From: Ron<[email protected]>
Subject: Re: [Drakelist] TR7 acting strange
To: [email protected]
Cc: [email protected]
Date: Saturday, January 30, 2010, 12:16 PM
Garey,
Even thought I had spontaneous healing of my TR7 per our
e-mail discussion, I opened up the rig and did some voltage
tests. Rig in SSB, all boards installed.
Pin spec measured
1 -5V -3.43
2 +25 23.3
3 gnd
4 AM 4.99
5 RTTY 7.01
6 CW 4.31
7 LSB 6.26
8 USB 3.83
9 DCin 13.53
10 +10VDC 10.01
11 +5V 4.90
The 24VDC line stayed solid as I moved the bandswitch and
up down buttons.
Per the drake service dept alignment procedures, pin 2
should measure between 23.25-24.0. Assuming my meter
is accurate, that voltage is very close to being out of spec
low. Maybe a weak/leaky C2110?
I could not get to the input of U2103 (24V regulator)
without pulling the DR7 board. Pulled it and installed
probes and then reinstalled the DR7. Input to the
78c24 was at 27VDC immediately after turning on the rig, and
then climbed to 32-35 volts w/i about 10 seconds. As I
recall the 7800 family of chips need 2 volts to regulate, so
I think input is w/i spec even at turn on. When
switching the bandswitch, it made the input voltage move,
but never under the 32 volt level. Caveat, using a DVM
so it may have "spikes" that I was not seeing.
After this, I pulled the DR7 and replaced it with the
service kit "jumper logic board". Basically had the
same results with it in place of the DR7 board.
TNX es 73,
Ron
--- On Mon, 1/25/10, Garey Barrell<[email protected]>
wrote:
From: Garey Barrell<[email protected]>
Subject: Re: [Drakelist] TR7 acting strange
To: "Ron"<[email protected]>
Date: Monday, January 25, 2010, 9:56 AM
Ron -
Definitely sounds like marginal VCO locking.
The bands from 160 - 20M will all wander around 17
MHz. 15 and 10M
bands will wander around 34 MHz.
An "open" AUX-7 position will result in an unlocked
VCO, as
will pushing
the FIXED RCV button in.
First step is to check that +24V DC supply bus.
That
is the most likely
cause of this, i.e., "random, occasional, loss of
lock" on
both PTOs.
Certainly there are other possible causes, but that
little
transformer
core is a problem, and the "super glue" that Drake
used to
put it
together is letting go (after only 40 years or so).
Easy fix, just glue
it back on.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service
Supplement
CDs
<www.k4oah.com>
Ron wrote:
Garey,
I started to look at the TR7 last night. First
was to see for sure what was going on frequency
wise.
Turned it on, 80 meters, where I had left it and it
was
fine. 2.5 then 1.5 wondering 17xxx.x 1.5. Back
to 80 meters fine, and of course everything else was
fine
too. So then I went back down to 2.5 and 1.5, they
too
were fine now. So I thought maybe temperature or
time.
Could not get it to fail after several hours.
Got to playing and went to aux settings. They
were fine with the band light lighting if I was not in
the
correct band. Then I went to an open aux location
and
got wondering 17xxx.x. I can not remember it that
has
always been that way or not. Looks like it could be
correct given the "block" diagram of the rig in my
head.
So I know it sounds like VCO/PLL issues, which
voltages are most likely. But, is there anything in
the bandswitch that exercise might cause to "clean
up"? Or am I in for what looks to be a PITA
intermittent?
Also, I have looked for how my TX is open. The
motherboard out of lock trace is not cut, and the
Q9001
collector on the DR7 board seems in tack. Maybe I
just
missed how they defeated Q9001. Is there something
with the aux board that also somehow "opened" the TX?
I
thought it was only for the modules in aux, not the
whole
TX?
Thanks in advance. Also thanks for being an
anchor for
this list. Your knowledge and willingness to share
that
knowledge is a tribute to the real meaning of Ham
Radio.
73,
Ron WD8SBB
--- On Sun, 1/24/10, Garey Barrell<[email protected]>
wrote:
From: Garey Barrell<[email protected]>
Subject: Re: [Drakelist] TR7 acting strange
To: "Ron"<[email protected]>
Cc: [email protected]
Date: Sunday, January 24, 2010, 4:40 PM
Ron -
You may need to recheck your frequencies.
~17 MHz is
the "target" frequency for the Lo Band VCO
(through 20M),
and 34 MHz for 15 and 10. This is where
the
VCO's
settle when unlocked.
First thing to check is the +24V DC
supply.
This
higher voltage is used for the Loop Filter
and
VCO
steering. If the voltage is low, check
that
"E" core
on the DC/DC converter transformer on the
little
power
supply board.
There are other possibilities, but this is a
start.
Unless the transmitter has been modified, it
won't
transmit
if the VCO is unlocked.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B,
C-Line& TR-4/C Service Supplement
CDs
<www.k4oah.com>
Ron wrote:
Got a strange one going on. Finished
and
80
meter net and was headed to 40 to listen to
the
Drake tech
net. On 80 meters it work find. But
when I go to
other bands, the display shows incorrect
frequencies.
Also on using the up/down buttons it will go
into
strange
frequencies as well.
1.5 show 1759x.4 and counts up slowly
2.5 same as above
3.5 80 meters okay and transmits
5 shows 1414.x
7 shows 3415.x14 displays okay
21 shows 17415.x
28 ok
I did not go further and attempt to TX
for
fear of
further injury.
It would appear the VCO/PLL are messed
up, but
why
such strange combinations?
First thing will be board removal and
reseating unless
someone has a specific I should be looking
for.
TNX es 73,
Ron WD8SBB
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