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Hi folks -?
Sharing this repair experience in case it helps others or if anyone has further advice to add.
After a couple of days working fine on 20m and 40m my QDX stopped transmitting and battery current on receive went up from 140mA->320mA. Reading Hans' excellent troubleshooting guide I updated the firmware and suspected at least one blown BS170. Indeed it turned out to have been a bad day for Q11:
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I replaced all four BS170s and, while the board was in front of me, I took the opportunity to resolder some of the inductor windings where it looked like dry-ish joints due to poorly burned off enamel might cause a problem.
The TX side seems OK: on the three bands I have enabled the transmitter is delivering around 2.5W on each of 40m and 30m and 4.2W on 20m. However I seem to have upset the RX side as this is what I get from RF sweeps on all bands:
Given that the TX side is doing OK, is it safe to assume that the LPF inductors are probably OK and I need to look for anomalies on the board around L12 and the trifilar transformer?
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Where is Han's troubleshooting guide?? There is alot of good info in the group if you search, but I didn't realize there was a single document that contained detailed? info.
Andy
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Go to the QRP Labs website and select the QDX. The the left hand column under QDX you'll see a link to the troubleshooting guide.
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On Jan 24, 2023, at 12:46, Andy W3SW via < w3sw@...> wrote:
Where is Han's troubleshooting guide?? There is alot of good info in the group if you search, but I didn't realize there was a single document that contained detailed? info.
Andy
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Finishing up sharing this repair experience, not because I claim any great sherlock holmes detective ability, but in case it inspires anyone else like me who has been away from the hobby for a few decades and feels daunted by fault-finding on boards that are genuinely smaller because of surface mount components and seem smaller because, well, the eyes aren't quite what they used to be.
So having got the TX side going first, as suggested by Hans, I checked for DC continuity on the ICs where the trifilar transforer and L12 connect. All seemed OK. So I did a more thorough check of all the other receive components and sure enough:
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IC10, the ADC, had a fleck of solder that must have either dropped off the iron or been picked up off the work surface
Once cleared I checked with an RF sweep again and all looked good
So three things I learned here. First up, like Hans' troubleshooting guide says, the chances are that if you're QDX isn't working it's really is likely to be a bad joint or a whisker of solder somewhere. Actually that's even true for my blown PA - I discovered a bad joint on my antenna feedpoint so that's what caused the SWR that blew up the BS170s that started me on this journey. Second, logical fault-finding from input to output still works just the same as it did 40 years ago. Finally, clean working conditions and scrupulous attention to detail on the board is really important in a way I don't remember it being 40 years ago and something like this gadget that I unexpectedly got from AliExpress for about $2 can reveal how truly gross and dirty things are down at the micro-level. I actually think 60X magnification is too much (hard to navigate on the board) but maybe 20X would be good:
Good luck if you are fault-finding on your QDX and I hope you have a good outcome as i did.
Hugh Mason 9V1SA
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I am fortunate enough to have a stereo zoom microscope (I prototype and repair boards in my consulting work) and I find that I set it at about 8X for most of my work.?
73, Don N2VGU?
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I was shocked one day when I looked closely at the wall behind my Solomon soldering pencil. There were quite a few specks of solder stuck on the wall (into the paint) from my just placing the pencil back in its holder. ?So beware, extra solder on the tip goes somewhere. ?And I usually wipe my tip on a wet sponge or the coppery thingy made for wiping the tip BEFORE putting it back in its holder. I am generous with solder when soldering and still will be but reading this email about the small speck (and remembering my wall findings) woke me up to the damage I could cause in my building. ?Thanks for posting.
Dave K8WPE since 1960 David J. Wilcox’s iPad
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On Jan 25, 2023, at 6:45 AM, 9V1SA <hugh.mason@...> wrote:
? Finishing up sharing this repair experience, not because I claim any great sherlock holmes detective ability, but in case it inspires anyone else like me who has been away from the hobby for a few decades and feels daunted by fault-finding on boards that are genuinely smaller because of surface mount components and seem smaller because, well, the eyes aren't quite what they used to be.
So having got the TX side going first, as suggested by Hans, I checked for DC continuity on the ICs where the trifilar transforer and L12 connect. All seemed OK. So I did a more thorough check of all the other receive components and sure enough:
?
