M20K - Annunciator Panel Issue - Fuel Low Lights Intermittent

[FlyWalt]

Good Morning Fellow Mooniacs,

 

I have my avionics guy chasing a Fuel Low light issue in our annunciator panel. They have been intermittently unreliable on the push to test item on the before starting checklist.

 

He has it narrowed down to something faulty in the 37 yr old  IC circuits on the board. Picture is attached. Part number is: 500D0038

 

Does anyone have a solution for this?

 

Thank you in advance,

W
 

[dtoelke]

I have the same issue with mine.  Haven't looked into fixing yet.

[FlyWalt]

Well I have a new philosophy regarding aircraft maintenance. If it doesn't work or doesn't work as certified., it gets fixed. Period.

 

After 3 years of owning 231LR she is darn near 99.9 percent restored mechanically. I will be posting pics soon after the next Meguiars wax job. :-)

[Geoff]

I had similar problem. First check the bulbs are working by swapping them with others in the annunciator that you know work. If bulbs are ok then your only choice is to send annunciator panel to IA in Dallas. Cost will be about 1.6 AMUs for a rebuild and they will rebuild the whole thing. They did mine and it is perfect and it took about a week.

Now before you worry about the cost, you should know that two years ago IA tried to sell this part of their business without success and almost shut it down which would have left us all in a real mess.

Hope this helps.

[ArtVandelay]

Does anybody have a schematic for it?

[FlyWalt]

It is in the electrical section of your maintenance manual. And on that note, I have narrowed it down to two parts thanks to an excellent job of writing by Mooney on that manual.

 

Question, does anyone have a pdf of the maintenance manual for the earlier 231s? I have the manual for the later models and I need one that covers serial no 25-0025.

 

Thanks,

Walt

[Guillaume]

Service and maintenance manual are not serial number specific.

For the M20K you should use MAN134 (latest revision 3-00) regardless of your s/n. The manual contains the differences between the early models and the late models.

[mooney2201]

any electronics shop can fix this unit...very simple....they can shotgun the unit and find most of the time its a bad transistor..only a couple of  ttl,s can get all parts on ebay...SIMPLE FIX

[FlyWalt]

Any decent ham radio operator could fix this box. 

[ArtVandelay]

any electronics shop can fix this unit...very simple....they can shotgun the unit and find most of the time its a bad transistor..only a couple of ttl,s can get all parts on ebay...SIMPLE FIX

Could be a capacitor as well, they can be checked with a fluke meter.

[Jimhamilton]

I had similar problem. First check the bulbs are working by swapping them with others in the annunciator that you know work. If bulbs are ok then your only choice is to send annunciator panel to IA in Dallas. Cost will be about 1.6 AMUs for a rebuild and they will rebuild the whole thing. They did mine and it is perfect and it took about a week.

Now before you worry about the cost, you should know that two years ago IA tried to sell this part of their business without success and almost shut it down which would have left us all in a real mess.

Hope this helps.

OK, so what is 1.6 AMUs exactly.  Shop hours?, Price in gold?  Just wondering.

[carusoam]

Exactly 1.6k. Or 1.6M, expressed in USD, depending on your finance administrator...

-a-

[ArtVandelay]

It is in the electrical section of your maintenance manual. And on that note, I have narrowed it down to two parts thanks to an excellent job of writing by Mooney on that manual.

Question, does anyone have a pdf of the maintenance manual for the earlier 231s? I have the manual for the later models and I need one that covers serial no 25-0025.

Thanks,

Walt

The version I have only includes wiring diagrams, the manual refers to separate drawings, but does include a nice troubleshooting section 24-39-05, unfortunately without corresponding drawings might be problematic.

[Jimhamilton]

Exactly 1.6k. Or 1.6M, expressed in USD, depending on your finance administrator...

-a-

OK, I am guessing the repair would be about $1,600.00 US dollars.  If I have converted it right.  Thanks.

[FlyWalt]

OK, I am guessing the repair would be about $1,600.00 US dollars.  If I have converted it right.  Thanks.

 

Yet the two parts that I found to be bad are about 88 cents at any electronic supply shop. Amazing how many "Aviation Businesses" make their way by ripping us off. And they wonder why aviation is in decline. Trust me, it is not just the government nor fuel prices that are to blame.

[Jimhamilton]

Yet the two parts that I found to be bad are about 88 cents at any electronic supply shop. Amazing how many "Aviation Businesses" make their way by ripping us off. And they wonder why aviation is in decline. Trust me, it is not just the government nor fuel prices that are to blame.

So, can you take a pic or describe how you fixed it for the rest of us. Please, this just may come in handy.

[dtoelke]

So, can you take a pic or describe how you fixed it for the rest of us. Please, this just may come in handy.

 

Yes I'd also be very interested to see this.

[FlyWalt]

Gentlemen,

 

In the electrical section of the 231 maintenance manual there is a troubleshooting list that describes all the possible symptoms and the associated parts on the schematic that if bad would cause said symptoms. It takes some digging and reading, but all of the information is there. As a ham radio operator I can say that the schematic is very well laid out.

Hope this helps,
W

[Jimhamilton]

Mooney MX Manual 24-39-05 is where you want to start.  The schematics follow a few pages later.  So.....there you have it.  Good Luck and good hunting for those of us, including myself, that are a little challenged in this area.

[ArtVandelay]

Mooney MX Manual 24-39-05 is where you want to start. The schematics follow a few pages later. So.....there you have it. Good Luck and good hunting for those of us, including myself, that are a little challenged in this area.

I believe the next section schematics apply to the late models, the 28V systems, the only doc on the older versions is in service instruction 74.

[Jimhamilton]

I believe the next section schematics apply to the late models, the 28V systems, the only doc on the older versions is in service instruction 74.

Yes, you are right.  You can find this service instruction 74 on the Mooney website.  Go to Service and Support then click on Service Instructions and then M20K.  The service instructions are in numerical order.  Look for 74.  Looks like a simple fix.

[dtoelke]

Yes, you are right.  You can find this service instruction 74 on the Mooney website.  Go to Service and Support then click on Service Instructions and then M20K.  The service instructions are in numerical order.  Look for 74.  Looks like a simple fix.

 

Looks easy enough.  I'm having a hard time finding that part number though.  Does somebody have a P/N for the equivalent at Radio Shack?

[dtoelke]

Nvm I'm just going to go pull it and stop by the local avionics shop which should have them.  Does anyone else with this issue also have the same issue with the "alt air" light?

[Jimhamilton]

Looks easy enough.  I'm having a hard time finding that part number though.  Does somebody have a P/N for the equivalent at Radio Shack?

Radio Shack?  They still in business?

[dtoelke]

I pulled the annunciator panel yesterday and opened it up. Low and behold the circuit layout is completely different than the one shown in the service instruction. I could only find two 100K resistors on the board so I'd assume they are the ones in question but I want to confirm before replacing. Has anybody else ran into this issue? I've confirmed the SI applies to my S/N and the annunciator box is original equipment (shipped date Feb 1979)