Replacement Suggestions for King KX-155

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write-stuff

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One of my KX-155s is slowly dying away. I'm sick of the crappy LEDs in the 155 and am considering replacing it with something else. Any suggestions?
 
SL-30 will do you solid.

@Bell206 - It's TKM... and they don't seem to have brought that thing to market after only 2 years.
 
From same site

The MX155X is on sale! This is the pre-certified version of the KX155 replacement. Please get in touch with our sales team for pricing and availability.

No help for @write-stuff
 
Yep, just saw that for the MX-155. Not a lot of dealers for the SL-30, but I'm looking.
 
Install non-certified slide-in replacement. Promise not to crash plane before they get the thing certified.
 
Ravioli said:
From same site

The MX155X is on sale! This is the pre-certified version of the KX155 replacement. Please get in touch with our sales team for pricing and availability.

No help for @write-stuff
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Here we go again. What certification is needed for a part 91 radio? Please show me the "certification" on those thousands of kx-170's installed in thousands of certified airplanes. It's not a major alteration, by the way, putting any radios in a radio rack is for the most part not a major alteration an does not Need a 337. Contrary to the belief of a lot of A&Ps. Weird Jim has the fsdo letter from the 70's on his web page somewhere. Weird Jim and bell 206 can explane the details better, but it's really up to the installing A&P to decide if the part is airworthy.

With that said, I have mx-155 serial number 25 in my warrior and so far it's been a great radio. It is not exactly cheap but better than the price of a 255 with instillation.
 
write-stuff said:
Not a lot of dealers for the SL-30, but I'm looking.
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The SL-30 is out of production and those that own them are usually of the "...pry them from my cold dead hands" variety. You might get lucky, but I wouldn't hold my hopes up too high.

The GNC255 is more or less the same thing except with a more modern display and a little bigger stack height.
 
Ravioli said:
From same site

The MX155X is on sale! This is the pre-certified version of the KX155 replacement. Please get in touch with our sales team for pricing and availability.

No help for @write-stuff
Click to expand...
Well, this is certainly confusing. Is it on sale or is it on preorder? Maybe "on sale" means discounted price for preordering?

Clipboard01.png
 
write-stuff said:
One of my KX-155s is slowly dying away. I'm sick of the crappy LEDs in the 155 and am considering replacing it with something else. Any suggestions?
Click to expand...

I'd love to have a KX-155 corpse to see if I can adapt very efficient, very cheap LED display to. If you ever decide you want to sell that sucker for nickels and dimes to somebody who will be able to design and supply replacement displays for a reasonable price, you will be a hero to lots of your aviation buddies.

But as I recall, the 155 had vacuum fluorescent displays, not LEDS.

Or, it may just be a doorstop if I can't do it.

Jim
 
weirdjim said:
I'd love to have a KX-155 corpse to see if I can adapt very efficient, very cheap LED display to. If you ever decide you want to sell that sucker for nickels and dimes to somebody who will be able to design and supply replacement displays for a reasonable price, you will be a hero to lots of your aviation buddies.

But as I recall, the 155 had vacuum fluorescent displays, not LEDS.
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Apparently B-K uses LCD rather than LED for their gas discharge display replacement.
https://www.avweb.com/ownership/bendixking-kx155-165-radio-obsolete-display-creates-refurb-program/
 
Ravioli said:
SL-30 will do you solid.

@Bell206 - It's TKM... and they don't seem to have brought that thing to market after only 2 years.
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Sorry ravoioli, got to disagree. The sl30 has been out of production for years. They still bring 2500-3000 on the used market. Foolish to spend that kind of money on a out of production unit when the 255 is only about 3900 new with warranty.
 
weirdjim said:
I'd love to have a KX-155 corpse to see if I can adapt very efficient, very cheap LED display to.
...
Or, it may just be a doorstop if I can't do it.
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It's actually quite easy, probably simple enough that a sufficiently motivated 7th grader could explain its operation. The display board schematic begins on the 254th page of this PDF (Figure 6-10):
http://www.mikeg.net/hobbies/aviation/avionics/combined/King KX-155-165 Combined.pdf

I102 is a CD4022B, which is a CMOS octal counter (1-hot with rollover). The 8 outputs go to I101 which is a level shifter. Although the schematic lists it as a DI512 I suspect it's really a Dionics DI510B. Either that or the +192v on the drawing is wrong:

http://www.dionics-usa.com/hv-display-drivers.html

As the counter cycles through, it selects which digit pair will receive inputs (A8/A9, A5/A12, A2/A15, etc). The COMM [a-i] bus and NAV [a-i] bus then drive the 9 segments of each digit pair. A1/A5/A9/A13 are 9 segments as they display "0" through "10" and A2/A6/A10/A14 are 8 segments as they include the decimal point. A4 also seems to be 8 segment as it includes the transmit light. The rest seem to be 7 segments.

