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Uniden 980 not transmitting

C

coolray

New Member
Apr 16, 2015
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florida panhandle
I just got my Uniden 980 back from the shop. I had it peaked and tuned. I have a megawatt 36 amp power supply powering the radio and the silver eagle 200 linear. I brought it all to the guy to set it up for me.
I got good reports yesterday, but today no one could hear me. I checked all the things I know to check, cb/pa switch, connections, all of that. The Mic works, it worked on the p.a. feature. I think the output finals may have blew. Is that what it is? Is it an easy fix that I could do myself or would o need to take it to the shop? Any help would be appreciated.
 

The finals in those radios are very weak ones. If you'll do some research you'll see that even stock they can blow with a long winded conversation. I set my radio wattage back to 10 watt pep on SSB and 2 watt dead key on am swinging to 4-6 watts. Plenty to drive a small amp. Or even a larger one. Take it to a shop if you don't have the proper test gear. The radio will need to be re tuned. Like I said do some research. You don't need a bunch of watts to make the amp work and the extra 4 or 5 watts you get out of the radio just makes more heat and not really a squat of difference to the receiveing station. JMHO.
 
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All you said was no one could hear you but no mention of having a watt meter inline and showing zero output. With the amp off and out of the tx chain does the 980 show any output on AM?
 
Ok, the Mitsubishi RD16HHF1 RF mosfet can be had here, 2 for ten bucks:
http://www.kitsandparts.com/transistors.php

I've purchased several times from these folks and have been very pleased. I have 4 of these mosfets on hand for my 980SSB. ;)

You can probably get it for around $4.50 from RFParts, but you have their $20 or $25 minimum order to contend with.

Replacing this device does take a decent soldering iron and some skill, I can elaborate further if there's interest.

Here's the concern though: I know from my work that a lot of switching-type mosfets will fail shorted from drain to gate. (dunno yet about RF mosfets) This means that if it fails in this manner, you will have your supply voltage dumped onto your driver device, likely taking that out as well. I do not know if this is the case with a blown final on the 980.

--->There is likely a good reason these radios come from the factory only doing 3W d/k! <---

I saw somewhere on these forums where a guy added an external heat sink on the back of his 980, just by adding a longer 4/40 screw. This is an excellent idea.

If there is interest, maybe later this weekend I can post a how-to on how to test a mosfet with a DMM set to the diode-test function.

Good luck,
807
 
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Disconnect the amp and run the radio through a wattmeter to the antenna or dummy load, make sure you are in AM mode and key the radio. Is the meter on the radio showing any output? Make sure it's set to show rf out.
 
Why not take it back to the shop who peaked and tuned it instead of buying new transistors. If there a legit problem just 1 day after the peak job he should fix it instead of investing more time and money.
 
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also if you were using one of those cheap truck stop meters you could have blowed the meter with the extra power of the amp assuming you put power in the meter. Some meters only are good for a hundred watts.and It's possible that no one is coming back to you today just out of luck. That happens sometimes. Is it Possible you're checking RF power in SSB mode?
 
AL567 said:
also if you were using one of those cheap truck stop meters you could have blowed the meter with the extra power of the amp assuming you put power in the meter. Some meters only are good for a hundred watts.and It's possible that no one is coming back to you today just out of luck. That happens sometimes. Is it Possible you're checking RF power in SSB mode?
Click to expand...
I was checking it in am mode. Thanks for the replies gentlemen. I'm going to take it back to the shop but I wanted to make sure it wasn't an easy fix before I drove an hour there and an hour back.
 
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I had a 980 that stopped transmitting after 6 months. I ran it straight into my IMAX 2000 with a 1.18 to 1.3 SWR across CB. There was nothing else in line except an occasional SWR meter. No linear ever! It sounded great one day. It had no RF output the next. If you look across the internet, you'll see a few too many similar stories.
 
Yep, like 330 said, there are a lot of stories of this happening, thus the reason for turning the output down instead of up!! The heat sink or a fan idea is a good one even on a stock radio, a must for a tuned one. Best to have the driver and final upgraded if you plan on running more than stock power or lower. JMHO.
 
807losangeles said:
--->There is likely a good reason these radios come from the factory only doing 3W d/k! <---
Click to expand...

I forgot to include with this: If you dig through the data sheets on the "classic" cb final PA devices, you'll see that they mention that they have some sort of high-SWR protection, they can just eat that return SWR and dissipate it as heat. You've probably keyed up an older CB a bunch of times saying "WTF is wrong with this POS?" Then realized the coax was disconnected, etc. and the radio was fine afterward. This Mitsubishi mosfet, and your typical IRF520-type device have no sort of protection built in.

Cheaper, better, faster, pick two. :)

807
 
Rick330man said:
but a CB radio isn't rocket science, or is it?
Click to expand...

Wrangling pocket-protector engineers, "un-effing" manufacturing, and delivering within budget are universal headaches anywhere "stuff" gets made. I think despite being pretty darn cheap and made in China, the 980SSB is a heck of a radio. I'd be interested to hear from someone who's installed one in a pickup truck or a jeep that gets hammered down dirt roads, to know how well the thing holds together under physical stress.

I clearly need to work harder at keeping my twin personalities separate, oops. ;)

807
 
For the money they are not a bad radio at all. Just don't turn the power up. Leave it stock and even sticking a heat sink or fan on the rear will help. Like said the cheap transistor used in the radio isn't very rugged and will blow with high VSWR readings and power. With mine tuned back to 8-10 watts SSB and 2 watts am swinging to 5-6 watts it works. Clean, clear audio. No drift on SSB, and was on freq out of the box. For the money what more could you ask for. They aren't a powerhouse but they do have clean audio. Just my experience with the one I have.
 

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