Dave -
OK, you gotta start somewhere! :-)
The AF Preamp stage, Q1113 on the 2nd IF/ AF board gets it's B+ from the
10R line coming in on Pin 11/14. So if you have 0V on that stage, then
the AF signal that you are hearing in the speaker when transmitting is
getting into the audio stages via another path. C1151 is a decoupling
cap on the Preamp B+ line, and C1155 is on the supply line to the AF
Output IC. The IC is fed directly from the main 13.6V bus. The whole
audio circuit is one transistor and one IC, so there aren't a whole lot
of ways to get there! :-)
Have you tried re-seating the 2nd IF / AF card just in case? Try
measuring the 10R line right at Pin 14 of the 2nd IF/ AF board to be
sure it's really going to 0 volts at that point. ALSO ... Be VERY
CAREFUL when measuring anywhere on these two busses, as even a momentary
short to ground will kill one of those two "fuse" transistors!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
[email protected] wrote:
Garey (and also Don who suggested the same),
I pulled the bottom cover and checked the 10R and 10T lines. They are
working correctly. I measured 9.9V on the 10R line in receive and
0.00 in transmit. I measured 0.0V on 10T in receive and 9.9V in
transmit.
Any other suggestions?
Dave
----- Original Message ----- From: "Garey Barrell" <[email protected]>
To: "Drakelist" <[email protected]>
Sent: Thursday, December 11, 2008 4:21 AM
Subject: Re: [Drakelist] TR-7 Question
Dave -
T/R problems are often associated with the 10R and 10T control lines
and their "fuses", Q306 and Q307.
Check both busses, marked on the parent board traces. Each must be
very close to +10 when receiving or transmitting respectively AND
very close to 0V inversely. You'll probably find that the 10R bus
does NOT go to zero in transmit as it should.
Q306 and Q307 are on the Transmit Exciter board. If you don't have a
Service Manual, you'll need help finding them.
Let us know.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
[email protected] wrote:
Hi Gents,
I recently acquired my first TR-7 (thank you Evan K9SQG for sharing
and thank you Gary W8PU for some technical guidance in finding a
shorted pin diode). When I transmit on phone, I'm getting some
garbled audio fed back into both the headphones and the external
speaker connected via the rear panel. It's very distracting and
makes it difficult to talk normally. Audio reports from distant
stations say my transmitted audio (Shure 444D) is fine. I'm using
a Steppir 2L, so I don't have a bunch of RF running around the shack
and the mic gain is set to just kick the ALC in on peaks. The
garbled audio is also present transmitting into a dummy load. I'm
using an Astron 35A power supply.
Using the same exact set-up (coax cable, speaker, speaker connection
cable, power supply, etc.) with my Tentec Orion, it's perfectly clean.
Any thoughts/suggestions?
73,
Dave / K8JDC
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