So really the only tricky part is to step down the 192 volts to something more usable. You might have to pick LED's that have good persistence but if the CD4022B is clocked fast enough you could probably use on the persistence in your retina instead.
 
Spend over 2K on a slide in replacement and be done or put that money towards an upgrade. Navs are going the way of ADFs and RNAVs and Lorans. tough decision. I dont fly IFR so I dont have much use for a NAV anymore,
 
Does anyone know if the TMK company is still in business. I have emailed and called with no response.
 
My radio went on the fritz, though about the TMK replacement. But it was the height of the pandemic, and I doubted strongly I could actually lay my hands on one. Now I see that they'll soon be ready for the non-certified version reinforces my doubts. I wound up installing a refurbished KX155. The Devil you know...
 
Thanks steingar, I am getting that impression as well. The readout is losing numbers and it seems to be developing some staticy backround noise. I may try the one rebuilder someone suggested in chat.
 
They refurbished one for me about a year ago.
 
William Clifford said:
The readout is losing numbers and it seems to be developing some staticy backround noise.
Click to expand...
Sounds like it could be electrolytic capacitors nearing end-of-life needing to be replaced.
 
When did King come out with the 155's? I'm surprised they still have any value in all honesty.
 
Racerx said:
When did King come out with the 155's? I'm surprised they still have any value in all honesty.
Click to expand...

Yeah, the value is due to a combination of factors including:
They're ubiquitous - probably the most popular nav/com ever made and tons of airplanes still have them installed, so big market
The are dying at a rapid pace - mostly displays crapping out - and there's no easy way to repair them
A new replacement might only be 2x the price, but it will be at least 3x installed. And shops are backed up months for the work.
Did I mention you probably can't even buy an new replacement because they aren't in stock? (Looking at you Garmin)

So while it may seem crazy to pay $2-$2.5K for a piece of USED 1980's electronics, if yours is broke and you want to fly anytime soon, you gotta pay up.

C.
 
Racerx said:
When did King come out with the 155's? I'm surprised they still have any value in all honesty.
Click to expand...

In my opinion the value is limited now, since they’re effectively two generations old. But there are still a lot of them installed and the cheapest way to deal with a failure of one is to replace it with the same thing.

It wasn’t that long ago that the KX170 was in the same position as the KX155 is now. I think we’ll see the number of installed KX155s shrink dramatically in the next 5 or so years. In the meantime, if you have a good one they’re still decent radios.
 
mondtster said:
In my opinion the value is limited now, since they’re effectively two generations old. But there are still a lot of them installed and the cheapest way to deal with a failure of one is to replace it with the same thing.

It wasn’t that long ago that the KX170 was in the same position as the KX155 is now. I think we’ll see the number of installed KX155s shrink dramatically in the next 5 or so years. In the meantime, if you have a good one they’re still decent radios.
Click to expand...

As the owner of a kx155, I'll disagree, but only a little. The 155 is the first "modern" nav/com with digital tuning and flip/flop button. It truly made the 170 obsolete. As a #2 radio, there's really nothing a more modern radio offers that the 155 doesn't. The only useful feature it doesn't have is a display showing which radial you're on like the kx165.

I thought mine was going out (the nav side quit working), so I went through this exercise a couple months ago. Options were basically $8k installed for a Garmin 255, or $1000 for a used kx155 I could swap myself. My plan was/is to buy a working unit and send mine for repair. The real problem is the displays, which at this point are all in varying degrees of failure, with no real repair option.

Turned out that removing and reseating my radio seems to have resolved my issue; hopefully that buys me a few more years. If money were no object I'd stick another gtn in there, but there are numerous higher priorities.
 
