Hi Jeff,
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I wanted to give you an update since your previous post was so helpful.? You may remember this issue from back on June 30.? I've been letting this QMX+ get the better of me.? I did prove that the cpu was bad as you described: pin 53 behaved exactly the same, only lifting? about 0.7 briefly on power up, with the pin floating - and the trace in the board between pin 53 and the SMPS board was continuous and not shorted.? And of course I checked the behavior on a working QMX, so I knew I was on the right path. I ordered a chip from Digi-key, along with some aluminum tape to protect surrounding components from my heat gun.
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I removed the chip easily enough, and cleaned everything up, but I knew the soldering would quite difficult.? This is about twice the pin density of any SM chip I've done (and that was probably 15 years ago, when my hands were steadier and I had full use of both eyes) so I took some time getting my courage up for the replacement phase.? I did struggle getting the thing installed.? I just use my phone magnifier to see the pads, but I suspected I had somehow damaged the chip.?? I did get a lot of practice though, and I think I have a process that will work on my next try.? The trick was finding a way to hold the chip still.? I think for my next try I am going to pull this chip, build up some solder on the pads, then with the new chip held still over the solder loaded pads, essentially heat each pad one at a time to flow the solder over the pin.?
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I was debating on ordering one more chip from Digi-key, or admitting defeat, then I saw your post from the 16th.? Now I know for sure it was never going to work. "You will need a cpu that has the boot loader programmed onto it for the replacement."?? I suspect putting in generic CPU chips without this boot loader will never get me anywhere.? I guess I have to ask Hans for a chip to get one with a boot loader?
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Thanks again for the help.? I am still hoping I can fix it up myself. :)
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73,
Jeff - KS7N
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