[TMC] Re: TMC Multi-coupler help...

[Jordan]

Ok.. well I am well into the repair of this unit... This unit appears to be
somewhat unique in that it uses a FET front end device, and it operates on
-26VDC from the internal power supply... It also uses common Drain circuitry
due the negative voltage operation... I would think it uses a 26 Vdc
potential for an increased dynamic range...The FET device , a 2N3823, Subs
to an NTE-459 , and I managed to find two of these in the entire city....it
feeds a pair of non-original ECG106 transistors which appear to be obsolete
devices, but the recommended sub is an ECG/NTE-159... these feed the 2N2368
buffer....
Can anyone provide hints as to what the value of the -26Vdc source dropping
resistor might be..? The replacement resistor is totally open, and the only
bands left appear to be a red first band, a second band that could be either
red,orange or brown... I think it may be red, as red/orange/x would be an
odd value....

The drain is bias above ground ( or below actually ), by a 1 K resistor...
there is also a slight bias applied to the gate through a 1.2M and 120K to
ground divider , in series with a 50K ohm 10 turn pot....
Looking at the circuit, I can't think of a reason for it to cook so severely
without damaging other components, and it is located right next to the 1K
drain resistor which has been replaced as well, but there is no sign of the
board being burned...
The unit was tried and found to be functioning very poorly, and that may be
due to the open resistor alone, or the FET device may be shorted, although
FET VOM testing does not show any shorts....any ideas...???  73 de
Jordan....

Jordan wrote:

> I'm looking for docs and or a manual for a TMC , or even someone who
> could verify a few component values for a TMC Solid State HF Receiver
> Multi-coupler...
> The unit I have is Labelled as a TMC 6806 Multi-coupler, but that is
> probably not the "Official" ID....
> This unit uses a JFET RF device in the pre-amp board, a 2N3823, followed
> by a pair of unmarked ( unreadable ) transistors, and finally a 2N2368 (
> Buffer?) on the preamp board before the signal goes to the individual
> dual BNC output boards....
> I have pictures of the unit , and the board in question if that is of
> any help...73 de Jordan....