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Hi all
Some people appear to have issues with their QCX not starting up at first power-up; they must switch off, then soon after switch on again, to get the microcontroller to boot up properly. I have STILL never seen that issue here on any development build, prototype, pre-production build or production build versions. I have tried chips from different batches, and four different power supplies. I tried switching on/off at the power supply, and with a switch in-line from an already-on power supply. I just can't get it to happen, mine always start right! Grrrrr
Peter G3JRH is a chip designer and has seen similar issues before. Peter stated that his QCX also did not power-up correctly, and he has investigated in detail. He says:
"It is not really a question of the slow rise on DVcc pin, but it is that the AVcc pin rises more quickly as it only has a 100nf capacitor to charge. This violates the requirement for the AVcc not to differ from the DVcc by more than +- 0.3V (see ADC converter section of the ATmega328 datasheet). I see 2 solutions to this, either place a 470uf capacitor on the AVcc pin or better still place a small schottky diode between the AVcc and DVcc pins (cathode to DVcc anode to AVcc), I have done this on mine and it now starts correctly every time.?What happens when the 2 Vcc¡¯s differ is that one or more of the internal diodes gets forward biased and the silicon latches up, even the reset pin does not work. I suspect that the reason some batches of 328¡¯s work and some do not is simply minor processing differences."
I believe Peter's comments and suggestion make a lot of sense. In summary, fit a Schottky from processor pin 7 (cathode), to processor pin 20 (anode). The diode cathode is the end with the stripe on it, and should go to pin 7. It is possible to fit this diode on the underside of the board quite neatly.?
With reference to the circuit diagram, another way to keep the voltages on AVcc (pin 20) and DVcc (pin 7) equal is to remove inductor L5, and solder this inductor between pins 20 and 7. This method will also work. It has the advantage of not needing any additional components. But, the disadvantage that you need to desolder L5.?
If someone else could try these and verify Peter's results it would be a very nice confirmation.?
73 Hans G0UPL
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Hans,
Just tried schottky from pin 7 to 20 with 470uf tacked on to the 10uf I put there earlier, so 480uf in total at C47, and starts up fine first time.
73
Simon VK3ELH
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On Fri, 2017-10-27 at 16:42 +0300, Hans Summers wrote: Hi all With reference to the circuit diagram, another way to keep the
voltages on AVcc (pin 20) and DVcc (pin 7) equal is to remove inductor
L5, and solder this inductor between pins 20 and 7. This method will
also work. It has the advantage of not needing any additional
components. But, the disadvantage that you need to desolder L5. I tried to de-solder L5, but it didn't survive :-( So until I can get a replacement I've linked the top L5 hole (Pin 20 and C36 end) to the Pin 7 end of L6. And now mine starts up first time every time where as previously it took two connections each time. PeterO G0DZB
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Still cant get my QCX to display anything other than blocks. Not even got to the alignment part yet. Might the Diode trick work? I have a spare Schottky Diode but not sure of its specs.
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It is neither a high voltage nor high current application. Just about any small Schottky diode should work. On Fri, Oct 27, 2017 at 12:45 PM, simon.oliver90 via Groups.Io <simon.oliver90@...> wrote: Still cant get my QCX to display anything other than blocks. Not even got to
the alignment part yet. Might the Diode trick work? I have a spare Schottky
Diode but not sure of its specs.
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Thanks Jack
73 Hans G0UPL?
On Oct 27, 2017 5:27 PM, "Kelly Jack" < kellyjack1968@...> wrote: Hans,
Just tried schottky from pin 7 to 20 with 470uf tacked on to the 10uf I put there earlier, so 480uf in total at C47, and starts up fine first time.
