Re: Qmx in receiver mode tx voltage in red
I forgot to say…
clean up the Q507 pad after removal. ?Clean off leg pieces and all solder. ?Then apply fresh flux before soldering in a new one.
Jeff
W1NC
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Re: Qmx in receiver mode tx voltage in red
Thank you, Jeff!
Good Luck, Giovanni!?
BTW,? I am looking at your photo and also studying Hans' layout to see what you are flagging. Do I see a subtle BS170 gate to drain short in your photo?
JZ
On Sat, Feb 24, 2024, 8:29?AM Jeffrey W Moore via <jeffreymoore= mac.com@groups.io> wrote: Hello Giovanni,
John alerted me to your post.
the safest way to remove Q507 is to first carefully remove the inductor L502.? That should be easy with flux, solder wick and a decent iron.? Then cut the two legs of Q507 with small sharp diagonal cutters.? That frees Q507 at that end.? Then with a medium tip on your iron and lots of flux, heat the main pad under the drain.? Be sure to touch the pad and the drain.? This should free it for removal with tweezers.? If not, your iron is not hot enough or enough wattage.? In this case you can flood the pad with low temp solder and flux then remove.
good luck,
Jeff
W1NC
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Re: Qmx in receiver mode tx voltage in red
Hello Giovanni,
John alerted me to your post.
the safest way to remove Q507 is to first carefully remove the inductor L502. ?That should be easy with flux, solder wick and a decent iron. ?Then cut the two legs of Q507 with small sharp diagonal cutters. ?That frees Q507 at that end. ?Then with a medium tip on your iron and lots of flux, heat the main pad under the drain. ?Be sure to touch the pad and the drain. ?This should free it for removal with tweezers. ?If not, your iron is not hot enough or enough wattage. ?In this case you can flood the pad with low temp solder and flux then remove.
good luck,
Jeff
W1NC
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Re: Qmx in receiver mode tx voltage in red
I remind a short cut there
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Re: Qmx in receiver mode tx voltage in red
Ouch! That looks pretty bad, Giovanni! ? That transistor is a pretty robust device. Whatever killed it must have been an energetic event. Carefully inspect around the PA circuitry and make sure there are no solder balls or wire bits lurking!
Yes, removal of Q507 is not easy. Lift-up damage to the G and S pads is possible! You might carefully cut those leads first and remove them individually.
After that, heating the drain connection and perhaps flooding it with a solder that has a lower melting point than the lead-free solder used in production might do the job.
Jeff Moore may have additional tips for you on safe removal.
JZ
On Sat, Feb 24, 2024, 7:48?AM Giovanni Ilari IT9XJJ < giov.ilari@...> wrote: Gate source 0.6 ohm, source gate 0.6 ohm, gate drain 0.8 ohm, drain gate 0.8, source drain 0.3 ohm? drain source 0.3
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Re: Qmx in receiver mode tx voltage in red
Gate and l502 are far away
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Re: Qmx in receiver mode tx voltage in red
Gate source 0.6 ohm, source gate 0.6 ohm, gate drain 0.8 ohm, drain gate 0.8, source drain 0.3 ohm? drain source 0.3
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Re: Qmx in receiver mode tx voltage in red
G., One more thing...
If a short (e.g. solder bridge) exists between gate and L502, as was the case prior, it will read as a hard short gate-to-drain at Q507.?
You should check that as well before any attempt at surgery.
JZ
Giovanni, Before you attempt removal, please post what readings you obtained. Remember, there are other circuit elements present that must be considered.
JZ
On Sat, Feb 24, 2024, 7:29?AM Giovanni Ilari IT9XJJ < giov.ilari@...> wrote: Yes! Q507 shorted! Measured drain and source and also shorted with gate! Vy difficult desolder! I have not hot air desolder, is there a fast solution??
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Re: Qmx in receiver mode tx voltage in red
Giovanni, Before you attempt removal, please post what readings you obtained. Remember, there are other circuit elements present that must be considered.
JZ
On Sat, Feb 24, 2024, 7:29?AM Giovanni Ilari IT9XJJ < giov.ilari@...> wrote: Yes! Q507 shorted! Measured drain and source and also shorted with gate! Vy difficult desolder! I have not hot air desolder, is there a fast solution??
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Re: Qmx in receiver mode tx voltage in red
Yes! Q507 shorted! Measured drain and source and also shorted with gate! Vy difficult desolder! I have not hot air desolder, is there a fast solution??
