Giday from the Blue Mountains in NSW Australia

[fiero128]

Radio Make and Model: Uniden 810e
PCB Number:
PLL Number: ??
Test gear available: Can't afford
Symptoms: No Tx Audio on AM

What is working: Adio on Q19 nothing into IC3

What has been tried: replaced TA7205 and Q19

Did it suddenly happen ?: Not mine, don't know
Anything else that may be of help?:

[lbcomms]

Is the RX audio OK? If so, measure / adjust the AM power.
If it is too high (10 to 15 watts) or stays too high (can't be adjusted) then the modulator transistor is shorted.
It's a PNP power transistor in a TO220 case, usually somewhere near the finals.

Failure of this transistor is very common in all Uniden SSB radios.
Easy to spot, on AM there will be 13V on the "tabs" of the finals during AM transmit, you should have 6 to 8 volts on them, depending on what you set your AM power to. The part will cost $5 to $10, a good shop will charge you $45 to$75 for the repair.

replaced TA7205

If that part is bad, there will be no receive audio.

Cheers

[fiero128]

the RX audio is fine,
this pe810e SSB radio is perfectly OK on SSB
I have repaired FM commercial radios for the past 20 years but i have never come across this fault

[lbcomms]

this pe810e SSB radio is perfectly OK on SSB

I mentioned AM power, not SSB! When this fault happens, the RX on all modes and SSB transmit are OK.
Only the AM TX is affected.

I have repaired FM commercial radios for the past 20 years

You said earlier you couldn't afford test gear (like a multimeter) and you didn't know the audio output IC is used on RX (you already stated the RX was OK and you replaced the IC anyway). From that I assumed you were very inexperienced and now you repair commercial FM two ways?

but i have never come across this fault

You obviously haven't repaired many AM/SSB radios then... the 3 most common faults with these are:
1) Reversed polarity be owner, blowing diode
2) Shorted modulator
3) Blown (open) power semis, such as audio or RF output devices.

Modulators going short are very common in Uniden SSB radios. I've repaired hundreds of these, if not thousands, in the last 15 years. At one stage we were averaging 3 a day...

I have repaired FM commercial radios for the past 20 years

I'll assume you have some RF knowledge and a multimeter (at least) then.
On AM transmit (meaning put the rig into AM mode and press the button on the microphone all the way in), what DC voltage do you have on the little mounting tabs of the driver/final transistors (with the black multimeter lead connected to the negative of your power supply)?

You should have 6 to 8 volts. If you have anywhere from 11 to 15 volts, your modulator transistor is shorted.

Good luck
Sue

[fiero128]

its now working fine
found short in Q37 , thats up near the regulator . On the other side of the PA transistors.
As for test equipment , yes I have a Multimeter and a CRO but nothing to monitor the output Audio for a bench
I found it worked by asking my wife to talk on it while I go to the car and listen to the radio on the car.
I can't afford a sig gen or a comms alalyzer is what I mean't