K1 transmitter problem...any help appreciated.

[Ron ZL1TW]

Hi Guys,
             As a last resort I am appealing to the "Elecraft collective" to
see if I can get help with this problem.
I have a K1 that has been going great for years , but during a band filter
change it was fired up without the ATU replaced and it fried the output
transistor and D19.(also damaged T4 which has been re-wound....and double
checked since)
I replaced both the output transistor and D19 and it "sort of " went for a
while then decided to die on transmit completely.
I replaced the driver.....no change... Then I started looking with my very
limited quality "scope". I appear to be getting drive through the Transmit
mixer OK, and the buffer stage appears to giving me a 10x increase in drive
level. The signal looks OK until I get to point "TR1" at the junctions of D5
and D14 where it goes into the BPF. There is not much drive appearing at
point "TR2" ....certainly not enough to get the driver excited enough to
work
This problem is common to each band on two different 2 x Band boards, so I
have to presume they are OK.
Because the level drops at point "BPF" on the cct diagram, I immediately
thought there was a problem in the T-R switching circuit.The diodes tested
OK , but to make sure I removed all diodes and they did indeed test fine, so
did the resistances associated with them. Q4 appeared to be doing it's job
OK but I swapped it out for a new one....replaced all the diodes. OP1 still
showed on transmit....nothing on the power meter.
I then decided it might be a lack of drive earlier on so replaced Q5
...still no change....from memory there was about 6v being applied to the
Drain of Q5 from the MCU.
I might be wrong, but I expected to see about the same outputs from the
Mixer/Osc chips U7 and U8.....they are pretty much the same.
The set receives just fine...another reason not to suspect the BPF's. If I
listen to the weak signal that *is* produced, I can peak all the filters on
it while listening to the signal on another receiver.
So...where does one look from here? What is a very basic transmitter circuit
has me bluffed at present...luckily I have little hair left to pull out. Any
Ideas???
Regards.....Ron ZL1TW


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[Ron ZL1TW]

Hi Tom,
             Thanks for the reply.....I will answer each question below:-
----- Original Message -----
From: "Tom Arntzen" <[hidden email]>


> Hi Ron!
> The TR1/BPF will have 1/3-1/2 level of BUF.
> After looking on the schematics I would like you to check following
> points.

My measuremens show about 1/3 the level between in/out ....

> Measure DC-voltage collector Driver Q6.
> If missing check both sides of RFC5.

Voltages OK @12v.

> Also take a close look at T3 , high currents can go through T3 if Q7 is
> fried the right/wrong way.

T3 appeared OK but I rewound that as well when I replaced the driver.(
yes.... I double checked since)

> Also make DC measures to TR-switch D10 and D9 and see that D10 is closed
> during TX.

Yes D10 is biased "on" during receive and "off" during Transmit ( by way of
the 6R/aux and 6R_2 voltages being applied in receive and removed during
Tx.)

> Also verify that D9 does it's job ok.

D9 is turned on OK by the 6T voltage during transmit.

> You may want to swap out or check r31 and r32.
> They are in the "dangerzone" during PA failure.
>

Both R31 and R32 have been lifed one end and each verified OK.

> I really can't see any points in path where the signal could get lost
> between BUF and TR1 other than normal loss.

Nor can I !!

> I guess you can hear your K1 on the right frequencies on another rx when
> sending , and the rx is OK.

Yes receive is fine and in the right place

> If so the problem is still in the PA or D9-D10.
>

D9 and D10 have been replaced...so has Q6 and Q7 ...the same manufacturer
and part numbers.

