What happens when you "burn out your finals"?

[LavaLight]

That's about as simple as I can make it. I keep hearing about "burning out your finals" if you do this or that incorrectly. What exactly would one hear (or NOT hear) if something fried up inside your radio?

I've got a year old Uniden PC78 Elite that I use in a slipseat box but in the same tractor with a Wilson 5000 antenna and 18 ft of quality coax.

I'm having a problem where I'm periodically getting incredibly bad reception/interference even when the vehicle isn't running. It's not an antenna issue and it's not a power source/grounding problem. I took the cb/FM radio set up out of one slipseat box and put it in another box which is more plastic than steel. But even if the steel box acted as a noise shield, it couldn't possibly sound this bad, could it? I'm stuck and I've tried to do my homework before I came running to you all for help.

One minute I'm listening to clean, clear transmissions and I can reach out pretty good (I"ll ask for a call back to verify I am getting out there) and the next I'll get static/interference like crazy and I can't hear/transmit more than a few blocks. Sometimes it can last just a minute or two and sometimes it will go on for days until it just kinda stops and begins working correctly again. . When it works, I don't even need to turn the squelch at all. I almost need to look to see that the radio is on, it's that quiet. When it's on the fritz, squelching it out makes ALL transmissions go away becasue I need to crank it up well past the half way point.

Either my radio is working perfect or it's so fuzzy/grainy sounding it's unlistenable.

Suggestions?....everybody else in the yard just says "you may have burned out your finals" and none of them know what the hell they are talking about (kinda like me) and that's how I found this place

[Gadfly]

If you are still talking, you haven't "burned up your finals". That is an "either-or" situation and there's no in between! That phrase means that you have popped the final output transistor (PA amplifier, etc) in your transmitter. This occurs from overstressing the transmitter either by turning the PA UP trying to get more power out (BAD idea!), or excesssive VSWR caused by a mis-tuned antenna, or by trying to operate WAY outside the antenna's design limits. (Such as trying to talk up in the illegal 10 Meter band).

Distortion in the transmitted signal is another issue not likely related to "popped or burned up" finals.


Gadfly

[LavaLight]

I took it home this weekend and put it in my 4 Wheeler, with a mag mount 'Lil Wil so that changes the vehicle and the coax...and I'm getting the same results. I KNOW the engine noise from my little Ford 4 cylinder isn't creating this much disturbance. It sounds like I get "bleed through" from the surrounding channels in addition to tons of white noise that doesn't increase with stepping on the gas pedal.

Is it possible that the radio has been knocked around so much in the lat year or so something could have broke off/shook loose? I run some pretty bumpy roads (potholes this winter in the urban area I drive in have shook the fillings in my teeth loose) so if a radio is jarred hard for long enough can it become unusable?

Could I have broke/loosened/burned out a transistor or diode internally? I unscrewed the cover plates this morning just to take a look and nothing was rolling around loose but that is the extent of my expertise

This has been a great radio for the last year...is it time to bite the bullet and just get a new one? I'll go nuts if I spend the money and the new radio does the same thing but I know I assembled and connected everything into the slipseat box as it's supposed to be done.

[danc694u]

It's possible you've gotten some stuff shaken loose.

Shielding can get worn out from the vibration, and cause a ground issue.

The shielding I refer to, is typically rubber or cardboard spacing between points of contact within the radio itself.

Have it looked at by a competent radio guy/gal. They know what to look for.

[Double L]

When you say PA do you mean the rf power,rf gain, and mic gain? I have all three of them turned all the way up.

[Dave27107]

Since you have tried the radio in a different vehicle, with different antenna and coax, and still have the problem, my guess is there is an internal problem with the radio.

[Red Fox]

It sounds like the internal antenna connection COULD be at fault, and that's one you can check yourself. Look VERY closely at the solder with a glass...if you see hairline cracks, get out your trusty soldering gun and hit that sucker to reconnect it. (shouldn't have to add solder, just wet it)
Otherwise it could be the oscillator, but I think that just messes up the frequencies...but you said you have bleedover, so it could be. If it's the grid, it's toast for the most part, unless you have a really good mechanic. IME, many truckstop mechanics are hack artists, and take shortcuts to do things like strapping a radio instead of adding crystals to add channels, or other little whippy things for peaking or repair.