[Drake] TR-7 Problem Update

[David M. Nance]

Many thanks to several of you for suggestions.  I located my service
manual and; although I'm a vacuum tube guy in a microchip world, I
decided to do some voltage checks.

I checked the transceiver power supply board (#21).  Here is what I
found:

Pin 21/9:  13 vdc (this is the supply to the board so this should
eliminate the PS-7 as the problem)

Pin 21/11:  slight deflection of meter on 3 volt scale (this is the +5
volt regulated output)

Pin 21/10:  +0.4 vdc (this is the +10 volt regulated output)

Pin 21/2:  0 vdc (should have read +25 vdc)

Pin 21/1:  0 vdc (should have read -5 vdc)

Pins 21/4, 5, 6, 7, & 8:  all pins read less than 0.3 vdc

Looking at the schematic and reading the circuit description on the
power supply board, I would suspect Q2101, Q2102 or U2101.  They create
the 10 volt regulator circuit from which all other voltages are derived.

Am I on the right track?  Are there any resistance readings I can take
to make sure there is not a short circuit somewhere.  From the circuit
description it appears there is some protection built in which would
shut things down (Q2103?)  I don't have any of the extender boards
(don't even know if there was one for the power supply board) so I'm at
a bit of a loss as to where to go from here.


-------- Original Message --------

I've been enjoying my "new" TR-7 for the last three months.  However,
this morning while having a QSO on 75 the digital display went blank and
now it won't transmit or receive.  My suspicion is the power supply
board in the transceiver, since the FA-7 fan still works and the meter
and analog dial lights are still working.

If this helps, the TR-7 did the same thing a few days ago, but only for
a split second.  I suspected then I was going to have problems.  

Since I have had little experience with the TR-7, I thought some of you
on the list might have some ideas as to where I should start looking. 
All of my service experience has previously been on tube rigs.

Thanks,

David Nance - W4SSE
dmnance@earthlink.net


-------- Original Message --------

I've been enjoying my "new" TR-7 for the last three months.  However,
this morning while having a QSO on 75 the digital display went blank and
now it won't transmit or receive.  My suspicion is the power supply
board in the transceiver, since the FA-7 fan still works and the meter
and analog dial lights are still working.

If this helps, the TR-7 did the same thing a few days ago, but only for
a split second.  I suspected then I was going to have problems.  

Since I have had little experience with the TR-7, I thought some of you
on the list might have some ideas as to where I should start looking. 
All of my service experience has previously been on tube rigs.

Thanks,

David Nance - W4SSE
dmnance@earthlink.net