> Hope you get on the air with your K1 soon.
>
Yes ...so do I.
I have even tried "bush practices" like disconnecting Q7 and lifting
terminal 3 of T3 and using the old trick of connecting a very low wattage
torch bulb from the removed lead to ground to see if there is drive....there
wasn't enough to even get a glimmer.
Thanks for the suggestions Tom, but I think I have those covered.
> Tom LA1PHA
> K1 1491
Cheers......Ron ZL1TW  K1 #575
>

> ----- Original Message -----
> From: "Ron" <[hidden email]>
> To: "Elecraft Reflector" <[hidden email]>
> Sent: Monday, August 20, 2007 2:18 AM
> Subject: [Elecraft] K1 transmitter problem...any help appreciated.
>
>
>> Hi Guys,
>>             As a last resort I am appealing to the "Elecraft collective"
>> to see if I can get help with this problem.
>> I have a K1 that has been going great for years , but during a band
>> filter change it was fired up without the ATU replaced and it fried the
>> output transistor and D19.(also damaged T4 which has been re-wound....and
>> double checked since)
>> I replaced both the output transistor and D19 and it "sort of " went for
>> a while then decided to die on transmit completely.
>> I replaced the driver.....no change... Then I started looking with my
>> very limited quality "scope". I appear to be getting drive through the
>> Transmit mixer OK, and the buffer stage appears to giving me a 10x
>> increase in drive level. The signal looks OK until I get to point "TR1"
>> at the junctions of D5 and D14 where it goes into the BPF. There is not
>> much drive appearing at point "TR2" ....certainly not enough to get the
>> driver excited enough to work
>> This problem is common to each band on two different 2 x Band boards, so
>> I have to presume they are OK.
>> Because the level drops at point "BPF" on the cct diagram, I immediately
>> thought there was a problem in the T-R switching circuit.The diodes
>> tested OK , but to make sure I removed all diodes and they did indeed
>> test fine, so did the resistances associated with them. Q4 appeared to be
>> doing it's job OK but I swapped it out for a new one....replaced all the
>> diodes. OP1 still showed on transmit....nothing on the power meter.
>> I then decided it might be a lack of drive earlier on so replaced Q5
>> ...still no change....from memory there was about 6v being applied to the
>> Drain of Q5 from the MCU.
>> I might be wrong, but I expected to see about the same outputs from the
>> Mixer/Osc chips U7 and U8.....they are pretty much the same.
>> The set receives just fine...another reason not to suspect the BPF's. If
>> I listen to the weak signal that *is* produced, I can peak all the
>> filters on it while listening to the signal on another receiver.
>> So...where does one look from here? What is a very basic transmitter
>> circuit has me bluffed at present...luckily I have little hair left to
>> pull out. Any Ideas???
>> Regards.....Ron ZL1TW
>>
>>
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>>
>>
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[Don Wilhelm-4]

Ron,

Since you have apparently exhausted most of the things that seem
logical, perhaps it is time to look at some of the things that border on
the 'strange and unusual'.   Suggestions follow:

1) check for a poor connection at J7.  That is best done by comparing
the signal level on both sides of a connector pin (with a filter board
plugged in).  Check both at pin 1 and pin 8.
2) Check the signal path through the signal path through the BPF itself
to see where it is getting lost.
3) With a frequency counter, check the frequencies at the premixer
output (PRE), the transmit LO (OSC), the mixer output (MIX), and buffer
output (BUF).  There is the thought that perhaps the transmit LO could
be way off, and the resulting frequency that you are feeding to the BPF
is not correct.  This condition would not show up until you try to put
the signal through the bandpass filter - and it would produce exactly
the conditions you report.

73,
Don W3FPR
 
Ron wrote:

> Hi Guys,
>             As a last resort I am appealing to the "Elecraft
> collective" to see if I can get help with this problem.
> I have a K1 that has been going great for years , but during a band
> filter change it was fired up without the ATU replaced and it fried
> the output transistor and D19.(also damaged T4 which has been
> re-wound....and double checked since)
> I replaced both the output transistor and D19 and it "sort of " went
> for a while then decided to die on transmit completely.
> I replaced the driver.....no change... Then I started looking with my
> very limited quality "scope". I appear to be getting drive through the
> Transmit mixer OK, and the buffer stage appears to giving me a 10x
> increase in drive level. The signal looks OK until I get to point
> "TR1" at the junctions of D5 and D14 where it goes into the BPF. There
> is not much drive appearing at point "TR2" ....certainly not enough to
> get the driver excited enough to work
> This problem is common to each band on two different 2 x Band boards,
> so I have to presume they are OK.
>

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