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It's kind of odd, but not really, if I were trying to diagnose something that I built myself, I would have no problem. I have no problem doing mods to commercial built equipment. But, yes, I would be lost if something on a commercial transceiver
went poof. It is a great learning experience though! I also tend to have multiple projects going on as well, I am concurrently trying to figure out a new Radioberry v2 as well. I finally got it going, even got the preamp board working, but I have to verify
output yet. That whole project could use a well organized wiki and repository too. Thanks Gordon!
Mike - K8MCB?
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-------- Original message --------
From: "Gordon Gibby KX4Z via groups.io" <docvacuumtubes@...>
Date: 3/6/25 8:53 AM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
You're going to learn a lot in the process of this repair.? ?Be certain to protect Q101 with a small resistor in its drain lead or you are likely?to just repeat the whole performance all over
again.
Q101's purpose is just to drain power from the transmitter side quickly, so the transmitter doesn't STAY ON when the receiver startups up-- this could lead to an RF loop.? ?At least I think
that is what it is for!!
My V2 #1 has all these fixes in it (because it got damaged, and some of it may have been ME rather than IT)
My V2 #2 has none of this YET -- hurt my knee and just barely now able to walk and climb stairs.? ?A zillion projects going on.? ?And teaching two AP classes.? ?And a ham radio group.... so
it may be a while yet before I get that done.? ? It will take half a day to do everything I need to do on that radio, even if I manage to put all the parts together in one place!!
I looked inside my Icom 7300 once....(I've unsoldered diodes in there before on 2 or 3 units) and there is almost NOTHING I would be able to repair in there.? ? If it breaks, I'm toast.? Meanwhile,
I have 50+ year old Heathkits that I'm able not only to repair but to upgrade!? ?We will move to jusst?dealing with "modules" at some point.
73
Gordon KX4Z
Old 2n7000 datasheet
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
Evan,?
?Is it possible that R5 and R6 are mislabeled on the schematic? After I removed Q9,Q10,Q101,R5 and R6, to check continuity of pads and traces, I found that bottom of R6 connects to the gate-pin1 of Q10, not the source-pin3, and connects to the source-pin3 of
Q101 and not the gate-pin1, as indicated in the schematic. The schematic is from Farhans github, titled sbitx v3 production. Let me know, thanks!
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Yes, I was somewhat relieved that I am getting the proper Tx signal. I feel that I may need to remove Q9, Q10, Q101 and check the continuity, rule out damaged pads/traces, and swap in new components. Also when I mentioned using
through hole for Q10,Q101, I was thinking about using regular 2n7000 in place of the sot23 2n7002. Would those work?
-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/6/25 2:07 AM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Michael,
?
The TX signal works (recieve at 0.15 volts, transmit at 3 volts).
?
?
The pins on Q9 are marked in this photo:
?
The gate (pin 1) of Q9 should be higher, and the tab (Pin 2 or drain) should be 0 volts when receiving and close to 12 volts on transmission.? It could be a failed Q9, Q10, Q101, or combination.? I would start with Q10, as it should pull down the gate
of Q9 to turn it on and supply the 12 volts to the driver stages.??
?
?
Q101 is a 2n7002 MOSFET.? This can not be replaced with a 2n2219.??
?
?
The above is based on not getting 12 volts on the tab of Q9.
?
73
Evan
AC9TU
?
-- Mike - K8MCB?
|
Hi Michael,
?
AFAIK The schematic is correct. Double-check your tracing. Solder bridges on the board could also confuse the measurements. I use a magnified headset to verify traces. Since it is a two-sided board, no hidden traces exist between layers.
?
73
Evan
AC9TU
|
Evan, I have gotten things mostly straightened out, proper voltage to R77, 5.6v to D6, etc. I still get the 3v on Q10 for the Tx signal, but Q9 just doesn't switch. The voltages on the excel sheet match the steady receive state, but things aren't
switching when the Tx is applied. Suggestions?
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/6/25 2:07 AM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Michael,
?
