Hello everyone!
I'm THRILLED to report that my QDX is back up and running after being QRT for 16 days! ?Replacing the 4 BS170 MOSFETs and the IC5 driver fixed it!

What have I learned or done this month especially in the last 16 days?

• There are a great group of patient people on this board willing to share tips, practical knowledge, encouragement and words of wisdom!
• QDX cannot tolerate high SWR even for "short" periods of time,
• Researched impedance matching units (commonly called antenna matching units) automatic vs. manual tuners,
• Learned why a manual antenna tuner with a 50 ohm resistive bridge is really necessary vs. automatic antenna tuners which often present high VSWR while chasing 1:1. (I am now using the recommended EMTECH ZM-2.),
• Located the QDX troubleshooting information on Hans' website and found it helpful,
• Learned how to tweak my QDX power output by adjusting the windings on L2, L3, L4, L6, L8 and L10. (done)
• Better understanding of the QDX design after reading through the comphrensive design notes in the manual,
• Understand how to update the firmware (done),
• Understand how to get into QDX terminal applications mode and review information (done),
• Upgraded/replaced my almost 40 year old Weller TC201/202 soldering iron to a variable temperature controlled Hot Air Rework and soldering station,
• Learned surface mount component rework techniques (paste, ideal temperatures, types of solder, tricks, etc.) and
• Upgraded/replaced my coax jumper cables (between QDX, pwr/swr meter and ZM-2) with high quality cables and connectors to mitigate potential intermittent connections.

With the 4 BS170's and IC5 replaced, I now see 4.7 watts on 80m, 4.9 watts on 40m, 4.1 watts on 30m and 4.8 watts on 20m! ?(9 volts input)

When I obtained IC5 from Hans, I also ordered the parts (less the case) for another QDX (80-20m version). ?Since I didn't use it, at some point, I'll order another case and the QDX high band components to get me on the higher bands. ?I may wait a while in case Hans tweaks the high band specific components with the additional feedback and ongoing experimentation.

I also have the 40m QCX+ (and companion 50 watt amplifier) kits here awaiting my attention. ?For now, my day job continues. ?All in good time!?

I would like to thank N1JBJ, NM3A, VA3SYS, K8WPE, N2VGU, N6OTQ, "Mark", AE5ZA, VK3ELH, DJ4DI, KF4AYT and OH2AWG! I sincerely apologize if I neglected to mention someone! You have all been super helpful! ?Also, thanks to Hans for designing, documenting and distributing such great and affordable kits!

Ciao! and 73, ?Peter W1DAD ? Windham NH

Peter,

I am glad that you have your QDX back up and running.

Here are a couple of tips that may help you maintain the 'status quo' - your build is 9V - I would be inclined to use a 'buck-convertor' to enable you to reduce the 9V to perhaps 8.7 or 8.8.. reason your RF Output looks 'Maxed' and from experience if you are noticing the case getting 'warm' your BS170's are dissipating too much heat. IF THIS IS THE HAPPENING? You perhaps need some additional cooling?

Lots of options - Fan, Better Heat-sink, Lower voltage...

Keep an eye on the above and you should be okay!

73

Well, I guess I spoke too soon! ?VE3EGA, so much for maintaining status quo... (and you should buy a lottery ticket - you called it...)

Since repairing my QDX 24 hours ago (and making 20 FT-8 contacts on 80m - 20m over a few operating periods totaling about 3 total hours powered on and now utilizing the EMTECH ZM-2), my output power has dropped considerably as follows:

80m has gone from 4.7 watts to 1.8 watts
40m has gone from 4.9 watts to 1.5 watts
30m has gone from 4.1 watts to 1.7 watts
20m has gone from 4.8 watts to 1.4 watts

My measured voltage input is 9.16 volts DC utilizing a SoulBay 3V/4.5V/6V/7.5V/9V/12V Universal adapter rated at 2.0 A max.

The case had been getting pretty warm and I was about to take the suggestion above and measure the output with the adapter set to 7.5 VDC.

I've looked at Hans' troubleshooting guide and I believe that many of the "fixes" don't apply since I've made close to 400 contacts with this QDX and it had been working fine (likely not built wrong).

I've opened it up an reinspected it and nothing pops out at me. ?The search continues... ? ?ANY SUGGESTIONS?

73, ?Peter Schipelliti ?W1DAD Windham NH

Peter,

Been there-done that! - You popped one (or maybe two) of the BS170's - easy just to change all 4.

Some folks have even installed sockets for the BS170's - Like "Smarties" always keep a supply close by!

I will dig out some earlier posts for additional cooling (if you wish?) but I think your problem is the Universal PSU - not stabilised enough - over-voltage and/or maybe a voltage spike?

Look at (invest) in a different Power Source I use an "Alinco DM-330MV" for pretty much everything (with Buck-Convertors for different rigs) but you can also PU small LiPO batteries quite cheaply (and use a buick-convertor!)..
Another less expensive (low-noise PSU is made by "Pro-Audio Engineering", designed for the KX3, it will give you a useful PSU - but again, use a buck-convertor!

I'm sure others have favourite PSU's that will give you control over the VDC?

Good Luck!

73

Terry

Hi Terry, ?Thanks for the great feedback!

I'll change the BS170s. ?Should I in fact change all four at once or can I mitigate potential rework damage and simply change one at a time and test? Or will this present a potential electrical imbalance of more than one BS170 is blown and risk additional circuit damage?

