Re: Simpson 260 repair

On Fri, 04 Apr 2025 20:44:40 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Fri, 4 Apr 2025 11:36:40 -0400, bitrex <user@example.net> wrote:
>

Picked up a Simpson 260 6M at the local thrift store, I was initially
disappointed to find it had a sticking meter but some gentle rocking
freed it.

>
The Simpson 260 6M uses a taut band meter movement.  It shouldn't
stick.  Even though your gentle rocking "fixed" the sticking problem,
you should take a look around the meter movement for some remaining
debris.  You might need a microscope:
<https://www.learnbydestroying.com/jeffl/pics/microscopes/Olympus%20SZ30/SZ30-01.jpg>
If you see something, try dislodging it with some dry low pressure
compressed air.  Don't use freeze spray or you will condense moisture
on meter movement.  Use a dryer attached to an air compressor.
Something like this:
<https://www.amazon.com/Compressor-Separator-Regulator-Accessories-Air-Compressor/dp/B083XZ7THN>
>
I recently fixed my long forgotten Heathkit IM-105 VOM.  It had a
sticky taut band meter movement.  Snooping around inside, I found that
a tiny paper label inside the meter had fallen apart and jammed the
movement.  Compressed air didn't work too well, so I switched to a 20
gauge needle and an improvised vacuum pump.  The suction vacuumed out
the paper debris, which clogged the needle.  That was acceptable
because the movement was now clear of debris and moving normally.

I'll have to drag my 260 out and see how it's fared.

I don't know what to suggest for fixing the high resistance movement
problem.  Good luck.

It probably does not require repair:  1880/1800= 4.4%, which is very
good for a wound moving-coil meter.  My recollection is that those
coils were 5% or so, and the objective for lab instruments (versus
field tools) was overall errors of 1% max.

Joe