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QMX troubleshooting
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Hi all,
I hope this is the appropriate place to ask this... if not, please let me know and I'll redirect! I just finished my QMX kit build.? I've built other kits from Hans with no issue.?? After checking over all the connections carefully (including using my SMD microscope), I carefully fired up with a current limited supply. No current draw as per the manual.? I pressed the left rotary and this seems to completely short the power supply out.? I've much tracing through the schematic and boards, it seems I have the appropriate input and ground on the 8 pin connector to the 5V regulator board, but it appears that this board might be the issue (or something downstream).? With everything removed except that board (and the controls board), it dead shorts upon left button press. With the 5V regulator board out (but controls in) it does not.? Maybe it's an issue with the control board? I'll continue stepping through the schematic and testing, but wondered if there were any wise words here to "check this first" :) Many thanks, 73 James KI0KN |
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Did you check for a short between Q103/Q104? It's documented pretty
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well in this group. A search should turn up the proper threads. -mike/w1mt On Sat, Aug 12, 2023 at 11:50?AM James Cizek <james.m.cizek@...> wrote:
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Here's the message link:?/g/QRPLabs/message/106988, also insure the encoder body is not moving slightly and shorting against the power in connector. A little tape here would be good insurance.
On Saturday, August 12, 2023 at 12:02:39 PM EDT, mike/w1mt <w1mt.qrp@...> wrote:
Did you check for a short between Q103/Q104? It's documented pretty well in this group. A search should turn up the proper threads. -mike/w1mt On Sat, Aug 12, 2023 at 11:50?AM James Cizek <james.m.cizek@...> wrote: > > Hi all, > > I hope this is the appropriate place to ask this... if not, please let me know and I'll redirect! > I just finished my QMX kit build.? I've built other kits from Hans with no issue. > After checking over all the connections carefully (including using my SMD microscope), I carefully fired up with a current limited supply. > No current draw as per the manual.? I pressed the left rotary and this seems to completely short the power supply out.? I've much tracing through the schematic and boards, it seems I have the appropriate input and ground on the 8 pin connector to the 5V regulator board, but it appears that this board might be the issue (or something downstream).? With everything removed except that board (and the controls board), it dead shorts upon left button press. With the 5V regulator board out (but controls in) it does not.? Maybe it's an issue with the control board? > > I'll continue stepping through the schematic and testing, but wondered if there were any wise words here to "check this first" :) > Many thanks, > 73 > James > KI0KN > |
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Hans', assembly team checks all the QMX?assembled kits?for full function so there should be no problem with those.
QMX?Parts Kits?are a different story and there are 3 things to do: 1) READ THE MANUAL ......TWICE 2) The back of the external V_IN connector is rather close to the left rotary encoder. To insulate that point, put a piece of good tape (Kapton, electrical tape) on the back of the V_IN connector. 3) Some boards were manufactured with the?Drain Tab?of Q103 soldered too close to the?Drain?pin?of Q104 shorting those points. This can be easily checked with a DVM between the?Drain Tab?of Q103 and the?Gate pin?of Q105 (easier to get to). If there is no short, you can leave it alone and continue on with the build.?If there is a short?you need to remove it by moving Q103 or Q104 SLIGHTLY. You?MUST?do this?BEFORE?FIRST POWERING UP. If you don't, you will toast parts starting with D101. Being a worry-wart and an experienced kit builder. I?recommend looking at the "potential for a short" to see what the?gap?is between the?Drain tab?of Q103 and?Drain pin?Q104. Ask yourself "Is it likely this point will short in the future due to mechanical/temperature stresses". If the answer is "No" continue on with the build. If it ain't broke, don't fix it. If the gap is the thickness of a piece of paper or you can't see a gap, treat it as a short. Board assembly house placement varies. 73 Kees K5BCQ |
