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QMX 60-15m Rev 4 troubles
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Hi all,
I just assembled my first QRP Labs kit:? the QMX 60-15m version with the rev 4 board.? The assembly went pretty well and no smoke (to my nose, anyway) has been released after powering on.? I'm having high SWR and some 17m and 15m band issues.? I've attached a document that contains terminal screenshots of all of the sweeps and a representative diagnostics screen.? Weird SWR behavior across all of the bands, but the 15/17m bands are different than everything else.? It seems to me that something is definitely wrong with the high band portion of the rig.? The QMX RF output was connected to a known good 50 ohm dummy load and the device was powered by a benchtop CVCC power supply @ 8V. A few things I've? done to troubleshoot the transceiver myself (I am not an electrical engineer :) ): 1.? After finding some continuity issues with the tri-filar toroid, I removed it and did a better job? of removing the enamel and re-installed it.? It has good continuity according to the assembly manual, now.? The LPF sweeps of the lower 4 bands markedly improved after this procedure. 2. removed and re-wound and re-installed L401a (this made no difference to the issues that I'm seeing) 3.? removed and carefully re-wound the RWTST transformer (12V version) and re-installed (this made no difference to the issues that I'm seeing) 4.? read approximately 500 posts (felt like it anyway) in this forum to see what other issues that others might be having.? I especially read this thread, which seemed like it might have some commonalities that I was having (not but not exactly): ?/g/QRPLabs/topic/105973992#msg122851? I know it's a thread pertaining to the low band version of the QMX, but there was some helpful tips in it nonetheless.? I measured voltages on the ring-side of the LPF diodes and did see one discrepancy in one fo the diodes:? D513, which from what I can discern, helps select the 15/17 band LPFs.? Instead of seeing something close to my supply voltage when any of the lower 4 bands were selected, I was seeing ~0.5V consistently in receive mode in pretty much any band selected in the diagnostics screen, including the high bands (15/17).? When I switched to other bands, the "K" voltages as described in Ludwig's post track well (near 0 V in the pair of diodes that corresponded to a LPF pair when one of the bands corresponding to that pair were selected and near supply voltage when not selected). I did not measure "A" voltages.? I did measure the D513 diode with the diode testing function of my DMM and saw 0.6 V for that diode, just like the rest of the other diodes.? Not sure if any of this information is important or not, but I just wanted to put it out there.?? I don't have a lot of sophisticated test equipment (no RF probes, o-scope, etc), but I do have a DMM.? I would love to work through this, but I really need some guidance on what to check and how.? Thank you in advance for any help this fine community could provide. Spencer WD4AWD |
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Hi Spencer,
first of all: be sure that the current limiter of your PSU does not kick in as it will drop the voltage and thus trash the measurements ;-)? My 15m RF sweep looked similar in the first place - but it was shifted upwards a lot - but the shape of your sweep could indicate a wrong turn count on 401a: /g/QRPLabs/topic/106334083 Your 17m sweep looks like the 15m BPF configuration. But the SWR looks really bad - as if no dummy load was connected at all. On the diagnostics screen you can press and hold the T key to actually transmit this should give some more data. And there is the P key which will only switch the diodes. It could also be SWR measurement itself that is flawed - how about the binocular twin-transformer? 73, Andreas |
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On Sun, Jun 9, 2024 at 06:52 AM, Spencer WD4AWD wrote:
D513, which from what I can discern, helps select the 15/17 band LPFs.? Instead of seeing something close to my supply voltage when any of the lower 4 bands were selected, I was seeing ~0.5V consistently in receive modeHello Spencer, please check the direction of D513 and additional all the diodes. In some hours I have more time and will send some more information. You may also check the QRP Labs Wiki. There is a document about the PIN switching of the LPF section. 73 Ludwig |
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On Sun, Jun 9, 2024 at 04:59 AM, Andreas DM7AK wrote:
Hi Spencer,Current limiting was set to 0.850 A and I watched to ensure that it didn't kick in.? I've even set it higher than that, still same issues. My 15m RF sweep looked similar in the first place - but it was shifted upwards a lot - but the shape of your sweep could indicate a wrong turn count on 401a: /g/QRPLabs/topic/106334083I'll do this and add screenshots to this thread. It could also be SWR measurement itself that is flawed - how about the binocular twin-transformer?I've looked at this carefully and detect no issues, but I haven't removed it yet and rewound it. 73, Andreas |
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On Sun, Jun 9, 2024 at 05:08 AM, @Ludwig_DH8WN wrote:
On Sun, Jun 9, 2024 at 06:52 AM, Spencer WD4AWD wrote:I've triple checked the directions of all of six diodes and the solder points - all are in the correct direction and the solder joints look good. I also re-flowed D513 prior to my initial post (forgot to mention that).? Also, I forgot to mention that I performed a factory reset for good measure - this didn't affect anything.? I'll read the wiki... Spencer |
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Spencer,
