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Morning All, Firstly sorry to ask such an open, non technical questio, but asking it anyway...
After five months I turned on my uSDX v6 to find no transmit power, across modes and bands.
Looking at the meter, there's a momentary rise of the needle, then immediately drops back to zero.
Adjusting the trimmer does alter the extent of the momentary deflection a little.
I changed the IRF510s last night. This made no difference. It's possible the new mosfets are fakes, but unlikely - they were purchased from a retailer, not just from eBay.
Does anyone have an idea of where to start diagnosing the fault?
Thank you.
Best,
Nick
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Hi Nick,
Let's start by clarifying which radio it is. Is it a microBitx (uBitx) or a uSDX? They are different.
The next question would be the mode you use for the power test.? If it is SSB, there is no power unless there is audio.? What happens if you say a long HEEEEEELLLLLLLLOOOOOOOO (or a loud, long whistle) into the mic?? Also, are you connected to a dummy load or a matched antenna?
73
Evan
AC9TU
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Hi Evan,
Fair point - uBitx v6 (I have a uSDX too...) is what we're looking at. It was a long day...
Output is near zero on all modes as measured into a dummy load. Whistling on SSB makes no difference, ditto key down on CW.
Best,
N
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Nick, It is best to get the uBitx transmitting CW and then work on SSB. Both modes use the same power amp sections. The next most common problem after blown IRF510s is Q90. This transistor has been blown by having an antenna connected near another transmitter. A v4 spreadsheet in the files section gives voltage measurements for the different transistors. It applies to the v6, with only slight differences in the SSB sections. /g/BITX20/files/VU2ZAPThe method of measuring is included in the text on the spreadsheet. There is also a mod to protect Q90 with back-to-back diodes on the receiving line that are switched out when transmitting.? Here is a picture of a v4 that I modified:
The diodes are 1n4148.
73
Evan
AC9TU
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Thanks Evan. I'll check Q90.
Best,
N
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Hi Evan,
I've replaced Q90 with a wired transistor.
Unfortunately, no change.
I can hear the relay, see a small, momentary deflection on the power meter, but that's it.
I'll double check the mosfets, but then what..?
Best,
N
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Hi Nick,
Have you done the voltage checks in the spreadsheet?
73
Evan
AC9TU
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No.
I'll do that now..?
Best?
N
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raduino fully functional?maybe the alignment way off?
just throwing out some suggestions
73 David ac9xh
On Thursday, March 28, 2024 at 02:31:55 PM EDT, <nickredmayne@...> wrote:
No.
I'll do that now..?
Best?
N
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Receive is fine, so I'm thinking alignment is fine.
Thanks though.
Best, N
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A Raduino issue is possible. ?The alignment should not affect CE mode transmission. ?CW sets the output to the transmitted frequency.?
An oscilloscope is the best way to verify that the Raduino is generating RF.?
73
Evan
AC9TU
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Hi All,
I've checked voltages on the board, in most instances during tx and rx, against the uBitxV4 data sheet (I couldn't find q71 to q73 - perhaps not on v6 board)
Most things were pretty close eg Q90 TX was 10.79 3.43 2.71, against the V4 figures of 11.55 3.66 3.04
Q911/912 11.05 0.90 0.32 against 11.8 1.07 0.49
However, when I measured Q10, Q20, Q30,Q40 readings were all over the place. Q10, Q11, Q12 TX voltages on Collector were all 0v, against v4 readings of 7.47v, 11.58v. 11.58v respectively.
Q20, 21, 22 RX voltages C B and E were all 0v
Q30, 31, 32 TX voltages C B and E were all 0v
Q40, 41, 42 RX voltages C B and E were all 0v
Not wishing to waste anyone's time, am I reading the data sheet correctly?
Thanks as ever,
Nick
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Check is Q15 is working along with relay Q1. You should be able
to feel K1 clicking when you press PTT.
Since you are getting 0V on RX as well as TX they could be a
break in the PCB track.