IC10, the ADC, had a fleck of solder that must have either dropped off the iron or been picked up off the work surface
Once cleared I checked with an RF sweep again and all looked good
So three things I learned here. First up, like Hans' troubleshooting guide says, the chances are that if you're QDX isn't working it's really is likely to be a bad joint or a whisker of solder somewhere. Actually that's even true for my blown PA - I discovered a bad joint on my antenna feedpoint so that's what caused the SWR that blew up the BS170s that started me on this journey. Second, logical fault-finding from input to output still works just the same as it did 40 years ago. Finally, clean working conditions and scrupulous attention to detail on the board is really important in a way I don't remember it being 40 years ago and something like this gadget that I unexpectedly got from AliExpress for about $2 can reveal how truly gross and dirty things are down at the micro-level. I actually think 60X magnification is too much (hard to navigate on the board) but maybe 20X would be good:
Good luck if you are fault-finding on your QDX and I hope you have a good outcome as i did.
Hugh Mason 9V1SA
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Dave, Always put just a small amount of solder on the tip BEFORE putting the soldering iron back in the holder. It's important to tin the tip to prevent it from oxidation happening on the iron. Your tips will last longer and soldering will be easier too. It's also important to use the correct size of rosin core solder when soldering. Use a smaller diameter when soldering on the boards and a larger diameter when soldering larger items such as PL-259s and larger wires.
73,
Dean - KC9REN
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On Thu, Jan 26, 2023 at 05:29 AM, David Wilcox K8WPE wrote:
And I usually wipe my tip on a wet sponge or the coppery thingy made for wiping the tip BEFORE putting it back in its holder.? I am generous with solder when soldering Thanks for posting.
?
Dave K8WPE since 1960
David J. Wilcox’s iPad
On Jan 25, 2023, at 6:45 AM, 9V1SA <hugh.mason@...> wrote:
Finishing up sharing this repair experience, not because I claim any great sherlock holmes detective ability, but in case it inspires anyone else like me who has been away from the hobby for a few decades and feels daunted by fault-finding on boards that are genuinely smaller because of surface mount components and seem smaller because, well, the eyes aren't quite what they used to be.
So having got the TX side going first, as suggested by Hans, I checked for DC continuity on the ICs where the trifilar transforer and L12 connect. All seemed OK. So I did a more thorough check of all the other receive components and sure enough:
?
IC10, the ADC, had a fleck of solder that must have either dropped off the iron or been picked up off the work surface
Once cleared I checked with an RF sweep again and all looked good
So three things I learned here. First up, like Hans' troubleshooting guide says, the chances are that if you're QDX isn't working it's really is likely to be a bad joint or a whisker of solder somewhere. Actually that's even true for my blown PA - I discovered a bad joint on my antenna feedpoint so that's what caused the SWR that blew up the BS170s that started me on this journey. Second, logical fault-finding from input to output still works just the same as it did 40 years ago. Finally, clean working conditions and scrupulous attention to detail on the board is really important in a way I don't remember it being 40 years ago and something like this gadget that I unexpectedly got from AliExpress for about $2 can reveal how truly gross and dirty things are down at the micro-level. I actually think 60X magnification is too much (hard to navigate on the board) but maybe 20X would be good:
Good luck if you are fault-finding on your QDX and I hope you have a good outcome as i did.
Hugh Mason 9V1SA
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I avoid the wet sponge tip cleaner and instead always use the brass (or whatever) wool tip cleaner.? I believe that your spatters are from wiping the sponge, which snaps back and flings droplets; with the wool kind you just plunge the tip into the wad.
Also, the thermal shock of the wet sponge can cause cracking of the tip plating, resulting in early failure, and causes slow tip temperature recovery time when making repetitive joints..
But you want to clean the iron?before you make the joint, not after; you should re-tin the tip generously before putting it into the holder or shutting down.??
73, Don N2VGU
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Don,
Good advice but I use Metcals and always use the moist sponge. ?I have added a brass wool cleaner but not sure how much good it does. ?
I always tin the tip before I solder and before I shut the iron down. ?The Metcals have some special protections that help with tip problems. ?In 15 years, I have had very few tip problems. ?
Hot air and solder paste is better but 60 plus years with the irons work for me.
73
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On Jan 26, 2023, at 1:20 PM, Donald S Brant Jr via groups.io <dsbrantjr@...> wrote:
?I avoid the wet sponge tip cleaner and instead always use the brass (or whatever) wool tip cleaner.? I believe that your spatters are from wiping the sponge, which snaps back and flings droplets; with the wool kind you just plunge the tip into
the wad.
Also, the thermal shock of the wet sponge can cause cracking of the tip plating, resulting in early failure, and causes slow tip temperature recovery time when making repetitive joints..
