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Palomar 150watt bi-linear amplifier for c.b. radio-won't transmit

This RF amp. used to dead-key 3watts & swing to 150watts pep. Now, the unit is turning on,lights are working,pre-amp. is working. But when I key up my c.b., (dead-key set at 1watt) the relay inside of the amp. engages, But won't put out anymore than 1watt. I did find a snapped resistor(470 ohm) & replaced it,but didn't solve problem. Can you steer me in the right direction,to bring this ''SCREAMER'' back to life? Mark Hopkins

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  • markhopkinsj Jan 06, 2009

    Dear trapsenault: After I replaced the snapped resistor, I found a crack in soldier leading to "pill". Unit is back to being a "SCREAMER". Thanks markhopkinsjr47@gmail.com

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3W to 150? Now you got 1 W in and 1W out and a snapped resistor. I would look at the driver and or final, either something heated up bad and cooked the resistor or you might have a break in the pcb.

Good Luck, Tom

Posted on Jan 02, 2009

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The radio is either stuck in transmit or the RF power output section has a short in it. If there is no RECEIVE audio and the squelch is open, and the radio is not in transmit, the chances are pretty good that the audio power amplifier is shot.

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Now, if when you remove the squelch you hear the hissing but you still cannot hear transmitting from your other radio, it could be that the one transmitting is in fact NOT transmitting an not that the other radio cannot hear. You have checked that both radios can or can not hear someone else's radio right?

Assuming you do know that one radio cannot hear what the other can and make no sound other than hissing when the squelch is off the problem is either in the RF or IF sections of the radio's receiver. In general this used to be a more complex repair so let's go another easy fix by going to the very first place the RF comes in, the antenna.

Just like the audio section when a speaker wire is disconnected sometimes the wire or trace going to the bottom of the antenna can become disconnected or broken. To check this bring a good transmitting radio very close to the one that hisses but does not hear the transmitting radio and see if any place as close as you can get the two radios causes the non-hearing radio to hear the transmitting radio. If so, then look for a problem with the antenna connection.

If none of these easy things bring the problem to heel then there's probably something amiss in the RF or IF receiver sections. If the radio has one or two chips that do all the work here then see if you can get both and replace them. I haven't even taken apart my own small FRS radios to see how complex the receivers are in these so I won't go any further than that since I simply don't know your radio.

I hope that helps.

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The major problem with water in RF circuits is that even after it dries out, it leaves a residue, or worse still some corrosion, which adversly affects the tuning of the RF circuits.

It may be worth trying to dry it out a bit more - put it somewhere warm but not humid like near but not too close to a central heating boiler, for a few days. However, I suspect it is now beyond repair.

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1 Answer

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Your next problem is that if the radios have been used often enough with a faulty antenna circuit, your final amplifiers are probably toast from transmitting into an open antenna circuit, causing all the power to be reflected back into the radio and burning out the final amplifiers

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Longshorts.

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