Jim K said:
As the owner of a kx155, I'll disagree, but only a little. The 155 is the first "modern" nav/com with digital tuning and flip/flop button. It truly made the 170 obsolete. As a #2 radio, there's really nothing a more modern radio offers that the 155 doesn't. The only useful feature it doesn't have is a display showing which radial you're on like the kx165.

I thought mine was going out (the nav side quit working), so I went through this exercise a couple months ago. Options were basically $8k installed for a Garmin 255, or $1000 for a used kx155 I could swap myself. My plan was/is to buy a working unit and send mine for repair. The real problem is the displays, which at this point are all in varying degrees of failure, with no real repair option.

Turned out that removing and reseating my radio seems to have resolved my issue; hopefully that buys me a few more years. If money were no object I'd stick another gtn in there, but there are numerous higher priorities.
Click to expand...

My statements of modernity have nothing to do with features. They have to do with the age and ability to repair them.They’re old, and as you admit yourself, some components are unrepairable.

I personally believe that we didn’t see more SL30s and SL40s installed because of the saturation of the market with KX170s and 155s. But now that those are getting flushed out of the system we’re seeing a rising wave of current radios being installed with avionics upgrades or even just as a replacement for a dead KX155.

As an aside, I think the narcos were better radios but you don’t see them around much anymore either due to their age and limited repair options.
 
mondtster said:
My statements of modernity have nothing to do with features. They have to do with the age and ability to repair them.They’re old, and as you admit yourself, some components are unrepairable.

I personally believe that we didn’t see more SL30s and SL40s installed because of the saturation of the market with KX170s and 155s. But now that those are getting flushed out of the system we’re seeing a rising wave of current radios being installed with avionics upgrades or even just as a replacement for a dead KX155.

As an aside, I think the narcos were better radios but you don’t see them around much anymore either due to their age and limited repair options.
Click to expand...
That's why I only disagreed a little ;)

You're absolutely right about their age forcing their retirement, but I was more addressing the value question. I think the value of a working unit is going to remain very strong for a long time as there is no good alternative. 170's became worthless because newer radios are significantly easier to use. The cost to replace a 155 is ludicrous when you consider you're really not gaining any features. There's a GNC255 in the club plane I occasionally fly, and honestly I'd rather have a kx155. Ironically the other radio in there is in fact a Narco that's well past its prime. I'm not as familiar with the Narco radios, but the last time I checked fleabay, that model was commanding about the same money as a kx155.

It feels like there's a tremendous market opportunity there for the likes of TKM to replace all these antiques. Maybe it actually costs $5K to make a quality certified nav/com?
 
William Clifford said:
Thanks steingar, I am getting that impression as well. The readout is losing numbers and it seems to be developing some staticy backround noise. I may try the one rebuilder someone suggested in chat.
Click to expand...
I wound up going with Midcontinent Avionics. A bit spendy, but they did me a solid a few years back when they didn't have to, so I gave them the business. No complaints (yet).
 
Jim K said:
As a #2 radio, there's really nothing a more modern radio offers that the 155 doesn't. The only useful feature it doesn't have is a display showing which radial you're on like the kx165.
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A bit of avionics trivia: There was actually a STC for that, known as the Doss KD155 DVOR Conversion.
Bendix-King-KX155-navcom-DOSS-DVOR-conversion-oper.jpg
 
Jim K said:
It feels like there's a tremendous market opportunity there for the likes of TKM to replace all these antiques.
Click to expand...

Yep, would have sold like hotcakes. Not sure why they couldn't get their product over the finish line. But I feel like it's almost too late now.

C.
 
camorton said:
But I feel like it's almost too late now.
Click to expand...

Since the KX155 is getting long in the tooth, and difficult to repair, I'd think this is the perfect time for a slide-in replacement.
 
They have been long in the tooth and difficult to repair for years. The difference now is that Garmin can't seem to deliver the GNC 255 in quantity, and avionics shops are super busy anyway. Once we're past this (6-12 months?), the price delta for installing something new will drop, and the value of a working KX155 will fall with it. That's why I think the window of opportunity for TKM is closing fast. More power to 'em if they can do it, though.