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I agree with your approach regarding the input and output impedance measurements.
?
During the construction and measurements, I must admit that this 10W PA is a well-thought-out design
Wel done Hans.
Other designs on 2 x IRF510 perform a lot worse.
?
?
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Re: QDX 15m RF sweep real bad
#qdx
Good catch, Timo. That explains a lot. JZ
Evan and team,
Very interesting observation I would not have seen if I did not replace R13 and C33.?
L13 was soldered on its one side only.? The other side is totally without solder meaning there was no blocking of AC signals to ground.? Don't know if this is perhaps just my board (v4) or if this is the same on other V4 boards.
Worthwhile to just check.
73 de ZR6TM
Timo
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Re: #key #qmx QMX Straight Key Mode incorrect
#key
#qmx
Hi Gary,
thanks for posting that - I second your findings. I had posted a description in the "ALPHA 1_00_015" topic [1] together with some other thoughts, where Adrian YO3GFH's answer led me to thinking it was me doing sth wrong :). As at that time Hans was busy fixing the keyer (... and that it's just a mislabeled config) I didn't bother to dig deeper.
73 de Cedric DJ3CE
[1] /g/QRPLabs/message/117466
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On 24/02/2024 10:34, Dan Hurd W5DMH wrote: I am wondering if I tried powering directly from the USB 5v (no buck converter at all) could damage the QDX? Dan, There would not be enough voltage to run the QDX if you put 5 volts to the power socket. I see no reason that it would be damaged, just not work. It is possible that with a slight mod to the QDX it could run at low power from 5 volts directly. Possible but probably not worth the effort. 73 Alan G4ZFQ
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Re: Qmx in receiver mode tx voltage in red
Low power on all high band about 1-2 watts, kit 12v, tks for answer, i will check what you tell me. Tks, i will inform you next. 73 de it9xjj
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I am using it on a Panasonic Toughbook, USB 3.0 and probably higher current rating than a standard USB 3.0 port, but I have been unable to find a specification for the current on those ports.?
I see no noise in the waterfall at all and reception appears to be the same as on battery.?
I am wondering if I tried powering directly from the USB 5v (no buck converter at all) could damage the QDX??
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Re: BNC connector doesn't work.
FYI Allison most recent production of BNC's are mechanically compatible.? Makers could get a long way towards 75 ohms with different insulation materials? and adjusted internal dimensions at the solder /crimp end so the volume production is indistinguishable by fit.
?
Of course the two impedances still exist and old cables are still around with different part? numbers for the two types (except on ebay ?)
?
The OP's problem was a dimensional issue on the threaded part.
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Re: Qmx in receiver mode tx voltage in red
Giovanni,
Factory build or kit? Does TX work OK?
Assuming that the voltage reported has not been requested via settings, here are a couple of possibilities:
1) Q507 has failed, shorted. An ohmmeter check should reveal that.
2) Q507 is OK but something is drawing the gate of Q507 downwards, turning it on.
?A similar case long ago revealed a solder bridge between Q507 gate and one leg of L502. An ohmmeter check and visual inspection should find that.
73 JZ KJ4A?
On Sat, Feb 24, 2024, 2:39?AM Giovanni Ilari IT9XJJ < giov.ilari@...> wrote: 
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Re: #QMX first powered test -- is this right?
#qmx
On Sat, Feb 24, 2024 at 01:27 AM, Eric W. Hansen wrote:
Despite the lack of a backlight, my computer recognized the QMX, so I installed the firmware and it worked (even got a backlit display).? Maybe the processor thought I was in firmware update mode rather than initial setup mode?
Setup and testing will continue tomorrow.
This is the expected behaviour.? When you very first power up a QMX it looks completely dead - no display or anything and is in a state expecting to be connected to a PC and have the firmware loaded in.? Once the firmware is in it then springs into life :) Good luck with the rest of the testing - they are great radios.
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Re: QDX 15m RF sweep real bad
#qdx
Evan and team,
Very interesting observation I would not have seen if I did not replace R13 and C33.?
L13 was soldered on its one side only.? The other side is totally without solder meaning there was no blocking of AC signals to ground.? Don't know if this is perhaps just my board (v4) or if this is the same on other V4 boards.
Worthwhile to just check.
73 de ZR6TM
Timo
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Bruce Akhurst