[Drake] TR-7 problems

[Larry Taft]

Turn the rig over and remove the bottom cover.  With the front facing 
you the 4 traces of interest are located apx 2 inches from the right 
edge of the mobo and run north to south from the rear to the front.  The 
order of the traces left to right is 10T, 10R, +10 and +5.

Power up the rig.  There is 120VAC running from the 10 pin Jones plug in 
the rear to the audio/RF/on-off switch on the front, now on the left 
side.  The rest of the rig is low voltage DC.

In receive 10T will be 0 and 10R will be around 9.8 volts, +10 will be 
10.0 volts and +5 will be 4.95 or so.

Have the mic gain and carrier gain pots turned CCW as we don't need 
power out.  Key the PTT and again measure the 10T and 10R lines.  10T 
should be 9.8 and 10R should be 0.   If these values aren't there then 
start tracing back to see what went wrong.  As Garey said, if both 10T 
and 10R are on at the same time strange things happen.

So you can learn your way around the mobo study the rear row of pin tips 
sticking out of the board.  There are 40 pin spaces along the rear with 
most of them occupied by pins.  There are circuit traces running through 
the spaces w/o pins.  The nominal spacing of the pins is around 0.160 
inches or 4 mm.  The Pin 1 location is on the right near the bandpass 
filters and pin 40 is on the left edge of the board.  All the cards 
follow this pin numbering layout even if there are only a few pins used 
on some of the cards.  Look at the schematic for the 2nd IF/audio card, 
the rear card in the cage.  You can now see the board connector numbers 
corresponding to the mobo pins.  Pin 12 is +5, pin 13 is +10, pin 14 is 
10R and pin 15 is 10T and pin 40 is BFO 5645 KHz from the reference 
board.  Connector numbers above 40 are for the pins on the top edge of 
several cards in the front cage under the DR-7 display.  You'll get to 
know those numbers when the synthesizer craps out.

You will need some way of accurately measuring the frequency of the 
oscillators when doing the alignment.  A sensitive counter that can read 
down to cycles or 10s of cycles would be good.  The highest freq is 
53.695 MHZ.  Or a modern receiver that can cover the range would work 
also.  The Oscope with a good high frequency probe can help with 
checking the signal levels in and out of the cards.

You'll find after a while that the TR-7 is a neat design and is 
reasonably easy to fix.  At least it has parts that can be seen with the 
naked eye. 

Have fun.  Remember, STAY OUT OF THE 120VAC.

73, Larry  K2LT
drakerepair.com  800-687-9161

transmaster wrote:
> Can somebody sent me, or direct me to,  a hi rez photo of the area of
> the parent board where 10R and a10T busses are, and the Q306, and Q307
> on the exciter board. My manual is a downloaded copy and the photo's
> are just black blots on the page. What is the modern part numbers of
> Q306, and 307.
>
> Big time thanks in advance
> Ken
>
> On 2/13/07, Garey Barrell <k4oah at mindspring.com> wrote:
>> Ken -
>>
>> Check the 10R and 10T busses.  Marked on the bottom of the "parent 
>> board".
>>
>> 10R should be very near +10V in Receive and 0 in Transmit.
>>
>> 10T should be very near +10V in Transmit and 0 in Receive.
>>
>> I suspect you might find that 10R is +10 in both!  If this is the
>> problem, check the 10R and 10T "fuses" (cleverly disguised as
>> transistors) at Q306 and Q307 and located on the Transmit Exciter
>> board.  (Where else?!?)
>>
>> 73, Garey - K4OAH
>> Atlanta
>>
>> Drake 2-B, 4-B & C-Line Service Supplement CDs
>> <www.k4oah.com>
>>
>>
>>
>> Transmaster wrote:
>> > Well I finally got the TR-7 fired up and it has a serious problem in
>> > the transmitter.
>> > When I key i t it sounds like it is in some demonic digital mode. It
>> > is a staccato high pitched tone "dee-dee-dee" you can hear my voice in
>> > the background but it is totally unintelligible. If this was a vacuum
>> > tube transmitter I would say there is RF getting into something but
>> > being solid state I don't really know.  I am not set up for DX'ing
>> > solid state gear.  What kind of test equipment do I need to add to my
>> > collection to work on this rig?  I have the usual VTVM's, digital
>> > multi-meters, O scopes, tube testers, RF/audio signal generators, etc
>> >
>> > Ken de W7ITC
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>
>