Kenwood NX-700K : Extremely Poor Reception On Conventional Analog

[762mm]

Hello again everyone,

As an update to my previous thread about the NX-700K I accidentally received (instead of a TK-7180) with the wrong control head on it, I managed to get the proper NX-series control head from the same eBay seller and now the radio powers on!

Original issue thread :

Kenwood NX-700K No Power-on Issue

Hello, I've recently bought two "untested" TK-7180H radios, both having their harnesses cut and in quite a rough shape cosmetically (dirty + scratches). I have the Kenwood wire harness connectors and pins from DigiKey and so I made new harnesses for both units. The first unit required that I...

forums.radioreference.com

Yesterday I downloaded the original NXDN channels data that were programmed by previous owners, then programmed the radio with a new (starting from a blank KPG page) "conventional" set of frequencies using KPG-111D v5.30 with the "Lab Patch". The frequencies include MURS, HAM, Weather and local VHF repeaters, in 4 separate zones.

Now I unfortunately have a new problem that has me dumbfounded :

• The radio will not receive any of the normal channels that should be transmitting, like my two local analog weather channels and local VHF analog repeaters. I have tried two UHF / VHF antennas that work well with all my other UHF and VHF mobiles, but there's no RX on this NX-700K.

• The squelch level is set to 2. When I set it to 0, I can faintly hear the strongest local weather channel. The same weather channel comes in strong on my TK-2180 and TK-2140 portables without any issues. So, the NX-700 is most definitely not reading the signal correctly.

• When I use the portables on MURS, HAM or marine frequencies, the NX-700 is able to hear the transmission and everything is good. It can also transmit just fine to the portables. The NX-700 acts almost as if the antenna wasn't connected and only "hears" the strongest of analog signals.

• I've taken the radio apart to look at the internals. I can't see anything burnt out or any loose solder points where the antenna connects. The tiny little black SMD diode or resistor (R150) next to the antenna connector does have continuity to the radio body, but no continuity across to the antenna solder point. I'm not sure if that's normal.

• I've looked under the tuning options in KPG-111D, but it's beyond my capabilities. There are separate settings for analog and NXDN, plus a lot of them are not self-explanatory. I did save the tuning data (.tun file) of the current configuration, in case this is a tuning issue.

• I've read parts of the user's manual to find answers. There are many optional features of this digital radio that I have no clue about, including digital keys, scramblers, compressed signals, etc. Perhaps this is not a hardware issue, but a programming issue...?

I would really appreciate some guidance in what I should do next. Also, does anyone have a "stock" tuning file for the NX-700K unit? It is a Canadian version of the NX-700K which is not supposed to be restricted to Narrow band. Firmware version is 3.05, I believe.

 

[mmckenna]

Yesterday I downloaded the original NXDN channels data that were programmed by previous owners, then programmed the radio with a new (starting from a blank KPG page) "conventional" set of frequencies using KPG-111D v5.30 with the "Lab Patch". The frequencies include MURS, HAM, Weather and local VHF repeaters, in 4 separate zones.

Just some well intentioned advice:

Don't mess with lab activation of the software. Seriously. There are settings in there that will mess up your radio if you don't know what you are doing and unless you have the $$$correct$$$ test equipment, getting the radio back will be impossible.

Stick with the standard KPG-111 user activation. There's nothing special in the engineering software that will do anything you need.

Also, since you are in Canada, MURS isn't a radio service up there. Be careful about transmitting there to avoid interfering with licensed users.

The radio will not receive any of the normal channels that should be transmitting, like my two local analog weather channels and local VHF analog repeaters. I have tried two UHF / VHF antennas that work well with all my other UHF and VHF mobiles, but there's no RX on this NX-700K.

That would indicate that either the radio is horribly out of alignment or someone overloaded the front end and smoked it.

The squelch level is set to 2. When I set it to 0, I can faintly hear the strongest local weather channel. The same weather channel comes in strong on my TK-2180 and TK-2140 portables without any issues. So, the NX-700 is most definitely not reading the signal correctly.

That would indicate overloaded/deaf front end, or horribly out of alignment, or some mechanical issue at the antenna jack.

