Re: #bitx40 Q8/Q9 dead - no TX or RX #bitx40
Ryan,toggle quoted messageShow quoted text
Well, I haven't posted in some time as well.
A possible quick fix: remove Q7, Q8, Q9.
Drive the mixer exactly as Farhan now does in the uBitx with a 4 resistor network at the transformer.
The only reason Q7,Q8,Q9 are in there is because the Bitx40 used to have an analog VFO.
Longer answer, if you feel compelled to keep your rig unmodified:
I assume L4 has been removed, it must be if this rig is used with a Raduino.
And as you say, C91 and C92 have been removed, mostly so it works with a high side VFO under Allard's firmware.
Unplug the two pin cable from the DDS1 connector, just to make sure that is not fouling things up.
.Now when you power up, R92 and R93 should be putting 4.5v on the base of Q9,
and the emitter of Q9 should be about 0.6v lower than the base, so about 3.9v.
WIth no Raduino connected, those should all be DC voltages and easy to check with a DVM.
If the emitter is not 0.6v lower than the base, then Q9 is suspect.
If the emitter still appears to be shorted to ground, check it out with an ohmmeter with power off.
Moving on, the base of Q8 should be the same DC voltage as the emitter of Q9.
And the emitter should again be 0.6 volts below the base.
Q7 is AC coupled by C72, but if you jump across C72 with a wire you should see
the emitter of Q7 at 0.6v DC below the emitter of Q8.
Checking things out at DC does not guarantee proper AC operation,
but may be the best route to figuring out this particular problem.
Maybe put a separate voltmeter full time on the 9v rail, my best guess
is that it looked fine at first but for some reason went to 0v later.
Having 12v DC go to some random point into the radio might be very bad news,
you could have a significant learning experience ahead of you.
On Thu, Sep 17, 2020 at 06:09 PM, Ryan Flowers wrote:
Hi everyone, it's been quite a while since I posted here!