Hi Dave
I found no fewer than three different versions out there for lk qsk
boards. I repaired/refurbed 5 of these amps. Let me look at my notes and
I can likely tell you what accurate k3.
Curt
KU8L
On Tue, Nov 14, 2023, 4:14 PM wb0gaz via Amps <amps@contesting.com> wrote:
> (I can supply schematic section cited by e-mail upon request to
> wb0gaz@yahoo.com, as it is a photo of the manual page I am referencing.)
>
> Next step in my continuing work on recovery of a LK550 with a history many
> prior adverse experiences.
>
> (some acknowledgements of prior topics I've raised during this project):
> Thanks Curt/KU8L re clarification on TS590 integration with LK550 - now
> have it set for relay enabled switching and connected to the amplifier's
> RELAY input (with QSK board present.) The wording in the TS590 manual
> around switching an amplifier wasn't very clearly worded, but it did
> eventually sink in what was happening, and it is working fine for the
> needed use. From previous advice here, I've de-powered the ALO/Meter board
> (it is now only serving as a passive mounting for the two meter scaling and
> protection components), and while I have repaired the step-start board, I
> cannot re-install it due to lack of correct mating connector - it is
> bypassed by prior owner. None of these issues (TS590 interconnect,
> ALO/Meter board faults, nor step-start board) are of concern today.
>
> The QSK board is not the original item from Amp Supply - that board was
> damaged beyond repair by too many previous butchery attempts (attempted
> butchery of electronics evidently cannot be prosecuted in Colorado). For
> this reason, I'm not starting from a "clean" broken amplifier, but rather
> one with prior ill-fated modifications/repairs, and a cloned QSK board. I
> cloned the QSK board (creating PCB artwork from the schematic in the
> manual, roughly following the physical dimensions, mounting holes, and
> component placement on the original board, but adding silkscreen
> nomenclature, a connector for closed-box test point measurements, and
> taking advantage of double-sided plated-thru board fabrication.) Copies of
> the cloned board were made from an online PCB manufacturer, they seem to be
> of good quality.
>
> From what I can ascertain, the cloned QSK board is doing most of it's job
> correctly, however, K3 does not appear to actuate (K3 would route the
> amplifier's driver/input SO-239 port to the input (ATI) filter board when
> amplifier is enabled and radio is transmitting.) I've been able verify the
> radio is controlling the cloned board's K1 (amplifier enabled whenever
> STBT/XMIT switch on amplifier is in XMIT setting), K2 (bias cut-off control
> relay and cascade control to K3), and K4 (main vac relay for amplifier
> output T/R switching), also the associated circuitry for driving K4 is
> causing the STBY/XMIT switch on the amplifier to illuminate whenever the
> radio is in transmit mode (no RF, just using it to verify the radio can key
> the amplifier). The notable problem remaining is at K3 (small relay for
> amplifier input T/R switching) - it not appear to be getting energized.
> This is probably a board layout error inhibiting K3 operation, but there
> appears to be a schematic error (see below) of con
> cern.
>
> Half of K2 (pins 4, 6, 8) appear to create a ground-on-transmit condition
> (passed via CR10) to energize K3 (the RF input/drive path switching relay)
> to allow the transceiver's transmit RF (from the back panel SO239) to reach
> the ATI (relay selected input band matching) board. Symptom right now - it
> appears that K3 never gets it's "lower" relay coil connection pulled to
> ground via CR10 and K2 (4, 6, 8) - both sides of it's coil sit at 12V
> regardless of TX or RX state, as long as the amplifier is enabled (which
> delivers 12V to power-up the QSK board).
>
> When I cloned the board artwork from the schematic (with hints from the
> original board only about rough component placement and board dimensions),
> I didn't catch a likely error in the schematic: pin 4 (common of the
> section of DPDT to control K3 coil via CR10) goes to ground. Normally open
> (de-energized position) pin 6 is left open. Pin 8 (energized position) goes
> to board holes/contacts 8, 12, 13, and the cathode of CR10 (anode of CR10
> goes on to K3's coil "lower" end of winding, so that pulling that end of
> K3's coil to ground would cause K3 to energize.) Here's the hitch - in the
> schematic, pins 8, 12 and 13 all show going to ground (as the schematic
> shows board contacts 8=ground tied to 12/13, which causes those to be
> grounded. If the board were following this correctly, CR10 cathode would be
> grounded, leaving K3 forever energized. Operationally, the board is not
> ever energizing K3 coil, so on top of a schematic error, I appear to have
> incorrect handling of K3 coil, preventing it
> from finding ground during transmit.
>
> As the original QSK board is mangled beyond recognition, I cannot yet
> determine what the correct wiring around this part of K2 should be. It
> seems from the schematic that CR10's cathode would be forever grounded,
> however, the board is not actually doing this, so not only is there
> possibly a schematic error, I may have misrouted (on the PCB artwork) the
> handling of CR10 cathode.
>
> Anyone care to take a look at the QSK board schematic and/or board itself
> and let me know whawt should be going on around this part of K2?
>
>
> Thanks!
>
> Dave
>
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