Sticky meters

[K3ZW]

I have a couple boat anchors that work great but have sticky meters. Anyone have experience disassembling and cleaning D'arsonval meter movements ??

[KA2DZT]

If you can open the meter, try gentle blowing any dust that may be caught between the coil and magnet.  Most meters have three small screws along the drum,, remove them and open the meter.  Use a bright light and a magnifying glass.  Also check the needle is not hitting the face. A lot of old meters may have lost some paint off the needle which can get into the movement.

Don't try to adjust anything as it requires special tools. especially the little spring weights that are on the needle movement.  Don't try to adjust the needle pivots.

If the meter is one of the square plastic case meters, these are more of a problem to open and you may not be able to open it without breaking the case.

What type of meter is it??

Fred

[k4kyv]

I have repaired a few of the older D'Arsonval movements that have plenty of room inside the mechanism by sliding a narrow strip of Scotch tape in between the coil and pole piece.  Sometimes a particle of dust gets lodged in between, and the sticky tape will grab it.  Try inserting both ways into the gap. Be very careful when you have any meter out of the case.  It takes just one microscopic particle of ferrous metal to stick to the pole piece and block the movement of the coil, something just about impossible to remove even if you find where it is.

Many times, I have swapped around movements, cases, scales, and have modified or homebrewed scales, to come up with a custom meter.  I always make sure the table where I am working is as clean as possible, and preferably I lay down a large sheet of white paper, like poster board, for the working surface. A magnifying glass and set of jeweller's screwdrivers is essential.  I have managed to successfully adjust the pivot tension, although I don't like to fool with it unless I have exhausted all other measures to fix a problem. I have also managed a couple of times to repair a mangled hair spring, but that takes a steady hand and a lot of patience.

I rarely even try to work on a modern rectangular meter with plastic case.  Like contemporary consumer electronics, I tend to treat them as cheap disposable items. I despise the hermetically sealed military meters that have the zero adjustment sealed up inside the case.

One thing that can make a meter sticky, particularly the plastic case ones, but also the older bakelite and metal cases with real glass, is a static charge built up on the surface of the viewing window.  This can happen after you wipe the surface with a cloth to clean it. Wiping it again with a damp cloth will usually dissipate the static charge.

[W5AMI]

I managed to semi-repair one that had what appeared to be tiny hairs all around outside the coil in the gap using the scotch tape method.  Turned out to be what I think was tiny fragments of steel wool.  I didn't get all of them, but enough where it moved rather smooth and still functioned better than nothing at all.  Replacements can be hard to find, and I know of no one that still works on them.  If there is, I'd sure like to know about them.

[W7TFO]

Tom W3BYM does a few, I do fewer.

73DG

[w1vtp]

My only meter repair was this S meter of my SX146.  I had the companion HT46 and wanted the matching receiver.  Come the old Hosstraders, I determined that I would buy one if I could find it.  I no sooner walked into the main causeway and there it was.  The story was that it was owned by a blind gal who was upgrading but that the S meter was blown.  I bought it with the idea that I would replace it with a mongrel meter.  Took it into work and under a microscope discovered that the hair sized wire had burned off right at the solder connection.  I scraped the enameled insulation off, applied some flux and gingerly reattached the wire.  It worked!  

This picture was taken of Timtron on his SBE in the 5 KC bw position.  Not bad - both RX and S meter is working after all this time.

If you ever get a chance to buy a stereo microscope at a fester - after looking through it to confirm it is still working buy it.  It comes in handy for such operations. It's one of those instances where when you need it YOU NEED IT.

Al

[WQ9E]

I second Al's recommendation of a stereo microscope (aka dissecting microscope) for use in fine electronic repairs.  I bought our then 6 year old daughter a decent quality (~$700 on ebay) as a Christmas present figuring it was a good investment in her educational future and also something dad could borrow at times.  It has worked well for both of us and is perfect for meter repair and looking for cracks and other problems on circuit boards.  I have successfully repaired 3 meter movements using it (two sticking and one with a broken connection on one of the suspension springs).  Having a comfortable and clear view of a meter movement greatly increases the odds of a successful repair.