George -
If you are showing 12V across C165, it's probably ok. IF it fails
because of having power applied with the PTO removed it usually either
explodes or shorts.... If C165 is open, it would NOT keep the PTO from
operating. IF you have 12V on the power lead and NO output, you'll
have to open the PTO to find the problem. It's not particularly
difficult to work on, but you must be careful that you don't disturb
the wiring and components not on the board. The FET and Buffer
transistor can both be replaced without problems as long as nothing is
overheated. Another fairly common problem is failure of the tap on the
coil. The tap consists of a piece of wire that is laid on a winding of
the coil and soldered. This connection can fail, but is easily repaired
by CAREFULLY resoldering.
With the 3rd Mixer change, T7 was also changed by adding a tap to
compensate for loss in the narrow CW filters. Not a significant
change. Most of the other changes were related to minor changes in the
PTO to compensate for a device change. No functional difference.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
George Roberts wrote:
Dear List,
After checking for pinched wires as suggested by Chris Kovacs, and
cold solder joints, putting PTO back in, I still have no output from
the PTO. I finally ordered the 10 mfd. tantalum capacitot as suggested
by Garey and Lee. One thing concerns me though. I shunted the possibly
open tantalum with a 15 Mf electrolytic, and saw no difference. So am
not convinced the capacitor is really bad, but I might well be wrong.
I get +12 vdc at C165. Are there any other major differences between
pre and post 21000 s/n on the R-4C beside the mixer tube change?
------------------------------------------------------------------------
*From:* Garey Barrell <[email protected]>
*To:* Drakelist <[email protected]>
*Sent:* Sunday, March 15, 2009 11:27:27 PM
*Subject:* Re: [Drakelist] No signal on R-4C after work on PTO
George -
That is an early R-4C. I have attached the correct schematic for that
S/N range from my CD.
I believe I told you earlier that you cannot turn on the receiver with
the PTO out of circuit. The Zener regulator inside the PTO regulates
against R115, dropping from the +150V bus. With the Zener OUT of
circuit, the voltage across C165 greatly exceeds it's rating. Sometimes
they POP, sometimes they just short and burn up R68.
One of the three PTO leads is connected to a ground lug on the gearbox
just inside where the wires come out. That's ground! The Red wire is
the Supply, and will draw current if any voltage about about 11VDC is
applied to it. The Brown wire is I believe the OUTPUT, but if it is, it
will read infinite ohms to ground because the output is AC coupled.
The symptoms you describe below are the result of no injection signal.
The Preselector is peaking at around 5.5 MHz, which is the IF frequency,
giving you a single frequency receiver at 5.645 MHz. If the PTO is
working you will see 4.955 (500 on dial) - 5.455 (0 on dial) MHz output
at about 2 VRMS. This PTO set to 0 on dial, is mixed in the Premixer
with the 18.1 MHz Band Oscillator (40M Band) to supply 12.645 MHz LO to
the First Mixer. The difference frequency between 12.645 and a 7.0 MHz
Antenna input signal produces the First IF of 5.645 MHz.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com <http://www.k4oah.com/>>
George Roberts wrote:
> Dear List,
> I've been reading the mail in this site for a long time, with much
appreciation for the knowledge and willingness you guys have to share
it with the folks. This is my first input and question:
> No signal after cleaning PTO Drive on Drake R-4C as per
instructions on the K4OAH site. I first cleaned bearing and shaft on
preselector. Cleaned switches and tube sockets and pins. Tested tubes
with my Jackson Dynanic 648S Tube Tester. Had to disconnect 3 wires
(red, brown and white) on PTO to work on drive. Re-connecting PTO
wires to PWB #2, the white went to the pin next to the ground lug, the
Brown to the pin just above the white, and the Red to the right of the
Brown. After putting it all together, I get noise that I can peak
ABNORMALLY with preselector as follows:
> _Band Switch_ _Slugs_
> 1.5-3.0 Can't peak
> 3.5 6/64"
> 7.0 1/32"
> 14 Can't peak, louder with slugs
at bottom 21 Can't peak
> 28.5 Can't peak but no signal.
> .
> Connecting freq counter to INJ jack gives no reading. Connecting to
shielded cable leaving PCB 2 after adjusting disks, reading at 500 is
steady 4994.8 Khz. Reading at 0020 (can not go lower because the slug
is at its outer limit) is an erratic 1395-1540 Khz.
> Does any of this make sense? Note: I did not "adjust" any trimmers!
> Serial number is 20620 and uses 6HS6 instead of 6EJ7 in premixer
and 1st mixer. My schematic shows 6EJ7's.
> Wondering if the pinouts are the same?
> My test gear consists of a 20 Mhz scope, Precision E200D RF Signal
Generator, Victor VC 3165 frequency counter, a DMM and VTVM. I don't
have much successful experience trouble shooting, so I'm asking the
esteemed panel on this Drake website if there is any hope for my R-4C.
Thanks much and best 73.
> George K2HRS
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