Those two diets you were talking about are not normal diodes they are transient voltage suppressors. They won’t conduct until the voltage gets around 10 V.
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Be very careful with that PA bias. You can easily destroy the transistors with that. ?Turning it too far will cause the bias current to go to many amps!!
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The strange thing is that performing the bias regulation (as described on the website) I couldn't get the increase by 200 mA in the whole range of regulation.
May the transistors be partially damaged?
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73,
Wojtek
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Those two diets you were talking about are not normal diodes they are transient voltage suppressors. They won’t conduct until the voltage gets around 10 V.
Be very careful with that PA bias. You can easily destroy the transistors with that. ?Turning it too far will cause the bias current to go to many amps!!
There is some odd residue near the input of your output transformer. ?
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On Feb 28, 2025, at 19:39, Gordon Gibby KX4Z via groups.io <docvacuumtubes@...> wrote:
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be certain that you have correctly identified the PA bias potentiometer. It would be very odd if turning that too far didn’t destroy the MOSFETs
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when you press push to talk the voltage on L 80 and L 81 should go up— because it is controlled by Q9. if Q9 is continuously on, then you have blown a different MOSFET, one or more in that complicated switching system around Q9. ?You might want to figure out for sure if you really can’t see switching action going on there.
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be certain that you have correctly identified the PA bias potentiometer. It would be very odd if turning that too far didn’t destroy the MOSFETs
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when you press push to talk the voltage on L 80 and L 81 should go up— because it is controlled by Q9. if Q9 is continuously on, then you have blown a different MOSFET, one or more in that complicated switching system around Q9. ?You might want to figure out for sure if you really can’t see switching action going on there.
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In my board I have additional diodes D8 and D9 connected between the gates of Q16 qnd Q17 and the ground.
It seems that the voltage delivered by the bias circuit is limited by the those diodes to 270 mV.
However, when I set the DRIVE to 100, the voltage on the gates looks like in the picture below (probe x10 already considered):
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So it does not seem to be limited by the diode (GND level is on the central line of the screen).
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The picture of the board is below. The D8 and D9 diodes are above Q16 and Q17, next to L80 and L81 (which are in fact just jumpers):
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Re: Looking for the V2 Hardware Upgrade Info
JJ,
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I agree with Gordon's suggestions.? IRF520 would be a more robust part, and the TVS protection is a good idea as the driver circuit can deliver higher than the gate voltage if driven to full power.
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Also, Joel suggests that the pin diode current should be increased by 470 to 330 ohm replacements.? The bias increase is another good idea.
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Another suggestion is to add the resistors to the drain of Q101 and series with D20 and D21.? Gordon posted this here:
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You should verify the signal purity before putting it in the air.
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73
Evan
AC9TU
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I have one interesting finding. It seems that changing the PA_BIAS1 setting does not modify the current consumed by sBitx.
After pressing PTT It increases from 0.31A to 0.77A, and does not depend on further changes in the potentiometer setting.
The voltage on L80 and on L81 does not increase significantly when I push PTT in the USB mode (or press the key in the CW mode).
The voltage on the input of the potentiometer (node between R77 and D6) is correct.
Namely, the potentiometer is faulty or improperly soldered...
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Re: zBitx - Progress Update
one of the ports is for power, I don't think it provides data.
The RPi Zero 2 W has two USB 2.0 ports, I guess you could use an interposer board and include a USB-C connector, but it would only work at USB-2.0 speeds and increase the size of the radio.
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Re: uBITX v6 Low Audio - Back at it again
Unknown. I heated the end closer to the back of the PCB, and the cap fell right off the board, with a end still on the PCB. A check of the cap shows it is open, not surprising with the end missing.
Anyway, I found a 0.1uF cap in the junk box, just a tad too big, Hi Hi, to put in on the board, but connecting it to the board gives me LOTS of audio again. When replaced with an appropriate cap I'll be back in business. Then to calibrate the BFO, frequency, etc. And have it on the air again.
73, Richard AG5M
On Friday, February 28, 2025 at 02:25:59 PM PST, tomekdm sp7etd via groups.io <tomekdm@...> wrote:
Interesting why it cracked/failed... due to mechanical stress, like bent of PCB... temperature shock...? or was it already bad since new...
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If C202 (47pf) SHORTED, you would expect potentially what is being seen. If the 80 meter filter were invoked, and your frequency is above that, the input of the filter might act like a short. If D15 shorted, this could happen, or if Q24 shorted this could happen If the teflon insulation on the orange wire melted (this is not likely) then the output of the transformer might be shorted If the antenna output connector or coax shorted, this low output might happen.
But chasing down every one of those is very time consuming.? ?Again, it might be easier to just look at what is coming out of the orange wire, disconnected from everything else.....much simpler than all the other techniques.
Anyone see something better?
Gordon KX4Z
On Fri, Feb 28, 2025 at 4:48?PM Gordon Gibby KX4Z via <docvacuumtubes= [email protected]> wrote:
Good point Evan!
But I can’t figure out is how disconnecting a Lowpass filter would result in a lower voltage. It should result in a higher voltage. ?
I tried to look for what things might be shorting out. There’s a chance that the high-voltage system is shorting out but it’s only connected by 47 pf?
?and that’s not much. ?
Gordon?
