8T/8R problems
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Hi everyone,
Since everything but the BFO was working I decided to finish wiring the radio. Everything went down hill from there. At phase II all the control functions worked perfectly but now the transmitter parts are in the display flashes between the frequency, power output setting, and keyer speed. In fact the radio is transmitting all the time. The finals get warm plus the dummy load warms up. The voltage reading at the dummy load is between 18 and 25 vdc. I checked the 8T and 8R lines and 8T is 1.5 vdc and 8R is 7.1 vdc. The manual isn't very clear on what they should be. I figured 8T would be 8vdc when transmitting and 8R would be 8vdc on receive. In the circuit description is says that Q23 hold 8R at 0vdc on receive. As you can tell my reading are way off. Here are some more voltage reading that aren't right: Chip U6 pin 24 0vdc pin 25 5vdc pin 27 0vdc ok pin 28 4.2vdc pin 36 4.5vdc pin 39 1.0vdc Q23 pin S 0vdc pin G 1.5vdc pin D 6.2vdc Chip U11 pin 6 5.01vdc still low pin 7 4.66vdc still low I checked the whole radio again for bad solder joints and bridges - still nothing found. I checked for the correct parts in their locations - everything looks right. Like I said at phase II the controls all worked as they should and the display didn't jump around on it's own. The receiver peaked up fine on 40 meters. Because everything was working I figured it was save to continue. The 8T and 8R lines were probably messed up the whole time but since the transmitter wasn't wired the problem didn't show up. Any ideas will be appreciated. Thanks, Tom K2 #5020 _______________________________________________ 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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I'm new at this, so verify my comments.
On Wed, 3 Aug 2005 20:53:55 -0000, <[hidden email]> wrote: >Hi everyone, > >Since everything but the BFO was working I decided to finish wiring the >radio. Everything went down hill from there. At phase II all the control >functions worked perfectly but now the transmitter parts are in the >display flashes between the frequency, power output setting, and keyer >speed. In fact the radio is transmitting all the time. The finals get >warm plus the dummy load warms up. The voltage reading at the dummy load >is between 18 and 25 vdc. >I checked the 8T and 8R lines and 8T is 1.5 vdc and 8R is 7.1 vdc. The >manual isn't very clear on what they should be. I figured 8T would be >8vdc when transmitting and 8R would be 8vdc on receive. In the circuit >description is says that Q23 hold 8R at 0vdc on receive. As you can tell >my reading are way off. You're understanding of 8R and 8T are correct. The blurb about Q23 is a misprint. When transmitting, 8T is high and turns on Q23 pulling 8R low. >Here are some more voltage reading that aren't right: > >Chip U6 pin 24 0vdc > pin 25 5vdc > pin 27 0vdc ok > pin 28 4.2vdc > pin 36 4.5vdc > pin 39 1.0vdc > Q23 pin S 0vdc > pin G 1.5vdc > pin D 6.2vdc Control board U6 pin 24 is the clock that drives the quad 8 bit DAC U8. At zero volts, you have no clock so U8's output is most likely random in nature. Since U8 generates V BFO, that's probably why your BFO isn't working. I would check U6 for bent pins (not seated in the socket) shorted pins (solder bridges) or the like. Most of your other problems are probably related to the faulty outputs from U6 and may correct themselves when U6 is fully operational. >Chip U11 pin 6 5.01vdc still low > pin 7 4.66vdc still low > >I checked the whole radio again for bad solder joints and bridges - >still nothing found. I checked for the correct parts in their locations >- everything looks right. >Like I said at phase II the controls all worked as they should and the >display didn't jump around on it's own. The receiver peaked up fine on >40 meters. Because everything was working I figured it was save to >continue. The 8T and 8R lines were probably messed up the whole time but >since the transmitter wasn't wired the problem didn't show up. >Any ideas will be appreciated. >Thanks, >Tom K2 #5020 > >_______________________________________________ >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 _______________________________________________ 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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Matt,
You are not incorrect, but I thought I might clarify - the real control over 8R and 8T is done on the control board from the RX and TX outputs from the microprocessor - which drives the gates of Q3 and Q4, and in turn turns Q1 and Q2 on and off providing the 8R and 8T lines at the correct times. Q23 on the RF Board helps by providing a low resistance path to drain off any residual current on 8R during periods of transmit, it is just not the controlling element. - yes, the manual has it backwards, and the statement should read 'Q23 on th RF Board is used to guarantee that 8R goes to 0 V on TRANSMIT ...'. Possible causes for 8T being 1.5 volts during receive are - Q1 on the Control Board incorrect or installed backwards; Control Board Q3 shorted (the receive state voltage at Q1 base would detect that); or a diode installed backwards (check D6 and D7 especially). The voltage readings on RF Board U11 pins 6 and 7 are likely associated with the BFO problem. Find and correct the 8R, 8T problem first, and then move on to the BFO (you could have incorrect wiring, an unsoldered connection, incorrect varicaps, incorrect capacitors, a bad crystal, or a bad U11 chip. The most likely source of the problem is a bad or missed solder joint, followed closely by an incorrectly placed component - actual component failures do happen, but they are much further down the list. 73, Don W3FPR > -----Original Message----- > > I'm new at this, so verify my comments. > > On Wed, 3 Aug 2005 20:53:55 -0000, <[hidden email]> > wrote: > > >Hi everyone, > > > >Since everything but the BFO was working I decided to finish wiring the > >radio. Everything went down hill from there. At phase II all the control > >functions worked perfectly but now the transmitter parts are in the > >display flashes between the frequency, power output setting, and keyer > >speed. In fact the radio is transmitting all the time. The finals get > >warm plus the dummy load warms up. The voltage reading at the dummy load > >is between 18 and 25 vdc. > >I checked the 8T and 8R lines and 8T is 1.5 vdc and 8R is 7.1 vdc. The > >manual isn't very clear on what they should be. I figured 8T would be > >8vdc when transmitting and 8R would be 8vdc on receive. In the circuit > >description is says that Q23 hold 8R at 0vdc on receive. As you can tell > >my reading are way off. > > You're understanding of 8R and 8T are correct. The blurb about Q23 is > a misprint. When transmitting, 8T is high and turns on Q23 pulling 8R > low. > > > >Here are some more voltage reading that aren't right: > > > >Chip U6 pin 24 0vdc > > pin 25 5vdc > > pin 27 0vdc ok > > pin 28 4.2vdc > > pin 36 4.5vdc > > pin 39 1.0vdc > > Q23 pin S 0vdc > > pin G 1.5vdc > > pin D 6.2vdc > > Control board U6 pin 24 is the clock that drives the quad 8 bit DAC > U8. At zero volts, you have no clock so U8's output is most likely > random in nature. Since U8 generates V BFO, that's probably why your > BFO isn't working. > > I would check U6 for bent pins (not seated in the socket) shorted pins > (solder bridges) or the like. > > Most of your other problems are probably related to the faulty outputs > from U6 and may correct themselves when U6 is fully operational. > > >Chip U11 pin 6 5.01vdc still low > > pin 7 4.66vdc still low > > > >I checked the whole radio again for bad solder joints and bridges - > >still nothing found. I checked for the correct parts in their locations > >- everything looks right. > >Like I said at phase II the controls all worked as they should and the > >display didn't jump around on it's own. The receiver peaked up fine on > >40 meters. Because everything was working I figured it was save to > >continue. The 8T and 8R lines were probably messed up the whole time but > >since the transmitter wasn't wired the problem didn't show up. > >Any ideas will be appreciated. > >Thanks, > >Tom K2 #5020 _______________________________________________ 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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