On Mon, 1 Jul 2013, Jeff Liebermann wrote:

On Mon, 1 Jul 2013 21:18:05 -0700 (PDT), Peter Easthope
wrote:

I have a Sanwa BX-505 analogue multimeter where the needle wavers and
can not be zeroed on the x1, x10 and x1k scales. Zeroing is possible
on the x10k scale. The ohmeter is really an electromagnetic voltmeter
connected in a circuit with dry cell, resistor, zeroing potentiometer,
leads and a subject resistance.

Scans of the relevant pages from the manual are here.
http://carnot.yi.org/SanwaBX505Manual.jpg

What is the cause of this behavior?

In order of probability:

1. Dirty battery contacts. Clean the contacts and possibly replace
the battery.

2. Dirty test probe contacts, broken test probe wires, corroded test
probe tip. Clean or replace.

Sometimes it's just a matter of pulling the leads out of the jacks, and
putting them back in.

3. Dirty rotary switch. Spray with a small amount of contact
cleaner.

4. Dirty fuse contacts or bad fuse. Clean and/or replace fuse.

I didn't think analog multimeters had fuses.

But, one time one DMM was reading odd, and I ended up opening it up,
expecting the contacts on the switch to need cleaning. NO. It turned out
eh fuse was bad, it didn't open but had a higher than normal resistance.
I can't remember what was "high", but it wasn't a large amount, just way
more than it should have been.

Michael