The TX signal works (recieve at 0.15 volts, transmit at 3 volts).
?
?
The pins on Q9 are marked in this photo:
?
The gate (pin 1) of Q9 should be higher, and the tab (Pin 2 or drain) should be 0 volts when receiving and close to 12 volts on transmission.? It could be a failed Q9, Q10, Q101, or combination.? I would start with Q10, as it should pull down the gate
of Q9 to turn it on and supply the 12 volts to the driver stages.??
?
?
Q101 is a 2n7002 MOSFET.? This can not be replaced with a 2n2219.??
?
?
The above is based on not getting 12 volts on the tab of Q9.
?
73
Evan
AC9TU
?
-- Mike - K8MCB?
|
Michael,
?
The first step is to verify that the Q10 Drain goes to zero when TX goes to 3 volts (or higher).? If that happens, Q10 is OK.? If not, it is bad.
?
Once Q10 works, verify that the Q9 tab (Drain) goes to 12 volts when the TX signal drives the Q10 drain low.? If that does not happen, remove Q9 and check the operation of Q101.? Do this with Q9 removed to prevent damaging both devices again.
?
Q101 drain goes to zero when TX and Q10 are off.? When TX is low, the Q101 gate should go above 5 volts to make Q101 turn on.? When Q10 turns on with the TX signal, Q101 should turn off.? If Q9 is removed, you can verify that the Drain-to-source resistance is very high with an Ohm meter.? Q101 Drain to Source resistance should be close to zero when TX and Q10 are on.
?
An alternative approach is to remove Q101 so there is no short on the 12V line during receive, Verify and replace bad parts, and then install a verified working Q101.? I built a test jig on a small copper-clad board with wires to insert into a component tester.? I hold the device with tweezers to connect each lead to a separate pad.
?
?
73
Evan
AC9TU
|
Evan, I finally got it going! My problem was having more than one problem at a time. Once I replaced everything in the circuit, fixed dry or bridged joints, and put a new set of finals in, it now switches and has output. However, before I even
touch the bias pot, does the other pot have anything to do with this circuit? It doesn't appear to, but I mistakenly put it to full ccw with the bias pot too. What is the pot for and how should I set it?
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/10/25 10:10 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Michael,
?
The first step is to verify that the Q10 Drain goes to zero when TX goes to 3 volts (or higher).? If that happens, Q10 is OK.? If not, it is bad.
?
Once Q10 works, verify that the Q9 tab (Drain) goes to 12 volts when the TX signal drives the Q10 drain low.? If that does not happen, remove Q9 and check the operation of Q101.? Do this with Q9 removed to prevent damaging both devices again.
?
Q101 drain goes to zero when TX and Q10 are off.? When TX is low, the Q101 gate should go above 5 volts to make Q101 turn on.? When Q10 turns on with the TX signal, Q101 should turn off.? If Q9 is removed, you can verify that the Drain-to-source resistance
is very high with an Ohm meter.? Q101 Drain to Source resistance should be close to zero when TX and Q10 are on.
?
An alternative approach is to remove Q101 so there is no short on the 12V line during receive, Verify and replace bad parts, and then install a verified working Q101.? I built a test jig on a small copper-clad board with wires to insert into a component
tester.? I hold the device with tweezers to connect each lead to a separate pad.
?
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
Glad you fixed it!? The other pot is used to adjust the "bias" for the mixer:
?
?
?
The adjustment does not seem critical.? I would set it to the midpoint and verify that the receiver is sensitive and that the transmitted CW signal does not have spurs.
?
73
Evan
AC9TU
|
I figured it had something to do with the reception, as when I first turned it back on and the receiver appeared to be "deaf", but yes, right around the halfway point it picked up again. I appreciate the help getting the Tx switching fixed too!
Thx and 73
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/13/25 8:50 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Glad you fixed it!? The other pot is used to adjust the "bias" for the mixer:
?
?
?
The adjustment does not seem critical.? I would set it to the midpoint and verify that the receiver is sensitive and that the transmitted CW signal does not have spurs.
