Problem with Elit TMF 4C20/final transistor burned?

[BlackBeard]

Hi folks,

I connected the antenna, tried to power up the unit (Elit TMF 4c20), but the only output I get is 0w on the power meter on-board. The other inputs (audio signal strength, etc.) are measured correctly. Yesterday, I could still receive the transmitter's signal on the right frequency it was tuned to, the power meter still showed 0w and the audio input wasn't transmitted - only the carrier (silence). I changed the dip switches to another freq and tuned the filters, but now I couldn't receive anything. Looked inside, nothing seemed to be wrong or burned, also not the output transistor. The PLL light on the front of the transmitter was not on though.

I also don't know if the BNC-cables are connected right, but that's how the seller sent it to me.

Maybe the final transistor is burned? Looked normal though.

[3metrejim]

When testing it's best to use a dummy load, to eliminate the chance of a faulty antenna and unintended transmission. The cable connections look like two outputs are connected together (circle with arrow coming out) so I'd disconnect it to start with while testing. At a guess those connectors look like two output options and an input - did you mention it had an internal stereo coder before?

You're probably going to need the service / alignment manual to figure out what is wrong or get an electronics engineer in. If something doesn't work, then twiddling any internal parts is the worst thing you can do as you will definitely need some kind of instruction / knowledge and test equipment to get them back to the right place. CB'ers used to twiddle and then have to send their rig somewhere for it to be repaired when they eventually messed it up.

If you need remote fault finding on here, then you'll have to have a diagram of some sort to work from and an internal view for identifying parts of circuitry to test.

[Krakatoa]

You mentioned the Pll light is not on after changing the frequency on the dip switches? It may need tweaking of the vco section also. But without detailed manual, it will only make matters worse if fiddled unknowingly.

[yellowbeard]

3metrejim has the right of it there, you have two outputs attached together on that back panel - have a look at the patch lead on this:
https://i.ebayimg.com/images/g/fEoAAOSw ... -l1600.jpg

[Marcel]

No probably not.

Usually it is a pre-driver that can cause problems.

I may have the complete service manual, first check to what extent the transmitter does with a coupling loop and a spectrum analyzer, then we can look specifically how or what.

Good luck.

[Marcel]

Completely forgot you need an extender to service the elit.

I can possibly post a photo of the original (service) extender.

[BlackBeard]

Okay, my fault. I managed to get that thing running. I connected the bnc jumper as shown in the picture (after 3metrejim mentioned that and I found it already suspicious to connect two outputs together). My mistake was not to turn the potentiometer for the power on high enough.

The PLL-light is still not on (it goes on for a sec in the beginning and then off). Frequency is stable though and setting the DIP-switches works.

RDS-insert also works the way 3metrejim proposed in a thread before. Thank you!

Also I noticed, that the tx is not outputting it's full power (150w) rn only 80w at 90.5 MHz at an SWR of 1.4 and 2w reflected power. Do I need to tune the antenna better? It's standing outside of course.

Finally, the potentiometers are not stopping on the right side, so you can basically turn them 360° over and over again. That goes for all of them. Are they some kind of special ones?

[Marcel]

The potentiometers on the left/back side of the module are for the ALC range and protection.

This type of transmitter is made for 100W output, but then you have to adjust both philips teflon trimmers in the module and you need the service extender for that.

I myself think that this repair / modification(RDS) will not end well because you lack the knowledge and experience.

Regards,
Marcel

[BlackBeard]

The potentiometers on the left/back side of the module are for the ALC range and protection.

This type of transmitter is made for 100W output, but then you have to adjust both philips teflon trimmers in the module and you need the service extender for that.

I myself think that this repair / modification(RDS) will not end well because you lack the knowledge and experience.

Regards,
Marcel

Thank you! I didn't mean those potentiometers on the left/back side that you mentioned but the adjusting screws that are on the front of the module (power output, SCA level, input levels, etc.).

Probably not easy to get the service extender for that model, I guess?

Also, the seller actually showed me how he set the power to 100w, probably on a dummy load. That's why I'm confused - he showed me photos where everything was already tuned/set to 100w.

