The meters on my 002A were in sorry shape from water intrusion. I couldn't repair the frequency meter as it was too far corroded. The dial was fine...
I found a 200 microampere full scale (fs) meter that would fit but it was for some other application. Price was right at $19 where others charge ten times that. New, old stock with NSN. Even had the mounting hardware.
I took both meters apart, extracting the dials and drilled the old dial for the new mounting scheme. Then touched up the corrosion spots with appliance paint. Slapped it together and PERFECT!!!!
The original meter's bezel was secured with a 4-prong threaded ring, this new meter had 3 small screws retaining the bezel to the case. Much easier to remove. Other difference is the exposed glass is larger, not a real issue. Function is spot on, indicates 60 Hz at an actual 61.5 Hz. Seems to be an offset because at indicated 65 Hz, the actual is 66.5.
Keith fom your pix it looks like you have a 'zeoing' adjustmnet on the meter. You should be able get the meter spot on 60 Hz by tweaking the screw adjuster.
Yes, I noted that after contemplation and a night's sleep. Fired it up today, set the engine speed via my digital multimeter, then adjusted the bias screw to match the meter to the actual. Then ran it up to 65 and down to 55 Hz, spot on.
Happy camper I am. 20 minutes of work and $19 nets me a new meter.
Yes, I noted that after contemplation and a night's sleep. Fired it up today, set the engine speed via my digital multimeter, then adjusted the bias screw to match the meter to the actual. Then ran it up to 65 and down to 55 Hz, spot on.
Happy camper I am. 20 minutes of work and $19 nets me a new meter.
lol - well done
in my early ham radio days we used to get surplus WWII radio equipment including some nifty meters. It was very common, once you knew what the basic movement was (1 milliamp, 500 microamo, etc) to either 'erase' the numbering on the face or repaint the face a flat white & use a transfer to get the scale back on & transfer the 'new' numbers.
Keith, Is there any way to keep the corrosion from accumulating again? Would drilling a small hole in the bottom of the case help? My freq meter stopped working because of corrosion.
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The issue is water and the design of the meter face causes it. Specifically, the bezel which extends up 1/3rd the way up the glass. There is a little drain at the bottom which plugs up, then the bezel traps water between it and the glass. Even the bias screw can be a leak.
The meter's sealing fails, water enters. Drilling a drain may help but without circulation, it won't stop corrosion. Cleaning the face of the meter and running a thin bead of clear RTV silicone sealant will help. Also, around the bias screw. But keeping the generator out of the rain is the best prevention.
The percent current meter on this generator also had the problem, the only damage was failed epoxy bond of the damping vane magnet which locked the meter (magnet clamped the damping vane to the pole piece). I was able to straighten the vane and re-attach the magnet. Tested fine with full scale current listed on the meter face.
The frequency meters are much more delicate of a movement. Instead of a permanent magnet-aluminum vane damping, the moving coil is formed around a thin aluminum ring.
I'm making a combination ASK/doghouse from 1/4" plywood and fiberglass for weather protection. But cannot do glass when temperatures are in the 40s so the generator is living under a tarp.
Sitting outside for however many years at DRMO then GL doesn't help. At least mine was sitting outside at Ft Bliss so is just bleached out. It's on a trailer with, what appears to be, a M105 cover over it now. It sat next to my shop for months with no issue until we got a big wind storm last week. I put off wrestling it back on and then we got 3/4" of rain . More rain on the way tomorrow so I just spent 20 minutes fighting it back over the bows. Decided I should probably cinch it down this time.
The issue is water and the design of the meter face causes it. Specifically, the bezel which extends up 1/3rd the way up the glass. There is a little drain at the bottom which plugs up, then the bezel traps water between it and the glass. Even the bias screw can be a leak.
The meter's sealing fails, water enters. Drilling a drain may help but without circulation, it won't stop corrosion. Cleaning the face of the meter and running a thin bead of clear RTV silicone sealant will help. Also, around the bias screw. But keeping the generator out of the rain is the best prevention.
The percent current meter on this generator also had the problem, the only damage was failed epoxy bond of the damping vane magnet which locked the meter (magnet clamped the damping vane to the pole piece). I was able to straighten the vane and re-attach the magnet. Tested fine with full scale current listed on the meter face.
The frequency meters are much more delicate of a movement. Instead of a permanent magnet-aluminum vane damping, the moving coil is formed around a thin aluminum ring.
I'm making a combination ASK/doghouse from 1/4" plywood and fiberglass for weather protection. But cannot do glass when temperatures are in the 40s so the generator is living under a tarp.
Very good advise - I have successfully waterproofed meters with silicone. You really have to do every penetration of the case and all mating surfaces (including glass to metal). It may not be direct rain water that's the problem but rather condensation
MEP-002A meter overhauling
. But keeping the generator out of the rain is the best prevention.
. More rain on the way tomorrow so I just spent 20 minutes fighting it back over the bows. Decided I should probably cinch it down this time.
