The recent post from W0SD, plus a customer 940 just received, reminded me
of some more TS940 potential problems, particularly when used with
Beverages. Other models and brands may have similar susceptibility.
- High TX levels (or lightning induced) can blow out the the tiny 1/6th W
resistors used in the attenuator circuit. Short of moving the beverage
further away fm the TX antenna or going QRP I have found that going to
1/2W resistors works here. They will fit and the extra wattage margin
eliminated any repeat failures.
- Those same signals can blow out L2 on the RF board which is part of a
45MHz LP filter. RX sensitivity will drop 10-20dB or more depending upon
band and remaining capacitance coupling remaining in the coil can. A
quick fix is to jumper the terminals on the PC board with a 1000pf
capacitor (value or cap material not critical). To be honest I left one
of my 940's this way for over a year and could never tell any performance
difference on any band even with the obvious impedance mismatch.
- Blown or leaky BP filter diodes as related by W0SD can result. If
you're into that level of repair, replace with PIN's anyway. Those Jap 1S
series diodes can be replaced by the 1N914/4148 USA types for a quick
non-PIN fix.
- Early 940's below the 8M series used 47 uh inductors, on the RF board,
for L82 and L83. These can overheat and have been known to cause some
strange symptoms for 160m operators; from RF feedback on SSB to some
reports of damage (parasitic??) to the RX. Later rigs used 470uh. I have
had the feedback-distortion problem here with 6M and 7M series 940's. My
8M and 10M versions had the 470uh factory installed. Get new chokes
direct from KW parts depots.
Thats it for now............gotta do final Christmas shopping.
73..............Carl
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