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K2 troubleshooting

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John Wiener

K2 troubleshooting

Hi everyone!

I am diligently trying to solve transmitter probs on a "nearly"
finished K2.

I would like to list here the aberrant readings so that someone much
brighter than I might see the source of the problem.
If this is an inappropriate use of the group, please let me know and
I will stop immediately.

On Alignment III, I could not reach 2.0 watts by adjusting L1 and
L2. I get a transient Hi Current reading at beginning of keydown.
The current drawn was 3.5 amps (the current limit) on transmit.
(About .24 on receive)

In the troubleshooting section, I checked ALL components in PA,
Driver, Pre-Driver, PA Bias and RF Output Detector.
I could find no solder bridges and all parts appear to be correct.
I checked the windings of T1 -T4 and their solder connections...seem
to be OK.
R50 was not open.

Now I know the signal tracing section suggests I do the receiver
signal trace first, since several circuits are shared. I do not have
a signal generator, however. I just ordered the XG-2 but won't have
it for a bit. So I did the signal tracing for the transmitter.

Signal tracing for transmitter (p. 12 of troubleshooting):
I am using a Radio Shack 25 Amp switching supply reading 13.9 volts
that goes to 13.6 on receive. Transmit V=12.9 A=2.5
D6 anode is 7.9VDC (correct) and D7 is 0.2VDC. Power output is
0.3W. I hear a normal cw tone on a nearby receiver at the proper freq.

VPWR is 1.2VDC (correct)

Now, Here are the aberrant values:

Band-Pass Filter Output: 0.12 (Expected is .03)
T-R Switch #1 Output: .141 (Expected is .029)
Driver Input: 0.16 (Expected .026)
RF Detector Input: 0.7 (Expected is 2.0)
Q7 and Q8: both have been replaced once already
Transistor test Pos. Lead on Base: E and C both read about .55
(volts, I guess..."k" is listed in the manual)
Neg. Lead on Base: "OL" on C, .55 on E(expected is 1.3)

That's where I am at the moment.

If someone can explain what the settings should be for DC Voltage
tables during TRANSMIT, I would really appreciate it.
In the manual (p14) It says no antenna...this doesn't sound right for
transmit. What did I miss? Then, I can tackle the DC readings.

ANY IDEAS?

John
AB8WH

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Don Wilhelm-3

RE: K2 troubleshooting

John,

The PA Transistor Test values will vary depending on your particular DMM -
some will show forward voltage while others will show ohms. Your .55
reading on the base to emitter with the probes either way would indicate
something to be concerned about - but since you are testing in-circuit, the
problem could be something other than the output transistors (we can get to
that later if need be).

When doing the transmit measurements (DC Voltages or others), it is always a
good idea to connect a 50 ohm dummy load. Make your measurements during
quick key-down (or TUNE) periods, and give things a chance to cool down
after each measurement.

Your RF voltage measurements look OK for a K2 that is not developing
sufficient power output - the 'too high' readings are to be expected under
such conditions. What is the Driver Output RF Voltage and the PA Input RF
Voltage? These measurements will tell if the problem is the driver or the
finals. If the Driver Output is low, the first thing to check is the
emitter resistor for Q6.

73,
Don W3FPR

> -----Original Message-----
> Now, Here are the aberrant values:
>
> Band-Pass Filter Output: 0.12 (Expected is .03)
> T-R Switch #1 Output: .141 (Expected is .029)
> Driver Input: 0.16 (Expected .026)
> RF Detector Input: 0.7 (Expected is 2.0)
> Q7 and Q8: both have been replaced once already
> Transistor test Pos. Lead on Base: E and C both read about .55
> (volts, I guess..."k" is listed in the manual)
> Neg. Lead on Base: "OL" on C, .55
> on E(expected is 1.3)
>
> That's where I am at the moment.
>
> If someone can explain what the settings should be for DC Voltage
> tables during TRANSMIT, I would really appreciate it.
> In the manual (p14) It says no antenna...this doesn't sound right for
> transmit. What did I miss? Then, I can tackle the DC readings.
>

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John Wiener

Re: K2 troubleshooting

Don,
Driver Output RF last measured at 2.3V rms (earlier it was 3.6)
which I think is normal.
PA Input RF(Q7) was .55 and (Q8) was .55 which I think is also normal.

John
AB8WH

On May 30, 2006, at 12:15 AM, Don Wilhelm wrote:

> John,
>
> The PA Transistor Test values will vary depending on your
> particular DMM -
> some will show forward voltage while others will show ohms. Your .55
> reading on the base to emitter with the probes either way would
> indicate
> something to be concerned about - but since you are testing in-
> circuit, the
> problem could be something other than the output transistors (we
> can get to
> that later if need be).
>
> When doing the transmit measurements (DC Voltages or others), it is
> always a
> good idea to connect a 50 ohm dummy load. Make your measurements
> during
> quick key-down (or TUNE) periods, and give things a chance to cool
> down
> after each measurement.
>
> Your RF voltage measurements look OK for a K2 that is not developing
> sufficient power output - the 'too high' readings are to be
> expected under
> such conditions. What is the Driver Output RF Voltage and the PA
> Input RF
> Voltage? These measurements will tell if the problem is the driver
> or the
> finals. If the Driver Output is low, the first thing to check is the
> emitter resistor for Q6.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>> Now, Here are the aberrant values:
>>
>> Band-Pass Filter Output: 0.12 (Expected is .03)
>> T-R Switch #1 Output: .141 (Expected is .029)
>> Driver Input: 0.16 (Expected .026)
>> RF Detector Input: 0.7 (Expected is 2.0)
>> Q7 and Q8: both have been replaced once already
>> Transistor test Pos. Lead on Base: E and C both read about .55
>> (volts, I guess..."k" is listed in the manual)
>> Neg. Lead on Base: "OL" on C, .55
>> on E(expected is 1.3)
>>
>> That's where I am at the moment.
>>
>> If someone can explain what the settings should be for DC Voltage
>> tables during TRANSMIT, I would really appreciate it.
>> In the manual (p14) It says no antenna...this doesn't sound right for
>> transmit. What did I miss? Then, I can tackle the DC readings.
>>
>