Dennis -
The best troubleshooting tool around for 'intermittent' problems. We used to be able to buy Freon
in cans that was the best and coldest, but no more. The stuff sold today isn't quite as fast, but
works. A 'tiny' Freon shot would form frost on a part!! :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Dennis Monticelli wrote:
If the problem is an intermittant connection somewhere (i.e. a bad solder joint) the point
application of heat or cold can change the problem (either aggravate or improve) thus allowing you
to isolate the troublesome region. Have you tried the point application of cold spray? Often
those cans come with a needle tip.
Dennis AE6C
On Sun, Aug 21, 2011 at 7:20 PM, Garey Barrell <[email protected]
<mailto:[email protected]>> wrote:
Steve -
NONE of the T-4X(any) had the low-pass filter on the output of the PTO.
Only the receivers
used the filter, and only in version 2 of the R-4A and up.
It would be OK to just bypass the LP filter in the receiver for testing
purposes. Also,
don't gloss over the possibility of a bad, (cracked?), or just noisy
resistor at R49. Or even
poor solder on those associated connections.
Also, don't overlook the possibility of erratic or intermittent operation
of the BAND
oscillator (listen at 18.1 MHz on 40M).
Possible other resistors associated with V8 are noisy. Since you have no
jitter in TRANSCEIVE
(XMTR control) the problem is in the BAND, PTO or PreMixer, as these are
all disabled in XMTR
mode.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com <http://www.k4oah.com/>>
Steve Wedge wrote:
I'm going to have to look again. I did swap the VR tube.
Something Garey mentioned made me check the T-4XB schematic. If that
schematic is
accurate, Drake put the filter inside the PTO at some point or just for
the T-4XB. I'm
suspecting this was done for all PTO's at some point, as I couldn't
imagine Drake building
different versions of the PTO at the same time (of course, not
everything follows what I
or anyone else would consider logical...). This could allow me to try
temporarily
bypassing the filter board. I did notice that shielded cable went
directly to the PTO
when I removed it. Given these differences, it also looks like I'll be
ripping the
receiver apart (again!) to put the original PTO back in.
Arrrggggghhhhh...
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