AndreiC Posted January 1 Report Posted January 1 I don't think the ammeter gauge is showing anything on my 1970 M20E. It never moves at all, even if I turn on the pitot heat without the engine running, which should be drawing a significant charge. I suspect it is the gauge itself, not the wiring. Can the gauge in the six-gauge linear cluster be replaced alone? Or are there whole clusters available for sale? Or does anyone refurbish these? The gauge is not needed for flight, and my EDM-700 shows me voltage, so I have pretty much the information needed about the electrical system, but it would be nice to not have an inop gauge in the panel. Quote
Andy95W Posted January 1 Report Posted January 1 It is probably not your instrument cluster. There are 2 fuses between the shunt and the gauge. They don’t normally blow, but the wires that attach to them often break. 1 Quote
FlyingDude Posted January 1 Report Posted January 1 28 minutes ago, AndreiC said: Can the gauge in the six-gauge linear cluster be replaced alone? Can you post a picture? Quote
AndreiC Posted January 2 Author Report Posted January 2 1 hour ago, FlyingDude said: Can you post a picture? This is a pretty bad picture but it shows the instrument pack at the top. Quote
N201MKTurbo Posted January 2 Report Posted January 2 5 hours ago, PeteMc said: It could also be a bad ground. I don’t think anything is grounded in the ammeter circuit. It is just a floating voltmeter across the shunt. Quote
AndreiC Posted January 2 Author Report Posted January 2 1 hour ago, N201MKTurbo said: I don’t think anything is grounded in the ammeter circuit. It is just a floating voltmeter across the shunt. This is correct. Do you happen to know what voltage range is it supposed to measure? I was going to try to hook up a 1.5v battery to it and see if it moves (after disconnecting one lead from it) but I don't want to fry it if it is a super-sensitive voltmeter. Quote
PT20J Posted January 2 Report Posted January 2 14 minutes ago, AndreiC said: This is correct. Do you happen to know what voltage range is it supposed to measure? I was going to try to hook up a 1.5v battery to it and see if it moves (after disconnecting one lead from it) but I don't want to fry it if it is a super-sensitive voltmeter. Many shunts are 50 mV at full scale current. Quote
N201MKTurbo Posted January 2 Report Posted January 2 If you just use your ohmmeter on a low range, it should make the meter move. Quote
AndreiC Posted January 2 Author Report Posted January 2 11 minutes ago, N201MKTurbo said: If you just use your ohmmeter on a low range, it should make the meter move. I thought so, and I did try this a few days ago with one lead disconnected. It did not budge with my ohmmeter at any range. So my guess is the meter is toast. (Or maybe just jammed? Can this happen?) Quote
FlyingDude Posted January 2 Report Posted January 2 8 hours ago, PeteMc said: It could also be a bad ground. Ammeter is not grounded. 1 Quote
N201MKTurbo Posted January 2 Report Posted January 2 8 minutes ago, AndreiC said: I thought so, and I did try this a few days ago with one lead disconnected. It did not budge with my ohmmeter at any range. So my guess is the meter is toast. (Or maybe just jammed? Can this happen?) It can. I’ve seen meter movements that had tape around the windings. The adhesive on the tape failed and the tape lifted and jammed the movement. if you can get the movement out of the plane, rocking it back and forth in your hand will usually move the needle. You can try to manually move it with a toothpick. I use a toothpick because there is less chance of chipping the paint off of the needle or the face. Quote
Yetti Posted January 2 Report Posted January 2 I believe Rochester is the manufacture of those. It's probably the Black inline fuse holder up near the shunt on the passenger side firewall. Quote
PeteMc Posted January 2 Report Posted January 2 (edited) 4 hours ago, N201MKTurbo said: I don’t think anything is grounded in the ammeter circuit. It is just a floating voltmeter across the shunt. @N201MKTurbo @FlyingDude Okay, I'll have to dig up the schematic. For some reason I thought those gauges did have a ground, but makes more sense that it doesn't. Edited January 2 by PeteMc Quote
DonMuncy Posted January 2 Report Posted January 2 My guess is most likely one of the fuses. Mine has two. Very different fuses. Located near the ammeter. Little short stubby ceramic cylinders. If you are diligent, you can find replacements at quite reasonable prices. 1 Quote
cliffy Posted January 4 Report Posted January 4 Most of them are regular BUSS glass fuses about 1/4 inch in diameter Available everywhere Many times it has been so many years (40+?) that they have never been removed they will be all crudded up and have bad connections Be prepared to clean the holder contacts and the fuse ends when you take them out. The wires may be very brittle. Bonus question- Regs state that any airplane that has fuses installed should carry spare ones for replacement Does this apply to these fuses? :-) 1 Quote
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