[1000mp] FT1KMP MK V Receive Break-in Problem

[Steven J Fraasch]

I am a relatively new owner of a Mark V, having purchased a used unit in
March.  I applied the key click and roofing filter mod before I used the
radio, and was very happy with how the radio worked.  In fact, I like it
better than my IC781.  BTW: I measure the 10-90% rise/fall time to be ~3
ms after applying the INRAD key click mod.

About 3 weeks ago, I had left the antenna switch on to a high 40m dipole
while it was connected to my Mark V, which was turned-off.  While I was
away, a brief snow squall came thru.  When I came home, I noticed that
the receiver was dead.  I troubleshot the receiver, (and made a few
"left" turns) but finally determined that Q6451 was shorted.  I presume
that the precipitation static had exceeded the VC-E breakdown voltage of
100V, and the transistor failed.

I replaced the part last night with a NTE equivlaent, a NTE289A from
Mouser.  After replacement, the receiver came to life.

Yet, I still have a problem:  In break-in, the S-meter does not recover
in time during initial transmit, such that the receiver path still seems
to be open during an initial "dit" from the keyer.  The problem seems to
be that the receive path is neither "opening" completely, nor quickly
enough during transmit.

I have not attempted further troubleshooting; hence the email, but my
next check is to check RL6451 and insure that it is operating properly. 
An open D6453 could keep the relay open longer than it should.  After
that, I'll look at the PIN diodes D1055 and D1056 in the RF unit and make
sure that they operate properly.

A couple weeks ago during one of the wrong "left" turns, I had also
replaced Q6453, a self-biased PNP.  I had failed to take into account its
series 10K limiting resistor; therefore, I had concluded that the B-E
junction was bad when in fact it was operable.  I replaced it with a
similar Digi-Key part, except the replacement part has a 10K B-E shunt
instead of the 2SA1563's 47K shunt.  Otherwise the base resistor is 10K,
same as the 2SA1563's.  The stiffer pull-up would not seem to cause this
problem; if anything, it would lengthen the rx open time, rather than
lengthen receive time.  Also, the circuit would seem to indicate a
stiffer pull-up is fine.  Therefore, the fact that I don't have the same
exact transistor seems to be a ruse.

Any other suggestions ?

73,

Steve, K0SF