P2 only works with the case back off

[corona with lime]

Works great on my external battery pack. When replacing the back it will SOMETIMES not operate with the back tightened down. I assume that the pressure from the batteries is causing an open circuit, but any suggestions on how to locate the problem?

Sometimes, when the back is replaced, it work fine for perhaps 15 minutes and then quits.

[Planet-LED]

The official name for that condition is "afraid of the dark".

If you put the module into the watch and bridge across the batteries, does the watch work? That would exclude the case and torque from being factors.

I have run into this a time or two and it is often a bit of sloppy soldering that makes contact with the case once the back is tightened down. This would short out the module and may it non functional.

[digibloke]

It could also be worth trying it with 386 batteries instead of 357's to eliminate the "pressure from batteries" problem. Sometimes if the battery contacts have been messed with (bent upwards in an attempt to improve connectivity) then there can be problems. Gotta make sure that your spacers are a snug fit with this solution though.

[corona with lime]

Woo Hoo!! I got the back on, put it on my wrist 14 hours ago, and it's still working and keeping accurate time!! :D

As much trouble as I had, I think the bloody thing is just waiting for me to take it off and put it in the box so it can die quietly while I'm not looking. Now I'm afraid to take it off to go to sleep.

Additional things noted while fooling around trying to get it working:
sometimes nothing would light up
sometimes one random digit would light in a random location
sometimes the : would light
sometimes a random digit would march across the display continuously
sometimes it would run for a few minutes and quit altogether

It would ALWAYS work on external power, although sometimes it took some mucking about to get it started.

Currently using a timing crystal I bought from Digi-Key for 27 cents. Same one I mentioned in my other post.

[bruce wegmann]

All the symptoms you mention point to it being the timing crystal all along. The fact that it operates with a modern replacement shows that the circuitry of the watch itself is functioning properly. Best, final, fix is to find a vintage replacement, and take your watch all the way back to "original". BTW, the 'single random digit marching' is actually the watch displaying the time, just in very slow-motion, as the multiplexer gets single, isolated signals from the timing crystal. Odd combinations of lit digits and/or illuminated segments often display on initial power-up even in watches that are functioning perfectly [can be cleared by running the watch through a full setting procedure].