Mike WM4B:

I like your idea of shifting the 78m05 one pin to the left to match the ground and output pads of the AMS1117, while tying the input pin to the output of the D3 diode. Once you get this done, please post a description of the process and a photo. We want to learn from your mistakes--  I mean success. :-)

Steve N9SZ

On Tue, Jan 26, 2021 at 09:51 AM, Fred Spinner wrote:

You don't use a 15V absolute max regulator at 13.8V.  You don't need a production test engineer like me to tell you that.  There I said it! 

 

In an actual commercial product those first boards would have been recalled and scrapped. 

Fred, I agree, to a point.

As I've stated some time ago, I would have been scared to death to do 1000 boards on first run, with new design.

I think Hans just got overly anxious to please everyone by shipping before Christmas...
Perhaps an initial run of a few hundred for PCB version 1.0 would have flushed out the issues before going all out.

Anyways, just an opinion, not really knowing/understanding all the ins and outs, in QL's business.

I think a lot of people really had fun, regardless...


What do they say about hindsight?


73
km6wt

Check if the 1PPS 2ignal gets through the MCU at pin 28. Maybe it is just a wiring issue between the GPS module and the main board assembly.
A oscilloscope or even a simple analog voltmeter can be used for this.
73 de Jakob, AA0JR

Checking the 3rd line on the opa2277’s on my uSDX, the ones that I can still see, none of them match any of the others. So 8 out of 8 the code on the 3rd line is unique

i checked the 20 meter crystal with scope and show 20 mhz.  I also listened for it on my shack rig with no luck.

Gary,

To hear it on a receiver you would most likely need a short wire antenna put close to the crystal.

I checked solder connections around it.  Swapping displays with my 20 mini I get the same results, only top row of squares.

This is putting the good mini display in the defective mini?

If so then check all connections between the display and IC2 for continuity. Apparently you have done that. Are the voltages the same at the LCD and the corresponding pin of IC2? Are all solder joints good including plug and socket? No shorts? Look again, resolder.

There is very little it can be, you only need to look at this small part of the circuitry.
There is always the chance of a defective LCD.

73 Alan G4ZFQ

Mike, I was thinking about having a 7805 and a limiting resistor. (I'm a 'belt and suspenders' kind of guy!)
--
73, Dan  NM3A

Thank you Howard. Informative.
Like you I make bad solder joints from time to time, now I'm aware I'll inspect more closely, especially enamelled Cu wire.
OTOH maybe I'll go back to soldering 555s, 741s, CMOS, 74LSxx, PIC or hand soldering 18pin SO uP packages, you know, something easier from 20-30yrs ago, until I improve my skills and can recognise a good solder joint.
I'll listen out for you on 160m.
73
Graham

Finally got back to QCX mini 40 problem of only top row of blocks.  I swapped out the IC2 with my 20 meter mini and it worked fine in the 20 meter mini.  So it isn't IC2.  i checked the 20 meter crystal with scope and show 20 mhz.  I also listened for it on my shack rig with no luck.  I checked solder connections around it.  Swapping displays with my 20 mini I get the same results, only top row of squares.

I really would appreciate any suggestions where to turn next.

Thanks.
Gary K4VIG

You did a good job documenting your voltages, and it looks like the numbers are good, so the ICs are probably fine. There may be a problem with C11 or C12, so measure the capacitances of those. Your power output will be related to adjusting the windings on the toroids of the low pass filter stage. Hans has a video in the troubleshooting section of the website:  http://qrp-labs.com/qcxmini/troublevideo.html
--
73, Dan - W2DLC

Dan,
Phantom Power in audio lines is VERY current limited and a short is not an issue. A short in the QCX +5V line to ground is a DIRECT short with no limiting resistor or other current limit protection. 

Apparently the 7805 can handle a transient short with no damage, but the AMS1117 cannot, leading to an unfortunate catastrophic failure. I am hopeful that going back to the 7805, even if it is a lower current version will markedly reduce these failures.

I agree that willing myself to refrain from hot-plugging a 3.5mm 'stereo' connector is probably an unreasonable expectation, given how used we all are to hot-plugging these type of connections. Also even if you never do this intentionally or absent mindedly, what about the unintended partial or full disconnection when someone or something trips on your cables?

For myself, who only wants to use this for barefoot CW QSOs, I simply did not install the PTT/5V nor the CAT jack (although the CAT interface is unlikely to be a problem.) this way I cannot possibly plug something into a jack that's not there. 

Question I would have is if it is possible to put a limiting resistor on the +5V line leading to the PTT/+5V jack? Would this protect the QCX enough? And would it still provide usable power to any attachment ?
--
73, Dan  NM3A

On Wed, Jan 27, 2021 at 03:30 PM, James Daldry W4JED wrote:

Hi, Guys

Radio station WWHG in Hornell, New York at one time (maybe still does) had station monitor audio wired to standard 120 volt type duplex outlets. They also had a number of interesting smelling studio monitor speakers with torn grille cloth.

HiHI brilliant!
73s Ted

On 2021-01-27 08:35, Mike Besemer - WM4B wrote:

What connector are you talking about?
None of my QRP labs products has an audio connector for a DC power
plug.
Mike
WM4B
On Jan 27, 2021, at 9:22 AM, kf4pv@... wrote:

Ted,
I agree. I like these rigs enough that I have 2 of them and will buy
more stuff here. But that doesn't change the fact that using an
audio connector as a power connector is not good practice.
I am not attacking anyone nor calling the rig junk, only pointing
out:
1. That this is not a user/operator error (which may be some small
comfort to the owners of smoked rigs).
2. Why it's a design error that should be fixed with an eventual
board rev
3. There are ways for builders to fix this until the kit is
changed
This may be a hobby, but it's also a business. All the builders have
paid money for these kits and assembled products, so having them
self-destruct, even if only occasionally, is a problem. The last
thing we need is for QRP Labs to get a bad reputation and go bust,
or to have to spend all their time and money replacing burned out
boards and go bust. That would be end of the fun toys for us. It was
in that spirit that I was pointing out the issues so that they can
be fixed. That included justifications beyond just "this sucks" so
that the design flaw could be properly recognized as such and my
comments taken seriously.
The other thing about it being a hobby, is that many of the builders
are not professional EE's, RF engineers, etc. They use these
accessible and well-documented designs as inspirations and examples.
For many this is the start of their career path. Because of that,
it'd be good if bad habits, such as using audio connectors to carry
power, were nipped in the bud.
So that's why I posted my comments. I've seen a lot of bad design
decisions over the decades, including the ones I made myself. It's
just part of the design process. This particular one, the
inappropriate use of connector types, is very common, especially in
small outfits that don't use the same design/review processes that
the large companies use. There will always be errors, the trick is
when you catch them. Following standards lets you avoid the errors
escaping into the wild.
73
Laszlo

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Hi, Guys

Radio station WWHG in Hornell, New York at one time (maybe still does) had station monitor audio wired to standard 120 volt type duplex outlets. They also had a number of interesting smelling studio monitor speakers with torn grille cloth.

73
Jim W4JED

It's pretty common to use an audio connector to carry power. In audio equipment it's called "Phantom Power" and is normally a much higher voltage.
--
73, Dan - W2DLC

PTT on the QCX series. It carries PTT, +5v and ground on a 3.5 mm stereo connector.