[Elecraft] KPA100 - Low Voltage output from High Voltage Bias Supply Circuit

[Michael Haygood]

Don,

I replaced D16 and D17 which fixed the HI CUR, HI REFL messages and lack of 
power control.

However, I am still reading a low output voltage from the high voltage bias 
supply.  When receiving, the high bias supply voltage at D1 cathode and 
R12/R11 is about 67 volts.

I've further investigated the low voltage output from the high voltage bias 
supply as follows:

1.  De-soldered the high bias voltage side of resistors R12 and R11, then 
remeasured the high bias output voltage - about 69 volts.  I did this to 
ensure that nothing in the T/R circuit was draining the high voltage supply; 
resoldered R11/R12 back into the circuit.

2.  Desoldered the D7 anode in the high voltage bias circuit, which connects 
to the VSS supply pin of the MAX1406 (RS232 Interface), then measured the 
high voltage bias output voltage at D1 cathode - measured 154 volts!  
Re-soldered the D7 anode back into the circuit and the high voltage bias 
supply dropped back down below 70 volts.

The high voltage bias supply output should be between 90 and 150 volts.  Is 
it possible that the MAX1406 is somehow draining this circuit?  Seems 
strange that it would be because it cuts the output voltage more than 50% 
when the MAX1406 VSS is connected into the circuit.

I've verified that D1 through D8 are good.

Any further thoughts or info concerning the low output voltage would greatly 
be appreciated!

Michael Haygood
KI5E

>From: Don Wilhelm <w3fpr at earthlink.net>
>Reply-To: w3fpr at arrl.net
>To: Michael Haygood <mhlh2 at hotmail.com>
>CC: elecraft at mailman.qth.net
>Subject: Re: [Elecraft] KPA100 - Low Voltage output from High Voltage Bias 
>Supply	Circuit
>Date: Thu, 19 Jul 2007 18:26:59 -0400
>
>Michael,
>
>You said the 'magic words' - HI CUR, Hi REFL messages and lack of power 
>control (other than low and high power selection) *after* a lightning 
>storm.
>
>That is an indication that the lightning surge zapped diodes D16 and D17 in 
>the KPA100 wattmeter - the result is that the base K2 microprocessor 
>*thinks* there is no power output and increases the drive until it 'runs 
>out of gas' - the K2 will produce max power output under those conditions.
>
>Replacement of D16 and D17 is in order as a first step.  If that does not 
>cure things, then we can help you troubleshoot it further.
>
>73,
>Don W3FPR
>
>Michael Haygood wrote:
>>Hi,
>>
>>I've been using my K2/100 for many months with great results.  After a 
>>recent storm containing lightning the next time I fired up the K2/100 I 
>>received the "HI CURR" message and the "HI REFL" messages upon initial 
>>transmit.  This was unusual, so the next thing I did was consult the 
>>troubleshooting guide in the KPA100.
>>
>>Using a wattmeter and connected to a dummy load, I measured the output 
>>power of the K2/100 with the power outupt contol set to less than 11 watts 
>>and noticed that for a setting of 5 watts the output of the K2/100 was 
>>about 10 watts.  For a power output setting of 15 watts, the output was 
>>very high - about 100 watts.
>>

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