Raj
toggle quoted message
Show quoted text
Hi All,
I've checked voltages on the board, in most instances during tx
and rx, against the uBitxV4 data sheet (I couldn't find q71 to q73
- perhaps not on v6 board)
Most things were pretty close eg Q90 TX was 10.79 3.43 2.71,
against the V4 figures of 11.55 3.66 3.04
Q911/912 11.05 0.90 0.32 against 11.8 1.07 0.49
However, when I measured Q10, Q20, Q30,Q40 readings were all over
the place. Q10, Q11, Q12 TX voltages on Collector were all 0v,
against v4 readings of 7.47v, 11.58v. 11.58v respectively.
Q20, 21, 22 RX voltages C B and E were all 0v
Q30, 31, 32 TX voltages C B and E were all 0v
Q40, 41, 42 RX voltages C B and E were all 0v
Not wishing to waste anyone's time, am I reading the data sheet
correctly?
Thanks as ever,
Nick
_._,_
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Hi Nick, Sorry for the delay in responding.? I am having medical issues and do not always have access to my computer. Focusing on CW transmission, do you have any output except a small bump when the CW key is pressed?? Is the radio set for CW or CWR?? Can you measure the input current supplied to the radio during transmission to verify that the supply can provide the needed current? As to measurements, until CW works, you do not need to worry about any of the other transistors.? Focus on measuring transistors in this section of the radio:  Note that Q942 and Q952 are alternatives to Q94 and Q95, respectively, and are not used for the stock V6.? Also, note that a 0 value for a component means it is not installed.? Examples are C260 and C261 in the above schematic. Once you have CW working, you can look at the other sections for SSB. 73 Evan AC9TU
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Hi Evan,
Thanks again for your help. I hope the medical issues are resolved soon.
I have a linear power supply, set to 12v. It has worked for this radio in the past, so I'm comfortable that adequate current is being supplied.
I'll look again, as you suggest, at transistors Q90 through 97, and Q911/912.
I have mode set to CWR?
Best,
N
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Thanks.
I hear the relay activate.
Will check Q15 anyway.
Best,
N
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Nick,
Sorry about the CWR.? The KD8CEC and other software have two forms of CW: CW for normal sideband use and CWR for reverse sideband use. It does not matter which you use for the CW transmitter tests.? It has been over two years since I used the stock V6 software with the rig.? I prefer the N8ME with VU3GAO mods.? The download is in the files section of this group.
73
Evan
AC9TU
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Hi Evan,
Have been busy, but finally got around to checking RX and TX voltages as suggested.
Q911/912
RX EBC all 0.01v
TX Emitter 0.32, Base 1.00, Collector 10.82
Q92/93/96/97
RX EBC all 0.01v
TX Emitter 10.75v, Base 1.0v, Collector 0.32v
The two IRF510s
RX EBC? 0.01v, 11.19v, 0/26v
TX Emitter 0.04v, Base rises momentarily to 17 or 17v, then drops to 10.87, Collector 4.08v
These readings were taken using battery power circa 12v input
I hope I read the transistor pinouts correctly.
I re-soldered the IRF 510s too, just to be sure.
And I don't think I twisted the non-surface mount replacement for Q90.
Sorry to pick your brains again, but can you deduce anything from these figures ( was on CW mode when taking readings)
Best,
Nick
?
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Nick, Please verify that you followed the "no modulation" instructions when taking the voltage readings when transmitting per this spreadsheet: /g/BITX20/files/VU2ZAPRaj VU2ZAP did it on a v4; however, the transmitter power sections are very close in value. If you have replaced the IRF510s, you must set the bias.? That is the first section on this page from HFSignals: Only do the bias adjustment, not the other calibration steps. The IRF510 is a MOSFET.? It has? source, gate, and drain leads:  Try measuring the voltages again according to the above diagram. With the data that you provided, I can not make any suggestions as to where the problem might be. 73 Evan AC9TU
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Hi Evan,
Again, sorry to haunt you.
I've biased the Mosfets, measuring current draw as described. Obviously no uptick in draw when shouting into the mic.
Measuring voltages, with supply set at 12v, gave the following results:
RX
G 0.17v 0.22v
D 11.47v 11.06v
S 0v 0v
TX (CW)
G 4.3v 3.95v
D 11.55v 11.10v
S 0v 0v
On TX G and D voltages seemed to rise, briefly, and then fall immediately to the levels indicated.
Is this at all useful?
Best,
Nick
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Raj vu2zap