Bob -
Another one bites the dust! :-)
Select R58 so that the meter indicates 70 mA when the current is 70 mA.
Calculate actual current against actual MEASURED value of R59. Then
select nearest value resistor for correct indication. Don't worry about
meter accuracy anywhere else, not important.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
Robert Ladden wrote:
Epilogue:
R59 looked good visually, but fell apart when tapped. Cannot trust appearances.
Box from Mouser arrived today. It took me about 90 minutes to replace five
resistors (I'm slow). Replaced the finals. Powered up, everything looked good.
Finals neutralized easily. Full power available. All is well again.
By measuring the voltage drop across my new 5% R59, it seems my meter reads 20 mills low. Who knows how accurate it was before. I have not played with R58 yet.
While the T-4XC was sick, I used my TR-3 and a near junk RV-3 to work S04R.
My thanks again to Garey for the R59 idea and his service CD. And thanks to all
for the other things to check and your support.
73,
Bob WW3QB
--- On Sun, 4/12/09, Garey Barrell <k4...@mindspring.com> wrote:
From: Garey Barrell <k4...@mindspring.com>
Subject: Re: [Drakelist] I Fried my T-4XC
To: drakelist@zerobeat.net
Date: Sunday, April 12, 2009, 12:52 PM
Bob -
You've gotten a lot of good suggestions. The Bias
supply is always the first suspect in this sort of problem,
but you say it is ok.
One thing I haven't seen is to check the meter shunt
resistor, R59. This is a 3.3 ohm, 1/2W resistor that
is located on the relay board under the chassis. This
resistor is almost certainly damaged, usually going up in
value, causing the meter to read way high. When you
replace it, you need to calibrate it using the resistor R58
which is located up on the slide switch behind the LOAD
control.
You will need to replace the cathode resistors, the screen
resistors and certainly need to check the RF chokes.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
Robert Ladden wrote:
I had an unfortunate accident. I was using my T-4XC in
CW. I finished but left it in CW mode. I was doing something
else in the basement (where the shack is) when I heard a
fizzle. I saw the T-4XC turn off. I ran to it and saw the
6JB6's fade from orange. The keyer did something bad, and I
was not paying attention (never leave it in CW mode). Not
good, but I have several spare 6JB6's. The fuse in the AC-4
blew. I replace the fuse and the 6JB6's and it powers up
again. I try to neutralize the finals on 10m but get little
output and high current. Not good. I try on 40m and it does
tune, but at .4 on the meter I get low output. Trying the
load control gets full output, but pegs the current meter
and I cannot dip the plate. I quickly turn it off.
Cathode resistors test inline at 16 and 30 Ohms. Needs
replacing, but probably not the source of this problem.
Tuning is too weird.
There is no obvious burns on the chokes or anywhere
else, but I fear for the bandswitch back there. Hard to get
a good look.
Is there more I can check? Or is it time for an expert
surgeon?
73,
Bob WW3QB
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