K2 build: receiver problem....it does not work.

[Chuck-50]

I am at the end of the part 2 alignment and test (everything up to this
point is checked out and working to the level spec'd in the manual) . I
should be hearing something with my XG2 set for 7040, but don't.

I am following the trouble shooting section and have found that I do not
have 8 volts at [the right side of D6] on the control board. I followed
this back to pin 22 (8R) on J7, which also does not have 8 volts on it,
but pin 6 of J7 (8A) does have 8 vols.

On the control board the 8 volt and 5 volt regulators are working and I
have 8 volts on the middle pin of Q1 and Q2 (the base), but don't on the
collector. I am just a want to be EE (at best) but believe that I may
have a bad components.

However, this is a switching power circuit, so I not sure if there is
supposed to be, but it seems like their should in order for 8R to have
the 8 volts for the receiver to be powered.

Any help or advice would be appreciated.

Thanks...
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[Don Wilhelm-3]

Chuck,

Yes, the problem you are having is most likely related to the operation of
Control Board Q1 (or Q2).  These are not a switching power supply, but they
do serve as switches to direct the 8 volts depending on whether the K2 is
trying to transmit of receive.  Q1 and Q2 are not likely your problem - the
problem is most likely with an unsoldered connection or a zapped 2N7000 JFET
(Q4).  Read on for more info:

The control for Q1 and Q2 comes from Q3 and Q4, and right now, I would
expect that the drain of both of them has almost 8 volts DC on it.  So check
the gate of Q3 and Q4 - if the K2 is in receive, the gate of Q4 should be
near 5 volts - which should turn Q4 on and make it conduct (producing a low
voltage at its drain).

Now that you have a bit of understanding about the circuit, you should be
able to discover the problem quickly - if the gate of Q4 is not at a high
state (3.5 to 5 volts), then the problem is in the RX signal from the
microprocessor, but if Q4 gate is indeed at a high level, the microprocessor
is doing its job and Q4 is not conducting as it should - likely because it
was damaged with static when it was installed, 2N7000 JFETs are prone to
static damage and must be handled with good anti-static practice.

If you are only at the part 2 alignment and test, you should have an
uninstalled 2N7000 that you can borrow should you need a replacement.  An
email to [hidden email] should bring one in your mail within a week.

73,
Don W3FPR

> -----Original Message-----
>
> I am at the end of the part 2 alignment and test (everything up to this
> point is checked out and working to the level spec'd in the manual) . I
> should be hearing something with my XG2 set for 7040, but don't.
>
> I am following the trouble shooting section and have found that I do not
> have 8 volts at [the right side of D6] on the control board. I followed
> this back to pin 22 (8R) on J7, which also does not have 8 volts on it,
> but pin 6 of J7 (8A) does have 8 vols.
>
> On the control board the 8 volt and 5 volt regulators are working and I
> have 8 volts on the middle pin of Q1 and Q2 (the base), but don't on the
> collector. I am just a want to be EE (at best) but believe that I may
> have a bad components.
>
> However, this is a switching power circuit, so I not sure if there is
> supposed to be, but it seems like their should in order for 8R to have
> the 8 volts for the receiver to be powered.
>
> Any help or advice would be appreciated.
>
> Thanks...
>

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