73
Simon VK3ELH
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On Fri, 2017-10-27 at 09:45 -0700, simon.oliver90 via Groups.Io wrote: Still cant get my QCX to display anything other than blocks. Not even
got to the alignment part yet. Might the Diode trick work? I have a
spare Schottky Diode but not sure of its specs. Sounds like a more fundamental problem to me. If it doesn't even start after a quick power-down power-up sequence I don't thing the diode will help. PeterO G0DZB
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Just tried the diode acress the pins, makes no diffrence at all. Dont think im cut out for kit building.
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A perfect opportunity to practice methodical troubleshooting and narrow down the possible culprits, half the fun of building kits (:
On Fri, Oct 27, 2017 at 7:31 PM, simon.oliver90 via Groups.Io <simon.oliver90@...> wrote: Just tried the diode acress the pins, makes no diffrence at all. Dont think im cut out for kit building.
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I¡¯ve tried the fix but no luck. I have two lines of bars with a pulsing thin line that moves up/down through the bars.. Thinking IC2 is not doing its job, but the pulsing makes me think there is something happening and it is maybe not fully dead? ? David. VK2NU ? Sent from for Windows 10 ?
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David
Has it started properly at all yet?
I had mine going but was having the issue of not starting first time but only on second power on. At one point when I was powering on and off to test possible solutions IC2 locked up on me and I got the top row of blocks indicating the chip wasnt running. I thought I had bricked IC2.
I reflashed the firmware and it came back to life.
Just an idea.
73
Simon VK3ELH
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Hello Nigel,
Nice enclosure, very neatly done, if you don't mind me saying so?
2E0ILY
Tuesday, October 31, 2017
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I had the start up issue, I changed the inductor to a 2.2uH I had
in my stock but warned there may be noise ordered and fitted a 47uH.
No start up problem. Today I boxed up my rig, the issue is back.
Looks like the Shottkey route is next. Ordering an audio amp to drive a speaker next. Nigel M0NDE -- 2E0ILY Best regards, Chris mailto:chris@...
--
Best regards, Chris Wilson (2E0ILY)
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Successfully de-soldered L5...? did the pin to pin mod.... no luck.? It still takes multiple power cycles to see a start on the QCX
Barry
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Check L5 with an ohmmeter for continuity. ?Those small inductors are prone to open up occasionally when you unsolder and resolder them. ?If it's open that might be your problem.
W0EB
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On Nov 11, 2017, at 12:54 PM, Barry Mercer < Mercerbarry0@...> wrote: Successfully de-soldered L5...? did the pin to pin mod.... no luck.? It still takes multiple power cycles to see a start on the QCX
Barry
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Indeed, when I pulled L5 out it looked fine but was open circuit!
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Great ideas.? ?Thanks? I checked mine... all good.
Barry
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I have a (rev 2) board to build and I'm reviewing the modifications list, particularly the suggestions about how to fix the analog/digital supply sequencing problem.?Obviously this problem arises from the size of C47.?
I am wondering why such a huge capacitor (220uF)?is needed on the ATmega digital VCC. What is the rationale for using such a big value, and does anyone know if it works OK if the capacitor is simply removed, or alternately, placed upstream of both inductors (at the output of the regulator)?
73
Eamon
VE2EGN
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Hi Eamon?
The correct diagnosis of the problem and the correct solution is described here? (change inductor position).
The capacitor helps attenuate any digital noise which might be thinking of finding its way along the supply rails to the analogue sections.?
Note that the current Rev 3 PCB already has this modification included as standard, on all rev 3 PCBs?
73 Hans G0UPL? ?
I have a (rev 2) board to build and I'm reviewing the modifications list, particularly the suggestions about how to fix the analog/digital supply sequencing problem.?Obviously this problem arises from the size of C47.?
I am wondering why such a huge capacitor (220uF)?is needed on the ATmega digital VCC. What is the rationale for using such a big value, and does anyone know if it works OK if the capacitor is simply removed, or alternately, placed upstream of both inductors (at the output of the regulator)?
73
Eamon
VE2EGN
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Shirley Dulcey KE1L
Daniel Ekman SA2KNG
Jim Sheldon