When I use the portables on MURS, HAM or marine frequencies, the NX-700 is able to hear the transmission and everything is good. It can also transmit just fine to the portables. The NX-700 acts almost as if the antenna wasn't connected and only "hears" the strongest of analog signals.

See above.

I've taken the radio apart to look at the internals. I can't see anything burnt out or any loose solder points where the antenna connects. The tiny little black SMD diode or resistor (R150) next to the antenna connector does have continuity to the radio body, but no continuity across to the antenna solder point. I'm not sure if that's normal.

R-150 is a 0Ω resistor. It's essentially a jumper to the antenna connector. Reading continuity to ground can be confused by various coils in the circuit that will show a DC path to ground.

I've looked under the tuning options in KPG-111D, but it's beyond my capabilities. There are separate settings for analog and NXDN, plus a lot of them are not self-explanatory. I did save the tuning data (.tun file) of the current configuration, in case this is a tuning issue.

Yeah, don't. Seriously. Unless you have a $ervice monitor and the skills to use it, do not mess with the tuning values.
And you can't take tuning values from another NX-700 or TK-7180 and try to use those. Tuning values will be different from radio to radio.

I've read parts of the user's manual to find answers. There are many optional features of this digital radio that I have no clue about, including digital keys, scramblers, compressed signals, etc. Perhaps this is not a hardware issue, but a programming issue...?

Those won't impact your receive in your tests you mentioned above.

I would really appreciate some guidance in what I should do next. Also, does anyone have a "stock" tuning file for the NX-700K unit? It is a Canadian version of the NX-700K which is not supposed to be restricted to Narrow band. Firmware version is 3.05, I believe.

Yeah, don't. There isn't a "stock" tuning profile. Tuning profiles are specific to individual radios and based on a lot of factors like component tolerances. If someone before you tried to jam a tuning file from another radio in there that can mess things up.

It's not uncommon to find radios like this, especially in the ham/hobby world. Sometimes well meaning individuals will try to "fix" the radio, or boost performance by diddling with the tuning. Unless you have all the right equipment, you can't align a radio by ear, or by using a multimeter. The other possibility is that someone transmitted too close to this radio/antenna and completely smoked the front end RF amp.

If you've ruled out the obvious mechanical issues like the antenna jack, then there's not really a whole lot you can do unless you have a service monitor.

If you really want this radio to work, it would be worth the $150 or so to send it off to a Kenwood shop for alignment. A good shop will have a service monitor with the 'auto tune' function that will align one of these radios in about 20 minutes back to factory spec. If there's an issue, they'll find it.

 

[762mm]

Just some well intentioned advice:

Don't mess with lab activation of the software. Seriously. There are settings in there that will mess up your radio if you don't know what you are doing and unless you have the $$$correct$$$ test equipment, getting the radio back will be impossible.

Stick with the standard KPG-111 user activation. There's nothing special in the engineering software that will do anything you need.

Also, since you are in Canada, MURS isn't a radio service up there. Be careful about transmitting there to avoid interfering with licensed users.



That would indicate that either the radio is horribly out of alignment or someone overloaded the front end and smoked it.



That would indicate overloaded/deaf front end, or horribly out of alignment, or some mechanical issue at the antenna jack.



See above.



R-150 is a 0Ω resistor. It's essentially a jumper to the antenna connector. Reading continuity to ground can be confused by various coils in the circuit that will show a DC path to ground.



Yeah, don't. Seriously. Unless you have a $ervice monitor and the skills to use it, do not mess with the tuning values.
And you can't take tuning values from another NX-700 or TK-7180 and try to use those. Tuning values will be different from radio to radio.



Those won't impact your receive in your tests you mentioned above.




Yeah, don't. There isn't a "stock" tuning profile. Tuning profiles are specific to individual radios and based on a lot of factors like component tolerances. If someone before you tried to jam a tuning file from another radio in there that can mess things up.

It's not uncommon to find radios like this, especially in the ham/hobby world. Sometimes well meaning individuals will try to "fix" the radio, or boost performance by diddling with the tuning. Unless you have all the right equipment, you can't align a radio by ear, or by using a multimeter. The other possibility is that someone transmitted too close to this radio/antenna and completely smoked the front end RF amp.

