Whitechapel CG-200

[Tony Duell]

> I'm trying to decide what to do about the whole battery aspect. If the
> machine isn't going to be used for long periods of time then it makes
> sense not to have any batteries in it in case they leak (or whatever).
> But then if it doesn't need batteries during normal running, it seems a
> bit of a waste to have them there at all (and need to open up the case
> to fit them each time the machine's used)
> 
> I presume they're normally used to keep some form of RAM containing
> configuration data alive though (plus maybe some kind of service

On the MG1, there are 5 NiCd cells in series with a tap 3 cells from the 
-ve end. The tap is used to hattery-back the real time clock chip (which 
probably contains a small amount of RAM to store configuration data, 
etc), all the cells are used to power the turn-on relay.

There is no service processor in an MG1 (unlike, say a Torch XXX). There is
an I/O processor, but it's not battery-backed, or anything.

> processor operational) as well as providing power to the start up relay
> - so I'm not sure what the implications are there of not having them
> fitted.

Unlike a XXX (again), the MG1 doesn't use the NiCds as a shunt regulator 
on the real time clock supply. A XXX's clock chip can be damaged if the 
thing is powered up with the NiCd battery open-circuit. I think you have 
my XXX schematics, in there I show a mod to use non-rechargeable cells 
with a zener diode acting as the shunt regulator.

> 
> Maybe an external NiCd pack is the way to go - there are plenty of screw
> points at the rear of the case from which a suitable bracket for a
> battery box could be attached. Mind you, I'm sort of at the point where
> I think any machine which is to be stored for any period of time unused
> should have its PSU disconnected just to stop anyone trying to randomly
> power it up before doing some basic checks - in which case they'd need
> to open the case anyway.

Good idea. Of course removing the NiCd cells from a XXX would ensure 
this, there is no way it'll power up without them. 

Personally, I'd put the AA cell holders I mentioned onto the power 
distribution board. It's drilled to take them, or at least the one in my 
MG1 was. Then you can clip in some normal, non-tagged NiCds if you want 
to run the machine.

-tony