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Last week I received my uBitX. AFter wiring up I discovered that I didn't have power on SSB.
The next day when i wanted to investigate my problem I smoked U1 when I plugged in my headphones.

Tonight I unsoldered U1 and after that I powered up. Measured with the scope and I see a signal at the Mike input and on the collector of Q6. So that first part seems to be okay.

What would be the next step to backtrack the fault?

John

So "didn't have power on SSB" means you didn't see power into a wattmeter (with dummy load) when attempting to transmit?
Have you tried transmitting CW with a hand key?
Is that scope good to 10mhz or so?

Inspect the entire board carefully under good light and with magnification for damage somewhere in shipping.
Often the torroids have trouble with broken or shorted wires, or enamel left on the wire, or an otherwise
poor solder job.? However, if the receiver worked, all torroids except those between Q90 and the IRF510's
are probably ok, and the mixers and local oscillators are fine.
The TX side of the BiDi amps is probably ok since they are simple and auto-stuffed and seldom have trouble.

Switch to one of the low bands like 80m or 40m, hopefully within range of the scope
Remove power (PA-PWR) from the IRF510's so you don't have to worry about dummy loads and such
while debugging the transmitter, when things are working you should see a couple volts of RF at the
gates of the IRF510's.

When pressing PTT with no input to the microphone, all those 2n3904's at Q90,911,912,92,93,96,97?
should have around 0.6 volts dc between base and emitter, and the emitter should be a little bit above ground.?
You can check this with a DVM.? Do they all look ok?

When speaking into the mike or using the hand key, I believe the base of Q90 will have something on the
order of 50mv rms of RF on it at the operating frequency, can you see that with the scope?

If Q90 is getting RF, then?follow that on through the other stages, should see a volt or two rms
of RF at the gates of the IRF510's.? The gates of the IRF510's should be biased by RV2 and RV3 to
around 3 or 4 volts (but DON'T twiddle RV2 and RV3 unless monitoring quiescent drain current at PA-PWR).?

If you do see RF at the IRF510 gates, then it's time to attach a dummy load and restore PA-PWR,
see if the dummy load gets signifcant power when attempting to transmit.
If not, do the drains of the IRF510's get 12v dc when ptt is pressed?
Does PA-PWR current go up to 200ma or so (100ma of quiescent drain current per IRF510) when pressing ptt
with no audio into the mike, demonstrating that the IRF510's are probably working fine?

Jerry, KE7ER

I did have power on CW, at least the first day before so smoked U1 with a stereo Sony noise canceling headset.
I didn't have my straight key yet bit i just shorted a cord that i had plugged in the key jack.

Had some trouble getting the scope to sync but the signal on the collector of Q6 was much stronger than the Mic input.

Scope has 10MHz bandwidth so it should work on the lower bands.

Most likely the TDA will arrive saturday than i can start from scratch again.
Will measure the voltages as you mentioned. But as CW seemed to work the first day I thought I had to look somewhere in the modulating circuitry. Have the schematics printed but in my professional career I worked more with higher voltages.
Am not afraid to try but just need some guidance as I am fairly new to radio electronics.

John

Yes, if you can transmit CW then it has to be somewhere between Q6 and Q22,
since CW is transmittted by unbalancing the modulator immediately following Q22.
If the receiver works, then the three mixers and local oscillator are ok.
So if you still have trouble transmitting SSB, then it's Q6 or one of the bidi amps on the TX side,
and the bidi amps seldom give us trouble.

You could try unbalancing the modulator by injecting 5vdc through a series 4.7k resistor
at T7 pin 3 (and pin 5).? This is how we generated CW on the Bitx40:??
? ??
If that does transmit CW, then it has to be around Q6.

Your 10mhz scope may just barely see something in the 12mhz IF section through Q42,?
and probably nothing at all in the 45mhz IF section at Q20,21,22.
If you wind up debugging those sections, you may need to build a diode RF probe or something similar.

Jerry

Don't know when I get to it.. but I will follow your lead.
I already ordered some germanium diodes to build a RF probe.

To be continued..

John

Well end of this week my TDA2822L and the sockets arrived so I could continue with my search.
I measured the antenna output with my scope parallel at my dummyload in the frequency ranges that I am allowed to use as General.
I measured from 160 meters to 15 meters. Strongest output is at the lower bands at 160 meters I have an amplitude of about 5V only the signal looks weird (hence I guess they mention you can not use it that low). Although at 2MHz it is almost a sinewave.
At 80 meters it is a sinewave with CW key down and an amplitude if about 3.2V. At the end of 80 meters output is a little higher.
At 60 meters 5.332 output us about 3.6V to end up with about 2.6V at 5.405.
40 meters give a fairly flat 3V drom low to upper frequency.?
At 30m (which would be the edge of my scope) I get a little over 2V.
I continued measuring and have about 2.4 at 20m.
At 17m about 1.8V.
At 15 m about 1.8V too.
These are all peak values.

They seem a little low to me. As I understand a 4V peak value would give about 160mW.
But at least there is some RF arriving at my dummyload. I also tested with voice and that seems to be working too, but with a little lower values.

I was using for this test a switched power supply 12V 5A. Output voltages is about 12.3V.

So everything seems to be working only the output is a little low. Could this be a bias issue? Haven't touched those settings yet.

John

If you don't have a low pass filter for 160 meters between the rig and your dummy load,
then the scope will be showing any second harmonic coming out of the final.
That could be why it looks "weird", and you would not be legal to transmit without an appropriate filter.
The rig only has filters suitable for use down to 80 meters.

Yes, 3v peak is kind of anemic, could be anything between the mike and the IRF510's.
Or the 10x switch on your scope probe, that would fully explain this.
I'd recommend you concentrate on 80m, where your scope should work well.
While transmitting CW, what is the RF pk-pk signal voltage you see at Q90,911,92,94 base or gate?

Check current into PA-PWR while transmitting SSB with no audio at the mike, should be around 200ma.
If anywhere near, leave the IRF510 bias adjustments at RV2,RV3 as they are.

There is considerable variance on output power for these rigs, would be interesting to someday figure out why.?
Increasing power is best done by increasing drive at RV1 or adjusting the gain of the mike amp at Q6.
But be sure your transmitted signal remains clean, overdriving the final will make it non-linear.
Though yours is more than an order of magnitude lower than it should be, so something else is wrong here.

Jerry, KE7ER

Very cool, good job.? Persistence often pays off.
Think of it as mostly educational, so time well spent.
?
That 160m trace seems to have a strong third harmonic, which makes sense.
The 80m low pass filter would have a corner around halfway between 4 and 7 mhz,
so the 5.6 mhz third harmonic of 160m is sneaking through.
Not much evidence of a second harmonic, as one would expect from a push-pull amp.

Jerry, KE7ER