¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. QRPLabs
  2. Topics

#qmx #QMXplus QMX dismantled awaiting QMX+ #qmx #QMXplus

 

Excellent!? Glad you got it working!
As for power output on the upper bands, I think the 'twisted sisters' winding helps with that, making the transformer more efficient.? But if it is already enough for your needs, I wouldn't change anything.? Just enjoy it!
Stan KC7XE
 

Thanks for the advice, Dan.
Well, I'm quite surprised. Retouched T501 again, no change. Checked Q507 traces, all OK, pins to pads OK.
I couldn't see anything wrong in that area so I heated up Q507 and added some solder to the connections. Weird, all now works!?
Power is a bit down, ranging from 0.8w on 6m to 4.5w on 80m. Probably some coil squeezing to do!
On 9v rx is 135mA and tx is 830mA all running cool on wspr 40m 3.7w into the dummy load.
Thanks to all for the excellent advice.
Phill EA5JHA
 

Phil,
The resolution gets reduced quite a bit here, but once you redo T501, I would resolder the pin diode connections. Some of them look like the possible cold joints. Also, It's hard to tell for sure, but it looks like there may be a little whisker of solder shorting the center to ground of the BNC connector. Soldering all looks pretty good on the LPFs.?
--
73, Dan - W2DLC
 

--
Phill EA5JHA
 

--
Phill EA5JHA
 

Well that went down like a lead balloon!
?
Replaced T501 with a conventional winding for 9v rather than twisted sisters. No improvement, in fact the lpf sweeps are now awful.
?
I couldn't screen print with P or T pressed so here is the diagnostic.
?
--
?
With P pressed BIAS is 30.4mA at 21% duty cycle.PTT on Yellow 0.4V
With T pressed 30.6mA at 21% duty RF output On RED 7.2V 0W SWR 3
?
IQ sweep
?
?
RF Sweep
?
?
?
Receive "was" working on all bands. Plenty of CW and SSB heard. Pin diodes all working, voltages close to zero and 5.88v
I haven't had a chance to try again as I took the antenna down to do some work on the roof!!?
?
I'll move on to testing around Q507 but it might be a week or so as I'm off to the UK for a while.
?
73
?
Phill
Phill EA5JHA
 

Thank you for your advice, guys. I'm away from home at the moment. I'll get some images when I get back. I also have a QDX which works fine. It makes me wonder about T501. The QDX is pre twisted sisters, and was wound standard. Perhaps I've misinterpreted the diagrams. I'll take T501 off and wind it standard and see if that has any impact.
Thanks again.
--
Phill EA5JHA
 

If you have the same fault in more than one kit, I can't help but think there's something you may be misunderstanding about the instructions.
--
73, Dan - W2DLC
 

Also, let us see a close up of the LPF section of your board, top and bottom.
--
73, Dan - W2DLC
 

Phil, are your LPF scans all OK?? Perhaps post a screenshot of one of them.
These also use the tx function, and if they are good, it helps point to the problem.
Stan KC7XE
 

Thank you, Guys. The QMX+ is finished!
Guess what? Same fault as the QMX. This isn't funny.
Everything works except transmit.?
I've checked the soldering of Q507 and continuity through L502. The LPFs all work on receive so that part of the circuit should be OK.
Diagnostic graphs are all OK except swr which I guess is due to zero output power.
Luckily a lot of fault finding data here so I'll start with testing the DAC input and R506? net and take it from there.
73
--
Phill EA5JHA
 

Sorry for the confusion Stan. I'm still in the build phase. I don't think I put too much heat in to it, soldering. Just one of those things! Luckily I had a spare so clipped the old bits out and soldered a replacement across the leads.
?
?
--
Phill EA5JHA
 

Careful, if that went pop, you likely have a short somewhere.? It should only get small current in receive from the Vcc (5V), or 30mA in transmit from the tx bias current.? Maybe you have a 12V short to one of those...
Stan KC7XE
 

And.......Poof!
First time I've seen an inductor self destruct! L523 now a two-part component.
At least I know what it looks like inside.
Luckily, I can use one from the QMX.
?
--
Phill EA5JHA
 

Jerry and Greg. Thanks for the great advice. I'm going to put it to good use but first try increasing the heat on the old QMX board.?
?
I'm surprised at how much heat the QMX+ needs. It must be nearly all ground plane!
?
73
--
Phill EA5JHA
 

Correction:? There was zero clearance from the desktop to the torroids.
Adding the screws to the top of the spacers gave me much more confidence.
?
Jerry, KE7ER
?
On Tue, Nov 26, 2024 at 11:10 AM, Jerry Gaffke wrote:

I've installed these spacers and screws without
the dev board to hold it up off the desk.? Was necessary to also install the top screws
or there was zero clearance from desktop to the spacers, which makes me wonder
if people will have trouble when using the dev board.??
 

