Date
1 - 20 of 27
Lightning strike nearby, QDX RIP or worth troubleshooting?
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Hi all
well I had my QDX up and running with WSPR on 20M-10M for just over a week and then on Sunday night with no warning whatsoever a dry lightning strike happened about 600M away (if there was any prior suggestion of that happening antenna would certainly be disconnected). Significant ESD event! QDX has some minor signs of life and I've checked IC5 because I am somewhat familiar with that component. My question is, is this worth troubleshooting, because sourcing components is problematic (freight costs), and my ability to replace and solder anything smaller than say IC5 (which I have done previously) would be marginal (shaky hands). Here are the symptoms/signs of life - Boots up and can access firmware/menu Draws 200ma on receive instead of 155ma Receive dead Upon activate PTT in firmware menu current draw drops from 200ma to 160ma (seems odd) Upon activate TX in firmware current draw 900ma instead of about 500ma Nil significant output power Can hear a transmitted FT8 signal on nearby receiver Limited test equipment available (DVM and scope) So, given above mentioned constraints I would appreciate some expert opinions please! Worth a go, or total replacement and put away in that old box on the top shelf. Thankyou Grant |
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Michael.2E0IHW
Grant, sorry to hear of your misfortune...
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I would think a strike that close would affect so many components as to make repair a major challenge. Maybe a write-off. But let us know of what you do next! Dextereously challenged and a non-purist, I might be tempted to re-build Manhatten-style with a commensurately larger enclosure - or none :-) In my tropic years, I always unplugged the inverted vee when the afternoon storms approached. But they were semi-predictable... My gear survived, but I received frequent requests to repair fixed-channel transceivers in our medical network. Our modern tech is far more sensitive to static surges. Members with experiential guidance on effective protection circuits might help us to preemptively minimise such misadventures. Michael UK 2E0IHW On 07/03/2023 00:13, Grant VK2LX wrote:
Hi all |
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Evan Hand
Grant,
As long as the QDX responds to the USB terminal, it is worth the effort to try to repair it. When you can not connect with the terminal program, it is time to put it on the top shelf. I would start with removing the 4 BS170s and verify that the current drops to around 160 ma when receiving. If you can not get the current down when receiving, there is a more significant problem. Possible culprits are: - IC5, as you mentioned - IC3 selects the bandpass filter. I verified the first pass operation by measuring the 2.5 volts bias value on the selected capacitor. - The PIN diode LPF selection. Verify that only the selected filter banded side of two diodes is close to zero volts. The other 4 should be close to Vin. There is also the troubleshooting page on the QRP-Labs web page. 73 Evan AC9TU |
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Hi Evan
thank you for your guidance. Findings as follows - BS170s removed and RX current remains 190 ma IC5 tested, delivering 0v on RX and 2.4v on TX to BS170 gates (BS170s removed for test). I presume this confirms IC5 is ok? IC3 delivers 2.5v bias to the appropriate capacitor on the bandpass filter. PIN diode filter selection also working as per your description. So far then, the high RX and TX (with no power out) current draw remains unexplained. I will now refer to the Troubleshooting guide but it appears, as you suggest, that just maybe all is not lost Thankyou 73 Grant |
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Evan Hand
Grant,
So far, there is still life in your QDX. Can you do RF and Audio sweeps? That would tell us if the ADC is working. That is the next most important part of the QDX. The STM32 is the most important. We know the STM32 is working; you can connect it to the terminal program. If the sweeps look good, we need to get the receiver to decode some FT8 or FT4 messages. 73 Evan AC9TU |
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Evan
Sweeps look ok, never pretty but I think similar to previously. As it happens there are a couple of very strong signals on 15M at present and I have just one FT8 decode. Its about 25 db or more down on the same decode on my main rig which has dozens of decodes. 73 Grant |
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Evan Hand
Grant,
What is the signal level on the top of the Audio sweep and the FT8 frequency of the RF sweep? 73 Evan AC9TU |
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Al Holt
On Mon, Mar 6, 2023 at 10:17 PM, Grant VK2LX wrote:
Sweeps look ok, never pretty but I think similar to previously.Grant, How about the levels of the sweeps, how far down dB-wise is it reporting? I don't have much else to offer, just wondering if maybe the T/R switch Q6 might be the cause, or C2, the cap at the front end? Also, having current drop when you test PTT is an interesting clue. With the PA FETs removed, what is current draw like going into transmit? What's the version of the board? Sorry I don't remember. --Al |
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Hi Evan
These are well below where they should be. The troubleshooting guide says wanted sideband should be close to 0 with about 60db suppression. On 20M my audio sweep max is -39 with unwanted sideband at -60. Similar results on 15M and 10M. RF sweep at 14.074Mhz is -38, at 21.074 is -17 and at 28.074 is -20 (BTW its a Rev5 PCB) 73, Grant |
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Hi Grant,
Recently had a similar issue with a QDX V3a that had an elevated receive current of about 0.200 ma and very little RF out on TX. The issue was Q6 (BSS123) had shorted. Jeff - KD8THX |
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Thanks everyone. I have more time today so will finish working through the troubleshooting guide again. I'll check Q6 and check for solder joints that might have changed in conductivity since it was built, just to eliminate anything else that I can. With the BS170s removed the current draw is about 160ma on TX (down from over 900ma with them in). I've replaced them too just to be sure, but no change in that current draw.
