[volt-nuts] Solartron 7081 randomly re-initialises

[BIll Ezell]

Repost from my response in the new Solartron group, :

 >I assume you've eliminated obvious things like power-line spikes? One 
other thing comes to mind, the power-up reset logic for the CPU, the 
RESET >signal. My schematics are so bad it's hard to tell for sure, but 
it looks like that's generated by R6 and C2, along with IC4 on the 
earthy board. I'd check >C2, if it's very leaky, could be pulling IC4-1 
down enough to give random triggering. IC6 is a possibility also, IC6-6 
is used to also trigger a reset by >pulling C2 to ground.

I'd think if there was enough ripple on the 5V supply to trigger a 
reset, you'd be seeing other bad things.

Regading the nvram, the comments on that are dead-on, my cross post 
about that:

 >The cal constants are in a non-volatile ram, it's possible you'll need 
to replace that. I've never seen a failure, but I've heard anecdotally 
that they can >fail. It's also possible that your meter has been sitting 
unused for so long that the nv-ness of the ram has leaked away.
 >They work by injecting a stored charge into effectively a 
well-insulated gate. Over many years, the charge can leak away. That's 
why there's a rewrite >cycle the meters can do.

I forget what the nvram refresh command is, but it's in the manual. 
Also, the nvram keeps two separate copies. I thought it would 
automatically try to read the second copy if the first was bad, and 
automatically rewrite the bad one. But, if enough charge has leaked, 
there could be multiple errors across the entire nvram.