Re: Bitx40 Circuit Diagnosis How To?
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Jerry,
What is the proper way to set R136? I have not been able to find any information for this adjustment.
Thanks,
Randy, K7AGE
On Sat, Feb 11, 2017 at 9:20 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote: Very weird that catching a cold solder joint at R45 fixed the receiver.? R45 is the emitter resistor at Q4, in the transmit chain.? I'd get some good magnification and bright light, heat up any other joints that look questionable.? Flex the board lightly while trying to transmit, see if that momentarily fixes it, suggesting another cold solder joint.? Cold solder joints can come and go, I can believe that the board worked just fine at hfsigs before being shipped.? You might yet have a problem in the receiver, but after all the probing it is something is now making contact.? That's in addition to an apparent problem on transmit. You might check for transmit audio between T4 pins 1 and 6 using some other audio amp to a speaker, or high impedance headphones. I assume you have PA 12v into the IRF510 hooked up to your 12 volt supply when testing that transmitter.? What are the DC voltages on the gate and drain of Q15 when you try to transmit?? You might look over the notes at the top of the files section under "1 docs of Tips n Mods" ?if you have not already.? Pots RV1 (bias voltage onto the gate of IRF510, carefully follow the hfsigs instructions or you may blow the IRF510) and R136 (determines the drive level into the final amplifier) apparently get set properly at hfsigs before shipping, but might be worth checking. Yet another case where we need a cheap and standard way of measuring AC voltages through the transmit RF chain.
On Fri, Feb 10, 2017 at 06:37 pm, KC8WBK wrote:
I made a list of the resistors in the three blocks of the circuit, and using the schematic tested and wrote down the resistance from the component on either side of the resistor.? I was able to find a cold solder joint in R45, which was fixed with a little bit of heat.? I went back and checked the Q voltages and things look much better with Q1-3 and Q4-6 all giving similar results.? The audio sounds good and seems stable.? I am very happy with the receiver so I call the receiver fixed.
There is no change in the transmit problem, unfortunately.? I don't believe I ever transmitted with this radio earlier, so I don't know for sure if it worked originally.
The relay clicks, and I hear a hum while transmitting, but no output showing on the swr/power meter.
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