73 Grant |
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I have finally got back to this. I have gone over all of the Troubleshooting tips including the checking and rechecking of solder joints to the enameled copper wires in case of a change in electrical conductivity, unfortunately all to no avail.
Today I verified that a low level readable FT8 signal is being generated on TX by decoding on my nearby main rig. Similarly I can also use the QDX to decode an FT8 signal transmitted on my main rig into a nearby dummy load. I guess this now leaves only certain semiconductor devices as suspect failures here? If anyone has advice on further testing or if its possible to narrow this down further I would be most appreciative. My issue will probably be sourcing such devices without incurring about half the cost of a new QDX kit in freight alone for parts worth just a few cents, so of course I'm keen to try and get this right :) 73 Grant |
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John Zbrozek <jdzbrozek@...>
Grant, Any more progress on this? Consider checking capacitors C5, C6, and C7. They are rated at 50 volts. They would be among the first potential casualties of a nearby lightning strike. If they were shorted, - Receive sensitivity would tank, - So would Transmit power output. - Supply current in Transmit would be elevated. That is what happens when Zload is way too low. - Supply current in Receive might be somwhat elevated because of the simultaneous activation of all PIN diode paths, and the compensating action of the buck converter regulator. You are very close to recovering your QDX, I think. Good luck! 73 KJ4A On Thu, Mar 16, 2023, 8:17 PM Grant VK2LX <grantrawstorn@...> wrote: I have finally got back to this. I have gone over all of the Troubleshooting tips including the checking and rechecking of solder joints to the enameled copper wires in case of a change in electrical conductivity, unfortunately all to no avail. |
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Hi John
no progress I'm afraid! I checked those caps and they are not shorted (I wish they were in a way, just might have led to an easier fix!) 73 Grant |
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John Zbrozek <jdzbrozek@...>
Grant, Sorry to hear that. At the point where D7, D8 and C27 come together, in receive mode you should see a little less than your power supply voltage. If the transmitter amplifier is functioning you should see a much higher DC voltage there in transmit mode. Do you see that? Also, can you tell if choke L1 has suffered damage? An internal winding short would have effects similar to the capacitors I cited earlier. KJ4A On Sun, Mar 19, 2023 at 10:25 PM Grant VK2LX <grantrawstorn@...> wrote: Hi John |
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Hi John
No, I don't see that. At that point (D7 D8 and C27) the RX voltage is 1 volt less and it is also 1 volt less in TX. L1 appears to be ok, on the DVM measures about 1.7 ohm resistance which is the same as the others. 73 Grant |
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John Zbrozek <jdzbrozek@...>
OK Grant! Now we have a significant clue! The point I asked you to probe is the output of a reverse bias generator for the PIN diodes. Its voltage should read one diode drop less than the main supply voltage during receive and then be sent significantly higher during transmit. The higher voltage comes from a voltage doubling rectifier that steals a small amount of output power from the transmitter. You are not seeing that boost! That is the big clue. That says that the transmitter final amplifier is not sending RF power to that point, or that the power is being lost to ground somehow. Carefully inspect transformer T1. Make sure that the insulation on its wires has not been compromised and that all the solder joints associated with its leads are well formed, no bridges. As the assembly manual suggests, make sure that wire insulation has not been scraped away by the sharp edges of the binocular core. A shorted secondary winding at T1 is yet another way to dissipate both received signals and transmit power. Unfortunately you can't detect a short here with an ohmmeter as the winding resistance itself is so low. In the worst case you may just have to remove and rewind it. As I said earlier, Grant, I think you are very close now. Good luck! 73 KJ4A On Mon, Mar 20, 2023, 8:31 PM Grant VK2LX <grantrawstorn@...> wrote: Hi John |
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Hi John
thankyou for this further guidance. I was quite careful with the winding of T1 and did take the time to remove those sharp edges on the core but have rewound it with new wire anyway. Unfortunately there is no change in the symptoms. 73 Grant |
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John Zbrozek <jdzbrozek@...>
Hello Grant, I'm disappointed that your efforts have not paid off so far. It seems most likely that there remains a short to ground somewhere in the circuit path shared by Receive and Transmit modes. But where? Another QDX owner posting here with similar symptoms as yours finally found his short: a tiny bit of solder that bridged the BNC antenna connector. Removing that cleared up all the problems. At this point I am out of ideas. I can only encourage you to keep at it until you too find that elusive short. 73 and GL KJ4A On Sat, Mar 25, 2023, 8:44 PM Grant VK2LX <grantrawstorn@...> wrote: Hi John |
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Thankyou John
I've really appreciated your input and encouragement! Will keep at it for a bit longer before calling it quits I think. Concentration seems to fade quite quickly these days :( 73 Grant |
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