Hi Jerry, I did not try to isolate as the track went straight to the max chip pin 8, I just removed the chip. C38 was the cap that was cracked, so instead of 10nF it was a few 100 pF!!! Or less.
I bought my KP100 some 3 years ago, and since then it has undergone a lot of improvement from Elecraft, if yours is less than a year old then you will have the latest revision. There are changes to the TR and switching and bias circuits. I had around 150V to 200V at times, if pin 8 is low, then check the components to the right of C37. The high voltage supply is only bias and supplies very low current. Check Q6 as if this has a very small leak, it will drag the bias voltage down and check D11 to 14. Q6 has failed a few times in my rig prior to the modifications, however, this was due to me leaving the aerial connected when high winds and storms were about. 73's Andrew Don Wilhelm-4 wrote: > > Jerry, > > That answer depends on which set of "specifications" you want to believe. > > I am saying that the Absolute Maximum Specification for the Maxim > MAX1406 for Vss (pin 8) is -14 volts - you can check the data sheet for > yourself. Yes, many KPA100s exceed that value - note that the KPA100 DC > voltage chart lists the nominal voltage at U4 pin 8 at -22 volts. > Whether that is a cause for failure of the chip is reason for > speculation, there is not enough data to say yeah or nay. . > What I have offered is a way to reduce the Vss voltage to the MAX1406 > without also reducing the bias voltage to the KPA100 T/R switch. That > involves removing D8, and D8 alone. The data sheet Electrical > Characteristics current for pin 8 (Iss) is typical 185 uA with a maximum > of 500 uA. for a Vss of -13.2 volts Minimum to -10.8 Maximum - that is > not a lot of current draw on that pin. > > I am stating that a Vss (U4 pin 8) voltage less than -14 volts exceeds > the Absolute Maximum Voltage rating per the MAX1406 datasheet - nothing > more and nothing less. > > 73, > Don W3FPR > > n0jrn wrote: >> Don: >> >> Just to clarify ! >> >> The -28V's I'm seeing at pin 8 of U4 is measured without the IC >> installed. >> >> Lets say for the sake of conversation that I install a good MAX1406 and >> it >> draws on the rectifier circuit a minimal amount. >> >> Would / could that bring the -28V's back into specs for this chip???. ( >> I >> have to figure Wayne designed the circuit taking this draw into >> consideration ) >> >> OR is my -28V's so abnormal that I need to be looking at other >> issues >> in my rectifier pack to bring this negative voltage back into spec ??? >> >> Could the negative voltage I'm getting be responsible for damaging this >> chip >> ??? >> >> I have 2 new chips coming from Mouser. I'm not installing them until >> I'm >> satisfied that I've checked and double checked EVERYTHING involved. >> >> Thanks again and happy holidays to the group: >> >> 72 Jerry N0JRN >> ----- Original Message ----- >> From: "Don Wilhelm" <[email protected]> >> To: "n0jrn" <[email protected]> >> Sent: Monday, December 14, 2009 6:22 AM >> Subject: Re: [Elecraft] KPA100 problem >> >> >> >>> Jerry, >>> >>> I will take back what I said about U4 - it is faulty. >>> That negative voltage is there only to allow the RS-232 drivers to >>> produce >>> a negative level, the current draw should be minimal. >>> The only thing U4 does is convert RS-232 levels to TTL levels and >>> vice-versa. >>> >>> Actually -28 volts is a bit much and does exceed the maximum speced >>> voltage for the chip. -12 volts is more than sufficient and even -5 >>> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> ------------------------------------------------------------------------ >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com >> Version: 9.0.716 / Virus Database: 270.14.107/2564 - Release Date: >> 12/14/09 02:37:00 >> >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > -- View this message in context: http://n2.nabble.com/KPA100-problem-tp4161606p4168863.html Sent from the [K2] mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
