Re: QMX RX dead after testing TX with dummy load - can FST3253 replace CBT3253?
Bev, post a picture of the diode mod. It will be useful to all.
JZ
SOLVED
I replaced the smoked CBT3253 by an FST3253 from my home stock, everything works.
Then I was looking for the "safety diode" installation mentioned here:?/g/QRPLabs/message/115735
The "right end" of C508 was easy to find, it is the one not connected to ground, can be checked by a multimeter for continuity. Then it appears from the PCB sketch in assembly manual that the place for diode anode is the "opposite" end of L503. So if you look at C508 and cathode of the diode should be connected to the "south end" of C508, the anode the has to be soldered to "north end" of L503. The distance is just about far enough to acommodate through-hole 1N4148 with leads bent? tightly. Leave the bent leads of 1N4148 just long enough to keep the diode tightly above Q508. Before placing the diode to PCB, make sure to have ends of leads tinned by fresh solder, then solder diode leads to C508 and L503, adding a micro droplet of solder if necessary.
It took me several hours to figure out how to solder the diode, especially with regard to L503. In the process I mechanically damaged Q508 (BSS123) but luckily I had a few spare 2N7002's (exact equivalent) so I was able to finish everything without having to wait till morning when they open electronic parts shop :)
I hope the diode will finally prevent IC402 from further failure for good because my QMX produces 6 watts on some bands. Since I finished the kit, I had to do two repairs and one mod and I think now I deserve enjoying some fun with the QMX. It's a beautiful and effective radio, I have never had such satisfaction working other QRP rigs (NorCal 2030, KX3).
73 Jindra "Bev" OK4RM
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Re: QMX RX dead after testing TX with dummy load - can FST3253 replace CBT3253?
SOLVED I replaced the smoked CBT3253 by an FST3253 from my home stock, everything works. Then I was looking for the "safety diode" installation mentioned here:? /g/QRPLabs/message/115735The "right end" of C508 was easy to find, it is the one not connected to ground, can be checked by a multimeter for continuity. Then it appears from the PCB sketch in assembly manual that the place for diode anode is the "opposite" end of L503. So if you look at C508 and cathode of the diode should be connected to the "south end" of C508, the anode the has to be soldered to "north end" of L503. The distance is just about far enough to acommodate through-hole 1N4148 with leads bent? tightly. Leave the bent leads of 1N4148 just long enough to keep the diode tightly above Q508. Before placing the diode to PCB, make sure to have ends of leads tinned by fresh solder, then solder diode leads to C508 and L503, adding a micro droplet of solder if necessary. It took me several hours to figure out how to solder the diode, especially with regard to L503. In the process I mechanically damaged Q508 (BSS123) but luckily I had a few spare 2N7002's (exact equivalent) so I was able to finish everything without having to wait till morning when they open electronic parts shop :) I hope the diode will finally prevent IC402 from further failure for good because my QMX produces 6 watts on some bands. Since I finished the kit, I had to do two repairs and one mod and I think now I deserve enjoying some fun with the QMX. It's a beautiful and effective radio, I have never had such satisfaction working other QRP rigs (NorCal 2030, KX3). 73 Jindra "Bev" OK4RM
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Re: QMX no Rx after a few days of operation
OK4RM,
I don't have a way to make/send you an image at the moment.?
My suggestion is to take an ohmmeter set to a low range and ground one lead. Probe the inductor with the other lead. One terminal should read close to zero. The other terminal will read the resistance of the inductor, small but not zero. That is the lead you want to connect to.
If you look at the image of the PCB layout in the QMX documentation, you should be able to confirm your selection by following the inductor ground connection.
73, JZ
hello could you pls indicate which end of L503 at the PCB is the right one?
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Re: QMX no Rx after a few days of operation
Hello Hans.?In your case, do you hear band noise or do you not have audio at all?
73, Juan LU9CYV
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Please, some suggestion?
Thank you very much
73, Juan LU9CYV
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Re: QMX HW Diagnostics: No TX?
Todd,
In FW rev 1_00_011 a feature was added to enable the TX voltage (in RX)? to be set well above zero. (3a: Mod high in RX).
