[Elecraft] problem with K160RX

[Dieter Kuckelkorn]

Hi folks,
I need some help with the K160RX.

My K2 (# 1142) doesn't receive on 160m. Maybe it receives something, but 
certainly not at 1.6 to 1,9 kHz where it should receive. There are no medium 
wave stations to be heard, for example. Additionally, there seems to be an 
unwanted oscillation that can be heard as a tone the does not change its 
audio frequency when tuning the band.

Checking VCO voltage on the left side of R30 on the RF board, it shows only 
0.02 V. A normal voltage should be between 1.5 and 7.5 V. All other bands 
have the correct voltage.

I also checked the VFO frequency with th K2 tuned to 1800 kHz on the 
display. I measured 6951.4 kHz. The right value should have been 6715 kHz. I 
suspect I am receiving on 2036 kHz (6951 kHz - 4915 kHz = 2036 kHz) instead 
of 1800 kHZ.

Transmitting works with full output as measured with a QRP wattmeter, but it 
is probably on a wrong frequency as well.

I tried a few things to rule out certain problems. I checked all parts, 
especially C75, C13 and C14 that have to be installed on the RF board. I 
also rechecked the parts on the K160RX board and reheated most of the 
connections to rule out a bad soldering joint. L1 and L2 have the correct 
number of turns.

The K160RX is correctly recognized by the MPU and the RX antenna jack works 
on all bands. On the RF board there is continuity from pin 2 of U1 to pin 16 
of J14, as it should be. Measuring resistance between pin 1 and pin 10 of 
the relays on the K160RX  board shows the correct value of 250 Ohms.

BTW: I have already made the RF board modifications suggested for the KPA100 
(C45, C42, C48, C154, R10, R16, D8), but those modifications don't seem to 
affect the VCO (I think).

C75 has the correct value of 470 pF. Could it be as simple as that C75 is a 
bad capacitor that needs to be replaced?
I would greatly appreciate any other ideas where to look for the problem.

Thanks a lot and vy 73,

Dieter DL1DBY
at the moment in Stamford CT


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