Can I lubricate/clean this VU meter?

[62vauxhall]

There is a niggling meter issue on my recently WOPLized 700B. Since it's a generic meter question, I am going to post on AK also but thought there is way more PL expertise here and someone may have encountered the same situation.

One of the VU meters stays in the rest position at low volume levels. If the pre-amp's volume is increased, the stronger signal dislodges the needle and the meter will operate. The other meter works fine and does register when the volume is low. I realize that low level listening is probably not something associated with a WOPL but it's one of the drawbacks to condo living.

I removed the meter and took the lens off to inspect for debris or something that would impede needle motion but found nothing. I discovered by gently blowing on the needle, it would come to rest just slightly above where it normally would. If I "blew" it a little harder, to the left, I could nudge it to where it should be at rest normally. When in this position, it takes a little harder gust to dislodge it and make it swing.

I am including photos of the mechanism, the proper rest position where it sticks and the slightly high rest position from where it will swing freely. The difference is not even the width of the minus symbol on the dB scale.

I am wondering if there is a recommended lubricant or cleaner I could use that will get the needle over this "hump" and if by looking at the mechanism, can anyone say if/where there is a point to apply lubrication/cleaner? And if so, what would be a suitable liquid that's thin enough not to impede meter operation or gum it up later? A thought was that I could use a hypodermic to apply something in a minute quantity. That method would work only if whatever I used had a low viscosity.

 

[Northwinds]

Could it be the crap on the fork thing in your first image that is not reacting with the red coil wire at low voltage use? Kind of like a dirty magneto???

 

[laatsch55]

Gary, premiumplus has had some luck working on 700 meters. Let's wait for him or Joe to chime in..

 

[62vauxhall]

Could it be the crap on the fork thing in your first image that is not reacting with the red coil wire at low voltage use? Kind of like a dirty magneto???

That fork is not in physical contact with the movement and itself, does not move. Everything looks free and clear so I imagine that whatever the "obstruction" is, is located in the pivot point/axle of the needle.

 

[Gepetto]

I would not recommend any lubricants. Do you have a microscope to look at it under high magnification

 

[62vauxhall]

Negative on the microscope. I have no high power magnification anything. What about a solvent of some kind?

 

[laatsch55]

Let Premiumplus take a look at it before a liqui of any kind is used. To me it looks like the needle is bent below the face level and it may be over travelling the other way to make up for it. Dave has had some success working on these....

 

[premiumplus]

No lubricants!

Don't use any liquids. The movements are in jewel bearings and are meant to be run dry. The main thing would be cleanliness, but you sure don't want to blow it out with compressed air. The movement is too fragile and you'll likely do more harm than good. I'll try to attach some photos that I took of my disassembled movement. I had to re-shape the end of travel limits on the meter. You may have the same issue, if they came loose. They're just tiny wires with a nylon insulating bushing on them, and they attach with a tiny brass eyelet to the two posts. You'll see... hope these help. A jeweler's loupe or a magnifying glass would be a big help! Just be gentle and cautious. Don't rush, you can do this. Good luck!
-Dave

 

[MarkWComer]

Don't use any liquids. The movements are in jewel bearings and are meant to be run dry.

I was about to suggest a few grains of dry graphite, the kind you use on door locks. Jewel bearings are very low friction, so even graphite may prove an impediment to their free movement.

That little screwhead that's been painted over is also something not to be messed with- the other end of the screw is the jewel point bearing, and if it's taken apart you won't ever get it reassembled. Benefit from my mistake- I've done just that with an old VOM.

 

[Web Police]

I have freed up a few non responding meters by holding the needle in place with toothpicks and gently blowing spider webs out with my mouth. Listen to the experts first though.

 

[62vauxhall]

I was out for the afternoon (so was not reading the subsequent posts) and I got the idea to partially charge up a small compressor and shoot some air inside the meter. Since liquids were a definite no-no and my blowing into it did nothing, it seemed worth trying. Anyway, it seemed to work. at least for now. For the time being the needle moves at a low volume just as the other one does. I did make sure the air pressure was not high but more forceful than blowing air out of my mouth. If there was something inside, I thought having a nozzle to concentrate air flow would be the most effective way to get rid of it. At the risk of "putting the mouth on it", I guess the problem is gone.

 

[Web Police]

Well if it works and you are happy that is good.

 

[orange]

As we always say here, blowing it can't be bad.