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Thanks all.? That was it, Q105 was hanging over the Q104 pad by a pretty significant amount. With all the other incredibly detailed "check this first" steps in the instructions, this one seems like it would be a good addition :) Once I reflowed that part, I reassembled?everything.? It fired up, showed up as a USB drive. I dropped the firmware in and rebooted. The LCD comes up, shows the QRP labs page, then it flips to a 40M frequency, but only for a VERY brief moment, then it goes to "Shutdown!!" and sits there halted.? ?Could this be a result of the once-shorted regulator board? I don't see anything about this message searching the forums... so continuing this thread. Thanks for the tips on Q105... I searched the forums prior to asking but every option I tried came up with over 2000+ hits... the blessing and curse of a very active list! 73 James KI0KN On Sat, Aug 12, 2023 at 11:25?AM Kees T <windy10605@...> wrote: Hans', assembly team checks all the QMX?assembled kits?for full function so there should be no problem with those. |
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Hi James Unfortunately you need to replace the 1N4148 diode nearest the 2x4 pin connector at the end of the 5V board. The transistor drain short puts the input voltage directly across the 1N4148 which means bye bye 1N4148.? 73 Hans G0UPL On Sat, Aug 12, 2023, 10:02 PM James Cizek <james.m.cizek@...> wrote:
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Hans, thanks for the pointer on what to repair. Mitch, thanks for the offer, I ordered them on Amazon and they'll be here by 8am tomorrow? Appreciate everyone's help, continue this tomorrow after the new diode shows up... 73, James On Sat, Aug 12, 2023, 1:46 PM Mitchel Sayare <mitch@...> wrote: James, I experienced the same. Here's a link to get a pack of them overnight on Amazon:? |
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Hi Dennis Ok yes, I suppose D101 doesn't necessarily blow every time. The 1N4148 absolute maximums specify 2A for 1us, 150mA avg current, 0.5W dissipation... If the abuse was short enough and/or you were using a current limited supply and/or with a bit of luck... It could stay alive. 73 Hans G0UPL On Sun, Aug 13, 2023, 12:44 AM Dennis Rieger <kk5db@...> wrote: Hans, |
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Well, the new diodes showed up today.? I replaced the blown one, and while I was reassembling, I noticed an SMD part laying in the middle of the 3.3V regulator board loose.? It turned out to be D305.? There was almost zero solder on the part nor the board so guessing that part just never got adequately soldered in the first place. Easy fix there. After checking over all the other parts on all the boards, I reassembled?and fired up.? All is well.? About 4 watts on 8 volts out, signal on the service monitor shows clean as a whistle. Thank you all for the help in diagnosing and repairing this.? I can't wait to get it on a SOTA peak :) 73 James KI0KN On Sun, Aug 13, 2023 at 1:58?AM Hans Summers <hans.summers@...> wrote:
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Hello folks.? My QMX was finished? and working before the problem between Q103 and Q104 was talked about. I've made over 30 cw contacts with it without problems.? I became curious and had a look at that area.? Mine has only a tiny sliver of the green board between the two tabs.? Maybe the width of a cat hair!
Should I be alarmed?? If so, is there a way to move one part or the other without reflow gear? Thanks in advance for any comments and suggestions. Ken W4KAC |
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Hi Ken Golden rule: if it ain't broke don't fix it.? Yours ain't broke... 73 Hans G0UPL On Sun, Aug 13, 2023, 6:28 PM Ken W4KAC <oldjoeclark@...> wrote: Hello folks.? My QMX was finished? and working before the problem between Q103 and Q104 was talked about. I've made over 30 cw contacts with it without problems.? I became curious and had a look at that area.? Mine has only a tiny sliver of the green board between the two tabs.? Maybe the width of a cat hair! |
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Hans,
The lesson here is to use your recommended starting point of 7 Volts and the current limit of 250 ma. I did this and it probably prevented the failure of the 1N4148 (Part luck also). I also was quick to turn off the power as soon as I saw that there was a problem. It might not work all the time but in this case, it did.? I have a regulated linear bench power supply where the voltage and current limit can be easily set. A good investment that has probably saved me much in the way of frustration regarding damaged boards and the consequential repair. Dennis KK5DB |
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Thank you for bringing up this topic so recently. I helped me in troubleshooting once I found my fried D101. The replacement on Amazon for me is 2 days, but its a good interim fix with the delay on shipping of the new SMPS. I may still order a new board for peace of mind, but try my hand at some SMD replacement in the meantime!
Be well. -- Alex KM4FFB |
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