Davtron M811B wiring.

[A64Pilot]

I have an M811B clock, that I’m thinking it came from the factory with, I can’t set the time, a little reading suggests that there is a 6V backup battery to hold voltage that’s required.

But I look under the panel and can’t find anything that looks like the image of the Davtron battery, but I found what looks like a large capacitor, not saying it’s a cap just trying to explain how it looks. you know silver metal can about a inch and a half long and half inch around, but it has red and black wires coming out of one end and black and blue out of the other,

red and black correspond to power for the battery, the flight timer is a blue wire. I can’t follow the wires without a lot of zip tie cutting, so I thought I’d ask first

How did the factory wire the Davtron clock? Is there a replaceable battery, or did they do it smart and have a clock keep alive power wire and maybe a resistor for the 6V part?

Does this metal can have anything to do with it?

 

81 J model

Edited April 1, 2021 by A64Pilot

[N201MKTurbo]

Got a picture?

[N201MKTurbo]

https://www.aircraftspruce.com/catalog/inpages/davtron10-24560.php

 

[PT20J]

I had one of those in my 1978 M20J. I liked it because it was very easy to read in all light conditions. But the time adjustment only increments at half or double speed, so you have to connect the battery close to “on the hour”unless you want to spend a long time getting it set right. I remember calling Davtron and they told me that’s how they do it at the factory.

Skip

[A64Pilot]

I do now, had to crawl back under the panel.

‘I’m wondering if Mooney didn’t get smart and this is some kind of Cap/ rechargeable battery and or also operates the flight timer, which works by the way,I suppose it’s connected to the gear switch?

 

[N201MKTurbo]

You can see that a new one has the battery and that thing. It may be a connector.

[A64Pilot]

I bet it is a strange shaped connector, I had a plastic plug in my mind.

‘The battery wires are supposed to be separate, so I need to keep looking.

I intend to replace the battery with four AA lithium’s in series, that ought to last for years 

[A64Pilot]

I got the clock out, I assume Mooney added the plastic plugs, the Davtron battery apparently requires the wires to be cut and spliced to replace the battery, that’s why I believe Mooney added the plugs, and to make assembly easier.

‘Anyway my battery was missing, and the ground wire broken off, on disassembly it appeared that the ground wire was soldered to a chassis ground so I attached a new ground wire, removed the plug as I didn’t have the other half and spilced in the battery pack wire, the battery pack comes with the standard 9V connector so future battery replacements ought to be easier.

‘Now to see if I can get it back together without damage to existing harness, it was tough to remove.

 

Edited April 1, 2021 by A64Pilot

[Igor_U]

It seems you figured it out but here's an electrical schematics:

[A64Pilot]

Thanks for the wiring diagram, I can confirm that replacing with 4 AA’s in series works, still seems silly to wait until exactly on the hour to put batteries in a clock, what nut comes up with something like that?

[carusoam]

By the date on the drawing...  Oct. 1976...

A64,

You have been approved to buy a new digital clock...

Consider getting one that has multiple functions and USB sockets...

Its amazing that anyone could design a simple digital clock that could last 50 years...

That Apollo project really advanced the technical world, only a decade before...

 

Some people like their new digital clock to come with an AI on a different page...

Others have found the clock in their navigator meets the requirement of having a clock...

Still some MSers really like their 8day wind up clock...

Best regards,

-a-

[A64Pilot]

Nothing wrong with this one, I don’t need a clock, an approach timer maybe.

‘It’s just it’s on the panel and I have this thing about if it’s there, it’s supposed to work.

Having said that, I probably won’t fix the Radar altimeter, I will probably put an analyzer there.

[carusoam]

Radar altimeters are out...

Have you seen the their replacements?

-a-

For entertainment only...   mid 70s digital clocks usually looked like this... all analog, and motor driven...

Best regards,

-a-

 

[Andy95W]

Anthony, you seriously need a new clock radio.

[A64Pilot]

9 hours ago, carusoam said:

Radar altimeters are out...

Have you seen the their replacements?

-a-

For entertainment only...   mid 70s digital clocks usually looked like this... all analog, and motor driven...

Best regards,

-a-

 

Several years ago I had a very similar device added to our type certificate, name of the company was Aglaser. There is some advantage in an Ag aircraft especially in training knowing exact height above the ground. Proper dispersal altitude is higher than you might think, and many fly too low and this decreases swath width.

However laser altimeters can’t replace radar, they are too limited in range, they work extremely well at closer distances, not so good at telling you your at 500 feet though.

‘I say that never having seen the product you speak of, and basing it off or other products, most often devices like this, the laser transceiver is an off the shelf product bought to use, and the actual development is in the indicators and annunciators 

[A64Pilot]

The M811B clock is still sold. it’s still a good product, I wouldn’t pay $500 for a clock myself, but I won’t throw away a perfect functioning one either, besides the flight timer is kind of neat, I believe it’s wired to the gear switch, not sure, but it does time flights accurately.

https://www.aircraftspruce.com/catalog/pnpages/11-05874.php?gclid=CjwKCAjwpKCDBhBPEiwAFgBzjztJ8ipMHS_mWSdim-MSWxeJEBdqWaBiq-vgtPfmC2bEx-tn60rh0RoCIMcQAvD_BwE

 

Edited April 3, 2021 by A64Pilot

[PT20J]

1 minute ago, A64Pilot said:

The M811B clock is still sold. it’s still a good product, I wouldn’t pay $500 for a clock myself, but I won’t throw away a perfect functioning one either, besides the flight timer is kind of neat, I believe it’s wired to the gear switch, not sure, but it does time flights accurately.

https://www.aircraftspruce.com/catalog/pnpages/11-05874.php?gclid=CjwKCAjwpKCDBhBPEiwAFgBzjztJ8ipMHS_mWSdim-MSWxeJEBdqWaBiq-vgtPfmC2bEx-tn60rh0RoCIMcQAvD_BwE

 

Mine had an air switch located on an inspection hole cover near the leading edge of the left wing root.

[A64Pilot]

8 minutes ago, PT20J said:

Mine had an air switch located on an inspection hole cover near the leading edge of the left wing root.

I don’t believe I have a inspection hole on the leading edge.

‘I’m going to breakfast Sun morning, if I remember I’ll leave the gear down after takeoff and see if the timer starts with gear actuation.

‘I’ve seen stall warning switches mounted straight down in underwing inspection hole clovers that air would blow back to indicate flight, but I don’t member what they were for, what device they controlled.

‘Now I bet everything uses a GPS signal for speed to know flight

Edited April 3, 2021 by A64Pilot

[PT20J]

Just now, A64Pilot said:

I don’t believe I have a inspection hole on the leading edge.

‘I’m going to breakfast Sun morning, if I remember I’ll leave the gear down after takeoff and see if the timer starts with gear actuation.

‘I’ve seen stall warning switches mounted straight down in underwing inspection hole clovers that air would blow back to indicate flight, but I don’t member what they were for, what device they controlled.

‘Now I bet everything uses a GPS signal for speed to know flight

Sorry I wasn’t clear - it was under the wing near the leading edge. I think mine was a factory installation.