Tom, With R6 out, and DC voltage on U4 pin 3, but 0 volts on U4 pin 1, you certainly can suspect that U4 is toast. Unless you have a solder bridge between U4 pins 2 and 3 *and* no connection between pins 1 and 2 - that would be 2 failures, and we normally expect only a single failure, so a bad U4 is the most likely answer.
Do the test again, but this time measure the voltage at U4 pin 3. If that is different than the voltage at U4 pin 1, you have a problem with U4. (BTW, with 5 watts through the wattmeter, U4 pin 3 should measure between 3 and 4 volts). As I stated, U4 is a unity gain op amp, and the voltage at the output should be the same as the voltage at the input - that is the behavior of a working unity gain op amp. 73, Don W3FPR Tom Campie wrote: > As per Gary's suggestion, I removed and rewound T1. I also reflowed all the > joints in the SWR bridge and on U4. With R6 out, I still measure 0.0 V and > with it in I'm still under 3 v. With it in, I read the same 2.4V as before. > While I can't confirm the actual output power exactly, my MFJ tuner reads 5 > watts when it is tuned (I don't have an RF probe or wattmeter yet - I'm > getting the parts for the RF probe on Thursday) Could it be that U4 is > bad? Amps like that don't break very easily. > Still not sure where to look except U4 I guess... > > Tom > > On Tue, Jul 21, 2009 at 8:47 PM, Don Wilhelm <w3...@embarqmail.com> wrote: > > >> Tom, >> >> The voltage at U4 pin 3 should be between 3 and 4 volts with 5 watts of >> power flowing through the wattmeter section of the KAT2 *and* with the FWD >> potentiometer (R1) fully clockwise. >> >> U4 is configured as a unity gain op amp, and the voltage at the output (pin >> 1)should be equal to the voltage at the input (pin 3). If it is not, check >> the soldering at U4. That should be true whether R6 is connected or not. >> >> If the conditions (and results) are not as stated, then as the manual >> states, check T1, D1, C50, C52 and R1 for good soldering. Count the turns >> on T1 to be certain you have not wound an extra turn. >> >> Is the power that you are passing through the KAT2 equal to 5 watts? How >> are you determining it? >> >> 73, >> Don W3FPR >> >> >> Tom Campie wrote: >> >> >>> Still no solution for my power problem. Some correspondence with Gary at >>> Elecraft has me back where I started. I removed R6 and saw 0V at the >>> output >>> of U4 but 2.5V on the input of U4 coming from U1 (pin 3 on U4). According >>> to the testing in the manual this should be 3-4 volts with a requested >>> power >>> of 5 watts. I replaced R6 and now saw the 2.5V on the output of U4. This >>> is still low obviously. I reflow'd all the solder joints in the SWR >>> bridge >>> as it suggests and this has not helped. I'm not sure where to look next. >>> >>> Tom W0EA >>> >>> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