here you find Information to understand the DC voltages at the diodes and some possible faults. You will find also a link to a simplified DC schematics with DC voltage levels. If there are significant differences to your real situation you have to find the fault. A faulty PIN switching affects all the sweeps. There must not be significant differences between K voltage of D510 and D513. Otherwise search the problem. If at K of D513 0.5 V all the time, we have to find the problem. Please check voltages at S, G and D of Q511. The values should be: LPF 2 acive: S 0 V, G near 0 V, D a bit below external voltage LPF 2 not active: S 0 V, G near 3 V, D around 0 V 73 Ludwig |
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Spencer,
please check the simplified DC schematics. For DC cathode of D110 and cathode of D113 are connected. Both DC voltages must be equal. Something is wrong here. Regarding schematics Q511 drain voltage is eaqual to cathode voltage of D110 and D113. For D110 it's ok but not for D113. So D113 is not right connected. Please read the linked Wiki page for some debugging to find the issue. At first you should check continuity between K of D110 and K of D113 (see No 1 Wiki page). 73, Ludwig |
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On Sun, Jun 9, 2024 at 04:16 PM, @Ludwig_DH8WN wrote:
Spencer, All diodes are installed according to the diagrams as I interpret them (pictures attached). I removed L510, rewound it with new wire, and re-installed. (no change to testing results) I checked the continuity between the cathodes of D510 and D513:? there is no continuity (!).? I verified that there is continuity between the cathodes of the D509/D512 pair and the cathodes of the D508/D511 pair. When the 60m LPF_0 is selected, the voltage between D510 and D513 cathodes is near zero (about 10 mV).? When the LPF_2 is selected, the voltage jumps to 0.77 V. On the anode side, when the LPF_0 is selected, all anodes measure about 0.72V per the wiki, when the LPF_2 is selected the results are as follows (not correct according to the wiki!): D508, D509, & D510 = 0.75V D511, D512 & D513 = 1.0 V It appears there is a break in the circuit somewhere or one of my diodes is broken? Thanks, Spencer WD4AWD |
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I also verified that there was continuity between the cathode of D513 and the drain of Q511, but there is no continuity between D510's cathode and the Q511 drain (which according to your schematic, there should be)...? There is continuity between the cathode pad of D510 and the inner pad of L513, so the solder on D510 cathode pad is good.
Just before I posted this update, I checked the continuity between the L513 pads (which are in series with the D510/D513 cathodes path):? nothing!? I reflowed both pads and now there is continuity between D510 and D513 cathodes and Q511 drain.? I performed a LPF sweep and now the 15/17m bands look correct!? Breakthrough! However, the high SWR problem remains, though things do look better for the highest two bands.? See new SWR and LPF sweeps attached.? RF filter sweeps all peak between -3 and -7 dB.? Audio filter sweeps are all around -5 dB or so for USB and -50 dB or so for LSB, so those look good, too. Spencer WD4AWD |
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On Sun, Jun 9, 2024 at 11:45 PM, Spencer WD4AWD wrote:
However, the high SWR problem remains, though things do look better for the highest two bands.? See new SWR and LPF sweeps attached.? RF filter sweeps all peak between -3 and -7 dB.? Audio filter sweeps are all around -5 dB or so for USB and -50 dB or so for LSB, so those look good, too.Note:? SWR protection turned OFF gives the same SWR sweep results as above (with protection turned ON).? Power supply is solidly delivering 12V and a sweep pulls around 0.6A peak. Spencer WD4AWD |
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On Mon, Jun 10, 2024 at 04:11 AM, Andreas DM7AK wrote:
Hi Spencer,I saw that post and verified clearance (one was pretty close though!). Spencer |
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On Mon, Jun 10, 2024 at 05:45 AM, Spencer WD4AWD wrote:
I reflowed both pads and now there is continuity between D510 and D513 cathodes and Q511 drain.? I performed a LPF sweep and now the 15/17m bands look correct!? Breakthrough!Spencer, you made a big step forward. I'm sure you will resolve the remaining issues. However, the high SWR problem remainsThe SWR sweeps are also not so good. For both the SWR measurement and the LPF sweep T507 and the parts around are important. Please check the solders (remember L513) and construction of T507. I will search for an older discussion related to T507 and some expected voltages and send you the link soon. 73, Ludwig |
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On Mon, Jun 10, 2024 at 05:02 PM, @Ludwig_DH8WN wrote:
Spencer, one more question. Is the cable connecting QMX BNC to the dummy load ok? Could you use a different and good cable? I've checked the cable with another rig and no issues were found.? I've also used a different (also known good) cable and had the same type of SWR sweeps.? That was actually the very first thing I tried when troubleshooting (the real easy stuff first :) ). Spencer WD4AWD |
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Ludwig,
I've looked at all of the linked pages.? I don't see any of the obvious things as problematic for me, but I'm not happy with the solder joints on the binocular T507 transformer so I pulled it off of the board.? I've re-wrapped it and I've ordered a length of 22 awg bare copper wire and some 1 mm i.d. PTFE tubing to make the primary legs.? I don't like the fiddly-ness of trying to scrape the enamel and get everything exactly right, so hopefully the bare wire with tubing makes for a more reliable solder joint without excessive fuss.? Should arrive on Thursday or Friday after assembly, we'll see how the SWR sweeps go and I'll post the results... As always, thank you for your generous advice. 73, Spencer WD4AWD |
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