If you've ruled out the obvious mechanical issues like the antenna jack, then there's not really a whole lot you can do unless you have a service monitor.

If you really want this radio to work, it would be worth the $150 or so to send it off to a Kenwood shop for alignment. A good shop will have a service monitor with the 'auto tune' function that will align one of these radios in about 20 minutes back to factory spec. If there's an issue, they'll find it.

Thank you for your advice. This is what I was hoping not to hear, but it is what it is...

Could the fact that I attempted to power it on with the wrong control head (that of a 7180H) have "smoked" the front end on this NX-700K?

What is the front end anyway and is it a replaceable part?


Thank you!

.

 

[mmckenna]

Thank you for your advice. This is what I was hoping not to hear, but it is what it is...

Yeah, sorry to be the bearer of not great news. Otherwise, those are solid radios. I have one installed in my wife's truck.

Could the fact that I attempted to power it on with the wrong control head (that of a 7180H) have "smoked" the front end on this NX-700K?

No.

What is the front end anyway and is it a replaceable part?

It's a complex arrangement of filters and an RF amplifier. It's not something you can replace easily. It's not simple soldering, this stuff is surface mount components that require very specific tools, magnifying glasses and an extremely steady hand. This is specialist level stuff done in a shop that is set up correctly for it. It's not something that most hobbyists can do.

Plus, if that -was- the issue (and it may not be), you'd still need to realign the radio afterwards. I have a service monitor at work with the software that will auto align these radios. I'm in about $55,000 USD.

So, your best option is to take a gamble and send it to a Kenwood shop. They'll try to align it, and if there is physical damage, they'll give you a quote on fixing it.

Bench time down here south of the border is usually $100/hour.

 

[762mm]

Yeah, sorry to be the bearer of not great news. Otherwise, those are solid radios. I have one installed in my wife's truck.

No.

It's a complex arrangement of filters and an RF amplifier. It's not something you can replace easily. It's not simple soldering, this stuff is surface mount components that require very specific tools, magnifying glasses and an extremely steady hand. This is specialist level stuff done in a shop that is set up correctly for it. It's not something that most hobbyists can do.

Plus, if that -was- the issue (and it may not be), you'd still need to realign the radio afterwards. I have a service monitor at work with the software that will auto align these radios. I'm in about $55,000 USD.

So, your best option is to take a gamble and send it to a Kenwood shop. They'll try to align it, and if there is physical damage, they'll give you a quote on fixing it.

Bench time down here south of the border is usually $100/hour.

Considering that the whole radio cost me about $100 all in and that I ended up with it entirely by accident, I'm not sure how to proceed on this one. Logic would dictate to find another unit and keep this one for parts... but there's a part of me that still wants to hear it work! :|

What I will do first is attempt to take this one apart, remove the motherboard and attempt to re-solder / re-flow the antenna connector and perhaps some other obvious solder points I see. I've once done this on a GMC Jimmy 4x4 switch and it brought it back to life. It turned out that the solder points developed micro-fractures as they aged, a common issue on these. The ABS modules fail in the same manner on these GM's as well : micro fractures develop in solder, mostly due to temperature changes. GM is notorious for poor quality electronics. It's a Hail Mary for this radio, but it's worth a shot.

Well, that's a bummer.... but thank you very much for having taken the time to explain everything in such detail.

 

[mmckenna]

What I will do first is attempt to take this one apart, remove the motherboard and attempt to re-solder / re-flow the antenna connector and perhaps some other obvious solder points I see. I've once done this on a GMC Jimmy 4x4 switch and it brought it back to life. It turned out that the solder points developed micro-fractures as they aged, a common issue on these. The ABS modules fail in the same manner on these GM's as well : micro fractures develop in solder, mostly due to temperature changes. GM is notorious for poor quality electronics. It's a Hail Mary for this radio, but it's worth a shot.

I've got about 50 or so of these same radios in the 800MHz version in garbage trucks, transit buses, police cars and utility trucks. Never had one fail.

I won't hurt to try, but don't expect a miracle. With these modern radios, all the real stuff is surface mount, and you won't be able to reflow that with a soldering iron without risking doing permanent damage.

Well, that's a bummer.... but thank you very much for having taken the time to explain everything in such detail.

