Digital Clock Replacement in J Model

[FLYFST]

Anyone have experience replacing the digital clock on the left instrument panel, located above the Master and Avionics Master switches on a late model (1990) M20J?  I plan to replace the current MD-89 clock with another of the same make and model, so no changes to the wiring configuration.  The back of the clock assembly is very difficult to access from the top of the instruments panel after removing the glare shield. The best way to access the clock appears to be removing the entire left mini panel by removing the two mounting panel screws (red circles) at the top and bottom, correct?  The clock itself appears to be mounted with small nuts on the back of the panel securing the screws (red square) instead of blind screws, so pulling out the airspeed indicator for access to the clock, instead of removing the entire mini-panel does not seem a viable approach. 

thanks - Hank

[PT20J]

Disconnect the battery because there is voltage at the master switch and clock. Then, remove the 4 screws you circled. There are spacers behind some of the screws that will fall out, so catch them to replace when you put it back together. If you need a clock, Skyman Avionics has the one I removed. kelsey@skymanavionics.com.

[FLYFST]

47 minutes ago, PT20J said:

Disconnect the battery because there is voltage at the master switch and clock. Then, remove the 4 screws you circled. There are spacers behind some of the screws that will fall out, so catch them to replace when you put it back together.

Thanks very much Skip, I was planning to disconnect the battery but had not thought about the spacers.

Hank 

[Slick Nick]

I haven't seen a "one piece" master switch like that before. Is your alternator switch located somewhere else? Or is it just always on?

[FLYFST]

35 minutes ago, Slick Nick said:

I haven't seen a "one piece" master switch like that before. Is your alternator switch located somewhere else? Or is it just always on?

Just a circuit breaker for the alternator, not a separate switch.

best - Hank

[jetdriven]

Didn’t someone here figure out it was a Porsche clock for 200$?

[PT20J]

The alternator switch in my airplane is in the space between the master switch and the radio master. Maybe it went bad and someone just eliminated it, or maybe the alternator wiring is different than mine which is original from the factory. In mine, the Alt Field CB feeds power to the voltage regulator. The field output of the voltage regulator goes through one pole of the master switch and then through the alternator switch and then to the field terminal of the alternator. So, both the master and alternator switches have to be on to excite the alternator. 

[Aerodon]

I have a couple of those side panels with round holes for other clocks.  Send me a pm.

 

Aerodon

[Slick Nick]

2 hours ago, PT20J said:

The alternator switch in my airplane is in the space between the master switch and the radio master. Maybe it went bad and someone just eliminated it, or maybe the alternator wiring is different than mine which is original from the factory. In mine, the Alt Field CB feeds power to the voltage regulator. The field output of the voltage regulator goes through one pole of the master switch and then through the alternator switch and then to the field terminal of the alternator. So, both the master and alternator switches have to be on to excite the alternator. 

Same here in my 1991 MSE. I’ve never seen a setup like hanks before. 

[FLYFST]

Same here in my 1991 MSE. I’ve never seen a setup like hanks before. 

My J is the Advanced Training System (ATS) version, so maybe that’s why? Just a WAG but really no idea why.


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[LANCECASPER]

6 hours ago, jetdriven said:

Didn’t someone here figure out it was a Porsche clock for 200$?

VDO made the clock for the Porsche 944 starting in 1986. Mid-Continent bought the units and added a sticker with their part number (MD-89) and doubled the price.

[Slick Nick]

8 hours ago, FLYFST said:

My J is the Advanced Training System (ATS) version, so maybe that’s why? Just a WAG but really no idea why.


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Have you got a photo of your entire panel that you could post? I’m curious. 

[Slick Nick]

17 hours ago, FLYFST said:

My J is the Advanced Training System (ATS) version, so maybe that’s why? Just a WAG but really no idea why.


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I think you’re onto something there. I had a look at some photos of another ATS listed for sale on Controller, and it also does not have the alternator master switch. 

[FLYFST]

I think you’re onto something there. I had a look at some photos of another ATS listed for sale on Controller, and it also does not have the alternator master switch. 

Confirmed! My serial number specific flight manual has no reference to an Alternator Switch, only an Alternator Circuit Breaker and separate Alternator Field Circuit Breaker; mystery solved.


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[201Mooniac]

My 1980 M20J also doesn't have an alternator switch or a split master, just a single master switch.  It was that way from the factory AFAICT.