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>
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...
Steve Wedge, W1ES/4
"I can't complain, but sometimes I still do."
- Joe Walsh
If the above message appears, it came from Steve's Son of Laptop!
----- Original Message ----- From: <[email protected]>
To: <[email protected]>
Sent: Sunday, August 21, 2011 6:11 PM
Subject: Re: [Drakelist] You just know I'm not going to have any hair left...
Did you put a scope on the voltage to the PTO and watch it carefully?
As it fails?
73,
Lee, KC9CDT
-----Original Message-----
From: Steve Wedge <[email protected]>
To: Eddy Swynar <[email protected]>
Cc: drakelist <[email protected]>
Sent: Sun, Aug 21, 2011 5:30 pm
Subject: Re: [Drakelist] You just know I'm not going to have any hair
left...
That's the thing: it's a different PTO that was working properly before
I transplanted it.
Looks like I've got to try replacing the components on the filter
board. Something is pulling the frequency...
Steve Wedge, W1ES/4
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