RE: Further clarification of my troubleshooting steps for K2# 5061
Posted by
Don Wilhelm-3 on
May 10, 2006; 12:29am
URL: http://elecraft.85.s1.nabble.com/Further-clarification-of-my-troubleshooting-steps-for-K2-5061-tp389489p389490.html
Pat,
One further check - RFC7 (15 uH) and C104 (68 pF). This is a series
resonant circuit tuned approximately to the IF frequency - if for some
reason these 2 components are series resonant somewhere around 12 mHz, it
could reduce the 30 and 20 meter signals significantly. As a quick check,
you could lift one end of RFC7 and see if you can tune the bandpass on 30
and 20.
73,
Don W3FPR
> -----Original Message-----
>
> Over the weeks now of troubleshooting this problem here are some of the
> steps I have taken:
>
> * I suspected either a defective low pass filter or bandpass
> filter for this band and one other. (I had damaged K7 with a soldering
> iron that
> put an ever-so-small dimple in one end of the relay case.
> This prevented the slide from fully engaging one set of contacts. I
> replaced it and
> that band was then okay.) After replacing the defective relay
> I lifted one end of W1 to isolate the two sections of filters and hooked
> a
> signal generator to the antenna connection. I hooked my
> scope to W1 and found all low pass filter characteristics as one would
> expect,
> no loss of signal strength on the selected band but noticeable
> attenuation on the next higher band. I forgot to say that I had already
> reflowed all solder connections on both the LPF and BPF
> circuits.
>
> * I replaced C22 (2.7 pF).
>
> * I hooked a jumper to the BPF test point (I had soldered a loop
> of wire onto D7 cathode to prevent damaging the component leads with
> my scope probe) and could hear stations on both 20 and 30
> meters. I coupled this lead through a capacitor (to prevent shorting 8R)
> and
> the signals were as loud on the two bands in question as the
> other, functional bands.
>
> * My friend Ron used a high quality capacitance / inductance
> meter and found L9 to vary from, as I recall, about 3.9~4.9 uH with the
> slug
> top to bottom. The capacitors in circuit measured
> approximately their stamped values considering stray circuit
> capacitances. Each of us
> checked and rechecked the values of all components and they
> were correct. Neither capacitors nor inductor were shorted to ground
> except the ends of caps that were supposed to be.
>
> * I have measured contacts 2,3,4 and 7,8,9 on relays K3 and K4
> and they function as you would expect from the relay truth table. I even
>
> tried a relay reset (control board removed on power up) and
> then rechecked with identical results. I also have cheched that the
> signal line
> (W1, W6 and BPF T.P.) is not shorted to ground on 20/30.
>
> * When feeding a signal from my sig generator through the coax
> connector and checking at the BPF T.P. there is no noticeable attenuation
>
> on any bands except 20 and 30 which was down about 70 dB.
>
> * L8 peaks properly on 30 meters. With the added cap acrross L9
> it peaks about two turns from the top of the can.
>
> At this point I had already decided to arbitrarily replace C24 and C25
> but I don't really expect any change since they check okay with a
> capacitance meter in circuit. (C19 and C20 check the same as C24 and
> C25). I am really getting discouraged at this point, but like Little
> Orphan Annie sings, "The sun will come out tomorrow!" Thanks to all for
> your suggestions. If I have an epiphany, I'll let you know!
>
> 73,
>
> Pat-K4BEH
>
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