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On Wed, Feb 14, 2024 at 01:30 AM, Donald S Brant Jr wrote:

I do not have a schematic handy but I winder if there is a pullup resistor which might be changed to a lower value to put more current through the key contacts.??

Hi,
It could well be the case. The DIT has an external 2k2 pullup and the DAH has none. I also suspect it would help in this case.

What I would like to see HW-wise is a separate jack (pins) for the GPS input and an additional sandwich PCB for all analog stuff like BPFs and LPFs.
?
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73 Bojan S53DZ

My QMX was working fine and I made couple of QSO via FT8. However I noticed the receiver stop working:
1. I can still hear some strong signals.
2. When I plugin my attena, the S-meter in WSJT-x is not changed. keep in less than 10db. when it was working, it should be around 30-40db.
3. I use rs232 console to test RF filter, it show very large att.
I verified all bands are like this. Compare to operation guide, the Y-axis is significant small (-30db).

Any suggestions what I should check?


-Howard?

This does sound easy enough - to make the attenuator attenuate more, although it looks to me that there's a very happy frequency that this amp wants to operate, which implies that somewhere, this frequency of 10 Mhz is being set by a certain combination of components - capacitors, inductors, etc?

Could it be C2 or C3? And I don't know about changing the number of turns on T1, but maybe? I could experiment with a few things I guess.? Any suggestions for starting points from the crowd? I've attached the schematic for convenience.?


Andy KA1PLU

I found this little book of use:

McClanaham, J.??? Oscilloscope Applications for the QRP Enthusiast

Not really on-line, but quite cheap, even more so for the Kindle version.? Available at Amazon and probably many other places as? well.

Troubleshooting update.
Observing that 3.3V linear supply was not enabled, and that the linear supply needs to come on before anything else happens, I tested the supply board alone by connecting the battery supply to the '+12' pin and 'GND' pins on the 2X4 socket on the board, leaving the enable open the 3.3V output appears on its pin. The enable signal taken to GND turns the 3.3V regulator OFF.
Next, I plugged the 3.3V board in via a 2X4 socket with long pins so that I could bend up the enable pin to leave it open, then pressing the control panel button turns on the front section of the other supply board to send the battery voltage to the 3.3V linear regulator. Still did not work. Then I noticed that the input current from the battery jumped to about 500+ mA as long as the button is pressed. Ohmmeter indicates approx 0.6 ohm between Vdd and GND. So it looks like the orignal failure was some damaged component on the Vdd bus caused by a turn-off transient.
I examined a number of components with a sensitive DVM directly across the pads of each component, hoping to find one that showed a larger voltage indicating that it was the location of the short. First tried across supply chokes L201 and L202 (no voltage rise with supply ON). Then several other of the many bypass caps, IC directly connected to Vdd. Not really successful. Nevertheless, I removed C501, then IC501, IC502 but Vdd still shorted.

Strangely, after swapping back and forth between Firmware 12 & 16 a few times while testing - this problem has disappeared.
Still interested if anyone can think of a cause - was using a Dummy load.
None of the cables have been changed & the devices have remained in the same position.
Has me beat - but it is working fine now.

Rob
VK5ZIK

On Tue, Feb 13, 2024 at 02:43 PM, Adrian YO3GFH wrote:

In my previous post, I've mentioned very fine grained (800 grit) sandpaper used for shining guitar frets, that's the one you should use.

Or one could use the right tool for the job, a contact burnisher:??

I wonder whether the issue will return after cleaning.? A problem might be that too little current is being handled by the contacts, there is a minimum so-called "wetting current" required to break through contact film/oxidation and allow a low-resistance contact:??
Special contact materials and mechanical configurations are used when switching very low currents, to avoid this issue.? Mercury-wetted contacts are an example.
I do not have a schematic handy but I winder if there is a pullup resistor which might be changed to a lower value to put more current through the key contacts.??

73, Don N2VGU

Firstly - Thanks Hans for all the work you put in.

Since changing to firmware_1_00_016, I have no PTT & Audio error messages when trying to run JS8
WSJT-X runs fine. (Yes I have checked for the correct sound card settings).
When I switch back to Ver _1_00_012 everything works normally.

Just wondering if anyone else is seeing something similar..??
Rob VK5ZIK

Thanks for help with this Ron. I'll send the radio tomorrow.

I will just say that Hot air is fantastic once you have the hang of it.? ?

?

Brain surgery on your latest radio is probably not the right way to gain initial experience

?

I used a new heat gun (a decent one this time)? as a chance to collect up all those old broadband hubs, network cards, smart speakers etc that were in the 'chuck or not limbo' pile and amuse myself removing and replacing increasingly challenging components until suddenly after many torn tracks and 'collateral damage events'? it all clicked.? ?Now it works at least 95% of the time for me and I find heat shields etc are rarely needed.

?

I use a lot of wooden cocktail sticks.? They are great for sliding off or flipping hot air heated components out of the way and for holding down SMD components while soldering them in.? Unlike metal tools the board is never damaged and they are less prone to slip.? Furthermore if the cocktail stick starts burning too much I know to ease off a bit ! ?

Ill check it out Andy.

Don, good to know about 1x and freq resp. I was aware of the probe cal and all that was covered in the manual for the scope. I read somewhere today that the ones with 2 alligator clips was for the function signal generator output it has. I just dont want to use them for the wrong application and damage something. Im also going to run through Hans trouble shooting video and get familiar with what the QCX+? is doing.

thanks for the tips guys.
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regards,
Bryan, N0LUF

Rater that sandpaper which can remove contact plating, I use a strip of paper soaked in DeOxIt. Works every time.
Gary
W9TD

Hi Ron,

In soldered the jumper to the left side of R40 and to the 12v location you showed in image. There is now 12.5 volts at R40, and 6.5 volts coming out of R40 and into R39. But still can't adjust?I-Q Balance, Phase Lo or Phase Hi. Turning the screws has no effect on the signal level.

Any more ideas or is it time to send it to you?

Thanks.

A product such as Chip-Quik??or Fast Chip?
will drastically lower the melting point of the solder and cut down on the heat needed for removal.??
But if the part has leads which are accessible to be cut and removed individually that is my preferred method.? This is how we repaired hi-rel spacecraft PCBs.
I find that a #15 scalpel blade works well for this.
73, Don N2VGU

Just ran into an interesting problem. Not sure what if it's related to f/w or h/w.
Battery to QMX (12V build) reading 12.0 V- verified with DVM. Current draw 93 mA. QMX reads 10.3 V on screen, as does diagnostics on computer display.?

Yesterday, the voltage on the QMX read the same as the battery.

Any ideas?
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73, Dan? NM3A

On Tue, Feb 13, 2024 at 08:00 PM, Daniel Walter wrote:

Low temperature solder like ChipQuick works well too.?
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73, Dan? NM3A

Another vote for ChipQuick solder. It stays molten for a long time. allowing you to lift the device off easily with no damage to pads.
?
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Mike G8GYW

Yes it is very fine one! Sure! Thanks!

Joan

When I remove these, I cut a square out of Kapton tape and use it as the heat shield. It’s not really needed but it makes me feel better. I don’t pull until the air can make the chip swim. Then I add a tiny bit of liquid solder and drop the new one in.?
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Colin - K6JTH?

Low temperature solder like ChipQuick works well too.?
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73, Dan? NM3A