(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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