Low SSB TX power on K2
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I recently picked up an older K2 # 185. It's had all the important Elecraft-recommended performance mods and Alerts applied, including the "A to B" upgrade. The rig works FB on CW. I am disappointed with the SSB performance, even after using three mikes (and changed mike pin jumpers). I scanned the email reflector and decided to do voltage checks of the ICs and diodes on the SSB board. The SSB board is Rev. C. There is no reading on the S-meter when I transmit, and no reading on ALC. I do get a very weak signal when I used each of the three mikes and listened on my other rig. I also transmitted PSK and again get a weak signal, however, the IMD was -23. A couple of hams within 5 miles said they heard me on 20 meter SSB, but just at the noise level. Another ham who lives about 10 miles away could not hear me, but I heard him calling me. Firmware is 2.01H and IOC 1.02.
The following are 'unusual' readings, in that they are more than 2/10's off target or show a reading when the reading should be zero. IC/PIN RX(V)-Target RX(V)-Actual TX(V)-Target TX(V)-Actual U1-2 5.9 4.4 5.3-5.9 5.4 U1-6 5.1 5.5 0 0 U1-9 0.0 0.0 2.3 1 U1-16 6 6.1 5.4 3.7 U1-17 6 6.1 5.6 4.7 U1-21 5.8 5.8 0.1 0.0 U1-25 0.0 0.0 0.8-1.2 0.6 U1-28 5.6 5.6 2.4 4.6 U2-1 6 6.1 5.6 4.7 U2-5 0.6 6 0.6 0.4 U2-8 6 6.1 5.4 3.7 U3-4 1.7 1.3 1.7 1.3 U3-6 0.0 0.0 0.8-1.2 0.6 U4-3 0.6 6 0.6 0.4 U4-6 5.1 5.5 0.0 0.0 Diode CW(V)-Target CW(V)-Actual SSB(V)-Target SSB(V)-Actual D10 5.4 5.2 6 5.8 D11 6 5.8 0.0 0.1 D12 6 5.8 0.0 0.1 I also did readings on the other diodes on the SSB board, with targets unknown. D1 ??? 5.6 ??? 5.6 D2 ??? 4.4 ??? 4.4 D3 ??? 1.8 ??? 1.8 D4 ??? 5.8 ??? 5.8 D5 NOT FOUND ON THE BOARD. D14 ??? 5.8 ??? 5.8 Can someone provide some direction as to my next step? My only diagnostic tool, outside of the K2 built-ins, is a DMM. My background is in accouting and risk management, unfortunately not in eletronics. Thanks in advance Cal N9KO _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Cal,
First check the voltage on the collectors of Q2 and Q3 during transmit - you should find close to 8 volts. It sounds to me like you are not getting an adequate audio signal into the balanced modulator (U4 on the KSB2 board). Without some tool to observe the audio signal, that may be a tough thing to de-bug. The DC levels on the points you mentioned do not have a direct bearing on your problem. One thing that you could do is check the components in the audio path - look at the KSB2 schematic and find the components in the paths connecting to pin 4 and pin 7 of U3 on the KSB2 board. check all those for good soldering. It is unlikely that your DMM will respond to AC signal levels comparable to mic output voltages, so a tool (such as a 'scope) may be required if you cannot find a problem by inspection. The lack of D5 indicates that you have an older KSB2 board - that in itself is not a problem, all else on the board is pretty much the same as the newer boards. 73, Don W3FPR > -----Original Message----- > > I recently picked up an older K2 # 185. It's had all the > important Elecraft-recommended performance mods and Alerts > applied, including the "A to B" upgrade. The rig works FB on > CW. I am disappointed with the SSB performance, even after using > three mikes (and changed mike pin jumpers). I scanned the email > reflector and decided to do voltage checks of the ICs and diodes > on the SSB board. The SSB board is Rev. C. There is no reading > on the S-meter when I transmit, and no reading on ALC. I do get > a very weak signal when I used each of the three mikes and > listened on my other rig. I also transmitted PSK and again get a > weak signal, however, the IMD was -23. A couple of hams within 5 > miles said they heard me on 20 meter SSB, but just at the noise > level. Another ham who lives about 10 miles away could not hear > me, but I heard him calling me. Firmware is 2.01H and IOC 1.02. > > > Can someone provide some direction as to my next step? My only > diagnostic tool, outside of the K2 built-ins, is a DMM. My > background is in accouting and risk management, unfortunately not > in eletronics. > > _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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