Glareshield Lights

[markejackson02]

I can't seem to find instructions on replacing the lights in the glareshield.  Before I start removing screws, are they standard 330 bulbs?

 

Mark Jackson

N201TK M20J

KAXH

 

[N201MKTurbo]

They are not 330 bulbs. I don't have the number handy, but you will see when you take out the old ones.

 

There is a line of sheet metal screws in the plastic lens over the lights. Remove all the screws to remove the lens and you will see all the lights.

 

Don't over tighten the screws putting them back in.

[Marauder]

If he has a 14V J, I think they are GE 1819 and are bayonet type bulbs. Will look later today when I escape from work.

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[markejackson02]

It is a 1977 14 Volt J model.  The electrical diagram that came with the POH is rudimentary to say the least.  I have a parts manual but cannot find the bulbs referenced for the 14 V version.

[Marauder]

It is a 1977 14 Volt J model.  The electrical diagram that came with the POH is rudimentary to say the least.  I have a parts manual but cannot find the bulbs referenced for the 14 V version.

 

I will be heading home shortly and will pull the numbers for you. I had mine out during the summer when I was looking to replace them with LED version. Your 77 and my 75 will have many shared components.

[Marauder]

I tired to post a picture of my parts listing but I must be out of space on the server... The manual shows a GE 1816 or 1836. My bulbs are at the airport but suspecting I was dyslexic on the number, my guess is the 1816.

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[65C_flier]

Has anyone seen an issue where the glareshield lights don't dim or turn off? The other radio and instrument lights dim, but glareshield lights are on full bright regardless of dimmer position. 78 J. Glareshield lights used to work fine (dim with instrument dimmer) and this just started after a night flight.

[N201MKTurbo]

3 hours ago, 65C_flier said:

Has anyone seen an issue where the glareshield lights don't dim or turn off? The other radio and instrument lights dim, but glareshield lights are on full bright regardless of dimmer position. 78 J. Glareshield lights used to work fine (dim with instrument dimmer) and this just started after a night flight.

There are two dimmer circuits one for the radios and one for the lights. If it stopped dimming, the transistor for the glare shield lights is probably shorted. I have a dimmer assembly.

[65C_flier]

8 hours ago, N201MKTurbo said:

There are two dimmer circuits one for the radios and one for the lights. If it stopped dimming, the transistor for the glare shield lights is probably shorted. I have a dimmer assembly.

Thanks @N201MKTurbo
 Both the radio and instrument dimmer knobs/circuits still work, except they no longer dim the glareshield lights. Do the glareshield lights have their own transistor? Do you know if it is located in the dimmer assembly? 

[PT20J]

There are two knob: One labelled GLARE SHIELD and one labeled PANEL. Each controls a separate circuit via a separate transistor.

[EricJ]

2 hours ago, 65C_flier said:

Thanks @N201MKTurbo
 Both the radio and instrument dimmer knobs/circuits still work, except they no longer dim the glareshield lights. Do the glareshield lights have their own transistor? Do you know if it is located in the dimmer assembly? 

The schematic for the '77 J shows two different possible circuits;   one with a single transistor driving both the panel and radio lights, and one with two cascaded transistors, the first one driving the glareshield and the second driving the radio lights (so, presumably, if the first transistor failed or shorted, the second wouldn't work, either, based on the schematic).   Did yours used to work and just don't dim any more?   Otherwise I'd suspect somebody just gave up and wired them to the switched power in the dimmer, which also goes to the compass.

Edit:   Arg...for the '78 there's an independent knob and transistor for the glareshield.   The rheostat or the transistor may be failed, as previously noted above.

I keep seeing people mention this as a common replacement for glareshield lights, even in certified airplanes.   It looks tempting. 

https://www.aircraftspruce.com/catalog/pspages/sptlightstrip.php

 

Edited May 29, 2021 by EricJ

[65C_flier]

59 minutes ago, EricJ said:

Did yours used to work and just don't dim any more?   Otherwise I'd suspect somebody just gave up and wired them to the switched power in the dimmer, which also goes to the compass.

I keep seeing people mention this as a common replacement for glareshield lights, even in certified airplanes.   It looks tempting

Thanks @EricJ. Yeah they did used to work although the glareshield lights were pretty intermittent before they failed on. I'm definitely considering maxdim next annual

[AH-1 Cobra Pilot]

I just had this same sort of failure.  The glare shield lights became intermittent, now they are completely dead.  The really annoying thing is that it is so difficult to diagnose, since the voltage is there, but the current is not. 

I am pretty sure the transistor in the circuit has failed.  Can anybody tell me where to find it and what is a suitable replacement?  (1978 J-model)

Edited September 9, 2021 by AH-1 Cobra Pilot

[PT20J]

I believe the early M20Js used 2N2016. It may be obsolete; if so you could search for an equivalent part.

Skip

[65C_flier]

Yep, my 78J had a 2N2016 on the instrument circuit (likely original) which failed so the lights stayed full on or full off. The radio circuit had a different part number transistor, but same case. I can't recall that part number on thr radio circuit, but it didn't look original and the heat sink tray had been modified to allow easier removal.

2N2016 is obsolete and we replaced it with a 2SC5200N as suggested on a page here somewhere. It was quite difficult to do due to the location of the transistors behind the CB panel. In hind sight I would just replace it with a maxdim PWM and led strip. We replaced the heat sink (riveted to the tray) as the old one had big mounting holes that aren't very compatible with the 2SC5200N mounting. We also replaced the mica washer. The pic below shows the tray with the new 2sc5200n before it was reinstalled. It works, but we haven't done a lot of night flying since, so I don't know if it is a forever solution.

I think later Js collocated the transistors with the rotary switches which would be an easier job.

Edited September 9, 2021 by 65C_flier

[AH-1 Cobra Pilot]

Ugh!  I looked and looked for anything like that, but could find nothing.  I may just jump the lead to the pot that works.  It only lights two indicators as of now.

[PT20J]

The later M20Js have a control unit in the panel and a dimmer unit in the tail by the battery.

Skip

[AH-1 Cobra Pilot]

I spent another three hours looking for that damn thing and found nothing!  Checked the tail, too.  Any ideas would be most appreciated.

[PT20J]

1 hour ago, AH-1 Cobra Pilot said:

I spent another three hours looking for that damn thing and found nothing!  Checked the tail, too.  Any ideas would be most appreciated.

The schematic for S/N 24-0378 through 24-0757 shows the transistors mounted in the circuit breaker panel area. There is a fuse holder associated with each transistor. If you cannot see it from below, try removing the glareshield and looking from above.

Skip

[65C_flier]

3 hours ago, PT20J said:

The schematic for S/N 24-0378 through 24-0757 shows the transistors mounted in the circuit breaker panel area. There is a fuse holder associated with each transistor. If you cannot see it from below, try removing the glareshield and looking from above.

Skip

Exactly. If your J is in that SN range the only way to see it is from the top, and even then it is tough. Try shining a light down from outside. This is the best pic I could get.