K2 #2225 is Down

[Roy Morris-6]

Today I turned on my K2100/KAT100 and the receiver was dead.  Audio was working OK.  No RF output.  I stripped the KAT100 away and then the KPA100 and the problem was still there.  The basic K2 indicated transmit RF output between .2 to .4 watts.  The power display would randomly wander between these figures on all bands so there was no meaningful output.  No receiver signals on any band.  D6 anode measures 8.25V and D7 anode is 0 V.  I am only at the starting point for signal tracing.  It seems obvious something is down that is in common with both receiver and transmitting circuits.  This K2 has been completely updated with all mods and firmware.  It has all options installed including the VCOSHLDKT.  I hope I will be able to find the problem without having to remove the 60 meter board.  I have home brew rework eliminators, so I can remove the options if necessary.  All buttons and relays work as they should and the menu works as it should.  I would like to trouble shoot at the most likely place.  I suspect my problem is either in the PLL synth or VCO circuit.  I think it would be a stretch to find the problem in the bandpass filters or low pass filters.  A plan of attack would be welcome.   Thanks.  Roy Morris  W4WFB
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[Don Wilhelm-3]

Roy,

The first thing I would do in a case like that is to do a bit of Quick and
Dirty Signal Tracing.
Connect a known working antenna to the junction of D6 and D7 - can you hear
any signals as you tune the VFO?  If so, go on to check at W6.  If not, then
suspect the VFO or BFO.

Fortunately the VFO can be checked quickly with the internal frequency
probe.  Put the counter probe in TP1, then set the K2 frequency to the low
end of each band - enter the menu and set CAL FCTR.  The frequency displayed
should be quite close to that shown on the Schematic Key page - VFO chart in
the lower left corner.

Similarly, check the BFO at TP2 - the frequency should be that of the BFO
for the mode selected - if you read something close to 4913 kHz the BFO
should be good for frequency.

Next measure the RF voltages during transmit as indicated in the Transmit
Signal Tracing section of Appendix E of the manual (starting with page 12).
Comparison with the expected values should lead you to the first failing
stage, and that is the place to concentrate your search.

73,
Don W3FPR

> -----Original Message-----

> Today I turned on my K2100/KAT100 and the receiver was dead.
> Audio was working OK.  No RF output.  I stripped the KAT100 away
> and then the KPA100 and the problem was still there.  The basic
> K2 indicated transmit RF output between .2 to .4 watts.  The
> power display would randomly wander between these figures on all
> bands so there was no meaningful output.  No receiver signals on
> any band.  D6 anode measures 8.25V and D7 anode is 0 V.  I am
> only at the starting point for signal tracing.  It seems obvious
> something is down that is in common with both receiver and
> transmitting circuits.  This K2 has been completely updated with
> all mods and firmware.  It has all options installed including
> the VCOSHLDKT.  I hope I will be able to find the problem without
> having to remove the 60 meter board.  I have home brew rework
> eliminators, so I can remove the options if necessary.  All
> buttons and relays work as they should and the menu works as it
> should.  I would like to trouble shoot at the most likely place.
> I suspect my problem is either in the PLL synth or VCO circuit.
> I think it would be a stretch to find the problem in the bandpass
> filters or low pass filters.  A plan of attack would be welcome.
>  Thanks.  Roy Morris  W4WFB
>

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