Hello Radionecks!

I was out of scene for two years and now i am back again!

I got a transmitter from ebay. It is a 12 watt new condition old stock transmitter boxed.

http://m.ebay.co.uk/itm/281867965155

The problem is that i tried to work it with 12v instead of 13.8v having set the freq jumpers inverted! the ons to offs and offs to on!!! for a minute. It was of type press to on off and not move to on off. I thought the upper position is the desired but is the pressed position the desired.

Then i tried with 15v for seconds with the amp pot turned to about 4 watts.

It was Sunday -- most damages occur in Sundays!!!

The other day I got a 13.8v 2a meanwell ps and tested again.

The problem is that the pll board not giving enough drive for the amp to work. The pll drive light is not going on. The heatsinks of final transistors look like having some temperature but probably not enough output.

Also the rf output led is not lighting.

A pitty because it was a great bargain at only 85 pounds boxed shipped and new!

The stereo coder and pll driver working fine locking and getting sound at desired frequency but no rf output i suppose only a few mw because i have no reception after 10 meters.

The pll drive led is not turning on. Also the amp output led light.

The pll board is the easy tune pll3 version released in 2000.

The sound even with the cheapo stereo encoder inside it is very good to excellent. They are right all people saying the sound quality in these drivers is so good. I would say it has a relaxed modulation if these words make any sense.

Sorry for the "i have a problem" post as first post but you understand when a problem occurs probably due to your mistake you need help.

Any thoughts or ideas to make it work as it should?

Sounds like the PLL's output transistor has blown. (2n4427??)

Novaro wrote:Hello Radionecks!

I was out of scene for two years and now i am back again!

Clearly not! If your rig is dead ; )

teckniqs wrote:Sounds like the PLL's output transistor has blown. (2n4427??)

Thanks for your reply.

I will try. It seems that the 2n4427 which is before the final tr7 pt8860 is working but the pt8860 is stays cold during operation.
The problem is that 8860s are pretty rare now. I will try a 2n4427 for final to see what happens.

Is the unlock light flashing? Have you tried turning the frequency trimmer to see if it gets lock? I don't think this will produce any power until its locked...

Analyser wrote:Is the unlock light flashing? Have you tried turning the frequency trimmer to see if it gets lock? I don't think this will produce any power until its locked...

Analyser thanks for the reply .

The pll locking ok using the variable capacitor VC1 and is passing stereo sound ok. The problem is probably with the Rf stages. I have to dissasseble all the unit to replace the two final transistors.

Sounds like the final's popped. If you can't source the TRW PT8860 there's plenty of alternatives and personally I'd recommend something with a bit more output (30-50w) with the same sort of gain so it does about the same power output but a less likely to flash out.

Hello Mr Navaro!
If i was you? id do some more testing before you start replacing transistors!
maybe you could disconnect the PA from the driver board and check that the driver is doing what it should on its own? then proceed with the PA!

sinus trouble wrote:Hello Mr Navaro!
If i was you? id do some more testing before you start replacing transistors!
maybe you could disconnect the PA from the driver board and check that the driver is doing what it should on its own? then proceed with the PA!

Good advice Sinus. It's better to test each stage on its own and verify it's working than replacing stuff to see if it fixes the problem. Although Teckniqs is probably right, you need to adopt a methodical approach (and you learn more in the meantime).

Yeah I wasn't suggesting you just started replacing everything until you get it working again. Simply disconnect RF from exciter to the PA and connect the exciter straight to your meter/DL to see if your getting correct power output.

When you power on does the unlock led start to blink then go out with the lock led now illuminated and the unlock led fully off.

I was in no way doubting you Mr Teck! And you would carry out the same tests as i would before reaching any conclusion!

The thing that concerns me straight away is Mr Navaro stated he used 13.8v 2A PSU?
the Pa would probly Draw 3/4s of that alone!
After looking at the Ebay listing, It says atleast 2.5A is needed!
As we all know, An amplifier is only as powerful as its Power supply!

Lol apologies for spelling your name wrong (twice)

sinus trouble wrote:I was in no way doubting you Mr Teck! And you would carry out the same tests as i would before reaching any conclusion!

The thing that concerns me straight away is Mr Navaro stated he used 13.8v 2A PSU?
the Pa would probly Draw 3/4s of that alone!
After looking at the Ebay listing, It says atleast 2.5A is needed!
As we all know, An amplifier is only as powerful as its Power supply!

I was also thinking of that.
But with the amp trimmer set 1/3 of full is giving only 3-4 watts.
At 4 watts output the amp is not very possible to draw more than 2amps.

teckniqs wrote:Yeah I wasn't suggesting you just started replacing everything until you get it working again. Simply disconnect RF from exciter to the PA and connect the exciter straight to your meter/DL to see if your getting correct power output.

I will disconnect the exciter board and connect directly to aerial. I don't have an swr meter at the moment.
The RF stage of exciter has two transistors one 2n4427 and one TRW as final. If only the TRW is broken then alone the 2n4427 would give 100mw output enough to get reception 200 meters with aerial connected. I believe more possible that at least the 2n4427 is broken. Thats why my output is only from bf494 of previous stage only a few milliwatts in value.

sinus trouble wrote:Hello Mr Navaro!
If i was you? id do some more testing before you start replacing transistors!
maybe you could disconnect the PA from the driver board and check that the driver is doing what it should on its own? then proceed with the PA!

Thank you!

You are right! I have more possibilities to make more damage than to fix it!
When i first set the freq (in the opposite order ons to offs and offs to on position) i remember i got light from the DRIVE POWER led!

If i disconnect the rf input of amp module will i have to disconnect the power from it also? Is OK for the amp to work without rf input?

The drive power led is from the exciter so this should be lit if your getting rf from the exciter around 900mw, even if you'd fried the power amplifier output transistor the drive power led would still be illuminated, so if the pll cicuit is locked with the lock led light on and the drive led is still not lit, remove and test the 2n4427's on the exciter with a multimeter before doing anything with the power amplifier.

Novaro wrote: Is OK for the amp to work without rf input?

Usually, but to be safe disconnect the power to it as I've known transistors to flash without any drive like 'N's' S-ony Digital (BLF244).

Novaro wrote:
When i first set the freq (in the opposite order ons to offs and offs to on position)

Sorry Mr Novaro? Im not sure what you mean? The DIP switches??

I am totally confused now. The only thing I can think of at the moment is that the Ebay listing said this item was new, therefore one would have thought everything was working. If the OP has no power meter and only an aerial to test, where do you start????