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Qdx tcxo problems?

 

I am using qdx, rev 5, as a wspr rx, no tx function. After 3 months of continuous service it stopped working. After start up it will work for some ?minutes, and then signal disappear on wsjt-x. ?If I cool down the tcxo, just by blowing on that part, it starts working again for a short time. The tcxo is a little bit warm. Power is ok, all voltage is ok and current is 150 mA all the time. The tcxo part of qdx is to small for me to replace, but maybe a separate tcxo will work? Maybe qdx is not intended for continuous service? Any comments will be appreciated.
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On 04/09/2024 12:20, Gmail via groups.io wrote:
The tcxo part of qdx is to small for me to replace, but maybe a separate tcxo will work? Maybe qdx is not intended for continuous service?
? No name.

Whatever you do it will involve unsoldering/soldering the TCXO.

I suggest you read about working with surface mount.
It looks impossible but that's how I first successfully did an impossible soldering task.

I have 4 QDX running for years, nobody else has reported a TCXO problem. You are unlucky!

73 Alan G4ZFQ
 

Thanks for info, I will try to unsolder the Tcxo. I have build another qdx, and the faulty one has been replaced at my remote qth. Monitoring on 20 m Wspr.
73
Alf, LA1ZM.
 

I have been using Blue Tac to hold small SMD parts while soldering. I think it was a Hans suggestion.
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Also, I have lost a few parts flying out of my tweezers, so be sure to order a few.
 

I've seen more failed 5351's than TCXO's , but if you're sure Removing it is reasonable simple.? It's already dead right,?
- Stick the iron on top and leave it 5 to 10? secs before flipping it up with a wooden cocktail stick onto the nearby bit of paper you carefully placed

Replacing it is trickier to be fair.? ?Pre-tin the board, apply some flux to the new TCXO pads and holding the TCXO down/in place (the right way round!)? with a cocktail stick try to get one easy corner soldered, repeat at the diagonal corner then if the others haven't already 'soldered themselves' at this stage put a small blob of solder on the iron and try to make contact.? It will solder?
 

Thanks for importent info. Yes, it could be the 5351. I will investigate more. Just now it started working again, and I am confused.?
73
Alf
 

On Wed, Sep 4, 2024 at 10:09 PM, Bruce Akhurst wrote:
I've seen more failed 5351's than TCXOs
Yes, it might be an idea to monitor the 25MHz output to check.
A RX with an antenna wire close to the TCXO or a scope should help.
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I did wonder if the TCXO is soldered properly, missing parts have been reported on some boards.
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73 Alan G4ZFQ
 

Thanks, I will monitor the 25 Mhz output and the tcxo. I will not be home for a week now, but will start again to check when I am home again.
--
Alf, la1zm
 

Hi
The si5351 is the faulty unit, tcxo is ok all the time, but Lo disappear when the fault occurs. By cooling down the si5351 it is ok again. This smd is too small for me to replace, I have no tools for smd-work, so the less expensive for me will be to buy a new qdx kit.
In the meantime I will cool down the unit with a little fan, then the unit is working ok .?
( I have enjoyed building simple hamradio-rx and -tx for more than 50 years, but the si5351 is too small for my eyes and hands ). Except for this the qdx-kit is the most impressive kit I have build from Qrp-labs, and the one qdx I have with no fault is monitoring wspr on 20 m 24/7.
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73 de
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Alf, la1zm
 

On 21/09/2024 12:00, Gmail via groups.io wrote:
I have no tools for smd-work,
Alf,

Not much required to do the Si5351


Others have cut the IC pins with a Dremel-type tool or even with a scalpel.
It is worth trying rather than discarding the board.

73 Alan G4ZFQ
 

A soldering station with hot air is affordable and worth having.? ?I use YIHUA 8786D
 

On Sat, Sep 21, 2024 at 08:19 AM, Alan G4ZFQ wrote:
Others have cut the IC pins with a Dremel-type tool or even with a scalpel.
A scalpel blade, specifically a #15 blade, applied with a rocking motion adjacent to the IC body, will slice cleanly through the leads without putting undue stress on the PCB lands.
Then merely individually heat and pluck off the leads, clean up the lands and you are ready to reinstall.
Good luck and 73, Don N2VGU
 

Thanks for all info, I appreciate that, and I will try to replace the si5351.?

73
Alf, la1zm
 

At last my qdx is working again. Waiting some weeks for the si5351 to arrive. To remove the faulty one was easy with the scalpel. After the third try I succeeded to solder a new ic. ?.
Thanks for all info and encouragement.
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73
Alf, la1zm

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