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QMX+ D109 Failure

 

My QMX+ ceased to function last night after working well for a few days after build. It just didn't start up. After probing around I could see the output of IC101 linear reg was only at about 1v when the button was pressed. To establish if it was the regulator or load on VDD I removed D103.
The output of the reg went up to 3.3v , I checked it with a 15ohm load and it was still ok. I couldn't see a low resistance on VDD so planned to remove the obvious, like tant caps and check them when I noticed D109; I guess its for transient protection when the switcher changes frequency or on start up. So I took it out and measured it it was .5V one way as expected, but 0.1 V in the other direction at 1ma. So I Jury rigged a through hole device in its place, replaced D103 and everything burst into life. Just have to find the right component now.
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Hope this helps anyone with a non-starter, I wonder if anyone else has seen this diode fail?
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G0TXL (Paul)

Robert AD6XJ
 

YES. It is under a few threads typically "bumped" or "died".
I just removed my D109, disconnected it measures 1846Ω forward and 320Ω reverse or in Harbor Freight Cen-Tech VOM diode test mode 601? forward 123? reverse. It is marked "W4" and the schematic says "3.6V 500mW" and appears to me to be 0805 size.
Can I safely assume that it should be 0Ω reverse as any non-zener would be? In other-words is this component bad?
My symptoms were-- I bumped some external connector (DC, USB, Ear, and BNC were connected-- I was swapping BNC) and screen went black. When I pressed upper encoder, speaker "popped" with each press but screen remained blank and dark.
I apologize, I have not taken the time to read ALL the D109 posts, but could someone share a Digi-key part number for this (again)?
Thank you,
Robert AD6XJ
P.S. Is there anyone in our group located near-ish Knotts/Disney in Southern California? If so, do you have an extra zener I could buy or swap?
 

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From my previous post in this thread:
The QMX+ assembly manual says D109 is a 3.6V 500mW SOD-123?
One such part is this from Mouser?
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So you want a 3.6 Volt zener good for 500 mW dissipation in an SOD-123 package.
I believe that Mouser part is a reasonable choice.
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Use two soldering irons when extracting that part.
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Resistance through such a diode is a function of voltage, so not sure
if your meter readings say it's good or bad.
Since it is not a dead short (both directions), it has not failed in the manner others have reported.
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Jerry, KE7ER
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On Sun, Oct 20, 2024 at 06:08 PM, Robert AD6XJ wrote:

could someone share a Digi-key part number
 

That 3.6v zener is also on Digikey:
https://www.digikey.com/en/products/detail/onsemi/MMSZ5227BT1G/919745
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On Sun, Oct 20, 2024 at 06:50 PM, Jerry Gaffke wrote:

One such part is this from Mouser?
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So you want a 3.6 Volt zener good for 500 mW dissipation in an SOD-123 package.
I believe that Mouser part is a reasonable choice.
Robert AD6XJ
 

With D109 removed my QMX+ is back to life!?
Could someone explain why I don't just run it like this, with D109 absent?
 

DO NOT run it without D109.
An overvoltage spike on the 3.3v rail killed D109,
if that happens again it will instead take out the STM32F
and pretty much destroy the board for you.
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You're living dangerously.
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Jerry, KE7ER
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On Mon, Oct 21, 2024 at 11:08 AM, Robert AD6XJ wrote:

With D109 removed my QMX+ is back to life!?
Could someone explain why I don't just run it like this, with D109 absent?
 

On Mon, Oct 21, 2024 at 02:21 PM, Jerry Gaffke wrote:
You're living dangerously.
Given the lean nature of Hans' designs I doubt that there are any truly superfluous components.
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Who remembers Earl "Madman" Muntz???
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From Wikipedia:
"He often carried a pair of wire clippers, and when he thought that one of his employees was "" a circuit, he would begin snipping components out until the picture or sound stopped working.
At that point, he would tell the engineer "Well, I guess you have to put that last part back in" and walk away." ?
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73, Don N2VGU
 

Oh yea! “There’s Something About A Muntz TV” Watching Chicago TV, WBKB, in the 50’s I remember his commercials.

Mike Krieger


On Mon, Oct 21, 2024 at 3:49?PM Donald S Brant Jr via <dsbrantjr=[email protected]> wrote:
On Mon, Oct 21, 2024 at 02:21 PM, Jerry Gaffke wrote:
You're living dangerously.
Given the lean nature of Hans' designs I doubt that there are any truly superfluous components.
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Who remembers Earl "Madman" Muntz???
?
From Wikipedia:
"He often carried a pair of wire clippers, and when he thought that one of his employees was "" a circuit, he would begin snipping components out until the picture or sound stopped working.
At that point, he would tell the engineer "Well, I guess you have to put that last part back in" and walk away." ?
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73, Don N2VGU

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