At this point it looks like CR1501 is the culprit, but I won't know for sure
until I replace it and do some more testing.
Steve w7jsc
--------------------------------------------------
From: "Jim Shorney" <jshor...@inebraska.com>
Sent: Tuesday, March 04, 2014 11:27 PM
To: <drakelist@zerobeat.net>
Subject: Re: [Drakelist] TR7 Transmit Intermittent Power Problem
I was getting strange output variations when I had leaky driver
transistors on
the PA deck. Easy to check, the base voltage on the drivers should be zero
in
RX. If it's anywhere near 0.6V, there's a problem. When I lifted the base
leads, one of them floated right up to 13.8V. Be careful not to short the
base
to the collector when you measure, you will destroy the device instantly.
A similar problem that I have now is a dirty bandswitch. Depending on the
band,
I often have to wiggle and jiggle it to get proper output. It's due to hit
the
bench soon for another project, so I'm going to DeOxit the band switch at
that
time.
73
-Jim
NU0C
On Tue, 4 Mar 2014 07:35:19 -0700, J. Steven Cochrane wrote:
I have run out of ideas. One of my TR7s has intermittent output power
problems. Sometimes there is no output, sometimes there is 40 to 10 watts
output depending on band and sometimes there is full output.
When I change bands there usually is no output as well as low receive
sensitivity. When I tap the PTT button on the mic the receive comes up to
normal and I usually get 40 to 20 watts (CW) out on transmit. Sometimes
when
I push on the High Pass Filter section boards I get full output, sometimes
I
don't. Sometimes I get full output when talking into the mic (with the PTT
button depressed of course) and not doing anything else. I searched the
archives with little luck.
What I have done so far:
1. Pulled all the boards and reseated them (some numerous times).
2. Loosened and tightened all screws I could get to, externally and
internally.
3. Cleaned all switches at least twice.
4. Pulled the power supply board and replaced C2108.
5. Readjusted 10 volt supply and checked Fixed pass band adjustment (all
good).
6. Checked 40, 13.695, and 8.05 Oscillators (all Good)
7. Attempted to do Transmitter Alignment and ALC Adjustment but with only
intermittent power output it was hit-and-miss at best.
8. Disconnected Diode CR1402 on the High Pass Filter Board (no change).
9. Checked 10 Volt transmit voltage on Parent Board when in transmit
(right
on 10 Volts).
10. Changed out the T/R relay twice ( no change).
11. Changed cables and dummy load (no change).
12. Cussed a lot (didn't help).
Any ideas where to go next other than crazy?
Steve W7JSC
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The Doctor, "Amy's Choice"
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