As a general rule, if the solder isn't flowing you need to give it more heat.
No way around it.??
?
Except for plastic parts like the connectors, it's astounding how much heat this stuff can take.
Hot air rework on large parts with lead free solder is way worse then what I do with my iron.
Don't tug at the part or you'll lift the pads off the board when removing a part.
?
Jerry, KE7ER
?
On Tue, Nov 26, 2024 at 09:28 AM, Phill wrote:

Thank you both. I'll use a bigger bit and 440C and see how it goes.
I built the QMX and QDX with a similar iron to that one Jerry but perhaps I was just a little shy with the heat. I didn't like going over 420C. I'll experiment on the QMX first as it's a bit the worse for wear.
 

I usually scrape magnet wire with a knife to make sure the enamel is off.
With the wire in the QMX+ kit, I am just poking it through the hole and soldering.
Hold for a few extra seconds while rubbing the tip of the iron around the base of the wire
to rough up any insulation that might still be there.
?
I am often flipping the board over and setting it flat on the desk to work on the back.
The has it resting on any upright torroids, and those wires will eventually break.
I also ordered the dev board for the QMX, it comes with 4 nylon spacers and 8 nylon
screws for mounting the dev board.? I've installed these spacers and screws without
the dev board to hold it up off the desk.? Was necessary to also install the top screws
or there was zero clearance from desktop to the spacers, which makes me wonder
if people will have trouble when using the dev board.??
?
?
All the surface mount parts on the board got auto-stuffed and then reflow soldered
using lead-free solder.? That solder will take much higher iron temperatures to melt
than the solder with lead that most of us use.? If I were to take off a part like the
PCM1804, I'd try to get some ChipQuik alloy in there with an iron at each pin
before torching the board with hot air, the ChipQuik melts at a very low temperature.
?
On some parts it's best to clip the pins one by one with fine tipped diagonal cutters,
then remove the pins with an iron.? But with surface mount parts, that will rip the
pads off the board unless you do it just right.?
Best to practice on some old junk boards first.
?
Jerry, KE7ER
?
On Tue, Nov 26, 2024 at 09:50 AM, Greg McCain wrote:

I've successfully built several Q's. I use a 2mm conical tip on my WEP station at 400 C for just about everything. I have bumped the temp up to 480C to throw more heat quickly into large components like BNCs or other jack connectors.
?
I generally mentally count off about three to four seconds for most joints, after the solder is fully flowing into the leads and surrounding pads. Maybe a bit less for very fine pins.?

I might drop down to a 1mm conical at 400 C for sneaking into tight spaces especially on the topside for adding a bit of solder on topside components, to help mechanically stabilize toroids leads for instance.??
?
I drop down to a very fine 0.5mm tip only for touching up individual IC pins or small SMD work.?
?
I use good 60/40 or 63/37 fluxed solder.? Mostly 0.31 diameter but occasionally 0.15 for really fine work. Kester makes outstanding products.?
?
And ChipQuik brand liquid flux as needed and their low-temp solder paste for certain SMD rework.
?
GREG
 

I've successfully built several Q's. I use a 2mm conical tip on my WEP station at 400 C for just about everything. I have bumped the temp up to 480C to throw more heat quickly into large components like BNCs or other jack connectors.

I generally mentally count off about three to four seconds for most joints, after the solder is fully flowing into the leads and surrounding pads. Maybe a bit less for very fine pins.?

I might drop down to a 1mm conical at 400 C for sneaking into tight spaces especially on the topside for adding a bit of solder on topside components, to help mechanically stabilize toroids leads for instance.??

I drop down to a very fine 0.5mm tip only for touching up individual IC pins or small SMD work.?

I use good 60/40 or 63/37 fluxed solder.? Mostly 0.31 diameter but occasionally 0.15 for really fine work. Kester makes outstanding products.?

And ChipQuik brand liquid flux as needed and their low-temp solder paste for certain SMD rework.

GREG




On Tue, Nov 26, 2024 at 11:00 AM, Phill via groups.io
<rocinante2021@...> wrote:
Thanks Jerry, excellent advice. My QMX+ arrived today and I've already started with the build. I'm concerned about making good joints to the ground planes. I've done a couple of capacitors and I'm not happy with them. I'm using a Hakko 888D with a fine 0.5mm tip and extra flux. I can get the heat on the component lead but the pcb solder pad is really small. What temperature do you recommend to get a solid joint without frying everything.?
Kind regards
--
Phill EA5JHA
 

Thank you both. I'll use a bigger bit and 440C and see how it goes.
I built the QMX and QDX with a similar iron to that one Jerry but perhaps I was just a little shy with the heat. I didn't like going over 420C. I'll experiment on the QMX first as it's a bit the worse for wear.
73?
--
Phill EA5JHA

1 - 20 of 30