I put the heatsink back on and there was no change. The Q5 collector was
> Robert,
>
> OK, the Pre-driver output is low - next step is to check the DC voltages
> for Q5 - but that must be done during transmit. It is difficult (almost
> impossible) to check the emitter without removing the heat-sink. WARNING -
> even though the power output is low, do not operate the K2 without the
> heatsink attached.
> So during transmit, check the collector voltage - should be close to 12.4
> volts
> And check the base voltage which can be reached at the end or either R40 or
> R41 - should be 1.3 volts.
> If all was well for those checks, remove the heatsink and measure the
> resistance between the emitter of Q5 and ground - if it is more than 27
> ohms, check the values of R42 and R43 and check their soldering.
> If the resistance was correct, check the value of C117 (should be .047 uF)
> and reflow its soldering. Also check C116 (33 pF), C118 (.01 uF) and C115
> (.01) and reflow the soldering for those too. Then put the heat sink back
> on and see if there is any change.
>
> BTW - you can consider the division between the pre-driver and the driver
> as being between the primary and the secondary winding of T1.
>
> 73,
> Don W3FPR
>
> Robert Greenwalt wrote:
>
>> Hi,
>>
>> When doing the 40-Meter Transmitter Alignment, I couldn't keep the output
>> power in th 1-2 watt range. Turning the power all the way up only got up
>> to
>> .7 watts. I checked the output across the dumy load and it was
>> practically
>> non-existent (.007Vrms) though key-down was noticeably different than
>> key-up.
>>
>> I walked through the Transmitter signal tracing. Everything was within
>> tolerances until I got to the pre-driver output. I expected about
>> .132Vrms
>> but got .07 Vrms.
>>
>> I've checked all the components in the pre-driver section up through T1
>> (not
>> sure where pre-driver ends and driver begins) and they all have the right
>> markings. I verified T1 and reheated the connections.
>>
>> On qth.net I only found references to high pre-driver issues.
>> Suggestions?
>>
>> Transmit mixer output: .016 Vrms
>> Buffer output: .216 Vrms
>> Bandpass filter output: .035 Vrms
>> TR switch output: .033 Vrms
>>
>> Predriver output: .072 Vrms (expected .13 )
>>
>> Robert, K6RJG
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>