[Heathkit] IM-11 question REPOST to group

[rbethman]

Mailman at QTH.NET hacked up a hairball because I attached schematic.

So I cancelled the original post to list.  This is to include the list 
in the conversation.

N0DGN

Ronnie,

Looking at the schematic, (you have one?  I attached a copy - you'll get 
it as I cc'd you.), I can see a whole lot of resistors attached to the 
end of that battery, then connections to the range switch wafer.

Wafer contacts:

1) May be iffy.
2) Cleaning is good idea.
3) Yes - It's a PIA.

Meter connection:
Clean and ensure good bond.

You know the drill.  Capacitors, resistor values, Potentiometers always 
suspect of being dirty.

Touching the probe tip with your finger and reading drifting to infinity 
is something that most of us would see with either a VTVM or even a DMM. 
  Anytime the skin resistance is involved, the capacitance does end up 
getting into the mix.  Best solutions I've seen and use is an ESD mat 
that has itself bonded to ground through it's resistor, and the wrist 
strap on - also bonded to the mat by the snap on it's end.

Usual disclaimers apply.  YMMV, It's my $0.02 worth.

I can get this response with and HP-410B - the caveat is that it is 
dependent on static and humidity.  This time of year humidity is very 
low.  Static is more of a problem.  That's why I got a hunk of the ESD 
mat and the wrist straps.  I probably have a few of the snaps that are 
NOS somewhere.

I can get similar "funny" traces on the TEK 5440 when I don't use the 
ESD elements.

Bob - N0DGN

On 12/30/2013 1:56 PM, Ronnie Hull wrote:
> I recently acquired a very clean Im-11 vtvm at a hamfest. It worked well on AC and DC volts scales but the ohms scales would not settle down when trying to calibrAte the upper and lower limits.
> After replacing the battery and it's spring which was corroded, it's better but still not right.
> I can set the infinity point, then the zero point. Then, all I have to do is just touch the probe and the meter will start wandering off the infinity point.
> I took the probe apart and made sure the contacts were clean.
> I did a fresh calibration but this problem on the ohms scale persists.
> Anyone have any ideas?
>
>