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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 |
