A lot, if not most, older VOM meters in resistance mode have the polarity
reversed on the probes. Red is negative and black is positive. Keep that
in mind when testing diodes.
Tony VE3DWI.
Sent from my BlackBerry 10 smartphone on the Bell network.
Original Message
From: Bob McGraw - K4TAX
Sent: Sunday, July 13, 2014 14:35
To: Walt K8CV; Discussion of Ten-Tec Equipment
Reply To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Paragon problem
Since there are no reed relays, or relays of any type, one would do better
to do a DC voltage check of each filter section for each band. This can be
done with the RX HP Filter removed but connected to the radio via the
ribbon
connector. This way the radio can switch bands and one can measure to
confirm switching is taking place by measuring the voltage across each of
the 16 diodes. There's 16 of them as indicated on the schematic.
Out of the radio and no power applied, each diode can be accurately
checked
for forward and reverse resistance with an ohm meter with a suitable diode
test feature. Or use one of the old fashion VOM type meters.
One other note, be mindful if the issue exists on all bands or just one or
two bands. The switching voltage can be observed on connectors #16 and
#14.
73
Bob, K4TAX
----- Original Message -----
From: "Walt K8CV" <waltk8cv@wowway.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Sunday, July 13, 2014 7:41 AM
Subject: Re: [TenTec] Paragon problem
Have you changed the reed relays or talked to TenTec about them? A stuck
/
pitted transmit reed will suck off the receive.
Walt K8CV
-----Original Message-----
From: Vic Klein
Sent: Sunday, July 13, 2014 6:34 AM
To: tentec@contesting.com
Subject: Re: [TenTec] Paragon problem
Thanks for the suggestions. A few days of sleuthing and talking to Garry
at
Ten Tec led me to discover that all the input (D1-D8) switching diodes on
the Hi-Pass filter board (81330) were "open". Garry said In4148's could
be
substituted, which I did, and now all the sections seem to test OK and
switch appropriately...but the same symptoms remain: all functions seem
normal, but sensitivity is off by around 4 S-units. None of the RF chokes
seem to be open, and bypassing the Lo-pass FX board by selecting the
external receive antenna makes no difference. I am looking at the 1st
Mixer
now, although I do get the appropriate 20dB reduction when switching in
the
attenuator, which shuts off the RF stage, so I am still befuddled.
One anomally I see is the the voltages on the band switching diodes seems
a
bit low. I would have expected a lower voltage at D1 as it has more
resistance in the path, but the reverse is true and it reads about 9.4v
as
opposed to the other 7 Hi-pass sections at about 7.25v when selected.
That
still seems plenty to bias the diodes and pull in the low-pass relays,
but
curious.
=Vic=
WA4THR
____________________________________________________________
To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Paragon problem
From: Wade Staggs <tvman1954@gmail.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 9 Jul 2014 17:39:05 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
*Far from being an Expert myself, The first place I would look would be
the
RX High Pass Filter Board ( 81330 ) At the Antenna Input to the High Pass
Filter Board, there are two LC Coils and a Diode ... Any of which could
be
Shorted or open in the case of the LC Coils. You should be able to inject
signal or an antenna input on each side of the High pass Filter Board. I
would use a Clip Lead and touch my Antenna to the output connection from
the board and see what happens. The High Pass Filter board uses Switching
Diodes to select the correct Filter for each Band. I am believing that
like
Ivory Soap, 99 44/100s percent sure that the problem is somewhere on the
High Pass Filter Board.*
* 73 and May God Bless from
Wade/KJ4WS*
On Wed, Jul 9, 2014 at 5:20 PM, K8JHR <jrichards@k8jhr.com> wrote:
Hi Vic -- I am far from expert on this, but I wonder if you can locate
ANOTHER protective diode in the receiver circuit. I once killed my Omni
VII receiver by hot-switching an "active" receive only antenna - the
power
connector arced to case ground of a bias-tee injector as I plugged it
in,
and that fritzed the receiver. Gary at TenTec service called me to
explain
it before he fixed it, and I believe he said there were multiple diodes
to
protect the rig in such cases.
So... perhaps you have more than one diode or fuse or other prophylactic
device to check?
-----------------------------K8JHr ------------------
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