The Dittel FSG71M becoming old and tired  A very nasty intermittent problem, as radio checks on the ground were always OK. Soon after launch, reception would seize. Transmission would still be working OK. But intermittently the radio would not let the audio through. Also when switching off the squelch, there would be no noise, when the problem state occurred. Upon a transmission coming in, a very faint clicking in the audio output could be heard, but no audio coming through. The silence stayed on for a while and then the radio starts to receive again. When the receiver is operating normally, both the audio receives well and the usual noise is audible when the squelch is deactivated. It was only possible to determine when the problem was present by running a handheld simultaneous. When switching off the squelch, there would be no noise. I got a hunch that something in the electronics was pressure sensitive (like altitude dependent) After many dis-assemblies, I found that the transmit relay turned out to be the culprit. Exerting pressure on it reproduced the failure behavior. Dittel has handed off all service of this old radio, including spare parts, to Anton Lang Flugfunk-Service. Prices for shipping, problem evaluation, parts and repair are high. For some parts, Anton Lang Flugfunk-Service does not even have any stock anymore, like in the case of my transmit relay. So, I had to improvise a solution with a replacement relay, placed off the Printed Circuit Board. My FSG71M is now working perfectly again. My repair cost was $5 material plus many, many hours of my time for trouble shooting (fortunately a winter project). As said, this radio (although a very good radio) is becoming pretty old and servicing it is becoming very expensive, if possible at all due to spare part situation. Soon you will be better off with a new radio. In case you run into a problem with this radio, make sure that you have checked all the obvious items like PTT button, antenna, mic, etc and you are sure the problem is in the radio itself and not in the wiring. (Wiring problems are the most common problems in sailplane electronics. If you have a carrier but no modulation, I recommend to check the audio transmit relay. If you are familiar with electronics yourself (or if you have a friend who is half ways at home in electronics) that is not too difficult. I have attached a PDF file of the schematics if you need it. The audio transmit relay is K301 in the red circle.  The culprit, relay k301, after dis-gracefull unsoldering from the board. Also for reference: the green-white round item in the hole on the right lower side of the top board is the Program Memory battery. Replace this battery if your radio looses the programmed channels. Update February 25, 2013: I received a report from another user, who had a similar problem on this FSG50 radio. He used the same procedure as I described above to replace the audio relay by gluing a standard relay to the casing and wiring this new relay into the footprint of the removed defective relay. Below a picture of his solution:  Update November 8, 2013: Every now and then I get some questions about how I did this fix and what parts I used. I don't have a particular partnumber or manufacturer. The exact part number is not critical. I was not able to find an exact drop-in replacement with the same footprint. So, I just got a small 12 Volt Printed Circuit Board relay in my local electronics dump shop. The relay just needs to be small enough such that you can stick it to the wall of the radio with a bit of double stick tape. Then short wires to the PCB. The relay should be officially 9 volts, but those are hard to find and the 12 volt relay is working fine for me. In the pictures below an example of a relay that I experimented with.    For commercially available products, you could have a look at this Digikey link: |