?Leaving it at zero was creating undesired capacitive loading of the RX path and potential diode-induced IMD as well. Restoring some voltage at the drains of the BS170s solves that problem.
Check to see if you have that option enabled on your QMX.
If not, and if you still have voltage showing in RX, there may be a hardware problem with the modulator circuit.
JZ KJ4A?
On Mon, Jan 1, 2024, 3:11?PM Todd W2TEF < w2tef@...> wrote: Hmmm... my diodes look like they're correctly oriented. I can't locate any evidence of damage or shorts to any components, particularly around the toroids and inductors. I'm absolutely willing to take another swing at the toroids if they're suspect. But I feel like the diagnostic screen gave me a clear pointer toward a problem:
 
When transmitting, the voltage is at 10.1v (and output of 0 watts!). The operation manual states (p. 73, v.014):
Additionally, the PA voltage is measured,
after the RF envelope shaping (amplitude modulation). In transmit, this should be a little less than
the supply voltage measurement. In receive, it should be near to zero volts. The PA voltage is
coloured green or red depending on whether it is within a reasonable operating range or not."
But in receive, it's still at 10.1v. I see other images in the forum showing that value at, e.g., 0.6v at receive.
Where is this reading being taken? Perhaps I need to look "near" there in the circuit for a nicked wire or a solder whisker??
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Re: QMX HW Diagnostics: No TX?
Hmmm... my diodes look like they're correctly oriented. I can't locate any evidence of damage or shorts to any components, particularly around the toroids and inductors. I'm absolutely willing to take another swing at the toroids if they're suspect. But I feel like the diagnostic screen gave me a clear pointer toward a problem: When transmitting, the voltage is at 10.1v (and output of 0 watts!). The operation manual states (p. 73, v.014):
Additionally, the PA voltage is measured,
after the RF envelope shaping (amplitude modulation). In transmit, this should be a little less than
the supply voltage measurement. In receive, it should be near to zero volts. The PA voltage is
coloured green or red depending on whether it is within a reasonable operating range or not."
But in receive, it's still at 10.1v. I see other images in the forum showing that value at, e.g., 0.6v at receive. Where is this reading being taken? Perhaps I need to look "near" there in the circuit for a nicked wire or a solder whisker??
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Re: QDX: WSJT-X indicates that QDX resides at COM3 but I'm still getting Hamlib errors when I try to test CAT there.
Try using the suggested baud rate. See operating manual, page 7 and note 3 on page 8.
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Re: QMX no Rx after a few days of operation
hello could you pls indicate which end of L503 at the PCB is the right one?
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QMX RX dead after testing TX with dummy load - can FST3253 replace CBT3253?
Hello, same problem as some other users (DG8YBJ, DG8RCN, DD6DO).
Checked the usual R and C parts, all are correctly populated. Voltage at IC402 pin 9 (MUX common) is between 4.86 to 4.91 V, when switched to 3.5, 5.3, 7 MHz, pins 10, 11, 12 are zero, pin 13 has 4.91 V. When switched to 14 MHz, pin 11 has 0.76 V and pin 13 = 0.59 V. At 10.1 MHz pin 12 has 0.76 and pin 13 0.59 V.
Obviously, IC402 has to be replaced. I have some spare FST3253. Are they interchangeable at this position?
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Re: QMX HI Band Rev 2. Immediate current limit on startup
Thanks Jeff.? ? I'm still looking it over some each day trying to determine if I messed up somewhere, but so far, nothing.? The only voltage that has ever been applied was the first attempt to power it up.? ?I don't have a milliohm meter, so will keep looking for errors for now.? I may get it to you sometime if you're willing to take a look.
Thanks for the comments,
Ken
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For Sale QDXs Rev 3 and a QCX mini
I have 2 QDXs Rev 3 unassembled with enclosures.?
I am asking USD 95 each with shipping to CONUS
If you buy both, I will include a QCX mini Rev 1 that is assembled but not working. The screen lights up but no text. ?I just don¡¯t have the patience to troubleshoot it and I don¡¯t want to throw it away in the garbage.?
Contact me via email as listed on QRZ
73
Chris
WA2SEM
?
