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My QMX+ has a .3 ohm short on VDD
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Dear Members,
Trying as hard as I could to assemble the this beautiful radio, I somehow screwed up.?? I did check everything twice and sometimes three or four.? I didn't have any solder whisks and I did use my lop viewer just to make sure.? But I did put the battery in wrong on the front panel and that shorted out VDD.? I did have a problem with the power modules and ordered another set but they wouldn't turn on either. ? My original had the drain short on SMS PCB#1 between Q103 DRAIN and the leadon Q104 but I found that before I turned them on and broke the lead on Q104 trying to move it over.? Other than that, the assembly was normal and all parts are in their proper places.?? I did use a reduced voltage made with diodes at 8 volts for my initial turn on with my wall wart.? I wish I had put a current meter in there too? but I didn't scrounge through my oversized junk box to find one.?? I think that was also a big mistake.? I won't make that mistake again when I order another QMX+ as I really need it to fill a QRSS monitor function on my SUPER GRABBER. I did have a rather weird thing happen.? I had finished the QMX+ and was looking it over and checking the solder connections and looking for solder whisps and such and I tapped the board lightly on the mat on my work bench and out popped a little black part.? I think it was a diode as they are all black.? I spent the next two work sessions with the part charts and my QMX+ board and there are no parts missing on my board. So, I don't know where that part came from but it isn't off my board and not related to my VDD short. There are a couple of things that would have really helped me when it got to troubleshooting. First there was not a trouble shooting theory of operation to help train me up on the new Technology that Hans put into this radio. His other manuals had a theory of operation of the different sections of the radio. Second I would like to see a mock up test board that we can put together to test the SMS PCBOARDS #1 and 2.? That would help some of us divide there troubleshooting up so we can quickly locate the problem. Also adding some LED's that are on the different power busses that would light up on that first power up to give us a warm fuzzy feeling that this thing is working since nothing comes on on the first power up to give any indication that the on/off switch on the front panel? even worked.? They could be put on plugs on some of the board positions and could monitor all the voltages and removed if you want to use the DEVELOPMENT KIT later.? That voltage monitor could have been very helpful.? I will also add these suggestions to my next build as I think they are really valuable. This radio is a BIG TECHNOLOGY JUMP from the QCX+ even though it has a lot of similarities. I enjoyed the learning session even though I didn't get it to work.? But I am ordering another one today so I can try again. Take care and have fun. 73 Dave WA5DJJ SUPER QRSS/WSPR (160m to 6m) GRABBER WEBSITE: |
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Dear Gregg, I think in the long run that was the right decision.?? Then try again reading the book carefully while I build the second one.?? I think that will work best for me.?? |
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Dear Greg, Does anyone know if the power supply modules are built with a crowbar circuit so if they are feeding a short they shut down.... or do they just try to kill themselves????? At the present time I am back to reading a .4 ohm short on the 3.3V bus.... the 5V bus isn't operating, so I am slowly trying to figure out how to proceed and how to go about troubleshooting to try to bracket the problem... |
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David,
the QRP Labs Wiki contains documents about the internal power supply system and the QMX start up. QMX and QMX+ startup QMX and QMX+ Internal power supply 73, Ludwig |
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Dear David,
I am glad you are seeing some progress. As best the reports say, shorting the VDD to ground will not necessarily kill the 3.3v switching supply. So hopefully, you don't need a new PCB #2. So... you were able to load the firmware which means the linear regulator of PCB #2 must be ok, which is connected also to VDD. Otherwise, the processor would not be able to boot. Now that you loaded the firmware, the processor is now trying turn on the switching part of VDD (or at least this is my understanding). But I wonder about your measurement check of VDD. You report 2.5v on VDD and a resistance (without power, of course) of 0.4 ohm. That would be I = V/R or 6.25 Amps. So I wonder about that resistance check and I'm not seeing on the schematic how that would make sense. You can unplug the switching board PCB #2 and measure the resistance again. Are you possibly using a current limited supply which is not able to provide the current necessary for full boot up? Remember the linear regulator is also connected (but get's disabled at some point in the boot process) so the VDD onto the main board should definitely not measure so low as 0.4 ohm, Otherwise I don't think you would have been able to load the firmware. 73, Gregg W7GRM |
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Dear Gregg. Here is the diagnostics page I was able to get and copy: |
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Dear Greg. Take care and have fun.?? Thanks for the hints. |
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Dear David, I think you are getting close. |