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
To be clear, both the receiver and the transmitter use that mixer.? It translates the signal from the 40MHz IF frequency to the operating frequency in both directions.
?
73
Evan
AC9TU
|
Makes sense. It does seem rather touchy and the effect on signal strength of the received signal is more like an on/off switch than a range, like you might expect. Anyway, it works and I am now comfortable proceeding with the bias adjustment
and band specific drive adjustment for the PA. Let me know if there is anything that I should be looking out for while I go through the process.?
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/14/25 1:26 AM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
To be clear, both the receiver and the transmitter use that mixer.? It translates the signal from the 40MHz IF frequency to the operating frequency in both directions.
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
Evan, doing a once over before setting the PA bias, I noticed that I am getting excessive heating of D30, D31 upon Tx. I still have output from the finals. It could be heating elsewhere as well, but I didn't want to leave it on Tx any longer than needed until
I can id the problem.?
Mike
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From:[email protected] on behalf of Evan Hand via groups.io
Sent:?Thursday, March 13, 2025 10:25 PM
To:[email protected]
Subject:?Re: [BITX20] reviving my sbitx v3
To be clear, both the receiver and the transmitter use that mixer.? It translates the signal from the 40MHz IF frequency to the operating frequency in both directions.
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
They should be back biased by the high-voltage supply. Either it’s not working or there might be a problem around Q 28, haul out the voltmeter meter and start looking at voltages in receive and in transmit and figure out what’s going on.
Study the schematic to understand how the switching works
Good luck!!!
Gordon kx4z
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On Mar 14, 2025, at 11:49, Michael Bales via groups.io <mikebales73@...> wrote:
?
Evan, doing a once over before setting the PA bias, I noticed that I am getting excessive heating of D30, D31 upon Tx. I still have output from the finals. It could be heating elsewhere as well, but I didn't want to leave it on Tx any longer than needed until
I can id the problem.?
Mike
From:[email protected] on behalf of Evan Hand via groups.io
Sent:?Thursday, March 13, 2025 10:25 PM
To:[email protected]
Subject:?Re: [BITX20] reviving my sbitx v3
To be clear, both the receiver and the transmitter use that mixer.? It translates the signal from the 40MHz IF frequency to the operating frequency in both directions.
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
Mike,
?
As Gordon points out, there is most likely a problem with the receiver TR switch.? As with the transmitter switching, verify the operation of Q28.
?
You can also try removing the RF from the circuit with a low drive setting.? Set it up as shown on the voltage measurement sheet.
?
If Q28 turns on and off with the PTT signal, then look at the diodes themselves.? You should be able to check the diode in the circuit without power.
?
It is good you found this before being forced to replace another set of finals and other components.
?
73
Evan
AC9TU
?
|
So, everything is still switching, but...when I was attempting to adjust the bias, which was about 800mA in receive, and about 1.2A with PTT engaged, in USB, 40m drive at 1 mic at 0. When I began to adjust cw from the full ccw position, the
pot didn't do anything until over half a turn, and immediately jumped to 3-5A, and proceeded to pop D7.
?If it's not one thing, it's another!!! Anyway, both D30 and D31 are both OK, dropping about .6v each. Aside from checking Q28 and the 2 finals, what else could be the issue, other than the likely blown pot for the bias?
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/14/25 2:00 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Mike,
?
As Gordon points out, there is most likely a problem with the receiver TR switch.? As with the transmitter switching, verify the operation of Q28.
?
You can also try removing the RF from the circuit with a low drive setting.? Set it up as shown on the voltage measurement sheet.
?
If Q28 turns on and off with the PTT signal, then look at the diodes themselves.? You should be able to check the diode in the circuit without power.
?
It is good you found this before being forced to replace another set of finals and other components.
?
73
Evan
AC9TU
?
-- Mike - K8MCB?
|
Mike,
?
D7 is for reverse polarity protection.? It should not blow unless the power is connected wrong.??
?
