack it is to make comparative measurements when the unit is cold and working and then again warm and failing.

Joel.