Avionics conundrum, caused by KX155

[AndreiC]

The avionics package in my 1970 M20E consists mainly of a GNS430W and a KX155 (no glideslope), connected to an ancient audio panel (KA134) and a Telex intercom. The radios also drive an STEC/30, either through GPSS or via the VOR receivers. It all works quite well, and as a CB I am happy to not have the latest and greatest if I don't have to pay for it.

Lately, however, I have noticed that my KX155 display becomes unreadable in dim light. From talking to a local, highly respected avionics shop (SkyCom in Waukesha) I understand that most likely the display in it is getting old, and it is will probably die slowly in the next year or so, to the point that it won't work even in daylight. Moreover, my KX155 has some other problems as well, like the frequency knob would not always change the frequency correctly (it would jump around a lot).

Thinking I was smart, I bought from eBay for around $1000 a replacement KX155 that was advertised as being in good working order. This new one, however, came with its own host of problems. The squelch button did not work (turns out it is a relatively easy fix), but what was even worse is that in dim light this one, too, is unreadable. It is a bit better than my old radio, but I fear it may also be on its way out.

From my research, there are a few options:

1) Bite a relatively big bullet, and send my old radio to the guy at KX-155.com. He said that for $2500 he would go through the whole radio, and replace the display unit with an LED one that should last another 25 years. 

2) Bite an even bigger bullet, and replace my audio panel with something like the PAR200B ($3250, plus install cost of around $4500), and get rid of the troublesome KX155 altogether. But I would lose my second VOR receiver (maybe not such a big loss), and I would end up with a lower (6 watt versus 10 watt) transmit power. According to the guy at KX-155.com, the KX155 was the best radio ever built (??) and I would not get anything like that communications quality in another radio.

3) Or be cheap, and buy for $720 from ebay a self-install LED solution for the KX155. I have not seen any reports on how well this system works.

In any case I would probably either sell my old radio (hoping to get $500-600 for it), or ask the guy who sold me the radio on ebay to take his back: he was offering a 30 day money back guarantee if one did not break the sealing stickers he had put on. However, my avionics shop had to open it up to see what was wrong with the squelch button.

What are your guys's opinions on what I should do? Sometime in the future I definitely intend to upgrade to a modern audio panel (I was thinking the PMA450C), but I was hoping to push that decision back by a year or two, given its high cost.

[MikeOH]

I've got the identical setup: 430W, STEC-30 w/GPSS/Alt, and a KX-155.  Mine is still 'ok' but when it's a warm day I'll get a weird buzzing that comes and goes.  Sometimes I can get it to go away be reseating the radio.  So far, not too bad but one day I'm going to be faced with the same replacement issue.  The kx-155.com guy used to be $1500...woulda, coulda, shoulda!  $2500 is starting to get painful enough to look at other options.  Looks like a brand new King KX-200 (slide-in replacement) is $5,000.  Twice as painful, but brand new.  It's going to be a tough call.

[Slick Nick]

I can’t remember, but doesn’t the KX155 have a dimmer adjust on the bottom if you pull it out of the rack? I’m pretty sure certain mod numbers did. I still have two 155’s in my plane. They’re a solid radio. Aircraft Engravers makes new display screens for all the old king stuff. Much easier to see the numbers now.

Edited Thursday at 05:59 AM by Slick Nick

[MikeOH]

@Slick Nick

How did you clean up the knobs/buttons?  Or, is there a source for new ones?

[AndreiC]

The problem is that it seems new gas plasma displays (or whatever was original in there) have not been available for about 5-10 years at least. So it is just not possible to replace the display with an original one. I was hoping to get some feedback from the list on how good the LED displays are, that are advertised to be good forever.

(I am aware that some KX155 units had bad capacitors, which leaked and ruined the PCBs. The two radios I have in hand now, my old one and the one I got from ebay, both look very clean, so this should not be a problem.)

[Slick Nick]

5 minutes ago, MikeOH said:

@Slick Nick

How did you clean up the knobs/buttons?  Or, is there a source for new ones?

Im not aware of replacement knobs. They’re not easily replaceable anyways. If you did manage to find some, you’d have to solder the replacement units to the board. Just clean the ones you have. 

[BrettD]

I would probably repair the KX155. I like the simplicity of those radios, they work well. Big displays, tactile buttons, and no touch screens.

[MikeOH]

2 hours ago, AndreiC said:

The problem is that it seems new gas plasma displays (or whatever was original in there) have not been available for about 5-10 years at least. So it is just not possible to replace the display with an original one. I was hoping to get some feedback from the list on how good the LED displays are, that are advertised to be good forever.

(I am aware that some KX155 units had bad capacitors, which leaked and ruined the PCBs. The two radios I have in hand now, my old one and the one I got from ebay, both look very clean, so this should not be a problem.)

Not sure if it matters to you, but I don't think the replacement displays are technically legal.  Something to check if that's a concern (I could be wrong).

[AndreiC]

8 hours ago, MikeOH said:

Not sure if it matters to you, but I don't think the replacement displays are technically legal.  Something to check if that's a concern (I could be wrong).

This is not something that worries me too much. My bigger issue is if a KX155 will last another 5-10 years after fixing the display issue, or if this is just throwing good money after bad. And if people are of the opinion that fixing it is the way to go (which I also lean towards), has anyone tried a KX155 with the updated LED displays?

[Slick Nick]

There are videos on YouTube. Personally, I'd just buy a new (used) one and be done with it. They're cheap, you can find them from all the usual suspects, even eBay for like $1500.

[Jake@BevanAviation]

The only approved display replacements are the mod kits produced by Honeywell that change the old gas display to a led. Honeywell, continues to increase the price of this mod kit so it has become more costly to fix these units.  We have had very few issues with the LED mod by Honeywell.  There is another person that advertises an OLED replacement.  However, this is not an approved mod, if you choose to do this good luck getting someone to sign off on the radio if it would need any future repairs.  We have seen a couple of them come in and we have rejected the units due to no service data being available.

The frequency knob issue is pretty common as these units continue to age. It is fairly easy to replace pending the parts are available and the repair shop knows what they are doing.  With the repair cost increasing more people are replacing the units with new modern radios.  The GNC215 by Garmin is a good option and you can buy them over the counter. We have installed several of them in multiple aircraft with no issues.  The KX200 is advertised as the replacement to the KX155., but we have yet to see one in the wild.  I have heard that the unit are finally available after being talked about for a couple of years.

We still repair the KX155 units and have the LED mod kit available.  The thing that really makes the units non repairable is when they have capacitor leakage and it spreads damaging multiple circuits in the radio.  This capacitor issue is more common in units manufactured between 1991 and 1998.

[Pinecone]

The KX-155 out of my CAP-10 had display issues.  I took it to the shop that did my avionics upgrade. They diagnosed an issue with the high voltage power supply and sent it to a shop they use.  It came back working great for $400.

I will see if I can get the name and contact of the shop.