FGT494HV - only works on outgoing calls

[M1ECY]

Good morning all,

I am working on a New Old Stock FGT494, received from Henning some time ago.

I have set the bridges inside the case for TW operation, and moved the straps for 2 wire operation.

I have also checked the function of the 2x 1uf Capacitors that seem to form part of the supply circuit for the telegraph relay coil.

I can make outgoing calls with no problem, but cannot receive incoming connections - it appears that the Telegraph relay is not being thrown into the correct position.

I have tried to adjust the contact spacing, to see if the travel was too large, but this makes no difference.

Manually operating the telegraph relay results in the system working as planned.

Can anyone offer some ideas where I should look for the problem?

Thanks

Sean

[M1ECY]

Just noticed, posted in wrong section, could one of the Super Mods move for me?

[M1ECY]

Still no luck with the repair.

I have replaced the Telegraph Relay with a known working device from another FSG, and still no incoming connection.

I have been studying the schematic found here on the forum, and can see that there are 2x1uf capacitors that are used to trigger the coil of the telegraph relay -I have tested these for capacitance, and both are around 0.8uf with no measurable leakage. I have tried adding some additional Capacitance just in case the value is very critical, and still no improvement.

The electrical control of the system is all otherwise working, when I manually push the Telegraph relay to operate, I can start the machine and receive incoming traffic, but for some strange reason I cannot seem to make any progress.

Any suggestions from the experts?

[M1ECY]

The problem has been found.

With reference to the circuit in post 15 of this thread viewtopic.php?t=3725&hilit=fgt494&start=10

Relay A (who only seems to activate a dial lock on the full TW39 with dial model) has two coil windings, one that is low impedance of 75r for outward calling dial lock, the other high impedance winding of 17,200r works directly in series of the Telegraph Relay coil. in this case, the winding was open circuit on the A relay.

Because I do not have an original dial fitted, there is no need for the dial locking function - it is easy to bridge the open circuit relay coil with a suitable resistor - in this case 22K was easily to hand - this has restored the incoming call facility.

If my reading of the Lorenz relay is correct, the high impedance winding is wound with 0.06mm copper wire - there will be many thousands of turns and I think almost unrepairable.

The good news is that although not technically correct, the FSG is now in a functional state - perhaps this information will be helpful for others.

[duddsig]

Du warst jetzt schneller als ich nachschauen konnte.
Die hochohmige Wicklung am Magneten für die Sperre stellt häufig ein Problem dar. Auch bei den Siemens TW39 Allstromgeräten. Die Schaltung ist hier sehr ähnlich. Manchmal hat man Glück und es ist nur der Draht der oberen Lage am Anschluß ab (korrodiert). Wäre schade wenn das schöne FSG einen Makel hätte. Wählen mit dem Nummernschalter kannst Du ja trotzdem noch, wenn Du die Sperre mechanisch deaktivierst. Habe ich an einem Siemens TW39 auch so gemacht.

[M1ECY]

The original FSG was for HV operaton - I fitted a dial, which is about 30 years too new,

So the dial lock function does not work anyway.

I might when I feel brave enough try to rewind the coil - I have a coil winding machine here that is designed for doing Telefone style relays.