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Re: Questions re: PA socketing and Zener & L14 diodes
On Sun, Dec 31, 2023 at 05:07 PM, Charles Johnson wrote:
, I also plan on installing a 1N4148 diode across L14. For those who have done this, what is the best method by which to wire it in? Also, which end does the anode need to connect to?
I soldered the diode across L14 on the top side of the board.....seemed to work for me. Hundreds of QSOs since and finals are still intact on my QDX. (Made it 440+ before blowing the original BS170s, replaced and added a 1N4148 across L14 and now have made over 800 since, and all good.) From what I found on this forum, Anode goes to the side that connects to/is toward the T1 transformer, and the cathode goes to the side of L14 that goes to +12V.? -Nate N8BTR
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Re: QMX HI Band Rev 2. Immediate current limit on startup
My experience with VDD shorted to GND on the main board is that it¡¯s usually but not always in the MPU chip. ?You can determine that with a milliohm meter. ?Find where on the board the lowest resistance is from VDD to GND. ?Sometimes it¡¯s a single pin on the MPU or sometimes it¡¯s the supply lines to the MPU. ?The over voltage that causes this is often a mistake in building or a solder bridge or a probe slipping when measuring. ?If 5V or 12V gets put onto any of those MPU lines, it¡¯s all finished. ?The MPU can be replaced. ?I¡¯ve done it a couple of times. ?But other chips could be damaged as well. ?Also replacement MPUs are expensive and to date not available from Hans by themselves. ?I¡¯ve always salvaged them from known working boards.
Jeff
W1NC
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On Mon, Jan 1, 2024 at 05:20 AM, Hans Summers wrote:
Which is normal because QMX uses DSP filtering.
?
...is it possible to set the center frequency for either of the QxXes? Happy New Year to all of you! 73 de Razvan dl2arl
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For accurate power measurements you need a 50 ohm output impedance, a short cable to a good through line meter and a high quality 50 ohm load right on the meter output (or a terminator type meter)?
if you have the equipment replace the above with a T adapter in the Tx output, the 50 ohm load on one port and a 100MHz or better digital scopes¡¯ x10 probe in the third port so you can use the scopes RMS output figure for your calculation ( fir extra points add a filter to be sure you¡¯re only seeing the fundamental frequency power)
if available see if if a 3dB attenuator on the TX output half¡¯s the power etc ?(if not somethings not 50 ohm?
with non 50 ohm outputs, different loads, different meters and different cables/connectors/lengths I can get any number of different power ¡®readings¡¯ you like?
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FB, Hans !
72,
Bill, WB4HIO
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I've spent some time this afternoon identifying bugs with the 1.00.014 firmware. This is what I have found:
- calling CQ on 30m CW into a well matched antenna (SWR circa 1.2:1), towards the end of my CQ call the QMX stopped transmitting and all I heard was a continuous tone. The only way to clear this was by entering the menus and existing them without making any changes. However on exiting the menus a very loud click occured.
- semi QSK does not work - setting the option to either on or off has the same effect (of full break in). The manual does not say that this feature is not implemented.
- SWR protection enabled and it trips on an antenna matched at 1.2:1, the swr bar graph shows 1 and occasionally 2 bars when transmitting, with the swr threshold set to 3. If I change the threshold to 6 it still trips.
- what is incredibly frustrating is that each time I change bands the default frequency that is set is the FT8 frequency. This is not good for my ears. I thought that there was a default frequency per band but can't see that this is editable anywhere.
Last week I made a couple of cw qso's but gave up because of the keyer behaviour. When doing the tests above I was on 30m and no-one answered my CQ calls but in my CQ calls I didn't really encounter any odd behaviour (what I did encounter I attribute to my keying).
In my opinion changing bands would have been better implemented by a single press of the encoder. It is all too easy to accidentally change to digi mode by a single click and get deafened. Hindsight is wonderful!
Attached are a couple of screenshots of my keyer and protection settings.
73 Simon
G0FCU.
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That sounds similar to what happened when I fried my output transistors.
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Juan
Todd W2TEF
Bill, N4QA/QRP
DL2ARL
Bruce Akhurst