C.
 
camorton said:
They have been long in the tooth and difficult to repair for years. The difference now is that Garmin can't seem to deliver the GNC 255 in quantity, and avionics shops are super busy anyway. Once we're past this (6-12 months?), the price delta for installing something new will drop, and the value of a working KX155 will fall with it. That's why I think the window of opportunity for TKM is closing fast. More power to 'em if they can do it, though.

C.
Click to expand...

If someone can develop and bring to market a slide-in replacement (looking at you, TKM), the opportunity to sell a bunch, without the hassle of having a shop do a complete installation for a new radio, seems to be huge. Slide-out, slide-in, get a sign-off. Done.
 
camorton said:
They have been long in the tooth and difficult to repair for years. The difference now is that Garmin can't seem to deliver the GNC 255 in quantity, and avionics shops are super busy anyway. Once we're past this (6-12 months?), the price delta for installing something new will drop, and the value of a working KX155 will fall with it. That's why I think the window of opportunity for TKM is closing fast. More power to 'em if they can do it, though.

C.
Click to expand...

There are other nav/com options besides Garmin, some of which are available right now (no waiting). But obviously Garmin is the main product and what they’re selling is nice.

As far as I know, TKM has always produced slide in replacement radios. They always seem to work but have one of the worst interfaces I’ve seen. For someone on a shoestring budget I could see there still being a market for a slide in KX155 replacement but with all the other radios on the market now I’d have to think a long time about a TKM rather than just starting over. Especially in an aircraft where everything else in the panel is equally as archaic as the KX155.
 
mondtster said:
There are other nav/com options besides Garmin, some of which are available right now (no waiting). But obviously Garmin is the main product and what they’re selling is nice.

As far as I know, TKM has always produced slide in replacement radios. They always seem to work but have one of the worst interfaces I’ve seen. For someone on a shoestring budget I could see there still being a market for a slide in KX155 replacement but with all the other radios on the market now I’d have to think a long time about a TKM rather than just starting over. Especially in an aircraft where everything else in the panel is equally as archaic as the KX155.
Click to expand...

I'm thinking that for a Comm/Nav 2, something like a basic TKM slide-in would be fine, and I'd certainly opt for that over having to spend a bunch AMUs on a new radio and installation.
 
camorton said:
They have been long in the tooth and difficult to repair for years. The difference now is that Garmin can't seem to deliver the GNC 255 in quantity, and avionics shops are super busy anyway.
Click to expand...
What, no love for the Trig TX56a?
 
mondtster said:
I'm guessing a lot of people don't know about them because Garmin overshadows pretty much everything else. Trig is becoming my go to brand.
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My complaint about the GNC255 is that the display seems to have a mode that says "I-am-a-COM-radio" displaying only COM info and a mode that says "I-am-a-NAV-radio" displaying only NAV info but not a mode that says "I-am-a-NAV/COM". Say you're on a VOR approach when a COM transmission comes in. Did it come from the active COM frequency? Or did it come from the standby frequency because COM monitor mode was turned on? I don't know because the display is in NAV mode. The Trig is better because it displays both COM info and NAV info side by side.

Also, the GNC255 lacks NAV monitor mode and BC mode, which the older SL30 did have and the Trig also does have. Plus, does the GNC255 really need to be 1.66" tall rather than the 1.33" of the SL30 and the TX56A?

I prefer Garmin EFIS, but make my audio panel a PS-Engineering unit and my NAV/COM Trig.
 
Garmin owns the rights to the SL30 since they pushed apollo / UPS aT out of business. They still overhaul them - I own 4- and they refuse to manufacture it out of arrogance and pride instead selling a garmin unit which is larger and in some ways inferior. ugh. I loved the size and performance of the SL30, and today they’re selling for retail prices even though they’re used. I’m thrilled that Trig now has the TX56a in the same size. Happy to refer people to use it.

I Can build a harness for an SL30 in about ….ummm…45 minutes or less, and anyone can do it. There’s only a DB15 for comm (a whopping 7 pins) and a DB37 (less than 20) - voila! The cost of avionics installs along with the current scheduling wait times is ridiculous - and shops seem indisposed to installing older, more difficult avionics. Nothing like installing an easy G5 and charging customers 50-100% of the retail cost of the hardware…yes!

Plug in power and antennas and you’re off to the races…

Friends don’t let friends pay retail for hardware and services….


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