Jim, Before being concerned about the DC voltages at U1 and U2, I would suggest concentrating on the BFO injection and the balanced modulator first. The digital signals from U1 and U2 will only occur when the conditions are correct and a variation from the voltages stated in the manual is not necessarily a cause for immediate alarm - check the audio and RF signal paths first.
Use a 'scope (with a 10X probe) or an RF Probe and check the BFO path from pin 12 of P1 to pin 6 of U5. You should have a good BFO signal to U5 pin 6. I would expect somewhere between .025 and .07 volts RMS for proper operation. If you do not have adequate BFO signal at U5 pin 6, look carefully at Q1 and Q2 and their associated components. The next place to check for an AC signal (but it will be audio not RF) is at the output of the Speech compressor U3 pin 7. I am guessing here, but I should think something on the order of 200 mV would be a good level. A 'scope is almost a necessity here to view voice peaks, but if you have an audio generator, you may be able to read the level with an audio frequency AC voltmeter. Before you begin this hunt, be certain the 5.6k resistor for your MD2 mic is properly soldered in place on the mic jack (check its value with the mic unplugged). Try another mic if you can or check your mic on another K2 - it could be that your mic element was going bad on you and there is nothing wrong with the K2. In other words, overlook nothing, particularly the simple things. If you have a cheap computer mic laying around, you can use that to verify the mic operation - hook the AF line (tip of the plug) to mic jack pin 1 and the ground to pin 7 then use the dot paddle for a PTT button. 73, Don W3FPR > -----Original Message----- > Hi, > > I have no transmit SSB audio on my K2. CW works fine. From voltage > readings on the KSB2 looks like the problem is in the area of U2 > - MAX522, > Q1 - PN2222A, U1 - 16F872 and U3 - SSM2165. I replaced Q1 with > a 2N2222A, > almost the same specs, and it did not help. Over the last 2-3 months I've > had to turn mic gain and compression to full to get any transmit > audio out. > Now there is none. I'm using the Elecraft/Heil MD2 microphone. > > The out of nominal (+ & - 10-15%) voltages are as follows. I'm using a > Fluke 8600A multimeter. Only transmit voltages are listed below. > > U1-10 sb 3.1 is 2.6 (~15%) > U1-16 sb 5.4 is 3.1 (~30%) > U1-17 sb 5.6 is 4.2 (~40%) > U1-28 sb 2.4 is 5.4 (~220%) > > U2-1 sb 5.6 is 4.2 (~25%) > U2-5 sb 0.6 is 1.6 (~280%) > U2-8 sb 5.4 is 3.1 (~90%) > > U-3 sb 0.8-1.2 is 0.0 (~?????%) > > The discrepancy on U3 appears to be a function of the setting of > the audio > compressor. But, could be otherwise. > > The radio is about 15 months old and I'm the original owner. I've been > solder certified by the Air Force and NASA and inspected medical > subassemblies for several years so there is a possibility I know my way > around soldering. Just the same I've reflowed all joints and > reverified all > components on the KSB2. I've also rechecked all menu setting and all are > fine. I'm using a gel cell battery rated at 8AH for power. It > is reading > 12.6 volts by the K2 meter obtained by tapping display. The battery will > deliver several amps with only 0.2 VDC drop in voltage. > > Any thoughts helps or other ideas would be appreciated. > > > Thanks, > > Jim, AB0UK > > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.394 / Virus Database: 268.8.3/360 - Release Date: 6/9/2006 > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