[mikroman]

it is a very old device, therefore there is a possibility that it is not a broadband design. for this reason, you cannot get full power by changing the frequency. the only correct way for a correct setup is to either find a service manual or some veteran to help you

[mikroman]

update.....Ctedb is the legal successor of Elettronica Italiana SpA. Contact them by e-mail and check whether it is possible to send the necessary documentation from the archive.

[BlackBeard]

update.....Ctedb is the legal successor of Elettronica Italiana SpA. Contact them by e-mail and check whether it is possible to send the necessary documentation from the archive.

I actually tried that already but got no reply to my e-mail to the info-line - I wrote it in English though. I'll now try to contact the technical support via Whatsapp in Italian, using Deepl Let's hope for the best. If I can aquire it - I'm even willing to pay lol - I'll post it here.

Edit: It seems like they've been merged into a new company: Teko Broadcast. Either that or Teko is part of CTE DB SRL.

[mikroman]

I had a good experience with Elettronika Bari. I needed papers to service an ancient device from the past millennium . For a fee of a few euros, they sent me everything I asked for. I hope that the business practice is similar in CTE/whatever it is called now. Good luck!

[BlackBeard]

I had a good experience with Elettronika Bari. I needed papers to service an ancient device from the past millennium . For a fee of a few euros, they sent me everything I asked for. I hope that the business practice is similar in CTE/whatever it is called now. Good luck!

They replied to my Whatsapp message. Sadly, they don't have the manual/papers anymore.

Marcel, do you maybe happen to have them? I'd even pay you, if you could send them to me.

[Marcel]

This week I will post a schematic of the part that I have had more problems with that resembles your problem.

The manual is comprehensive and complete with large fold-out pages, but do take a photo of the piece in question.

[BlackBeard]

This week I will post a schematic of the part that I have had more problems with that resembles your problem.

The manual is comprehensive and complete with large fold-out pages, but do take a photo of the piece in question.

Great! Many thanks!

I don't really know which piece might be not working. When I looked inside (I didn't tear it apart completely, just opened the top) nothing looked burned or wrong.

What I can say: The PLL light is not turning on - goes on for a sec after turning the tx on and then goes off. I turned up the power to max on the front panel. The transmitter pushes out 75w to a dipole with an SWR of 1.3. It should do 100w. The stereo coder is working and putting out the 19kHz pilot. The SCA-in is working. The meters are working.

What I'd like to know (if that's written in the manual): How can I tune the transmitter/the Phillips teflon trimmers correctly and what equipment do I need for that (service extender?). Then I can pass that info on to someone with more knowledge than me.

[BlackBeard]

What I forgot to say: The seller tuned the tx to 89.3 and on this freq it was definetely putting out 100w to a dummyload. That's why I guess it's working properly and just a question of tuning.

I changed the freq to 90.5 and also the filters according to the numbers/frequencies written next to them.

[jvok]

Are you testing into a dummy load or an antenna? The low power could be cus the antenna isn't matched properly. I'd buy/borrow/steal a dummy load and test on that before deciding anything is wrong. Or at least put an swr meter in line with the antenna and check the match is 1.1:1 or better.

Also are you sure the pll light is meant to stay on when its locked? Could be the light is meant to show when its making a correction and will go out when locked. But without a manual or at least a schematic we'll never know.

[BlackBeard]

Are you testing into a dummy load or an antenna? The low power could be cus the antenna isn't matched properly. I'd buy/borrow/steal a dummy load and test on that before deciding anything is wrong. Or at least put an swr meter in line with the antenna and check the match is 1.1:1 or better.

Also are you sure the pll light is meant to stay on when its locked? Could be the light is meant to show when its making a correction and will go out when locked. But without a manual or at least a schematic we'll never know.

I'm testing into an antenna (SWR 1.3), I'll get myself a dummy load and then I'll see. The seller sent me pictures of the unit putting out 100w into a dummy load - so it should be possible.

I also have a NanoVNA for antenna tuning.

[mikroman]

about pll indicator, as i can see on photo, it is red led on front pannel. jvok wrote well. when the pll loop is reached, the red led indicator turns off. A banal thing, but it needs to be repeated from time to time, the red indicator on equipment regularly means that something is out of the norm or fault.