Yeah, there comes a time to cut your losses. I suspect that $100 price tag is telling you something. Good radios like this usually go for $200 or so.

Maybe sell it as a "tech special" and tell the buyer exactly what's going on. Some hams do have service monitors and the hot air guns for doing surface mount stuff, and may be willing to tackle this.

I don't do component level repairs on any of my radios, just not worth the time, effort and cost of all the tools. Much easier/cheaper to send it to the professionals.

 

[762mm]

Update : I've opened one of my three 7180H's that I got from the same eBay seller (which all work properly, btw). I tested continuity on that same 0 ohm resistor on the 7180H and it does actually have continuity from the antenna solder joint to the other resistor leg on the working unit. The R150 on the NX-700K does not.

The leg of the resistor that enters the tiny hole on motherboard does have continuity to the aluminum radio body (ground) on both units.

My conclusion : the resistor on the NX-700K is probably damaged and the antenna doesn't have a proper ground. I will try to source a replacement and solder it in place.

Fingers crossed!


TK-7180H :

 

[mmckenna]

Update : I've opened one of my three 7180H's that I got from the same eBay seller (which all work properly, btw). I tested continuity on that same 0 ohm resistor on the 7180H and it does actually have continuity from the antenna solder joint to the other resistor leg on the working unit. The R150 on the NX-700K does not.

The leg of the resistor that enters the tiny hole on motherboard does have continuity to the aluminum radio body (ground) on both units.

My conclusion : the resistor on the NX-700K is probably damaged and the antenna doesn't have a proper ground. I will try to source a replacement and solder it in place.

OK, good job.

It's not really a resistor. In the world of surface mount type construction, it's easier for the automated machines to install something that looks like a resistor, but isn't. In the service manual, this is a "0Ω resistor". You could absolutely chase down that part and reinstall it.
Or, you can just use a short jumper of wire.

Just be super careful how much heat you put into that circuit board. They are not designed for hand soldering with a big ol' hardware store iron.

 

[mmckenna]

Before you get too far into this, you might try power up the radio with the lid off and using a short jumper wire touched to those two points to see if that helps reception. If it does, you know what to do.

If it doesn't, you can surmise that whatever shenanigans took out that 0Ω resistor/jumper did damage further down the chain.

 

[ojfd]

The leg of the resistor that enters the tiny hole on motherboard does have continuity to the aluminum radio body (ground) on both units.

Almost any radio is a 50 ohm transmission system. That means that most parts in the signal path are of relatively low impedance.
Impedance (at whatever MHz) is not equal to resistance at DC, when measured with multimeter set to resistance.
What you are measuring there is the resistance of 9,5 turns of wire (L116), which at DC is close to short.
By the way, do you know how to read schematics?

My conclusion : the resistor on the NX-700K is probably damaged and the antenna doesn't have a proper ground.

I don't think itš the antenna ground.
Just measure that R150 with your multimeter in both directions set to either R or diode test and see if it reads continuity.
If it does not, short the R150 with either a piece of wire or just with a tweezers and see if reception returns.

If reception returns, there's your fault. If it does not, either put you radio on the shelf for a better day or bring it to the repair shop.
Techs need to feed their families too.

 

[762mm]

Before you get too far into this, you might try power up the radio with the lid off and using a short jumper wire touched to those two points to see if that helps reception. If it does, you know what to do.

If it doesn't, you can surmise that whatever shenanigans took out that 0Ω resistor/jumper did damage further down the chain.

BINGO !!!

I did as you suggested. Jumped the connection with a piece of wire and BAM! The radio's RX came alive and the weather stations started coming in instantly, even the weak ones!

Should I just bridge it with a piece of wire permanently, or wait for my resistors kit to arrive...?

(I ordered a kit an hour ago on Amazon, should be here by tomorrow)

.

 

[762mm]

Almost any radio is a 50 ohm transmission system. That means that most parts in the signal path are of relatively low impedance.
Impedance (at whatever MHz) is not equal to resistance at DC, when measured with multimeter set to resistance.
What you are measuring there is the resistance of 9,5 turns of wire (L116), which at DC is close to short.
By the way, do you know how to read schematics?