I had trouble adjusting the bias on my DE sbitx.? The TR switching was not working correctly, allowing the amp to enter sustained oscillation.? The amp does not amplify until the bias is close to correct and the oscillation begins.
?
I would verify that both sections of the TR switching (Q9, Q28, Q29, and associated transistors).
?
73
Evan
AC9TU
|
Sounds like another case where something is screwy.
I don’t think you could blow D7 unless you had reverse polarity power.
?
so there may be a mislabeling or a screw circuit board here. Or maybe just a mistake in figuring out where things are blown.
?
but all of these combined to make it extremely difficult to figure out what the heck is going in very carefully measure and look and pride and think and compare figure out what really is blown and what isn’t and where it is really connected and where it isn’t!!
?
we’ve already seen one example where this unit was wired differently from everybody else. ??
?
gordon Kx4z?
|
Yes, it can be quite confusing. It's also possible that an errant hot wire from a bench psu touched somewhere. I had to step back from this one for a while, because I was beginning to get frustrated and we know where that can go! So I decided
to work on assembling a K9HZ 20w pa board that I will probably drive with my Lime mini 2. I also have a radioberry 2 that I am working on getting configured properly. So with the three different projects going at once, I can always move to another when I start
getting frustrated and tired of one.
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-------- Original message --------
From: "Gordon Gibby KX4Z via groups.io" <docvacuumtubes@...>
Date: 3/14/25 6:41 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Sounds like another case where something is screwy.
I don’t think you could blow D7 unless you had reverse polarity power.
?
so there may be a mislabeling or a screw circuit board here. Or maybe just a mistake in figuring out where things are blown.
?
but all of these combined to make it extremely difficult to figure out what the heck is going in very carefully measure and look and pride and think and compare figure out what really is blown and what isn’t and where it is really connected and where it
isn’t!!
?
we’ve already seen one example where this unit was wired differently from everybody else. ??
?
gordon Kx4z?
-- Mike - K8MCB?
|
Evan, or anyone else who may know. Looking at the sBitx v3 schematic, Share github, named sBitx v3 production, I am unable to locate D8 or D9. I lost D9 in the process of replacing yet another pair of 510s. It is in such close proximity that
it got heated and fell off the board.?
?It appears that their purpose is gate protection of 510s. Anyway, does anyone know what diode I need to put here?
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/10/25 10:10 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Michael,
?
The first step is to verify that the Q10 Drain goes to zero when TX goes to 3 volts (or higher).? If that happens, Q10 is OK.? If not, it is bad.
?
Once Q10 works, verify that the Q9 tab (Drain) goes to 12 volts when the TX signal drives the Q10 drain low.? If that does not happen, remove Q9 and check the operation of Q101.? Do this with Q9 removed to prevent damaging both devices again.
?
Q101 drain goes to zero when TX and Q10 are off.? When TX is low, the Q101 gate should go above 5 volts to make Q101 turn on.? When Q10 turns on with the TX signal, Q101 should turn off.? If Q9 is removed, you can verify that the Drain-to-source resistance
is very high with an Ohm meter.? Q101 Drain to Source resistance should be close to zero when TX and Q10 are on.
?
An alternative approach is to remove Q101 so there is no short on the 12V line during receive, Verify and replace bad parts, and then install a verified working Q101.? I built a test jig on a small copper-clad board with wires to insert into a component
tester.? I hold the device with tweezers to connect each lead to a separate pad.
?
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
Michael,
?
I believe these are the parts:
?
|
|
CDSOD323-T08CCT-ND
TVS DIODE 8VWM 18.5VC SOD323
|
?
?
?
?
?
?
I found them on Mouser and Digi-Key.
?
73
Evan
AC9TU
|
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/17/25 5:02 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Michael,
?
I believe these are the parts:
?
|
|
CDSOD323-T08CCT-ND
TVS DIODE 8VWM 18.5VC SOD323
|
?
?
?
?
?
?
I found them on Mouser and Digi-Key.
?
73
Evan
AC9TU
-- Mike - K8MCB?
|
