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QMX 5V SMPS not working

 

I just finished building my high-band QMX (rev3), connected power (7V, 250mA limit) and it showed up on the pc to upload the firmware. After the upload (1_00_017), it wouldnt stay on. When I press the power button, the QMX will run into the current protection, nothing on the display and no backlight, and as soon as I release the button, it shuts off.
With the jumper, I could enable the FW upload mode, and uploaded? 1_00_016, which is running on my low band QMX.

I tripple checked all solder joints on the 5V SMPS, even touched up all the joints of the SMD components, but it didn't help. Finally I pluged in the 5V SMPS of my low band QMX, and voila: It starts up.

Any Ideas what I could check? It seems I need a new one.
 

Is C107 flipped? I can't find the layout of rev3. If yes, could this be the problem?
 

I didn't uncase mine but the photo in the assembly manual sure shows it installed the 'other' way.

Probably a good catch.?

Greg

On Wed, Mar 20, 2024 at 8:13 PM, roebi via groups.io
<roebi@...> wrote:
Is C107 flipped? I can't find the layout of rev3. If yes, could this be the problem?
 

In the manual is rev 1,? so it could be different. On the other hand, if it is correct, then the zehner diod next to it is wrong, and this WOULD explain the problem. I can't find a layout of rev 3, but I should be able to find this out with a multimeter. See who is faster, the Internet or me :)
 

Ok my measurements confirm C107 is wrong, D108 correct.
Anyway, can anybody confirm this please? And please also take a look if there are obvious other problems.

Mni tnx!
 

Hi Roebi

Yes, that capacitor is the wrong way around. First time I've ever seen that. Wow. I don't even know how that could happen because?the SMD factory is all automated and the capacitors come off a reel, where they are all the same way around. So either all 1,000 in the batch have to be wrong, or none of them. But I just checked loads here and they are all correct. Very strange...?

Also strange that if connected in reverse, it didn't just blow up...?

Do you want to try changing it around? Or shall I send you a new one??

73 Hans G0UPL



On Thu, Mar 21, 2024 at 9:35?AM roebi via <roebi=[email protected]> wrote:
Ok my measurements confirm C107 is wrong, D108 correct.
Anyway, can anybody confirm this please? And please also take a look if there are obvious other problems.

Mni tnx!

 

Was an easy fix, and the QMX started up, so its not necessary to send a new one.

Tnx!
 

Regarding the survival of the capacitor, I think the current limit and resulting boot loop saved it. I measured the capacity with my cheap LC meter, it showed 480uF, so all good.

All final checks with th QMX went well, fired it up, and was spotted by RBN, so I guess everything works.?

Let's see if I can activate a park with it next week on my holiday in 9A. :)


Agn mni tnx fer support, cu on the bands.

73 de OE3RLV Robert

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