I don't think itš the antenna ground.
Just measure that R150 with your multimeter in both directions set to either R or diode test and see if it reads continuity.
If it does not, short the R150 with either a piece of wire or just with a tweezers and see if reception returns.

If reception returns, there's your fault. If it does not, either put you radio on the shelf for a better day or bring it to the repair shop.
Techs need to feed their families too. View attachment 192525

Thank you for the help, as always!

Unfortunately, I never learned to read schematics. Everything I know is self-taught, typically by trial and error.

I have no trouble feeding techs and their families, provided that I can trust their work. The only two local tech shops for radios are very shady and will nickel and dime you for literally everything, even the time it takes them for answering e-mails with your questions.

I've dealt with them on a professional level while servicing our Kenwood UHF feet radios at work and adding a new repeater, very recently. As such, I'd bring the radio there as a last resort to get a quote. I can almost guarantee that their quote would far surpass the value of a used radio.

.

 

[mmckenna]

BINGO !!!

I did as you suggested. Jumped the connection with a piece of wire and BAM! The radio's RX came alive and the weather stations started coming in instantly, even the weak ones!

Should I just bridge it with a piece of wire permanently, or wait for my resistors kit to arrive... (I ordered a kit on Amazon) ?

.

I would remove the old "resistor" and use the jumper. If you already ordered the resistor kit, pack it up and return it as soon as it arrives.

 

[mmckenna]

Zero-ohm link - Wikipedia

en.wikipedia.org

 

[762mm]

Zero-ohm link - Wikipedia

en.wikipedia.org

Understood, thanks!

Question : Does the "zero ohm" resistor also act like a fuse, to prevent overload? As in blowing (like this NX-700K one did) instead of some other component down the line?

.

 

[ojfd]

Question : Does the "zero ohm" resistor also act like a fuse, to prevent overload? As in blowing (like this NX-700K one did) instead of some other component down the line?

Not necessarily. There are special fusible resistors out there, but I haven't seen one for HF or currents that are present in 25 or 50 Watt signal/power supply paths.
Just install the piece wire and be done with it.
Use solid wire, not stranded. At high frequencies wire is inductive. You don't want to introduce unneeded inductance there.

 

[762mm]

Update : I soldered in a small piece of paperclip to bridge the R150 connection (in lieu of the bad resistor).

She'd be kickin' !

 

[ojfd]

I soldered in a small piece of paperclip to bridge the R150 connection (in lieu of the bad resistor).

Paperclip is plated steel! Solder won't stick to it in the long term. Unless you used agressive, acid based solder paste for soldering steel. But then, if the board is not cleaned properly, the acid might migrate and corrode the board at some point later.
Also, intermittent contact at output stage, i.e. connecting and disconnecting load (antenna) when transmitting at full power might blow the output stage.
Just cut off one leg of the resistor that you don't need and use that piece as a jumper. What you need there is tin plated copper. Silver plated copper is even better at HF, but that's another story.

 

[762mm]

Allright, gotcha...

It didn't stick very well indeed despite the flux, so I filled it with a solder trace along the tiny piece of paperclip to make a nice and thick connection. The old resistor leg is so small and short, I barely managed to get a small drop of solder on it.

I don't have tin plated copper wire on hand, but I've ordered a spool. I'll figure something out in the interim, or perhaps just put in another 0 ohm resistor tomorrow and be done with it.

 

[762mm]

UPDATE : Ok, so got my supplies earlier today (resistors kit and Weller solder) and corrected that sucker, as per recommendations above. My Aliexpress solder with which I did the initial repair turned out to be quite horrible : lumpy, dark and flowed like crap. Barely good enough to get the job done. This Weller stuff flows like a dream, in comparison.

Anyway, not wanting to mess with putting in a resistor or wait for my spool of tin-plated copper wire that should be here in a month, I cut off a leg on one of the 500 resistors in my new kit and soldered a bridge between the two points. She works like she should. Not sure if it's just me, but the weaker weather stations sound even clearer now. I get 4 out of 7 stations breaking the squelch, whereas most of my other radios pick up 2 or 3 at most.

This NX-700 appears to have the best sensitivity among all my VHF mobiles. From completely deaf to best, now that's an achievement!

Thanks for your input, guys!


The final fix :




Amazon resistors kit :