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

[John]

Hi Steve,

When you removed the 100 pF cap to fix the S-meter overshoot problem, did it
also decrease the click/thump between CW elements when operating QSK with
narrow filters?

I really like the 1000MP series - the poor QSK performance with narrow
filters is the only major negative that I've found. I always attributed the
delay in receiver recovery to a filter ringing problem, since QSK works FB
with the 2.4 kHz filters in line.

Thanks,

John  W0DC

----- Original Message ----- 
From: "Steven J Fraasch" <sfraasch at juno.com>
To: <1000mp at mailman.qth.net>
Sent: Sunday, May 22, 2005 3:17 PM
Subject: [1000mp] FT1KMP MK V Receive Break-in Problem: FIXED !


> I fixed my S-Meter overshoot problem following replacement of Q6451:
> There was an undocumented, leaded 100 pF (?) cap added across Q6451
> Collector-Emitter that I had re-installed on the replacement transistor.
> Being suspicious of something not documented in the schematic, I removed
> it.  The S meter no longer overshoots going from transmit to receive.
>
> It's possible that this cap went across something else, and I was off by
> a lead, but both the B-E and C-E junctions are bypassed (C6455 and C6459
> respectively); therefore, I don't know why another cap would have been
> added.  My only guess is that C6459 is relatively large (.1 uF), has poor
> HF bypass characteristic, and is located too far away from Q6451 C-E to
> be effective; hence, a smaller RF cap was added to improve the bypass
> characteristic, especially on the higher bands (rig again seems fine on
> all bands without the cap).
>
> Does anyone have a service bulletin pertaining to this extra leaded
> capacitor ?  If you refer to the tuner-main PCB parts layout (Page 6N-4
> in the manual) it is located between Q6453 and C6453.  Again, I am pretty
> sure it went across Q6451 C-E.
>
> BTW:  If you ever need to replace Q6451 (I noticed W7HV had to make the
> same repair, this seems like a weakness in the MP and Mark V), you don't
> need to take the tuner apart, nor remove any cables.  Merely remove the
> top rear cover, remove the tuner cover, solder-suck the junctions of
> Q6451, and reach in the side with a small screwdriver and pry the
> transistor out.  You can shake the tuner to get the transistor out once
> it falls thru.  Then, merely solder the transistor on the back-side of
> the PCB.  I think that side makes more sense anyways, as the transmitted
> E-field should be less intense on that side of the board.  Perhaps
> locating the transistor on the RF component side of the board had
> something to do with adding the leaded cap.
>
> 73,
>
> Steve Fraasch, K0SF
>
>
> On Sat, 21 May 2005 14:04:42 -0500 Steven J Fraasch <sfraasch at juno.com>
> writes:
> > 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
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