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

[Jordan]

P.S... this unit does appear to be a TMC AMC-21 Multi-coupler... although I have
not been able to confirm that.... 73 de Jordan...

Jordan wrote:

> 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....