Drake TR-7 Information Requested
Terry
About ten years ago a neighbor gave me his TR-7, which he had used on
his sailboat during a transatlantic crossing to the Caribbean. It had
been modified for use with a selective-call system consisting of a
selcal unit and a glass terminal. He said everything was working all
the way across and was OK when he took it off the boat when he sold
it. They relied on it for WX RTTY and I guess commo during the
transit. (I didn't go into that facet with him).
I fired it up (without the terminal) and it worked fine. Used it for
several years before moving here to NC. I had deep-sixed the terminal
shortly after receiving it, but the selcal unit had to be connected,
through a multiconductor cable, to the guts of the TR7 for the radio
to operate.
After the move, one box in the shipment was missing and could not be
found. (Yes, the selcal unit was in the box. I probably could have
figured out what was going on if I had the unit.) I fired the radio up
a few weeks ago, but all I got was no audio and no display. The
S-meter and dial lights illuminated, as did several LEDs, and the RF
gain control caused the S-meter to peg when rotated CW. Sounds normal.
Something's working.
First, I plunged into the TR-7 chassis (not an easy job I might add)
and located the spkr circuit. I remember there was a MUTE switch on
the selcal unit that closed the spkr circuit, so I traced from the
spkr to the selcal cable, jumpered the severed spkr leads, and the
speaker worked. Aha! One down.
Having worked with RTTY, AMTOR, FEC, etc., on my TS-430S and Drake
T4-XB I remembered that a PTT and audio in circuits will be needed.
Found those and restored them (they were jumpered from the mic
receptacle). Two more down.
Now comes the fun. Taped to the underside of the motherboard were two
miniature relays and two trimmer pots. One relay had a shielded line
connected to break the ckt to a pin on the mobo, to which I'm
confident it was originally connected to. The other had just one
circuit it switched. Both coils were in parallel. The pots connected
to the terminal cable as well as the mobo (audio-level trim?). A
spaghetti-patch of wires connected to various points under the mobo
and a few disappeared out through another cable to the terminal unit
(long-since gone). The connections made little sense when looking at
the schematics, which appear to be not the best I have seen, and I've
seen a lot.
Most external connections seemed to have been made to the 2nd IF and
Audio Unit (11). I am having much difficulty identifying the pins to
that board, the ones protruding through the bottom side of the mobo
("Parent Board" in Drakelese). I bought a TR-7 Service Manual copied
(not too well, I'm afraid) when I first got the radio. I'm not sure
what the pin-numbering is, for the mobo pictorial (Fig. 2-1) is
essentially illegible, particularly in the area of unit 11's pinout.
So that's where I am now. I get audio, however, scraping a screwdriver
along the dummy-load antenna yields no noise, which it should. All
bands produce the same rush, or shot noise, from the spkr. Voltages
appear to be OK on Vdd pins of the chips, but no display. As the unit
has been idle for about eight years, I sprayed all the controls and
switches with cleaner/lube for I remember the display would come and
go when I rotated through the bands a long time ago. Maybe I didn't
get all the crud off the contacts?
This is where I stand. Does anyone out there have experience inside
the TR-7 and would be willing to work with me long distance on this
resurrection project? If I had a clean, legible copy of the mobo
pictorial it would be a significant help.
Thanks very much in advance, and I hope I can get this thing perking
again. Great radio!
Cheers--
Terry--WB4FXD
Edenton, NC
Zootal
heavily modded. I might have a set of clean schematics, I'll look through my
stuff and see what I can find, but don't hold your breath...I'm not sure I
could be of much help with this one...
"Terry" <katam...@hotmail.com> wrote in message
news:4b2ea28f...@netnews.mchsi.com...
Terry
<use...@spam.zootal.nospam.com> wrote:
=>I have a TR-7 sitting on a shelf in my basement, but I suspect it
has been
=>heavily modded. I might have a set of clean schematics, I'll look
through my
=>stuff and see what I can find, but don't hold your breath...I'm not
sure I
=>could be of much help with this one...
=>
=>
=>"Terry" <katam...@hotmail.com> wrote in message
=>news:4b2ea28f...@netnews.mchsi.com...
=>>
=>>
=>> About ten years ago a neighbor gave me his TR-7, which he had used
on
=>> his sailboat during a transatlantic crossing to the Caribbean. It
had
=>> been modified....
Yes, I realize this is a sticky wicket, and without the unit on your
bench, not mine, it's tough, if not impossible, to give exact details.
The drawing I would like to see is Fig. 2-1 "Parent Board Pictorial"
from the TR-7 Service Manual. My copy appears to have numbers next to
the pins on the board. If they are not numbers, but merely bad-copying
smudges and QRM, then I don't need this illustration. (The schematics
are pretty good and with a good glass I'm so far OK.) I'm trying to ID
the pins on unit 11, for most of the wires of the mod connected to
this board. For example, on my schematic of the 2nd IF and Audio unit
a pin is shown as Gnd (com). That same pin in my TR-7 has the center
conductor of coax soldered to it. Can't remember the pin #--the radio
is out in my shop I'm inside the house, it's 26 outside and I'm still
on my first cup of coffee!
I think I'll have to re-read the manual. Maybe something will pop out
at me. I was head of technical publications for an electronics company
for 20 years and we had a motto: "When all else faisl, read the
manual." I should heed that motto!
Thanks for your offer!
Terry--WB4FXD
Edenton, NC