Stan Posted June 22, 2018 Report Share Posted June 22, 2018 1989 M20J, serial # 24-3101, 28 volt, started a decent to TPA and the High Low Voltage indicator started to blink, indicating low or no voltage from alternator. Start to turn off strobes, comm #2, etc... Enter 45, drop gear, flaps down, all OK, etc. Turn to base, small puff of smoke and electrical smell. Landing (not my best) but uneventful, no more smell, flaps up, cowl flaps down, shut down ok. No circuit breakers popped. Discuss with the mechanic on field, looks under the panel, nothing out of the ordinary, slight lingering smell. Do a run-up. No problems, high low voltage light blinks, but goes out above 1600 rpm. Talk it over and hope it is isolated incident. Let plane sit 3+ hours. Come back, startup, no smell, taxi to run up area, again high low voltage light blinks, but goes out above 1600 rpm. On taxi to active, another bigger puff of smoke and smell appears to come from behind the circuit breaker panel, no circuit breakers popped. Shut off radios and taxi back to ramp, no more smoke or smell. Do another run up with mechanic, no issues, but ammeter shows a discharge. Leave plane and drive 5 hrs. home. Question: blinking light show low/no voltage from regulator, but alternator is in engine compartment. Smoke and smell came from within cabin. Could it be voltage regulator, which is located behind the right side of the panel? Any thoughts or has anyone else had this issue? Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted June 22, 2018 Report Share Posted June 22, 2018 On 6/22/2018 at 8:54 AM, Stan said: Could it be voltage regulator, which is located behind the right side of the panel? Any thoughts or has anyone else had this issue? Sounds like you might have identified the problem - it could be the regulator. After the first puff of smoke and the safe landing and confirmed burnt smell I don't think I would be taxiing and running up the engine again. Anything from frying the rest of the electrical system to an electrical fire with you in the cabin and fuel on board would not be fun. I would let a mechanic figure this one out. Glad you are safe. Quote Link to comment Share on other sites More sharing options...
Kmac Posted June 22, 2018 Report Share Posted June 22, 2018 Had a very similar experience to you in the C-150. An electrical burning smell with smoke during take-off but to late to abort. Decided to remain in pattern and land. Searched high and low for the problem but everything seemed ok. I went flying with someone who had traffic on their aircraft and they said they couldn't see me. I knew right then that it was the transponder that was fried previously. Sure enough, took it apart and the electrical burning smell was inside the transponder. Quote Link to comment Share on other sites More sharing options...
ziggysanchez Posted June 22, 2018 Report Share Posted June 22, 2018 I had this happen shortly after taking delivery of mine. Puff of smoke behind the circuit breaker panel and electric burning smell, the whole nine yards. What it ended up being was the battery cable had been rubbing on the air box and exposed some wires. It was intermittently arcing on the firewall and would produce the smoke in the cockpit and smell. It may be worth it to take a look and see if there is any evidence of arcing on the firewall in that area. Quote Link to comment Share on other sites More sharing options...
neilpilot Posted June 22, 2018 Report Share Posted June 22, 2018 Since you say smoke and smell appear to be coming from behind breaker panel, inspect wiring and breaker connections carefully to determine if intermittent grounding may have occurred. If this occurs on one side of the breaker, then you could have a short without tripping a breaker. I once had a puff of smoke when I overloaded my cigar lighter, and it was the fusible link. However, if you had opened a fusible link you would have a single occurrence that would not repeat. 1 Quote Link to comment Share on other sites More sharing options...
Marauder Posted June 22, 2018 Report Share Posted June 22, 2018 9 minutes ago, neilpilot said: Since you say smoke and smell appear to be coming from behind breaker panel, inspect wiring and breaker connections carefully to determine if intermittent grounding may have occurred. If this occurs on one side of the breaker, then you could have a short without tripping a breaker. I once had a puff of smoke when I overloaded my cigar lighter, and it was the fusible link. However, if you had opened a fusible link you would have a single occurrence that would not repeat. I would definitely do what neilpilot recommends. The circuit breaker box is really tight and there is a chance something is rubbing. I certainly would not run it anymore until you figure it out. With the multiple puffs of smoke, there has to be something charred or melted. Your mechanic needs to find this. Quote Link to comment Share on other sites More sharing options...
triple8s Posted June 22, 2018 Report Share Posted June 22, 2018 (edited) Had a similar occurrence with a C model and the glareshield could be removed along with a flat aluminum piece between 201 style windshield and padded glareshield. Removed those and took a copilot for a taxi test. He carried a mirror and had right front seat removed. With the mirror and the seat removed he found chaffing and a short after 30 or so minutes of taxing it was a wiring bundle which had sagged such that the yoke brushed it and caused a momentary short. Had avionics work done recently. Only shorted when yoke was in a certain position. So be sure to also move controls in all possible positions while stopped and someone observing. Good luck Edited June 22, 2018 by triple8s 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted June 22, 2018 Report Share Posted June 22, 2018 Quick review of electrical circuits... There are fuses, fuseable links, and circuit breakers... all there to protect the finer electrical bits downstream... There are also some electrical bits that have been most likely to disappoint... diodes and other things... Before the electrons flow through those protective devices there is plenty of opportunity to escape the unprotected side of the electrical system... At the moment the smoke comes out, and an aroma is generated... there will be visible signs left to be sleuthed... There are plenty of hot locations for an errant fastener or other loose, grounding, miscreant to do an evil deed... Be sure to post a follow-up pic of what you find. Just know... after smoke and burning aroma... if a circuit breaker doesn’t pop... everything isn’t good to go... The thought of molten electrical bits dripping around my feet comes to mind. Somebody posted a nice picture of a melted shunt sort of recently.... lots of molten metal fell from there... Reminder, unknowns on the ground only get worse in flight... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
AaronDC8402 Posted June 22, 2018 Report Share Posted June 22, 2018 3 hours ago, Stan said: 1989 M20J, serial # 24-3101, 28 volt Any thoughts or has anyone else had this issue? Our J is S/N 3105. Looks like they were just a few planes away from each other in the factory. I'm guessing our planes have pretty similar wiring situations unless you've done a full electrical overhaul. We have not. I have found a few wires that have chafed against metal enough to show some burn marks. I've never seen a puff of smoke or smelled anything, thankfully. Look at the large guage cables coming in and out of the firewall. They bulkhead they pass through is metal lined with rubber grommet. In the same vicinity, there is a large guage cable that drapes over the "shelf" that the avionics relay rests on. We had some burn marks there. I think that wire is live any time the master is on. The picture below is from the right seat footwell looking up. Either way, please report back what you find. Quote Link to comment Share on other sites More sharing options...
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