? It should be possible to test the LPF selection process with a DMM.? Use USB, set the drive to 1 and the mic to 0.? Then, measure the voltages on the banded sections of the selection diodes.? Only one pair should be close to zero; the others should be close to the input voltage (12 volts) without the RF voltage doubler.
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73
Evan
AC9TU
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Re: uBITX v6 Low Audio - Back at it again
Interesting why it cracked/failed... due to mechanical stress, like bent of PCB... temperature shock...? or was it already bad since new...
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Re: uBITX v6 Low Audio - Back at it again
I hope so, you guys have been absolutely great! Stay tuned.
73, Richard AG5M On Friday, February 28, 2025 at 02:19:21 PM PST, tomekdm sp7etd via groups.io <tomekdm@...> wrote:
good to hear, radio will be fixed. 73
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Re: uBITX v6 Low Audio - Back at it again
good to hear, radio will be fixed. 73
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Re: uBITX v6 Low Audio - Back at it again
C30 removed. The end closest to the display came off when desoldering. PCB looks OK.
With C30 removed, voltages on Q30 are:
E = 1.74, B= 2.41, C=7.76 Pretty much as you mentioned.
C30 will be replaced with 100nF, Evan was so kind to send me one snail mail.
So until then, 73, Richard AG5M
On Friday, February 28, 2025 at 12:53:23 PM PST, tomekdm sp7etd via groups.io <tomekdm@...> wrote:
If after de-soldering of C30 voltages on Q30 will be near voltages of Q10, so:
E= 1.6, B= 2.4, C= 7.9
Then You need to replace C30 with any 100nF (0,1uF) ceramic capacitor.
If voltages will be still low as before:
E= 0.0, B= 0.28, C= 11.00
Then Q30 needs replacement.
Regards
Tomasz
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Re: zBitx - Progress Update
The RPi Zero 2 W has two USB 2.0 ports, I guess you could use an interposer board and include a USB-C connector, but it would only work at USB-2.0 speeds and increase the size of the radio.
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Re: zBitx - Progress Update
The micro USB is the pi , in the future if they decide to use USBC, hopefully in the same footprint we will just need to make the hole a little bigger?
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Re: Looking for the V2 Hardware Upgrade Info
JJ, that’s hard to say. ?I had huge Zener’s in mine, and I still lost a MOSFET with no obvious reason. I cannot guarantee it at that instant, but I had not seen any oscillations ever in my unit since whatever updates were done. ??
I decided to go ahead and put in the TVS diodes that Ashhar suggested and I also switched to 100 V IRF 520s. ? I searched for any isolations and did not see any with this new set up. I have not had enough operating time to guarantee this, but I suspect it will be satisfactory.
I have just about the same output with the 520s and I’m happier with them?
Gordon kx4z?
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On Feb 28, 2025, at 16:57, JJ - W9JES via groups.io <jj@...> wrote:
? I think some folks misunderstood what I was asking for.?
The sBitx V2 has IRFZ24N MOSFETs. We want to continue to use them for the finals. What mods have to be performed to prevent oscillations and early MOSFET failures?
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Thanks.
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Re: Looking for the V2 Hardware Upgrade Info
I think some folks misunderstood what I was asking for.?
The sBitx V2 has IRFZ24N MOSFETs. We want to continue to use them for the finals. What mods have to be performed to prevent oscillations and early MOSFET failures?
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Thanks.
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Re: Looking for the V2 Hardware Upgrade Info
On Fri, Feb 28, 2025 at 03:05 PM, WK4DS wrote:
I misunderstood you, I thought this was what you was searching for. Swing and a miss I guess. Haha
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David
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It's all good. Your information was useful for those who want to fully convert their V2 board to V3. Thank you.
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Good point Evan!
But I can’t figure out is how disconnecting a Lowpass filter would result in a lower voltage. It should result in a higher voltage. ?
I tried to look for what things might be shorting out. There’s a chance that the high-voltage system is shorting out but it’s only connected by 47 pf?
?and that’s not much. ?
Gordon?
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On Feb 28, 2025, at 16:35, Evan Hand via groups.io <elhandjr@...> wrote:
? It should be possible to test the LPF selection process with a DMM.? Use USB, set the drive to 1 and the mic to 0.? Then, measure the voltages on the banded sections of the selection diodes.? Only one pair should be close to zero; the others should be close to the input voltage (12 volts) without the RF voltage doubler.
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73
Evan
AC9TU
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Re: uBITX v6 Low Audio - Back at it again
Sorry, my bad. It is 0.82 kOhm, not 0.82 as reported. Thanks for catching that. Base of Q30 is in fact 50.8 ohms. i rechecked. OK, C30 will get removed and voltages checked on Q30. 73, Richard AG5M
On Friday, February 28, 2025 at 12:38:02 PM PST, tomekdm sp7etd via groups.io <tomekdm@...> wrote:
Hi Richard,
Really sorry, my mistake, I have measured C10 again to the ground and this is also ~823 ohm.
But don't bother with C10, nor C30. This is the same as measuring resistance from base of Q10 and Q30 to GND.
In both there is ~823 ohms. Your measurements brings confusion as I was thinking we have only trouble at 2nd RX chain,
are you sure its not 0.82 kOhm? If this is 0.82k then its OK.
Anyway 50 ohm on base of Q30 is NOK.
Can You de-solder C30 and measure voltages on Q30 before replacing Q30?
Regards
Tomasz
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Richard AG5M
tomekdm sp7etd