But you want to clean the iron?before you make the joint, not after; you should re-tin the tip generously before putting it into the holder or shutting down.??
73, Don N2VGU
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I have been using the wet sponge and the brass thingy for so many years…. And am using only the second tip on my soldering pencil…… so will keep doing that as it works. ?I was just setting the scene where solder flecks could show up on a PC board or anywhere. I was shocked to see all the flecks on the wall right behind the soldering station itself and it either meant I was missing the hole and tapping the pencil on the edge of the holder to get the pencil in the holder or solder flecks were flying through the end of the holder. ?It has ventilation holes. I put the pencil back without even looking at it, so automatic for me.?
I don’t flood my pencil tip with solder except when actually soldering. But there must be enough extra solder on it after wiping it on the sponge or the brass thingy… I sometimes do both before putting the pencil back in its holder. ?I wipe again before soldering the next part in place. ?The replacement tip cleans nicely and works. ?The first one worked well for 10 years or so. ? I must be lucky breaking all the rules and still making good connections.?
I have two Solomon soldering stations, one with the fine tip for regular PC board soldering and one with the largest tip for heavier soldering jobs. And still using the original tip on the heavier one. ?One set is 20 years old and the other one is somewhat younger. I have a whole Altoids box with extra tips because they came with the sets. ?My exact set is no longer available but Solomon still sells newer slightly different sets.?
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On Jan 26, 2023, at 3:35 PM, james jones <j2@...> wrote:
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Don,
Good advice but I use Metcals and always use the moist sponge. ?I have added a brass wool cleaner but not sure how much good it does. ?
I always tin the tip before I solder and before I shut the iron down. ?The Metcals have some special protections that help with tip problems. ?In 15 years, I have had very few tip problems. ?
Hot air and solder paste is better but 60 plus years with the irons work for me.
73
Jim w0nkn?
On Jan 26, 2023, at 1:20 PM, Donald S Brant Jr via groups.io <dsbrantjr@...> wrote:
?I avoid the wet sponge tip cleaner and instead always use the brass (or whatever) wool tip cleaner.? I believe that your spatters are from wiping the sponge, which snaps back and flings droplets; with the wool kind you just plunge the tip into
the wad.
Also, the thermal shock of the wet sponge can cause cracking of the tip plating, resulting in early failure, and causes slow tip temperature recovery time when making repetitive joints..
But you want to clean the iron?before you make the joint, not after; you should re-tin the tip generously before putting it into the holder or shutting down.??
73, Don N2VGU
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Hi everybody,
I would like to ask a question related to the initial message from Hugh. Do you find necessary to replace all the four BS170s when one of them had "a bad day". I do not care about the relatively cheap transistors but about the PCB.
73! Milo? OK1FMY
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Related to? Milo?‘ question is how do you detect if only one BS170 is destroyed (open). The reason why I’m asking is that I have a new hi-band QDX built for 9 Volts which needs 12Volts to reach 4 Watts output. Could that be a sign of a single failed BS170?
73 Sverre -- Sverre
LA3ZA
http://la3za.blogspot.com
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The high-band doesn't put out as much power on (say) 10M, I wouldn't push it or you'll have all four finals blown out.
73, Willie N1JBJ
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On Jan 28, 2023, at 7:34 AM, Sverre Holm <svholm54@...> wrote:
Related to Milo?‘ question is how do you detect if only one BS170 is destroyed (open). The reason why I’m asking is that I have a new hi-band QDX built for 9 Volts which needs 12Volts to reach 4 Watts output. Could that be a sign of a single failed BS170?
73
Sverre
--
Sverre
LA3ZA
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I forgot to mention band when I said my hi-band 9 Volt QDX needed 12 V to reach 4 Watts - it's even for the 20 m band. What can be the reason - a single open BS170? 73 Sverre -- Sverre
LA3ZA
http://la3za.blogspot.com
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Hi,
I would say the procedure for the blown MOSFET is the same for a short circuit as it is for an open circuit fault.
Since they are coupled in parallel it is impossible to tell in-circuit.
So, remove one by one and measure it.
- a short circuit by using Ohm meter and
- an open circuit by using a power supply and some resistors.
Removing from the board is best by using a hot air station to preserve the pads.
73 Bojan S53DZ
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... or for the n-channel MOSFET like BS170 something like this:
73 Bojan S53DZ
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Hugh Mason 9V1SA / G4MRE / AI7QX
Donald S Brant Jr
David Wilcox K8WPE