[TenTec] RE: Problem with Century 21 Digital

[Kenneth Stringham]

Hi Gene,

Your power supply trip point is the problem. There is
an SCR circuit (Q2) that is designed to cause this
behavior. It trips when the supply current is too
high.

Do you have anything connected to the external power
connectors? This will reduce the amount of power you
can generate in the transmitter. Remove these
accessories and connect them to another power supply.

Is this something new? If this is the case, the
sensing resistor (Rsc) may have changed its value or
one of the connections may be dirty. The sensing
resistor is a long PCB trace on the power supply
board. It may have been subjected to excess heat at
some thing during is life. This resistor is in the
power supply return circuit. All the supply current is
returned to the power supply through this trace.

If this not new behavior and you do not have external
accessories connected, a previous owner may have
changed trip point.

Do you have a copy of the manual for this transceiver?
Let me know, I will scan the appropriate pages for you
if you require it. Do have any previous experience
with electronics? This is not a major problem. Just
about any radio amateur should be a able to perform
this adjustment.

The manual indicates that you need a 2.5 ohm 100W
resistor and a 10A DC meter to set the trip point and
to calibrate the current meter. The supply trip point
is set for 6A which should happen at the 70W input
level as noted on the front panel power meter.

The required adjust is made using the pot (R1 on board
80353) that sets the power supply trip point. The
setting of this pot needs to be adjusted slightly to
increase the set point current. It is located on the
upper right hand side of the power supply board just
above the supply regulator IC1. It is the pot on the
right of the two that are so located. The other pot is
for calibrating the meter. You do not want adjust that
one.

Look over this pot. Is it sealed with a little bit of
paint? I would wager that the seal has been broken.
Adjusting it in the wrong direction will only further
lower you output before the supply trips. You can
safely experiment, but only adjust it slightly until
you know which direction to use to make the change. I
would adjust it slightly to increase the supply trip
point and then adjust the transmitter power to confirm
the trip point has increased.

If you are not comfortable making this adjustment
without help, I could walk you through it over the
telephone. It's not a hard project, but you may want
someone around with some experience. Should have a
more accessible ELMER in your community, you could get
help in that way as well. Let me know if I can be of
further assistance.

Ken

--- n0mq at sbcglobal.net wrote:

> I have a nice Century 21 Digital that works great up
> to 30 watts out.  At 31
> watts out (using a Bird Meter) it shuts down and I
> have to turn it off and
> then back on.
> Under 30 watts works for hours.  Help!!  Thanks
> 73
> Gene N0MQ
> 
> _______________________________________________
> Tentec mailing list
> Tentec at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/tentec
> 



		
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