BS170 sockets sounds interesting but I'm sure that has its pros and cons including proper heat dissipation.

I ordered a couple of HiLetgo LM2596 adjustable DC-DC step down buck power convert module 4.0-40V input to 1.25-37V output with LED voltmeter display.

I do have a 23 year old Astron RS-35M linear power supply (dedicated to my IC-756Pro) sitting under my desk. ?I suppose that I could try that with a buck converter. ?I also have a junk box full of various leftover wall warts / adapters but I suspect that they're not "clean enough" for this application. ?I also have some larger (3.5" x 7.5") flat bricks leftover from old larger laptops that are rated at 19.5 VDC @ 12.3 A. I suspect that the filtering may be somewhat better on these. ?Thoughts?

I looked at the specs on the Alinco that you mentioned. ?That looks like a great supply and something nice to have! The ripple spec is <15mV p-p at rated load. ?I went looking for the ripple spec on the universal adapter that I mentioned in my previous post. ?There were no significant spec details on Amazon but one reviewer did say, "Extremely noisy output, A nice Fluke multimeter will show pretty constant output, but o-scope shows 3V+ AC of noise. 3V voltage swings of noise and ripple that seems to scale a little depending on which voltage state you select. Don't use with sensitive electronics!" ?Please understand that I didn't doubt you. ?I'm simply trying to get to root cause vs. apparent cause. ?I don't want to keep changing BS170s. ?The amazon review above does confirm your suspicion that the Universal PSU may be the problem (along with me pushing it too much with 9+ volts in).

Another temporary option I could try is the solder rework station that I recently purchased has a 0-15 VDC @ 3A supply but I'm not sure how "clean" that is either. ?I may just end up with the Alinco which I could use for other things. :-) ?I still need to build my QCX+ and the 50 watt amp.

Thanks again for the suggestions; they are really appreciated!

73, ?Peter ?W1DAD ?Windham NH

Peter, If you change all 4 you can check them afterwards to see if any are still good - although at the price, its hardly worth it!

----------------------------------------

Here is a link to the PSU that I use with my KX3 -? ?You will need at least a 2-5A Buck Convertor ("DROK") or equivalent, to create a nice 19-2VDC supply.
(I use this combo up at my trailer in the Summer)

----------------------------------------

This is the heatsink I usually add to 'ANY' QDX - as the existing cooling system is inadequate!

?

Also, I have used this neat (FAN) product (originally designed for the RPi 4 (I use it with my "Inovato.com" "QUADRA"? (like a RPi3) that fits on the shelf below the QDX, making a neat WSJTX 'stack')



73

Terry

(Note: Also, Check out/join uSDX group)



Terry

I just completed a QDX build, I also just assembled a ZM-2 ATU.? I would love to know how to use the ZM-2 with the QDX.? If someone could help, I'd appreciate it!
Thanks in advance.
73, Bob KD2YUG?

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Bob,?

Hi Bob,

I have the ZM-2 and Cliff's post pretty much aligns with my experiences..

What I do is follow the basic instructions (I am using an OFCFD Windom for 40 thru 10) as follows:

1. Flip Tune Operate to TUNE Position -set both dials to 6 (half-way) and? GND LINK to GND and ADD (capacitance) to '0'
2. Apply Power (example 3 or 4 W) note TUNE LED will be BRIGHT - turn RH dial until it dims a little
3. Turn left hand dial until it dims MORE - then go back and forward until LED extinguishes!
4. If it doesn't dim completely ADD capacitance (250pf) and try again - DONT TUNE FOR MORE THAN 10 OR 15 SECONDS WITHOUT A REST!)
5. IF IT IS STILL NOT DIMMING ENOUGH SWITCH GND TO LINK AND TRY AGAIN..
6. Once it dims (extinguishes_ you are TUNED :) and can sw to OPERATE!

FYI, MY SETTINGS ARE AS FOLLOWS:

20M? 250pf, 4.5, 4.8 GND
30M? '0', 6.6, 1.2, LINK
40M? '0', 9.0, 8.9., LINK

Like Cliff says: RECORD your settings per Band for easy return to correct settings +_

Hope this helps?

73

Just one other thing - as its a NEW BUILD - before your plug QDX into your antenna - IF you have a power meter and a dummy load - make sure your QDX is ACTUALLY delivering 3-4W output into 50 ohm!

(Also, if its a 12V build I suggest reduce power to 11.2V - If its 9V Build reduce to 8.7V - watch for PA's getting too WARM (sign of mismatch)

Alternatively, visual-led-test - plug output of QDX direct into ZM-2 "SWITCH IN TUNE" and a 50 ohm DUMMY LOAD in place of the ANTENNA and if LEDS are BRIGHT you have 3-4 W OUTPUT and can proceed to TUNE ZM-2 into your?
(perfect 50 ohm) - DUMMY LOAD

After which, you should be an expert tuning any antenna with the ZM-2...

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Another method to get you in the ball park with your antenna tuner/antenna combo is to first connect them to a receiver tuned near the frequency of interest and adjust the tuner for maximum noise in the receiver. This method is suggested in MFJ documentation.

But, I do not think viewing WSJT-x's waterfall from the QDX will not work well using this technique.

Even better is to use an inexpensive antenna analyzer feeding the tuner/antenna combo to get you spot on.

--Al
WD4AH