NX-800 No Receive Audio

[kenwoodgeek]

Hey, everyone. It's been a minute.

Got a pile of dusty radios from one of our closing locations to fix, toss, or keep for parts.

On one of the NX-800Hs, I am getting no audio on the receive side. The radio transmits and receives perfectly fine. The speaker works, as I get the power on tone, PTT side tone, and key press beeps. The LED illuminates green and the LCD shows full signal strength. Microphone is off the clip, DPL decode tone is set correctly in the codeplug. Just absolutely no audio when receiving.

I'm sure there is a failed component somewhere in the radio, but what would it be? I have several boards from these radios, and I'd like to see if it's an easy solder job. Thanks!

 

[mmckenna]

I'm not in front of a computer that had KPG-111, but check the settings under the "Extended Function" tab.
Specifically look where rx audio is routed.

 

[kenwoodgeek]

I took a look at those settings, and I did not see anything about RX. This is a known working codeplug, however, that I'm using on all the other radios (just different IDs). That's why I assumed an internal issue.

 

[kenwoodgeek]

Alright, so I just did two things. I put the radio speaker right up to my ear and took a listen, and I also plugged headphones into the external speaker jack with the volume way down. In both situations, every time I keyed my portable, I heard a very faint white noise, and even fainter, the FleetSync ID bursts from my portable. The received audio is coming through, but it's nearly silent. Not the radio tones, though. Those are normal volume. I'm going to look at the service manual and see if I can find what component on the board might be causing the issue.

 

[mmckenna]

If this radio had the KAP2 speaker/relay interface installed at one point, it could be the jumper setting is wrong.

If the KAP2 is no longer installed, there needs to be a jumper across pings 2 and 3 on CN705 to pass audio to the speaker jack/speaker.
If the jumper is there, then suspect something wrong with the audio amp IC715.

A brand new radio will come with a white jumper on CN705 with those two pins jumpered. It gets removed with KAP2 is installed. If KAP2 was removed and the jumper not reinstalled, then audio won't get to the speaker jack/speaker. The tiny bit you are hearing my be bleeding through.

If you do have KAP2 installed, there's a jumper on that board for passing audio to the internal or external speaker.

 

[kenwoodgeek]

The jumper is in place. If I remove it, of course, I get no audio at all. When I plug it back in, it returns to the way it was. Like I said, the power on and key press beeps as well as the sidetone when the radio is keyed all sound normally at full volume.

It's just the received audio signal that is silent. Could this still be an issue with the IC715, or could it possibly be an issue in the RX circuit? I would think if the audio amp was bad, I wouldn't be getting any sound at all.

 

[mmckenna]

The jumper is in place. If I remove it, of course, I get no audio at all. When I plug it back in, it returns to the way it was. Like I said, the power on and key press beeps as well as the sidetone when the radio is keyed all sound normally at full volume.

Oh, right, forgot you mentioned that above. I thought I was on to something….

So, not the jumper, and not the audio amp IC.

It's just the received audio signal that is silent. Could this still be an issue with the IC715, or could it possibly be an issue in the RX circuit? I would think if the audio amp was bad, I wouldn't be getting any sound at all.

Yeah, unlikely it's the audio amp. Probably something in the receiver. If you've got a pile of these, it's probably not worth spending too much time on. Not really anything serviceable in these radios. Only option would be to put it on a service monitor to see if it's way out of tune.

 

[kenwoodgeek]

Thank you, Matt. Yeah, my company has thousands of these things floating around. Thankfully, there's an abundance of spares right now. In the same lot, I got another 800 with a wrecked chassis (mounting screws snapped off in the holes and someone attempted to make new holes but failed) but was fully functional. I tore that one apart and swapped the entire TX/RX board into this unit. She's working like new, and I have another bag of spare parts.

 

[mmckenna]

I got another 800 with a wrecked chassis (mounting screws snapped off in the holes and someone attempted to make new holes but failed) but was fully functional.

Oh, that's a pain. Someone likely using an cordless drill/impact driver to install mounting screws. I've run across that before. They make for good base radios...

 

[AM909]

Or, after snapping off the head of the screw (2 on the same radio!), they drill a new hole near by, right through the receiver front-end :|

 

[EWC_BDN]

On TK8302 if you lost your M4 screws and just used what ever length screw you could find. you would drill right through the Speaker audio trace.

 

[kenwoodgeek]

What I've found with these radios is that it seems the mounting screws are very poor quality.

Unfortunately, I learned the hard way a few years ago when I went to tighten one into a radio with a socket/ratchet and snapped the screw head right off. I guess unless you are extremely skilled, there's no getting that screw out. Now, I am extremely careful when I go to install the radios in the brackets. Just a little snug is more than enough. The other thing I have to be careful of is removing the screws from a radio that's been installed for years. If they were over-tightened, abrupt loosening with a ratchet will also snap off the heads. I've snapped off one or two additional screws just trying to loosen them.

As you said, Matt, these radios are great for just sitting on a power supply as base units. When I come across a unit with 2-all holes unusable in my company, I hold onto it and wait for another unit, like this one, with a board failure to pop up, and I'll put the good board in the good chassis.

 

[mmckenna]

I've run into that. One of the issues when a mechanic starts messing with radios is that they'll use the tools they have at hand, not necessarily the right ones. Installing bracket screws with a ratchet is pushing your luck. A nut driver will work just fine. Vibration usually comes from improperly installed mounting brackets, not the radio screws.

Drilling out those small screws is a pain in the butt. It's easy to mess up.

I had an Icom F-221 UHF radio that I accidentally broke a screw off of. I used it mobile, and it did fine with 3 screws. When I went to sell it, the buyer was going to use it as a base radio, so not an issue.


On the flip side, I've had some radios where the threads in the radio chassis were stripped out by the installer. Not much easier to fix.

Motorola had a good way of handling this years ago. Their radios used a thumb screw. Other than using a pair of pliers, there was no way to over tighten them.

 

[AM909]

...

Motorola had a good way of handling this years ago. Their radios used a thumb screw. Other than using a pair of pliers, there was no way to over tighten them.

Good idea. I forgot about that. We had a taxi company whose mechanics did their installs. After a bunch of problems of this type, they bought a bunch of thumbscrews somewhere and insisted on using them. Problem solved.

 

[wd8chl]

Yeah, the problem isn't the screws, it's the gorilla's putting them in. I have a 7mm nutdriver specifically for Kenwood screws. I also have what I guess is called something like ratcheting box end. It's basically a box end wrench that has a ratchet built in, good for tight spaces. Even that is only about 4 inches long, and you don't want to over tighten it, but that's universal for any radio. I've seen plenty of Moto screws get broken off just as easy, and just as hard to get out.
People use drill-drivers far, far too often, and they need to be told to stop.

 

[EWC_BDN]

never considered this, but are those Kenwood screws JIS? I know Phillips Sucked on them. Like I always used a 7mm because the Phillips looking end was so bad.

Anyone tried a JIS screw driver on them to see if it works better?

 

[mmckenna]

never considered this, but are those Kenwood screws JIS? I know Phillips Sucked on them. Like I always used a 7mm because the Phillips looking end was so bad.

Anyone tried a JIS screw driver on them to see if it works better?

I'll have to try, but I always used a nut driver. Just easier all around.