M20J Avionics Fan (not so fun) [FIXED]

[redbaron1982]

Hey,

I'm chasing down an issue with my KFC 150, which seems specifically related to the KC 192 and temperature-related. Yesterday I checked the avionics fan and is dead, plus there are several hoses that are disconnected.

I have a few questions:

• Is the Cyclone 21 a good replacement for my avionics fan? What I currently have is a KA 33 that is mounted on top of the front wheel well.
• Which equipment needs a hose attached to the back? I have a GNS430, an (obsolete) MX20, a KMA 24, Appareo Transponder, the KFC 150, a KX 155, GI 275 EIS, and the regular steam gauges (plus radar altimeter and storm scope). From what I've checked only the KFC 150 and KX 155 have ports for cooling on the back.
• Does it make sense to leave some hoses blowing air to the back of equipment that doesn't have a port to connect a cooling hose?
• Have any of you experienced KFC 150 malfunction due to an INOP avionics FAN?

Thanks!

Ernesto.

Edited August 8, 2023 by redbaron1982

[N201MKTurbo]

I was flying a plane with a KFC150 a while back. it would start rolling back and forth sometimes. When it would do that I would feel the box and it was very hot. I mentioned this to the owner and I think he put a fan on it and it quite doing it.

[PT20J]

There are several KA 33s on eBay for around $100.

[redbaron1982]

40 minutes ago, PT20J said:

There are several KA 33s on eBay for around $100.

Yes, I saw those. I was thinking that maybe there are some alternative ones that I can get new that have better performance.

 

[ZuluZulu]

1 hour ago, redbaron1982 said:

Yes, I saw those. I was thinking that maybe there are some alternative ones that I can get new that have better performance.

 

You could get a new GFC 500 with better performance that doesn’t need a fan at all 

[PT20J]

59 minutes ago, M20Doc said:

I recently replaced the motor on one, pretty easy job.

Where did you get the motor and what did it cost?

[0TreeLemur]

3 hours ago, ZuluZulu said:

You could get a new GFC 500 with better performance that doesn’t need a fan at all 

Sure.  Why not spend $30,000 to fix a $300 problem!  

The KFC150 is a great autopilot.

[PT20J]

17 minutes ago, 0TreeLemur said:

Sure.  Why not spend $30,000 to fix a $300 problem!  

The KFC150 is a great autopilot.

It’s a good autopilot. However, some parts are no longer available (microprocessors, for example), used 28 V computers are becoming scarce, and units built in the mid-1990s have electrolytic capacitors that tend to leak and damage the PC boards. It’s questionable how long they can be maintained. 

[ArtVandelay]

Sure.  Why not spend $30,000 to fix a $300 problem!  
The KFC150 is a great autopilot.

Here’s a thread discussing this:

https://mooneyspace.com/topic/34636-auto-pilot-kfc-150-vs-replacement/

[redbaron1982]

58 minutes ago, PT20J said:

It’s a good autopilot. However, some parts are no longer available (microprocessors, for example), used 28 V computers are becoming scarce, and units built in the mid-1990s have electrolytic capacitors that tend to leak and damage the PC boards. It’s questionable how long they can be maintained. 

I want to give my KC 192 a chance because it's a 1985 unit that everybody told me that is quite reliable. It's a -02 that I think have still some chances of being repaired. 

[redbaron1982]

4 hours ago, M20Doc said:

I recently replaced the motor on one, pretty easy job.

I'm also interested on knowing about this.

[1980Mooney]

4 hours ago, ZuluZulu said:

You could get a new GFC 500 with better performance that doesn’t need a fan at all 

That’s the classic General Aviation solution…. A $12-$15,000 solution for a $100 problem.

[ArtVandelay]

That’s the classic General Aviation solution…. A $12-$15,000 solution for a $100 problem.

In aviation, there’s no problem enough money can’t fix. ;-)

[EricJ]

2 hours ago, PT20J said:

It’s a good autopilot. However, some parts are no longer available (microprocessors, for example), used 28 V computers are becoming scarce, and units built in the mid-1990s have electrolytic capacitors that tend to leak and damage the PC boards. It’s questionable how long they can be maintained. 

Changing capacitors is usually pretty easy, though, and there's usually a nice burn mark near the one that failed so you know which one to change. 

[c1tice]

I did just that, installed a GFC 500 to replace my 42 year old KFC 150 that had already been repaired by the Autopilots Central in Oklahoma for $3000. They did a fine job and something else broke on it 6 months later. I chose to upgrade rather than be with out the AP for months and throwing good money at a unit that at some point will be unrepairable. 

 

[redbaron1982]

Trying to get back the post to my initial questions...

What do you guys think on pulling out an the cooling hoses and leaving only two for the equipments that do have a port for them? (KC192 and KX155). 

[laytonl]

On 7/31/2023 at 7:45 PM, redbaron1982 said:

Trying to get back the post to my initial questions...

What do you guys think on pulling out a the cooling hoses and leaving only two for the equipments that do have a port for them? (KC192 and KX155). 

That’s what I did. I used a cyclone 21 and I believe I had to make a new mounting plate.  Difficult area to work in, but overall not a bad project.  Lee

[Releew]

They are a PITA to remove and replace.  Take the seats out and get comfortable.  Pump in cold air!  Just keep telling yourself, THIS IS POSSIBLE....!

Rick

[redbaron1982]

Just for fun, I got to the task of repair the motor.

So, first thing I noticed is that it is labeled as a brushless DC motor, but had only two connections. So I thought that this little motor had to have some electronics packed inside.

Also, depending on which position the rotor was at, it started or not. My thought then was that one of the two driving circuitry had to be bad.

I took it appart and sure enough, one of the two transistors was (literally) melted, and just to make my task easier it was also desoldered! That thing really got hot when it melted!

The transistors are quite standard, NPN Darlington TIP 112. This exact model is not super common now, but the TIP 122 has the same characteristics except higher collector current. So I replaced the blown one with a TIP 122.

I put everything back together, tested, and worked like a charm.

For sure not super useful information in this day and age, but I thought it would be fun sharing.

[MikeOH]

Good for you troubleshooting down to the component!

Any idea/evidence for what fried the original?  One possible concern is a short in the one motor winding that's drawing excessive current; the TIP122 may handle it a bit better but....how long did you run the fan for testing?  Can you compare the temps of the two motor drive transistors?

[M20F]

You should be a purist and run the hoses to the cold air inlet on the side of the fuselage. 

[redbaron1982]

1 minute ago, MikeOH said:

Good for you troubleshooting down to the component!

Any idea/evidence for what fried the original?  One possible concern is a short in the one motor winding that's drawing excessive current; the TIP122 may handle it a bit better but....how long did you run the fan for testing?  Can you compare the temps of the two motor drive transistors?

I ran it for 30 minutes, not more. But I will leave it overnight to make sure it is ok. I did not notice any particular difference in temp between both transistors.

My guess on why it burnt is that the fan stucked because of dirt and the transistor that got burnt is the one that was ON in that particular position.

The motor was quite hard to spin by hand before cleaning and lubricating it.

[MikeOH]

That makes complete sense as the root cause.  I think overnight will be plenty.

Congrats again on taking the time to affect a low dollar cost repair!

[N201MKTurbo]

I would have replaced both with the same transistors, just to keep everything balanced.