I have problems with 2 aircraft receiver-transmitters.

The FSG-40 (1970's vintage PPL synthesizer unit) has has become
temperature sensitive, and receiver shuts off after about 1 hour
operation. Transmitter still works OK, so the problem is not in the PLL
circuit, and audio amplifier must be OK too (used in the AM-modulation
circuit). The squelch switch makes a sof click, but nothing else
happens. To continue troubleshooting, I need schematics, but Dittel has
only the current product documents on their website.

Another unit with problems is the FSG-12, 1969 vintage chrystal
controlled unit. Receiver sensitivity is poor. I think I can solve this
problem by reverse-engineering the RF stage, still I think a schematic
might help.

Matti

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Matti Adolfsen wrote in message ...
I have problems with 2 aircraft receiver-transmitters.

The FSG-40 (1970's vintage PPL synthesizer unit) has has become
temperature sensitive, and receiver shuts off after about 1 hour
operation. Transmitter still works OK, so the problem is not in the PLL
circuit, and audio amplifier must be OK too (used in the AM-modulation
circuit). The squelch switch makes a sof click, but nothing else
happens. To continue troubleshooting, I need schematics, but Dittel has
only the current product documents on their website.

You might try, with the unit opened up and operating, heating up
individual components with a 50-100W soldering iron to find the one(s)
that is temperature sensitive.

Tom

Tom Seim wrote:

Matti Adolfsen wrote in message ...
I have problems with 2 aircraft receiver-transmitters.

The FSG-40 (1970's vintage PPL synthesizer unit) has has become
temperature sensitive, and receiver shuts off after about 1 hour
operation.

You might try, with the unit opened up and operating, heating up
individual components with a 50-100W soldering iron to find the one(s)
that is temperature sensitive.

Tried that already. Unfortunately, the receiver demodulator circuits are
under the PLL divider board, invisible when the unit is operating.

Matti

Matti Adolfsen wrote in message ...
Tom Seim wrote:

Matti Adolfsen wrote in message ...
I have problems with 2 aircraft receiver-transmitters.

The FSG-40 (1970's vintage PPL synthesizer unit) has has become
temperature sensitive, and receiver shuts off after about 1 hour
operation.

You might try, with the unit opened up and operating, heating up
individual components with a 50-100W soldering iron to find the one(s)
that is temperature sensitive.

Tried that already. Unfortunately, the receiver demodulator circuits are
under the PLL divider board, invisible when the unit is operating.

Well, even if you have schematics you will have to remove the PLL
board, preferably in a way that the radio keeps operating so you can
test it fully opened up. I have found, from experience, that a modest
investment in test cabling/fixturing saves a WHOLE LOT of grief later.

Tom

Matti Adolfsen wrote:

I have problems with 2 aircraft receiver-transmitters.


I think I can solve this
problem by reverse-engineering the RF stage, still I think a schematic
might help.


When I needed to repair a Dittel Transceiver (other model) a couple of weeks
ago I contacted Dittel through their website http://www.dittel.de/ and
they sent me a service manual through their local (swiss) sales
representative quickly and at a moderate price.

George

Georg Holderied wrote:

Matti Adolfsen wrote:

I have problems with 2 aircraft receiver-transmitters.

When I needed to repair a Dittel Transceiver (other model) a couple of weeks
ago I contacted Dittel through their website http://www.dittel.de/ and
they sent me a service manual through their local (swiss) sales
representative quickly and at a moderate price.

George


I got the schematics to both units in electronic format. Both units have
been repaired now, thanks to averyone who helped. (the FSG-12 had a
broken wi a screw cut the wire to the protecting diodes in the
RF-stage, allowing too high signal in during transmitter operation, this
had killed the first transistor in the unit. The FSG-40 had a bad
transistor in the IF-amplifier)

Matti