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QDX rev3 low output vs rev5

 

I got two used QDXs, one v3 and one v5. The v3 was assembled by the previous owner, the v5 supposedly from QRP labs. The v5 had a shorted USB and almost fried my computer and itself, but thankfully I got to it in time, the shorted soldering seemed "factory"
.
Both are recognized on the computer and receive great, the v3 doesn't seem to transmit correctly though. The v5 seems to transmit ok although I have no way of knowing the exact output. All my tests are done on 40m since its the only band my antenna has low SWR, and just a bit on 20m where a little over 1.5.

My very unscientific method of measuring this since I don't own a SWR bridge or a power meter is leaving my RSP1a nearby without a connected antenna. The v5 shows as +10-20 on the RSP1a, while the v3 is much lower, something like a 6 S-units.

I also use BNC to SO-239 adapters and cables of dubious quality so those factors come in to play too. But it seems like the v3 is faulty in some way, probably that's the reason the previous owner got an assembled one too.
Any ideas where should i start? The solder joints and the toroids look acceptable. I haven't assembled one and have no experience with such kits, but I have a multimeter and can follow basic directions, perhaps reheat some solder points too.
 

Hans has a troubleshooting page for the QDX series.? I would start there:


The most common cause of low transmit power after the toroid connections is a failed BS170 pr IC5.

I suggest checking the receive and transmit current draw to see if those are within normal values.

73
Evan
AC9TU
 

QRP-Labs has a dummy load kit you can assemble and you can connect your DVM to it to determine the power output of your QRP devices. (No one should be without a dummy load) It's an easy kit to build and I think you'll really benefit by this. You can see it here.
Dean - KC9REN
 

Well, it seems I got scammed since both QDXs are faulty. Hopefully PayPal will cover me.

The v3 doesn't transmit any measurable signal, so I didn't bother into researching any more.

The v5 seemed to work, but it was way too hard to complete a QSO compared to my G90 on 5w, even on 1w. After spending two days trying to do POTA activations with it, severely frustrated and disappointed I visited a friend with a SWR bridge that can measure even mWs.

There it was, power output was 7mW on all bands. Enough to make contacts if you tried a lot, but not something I could tolerate. Nothing obvious wrong with the board, and the basic continuity tests shows no problems. Power draw was 0.3A at all times, nothing changed when transmitting.
?
I won't spend any more time with these, hopefully PayPal will refund me and if the seller wants he can have them back.

But asking out of curiosity, does the v5 seem like a case of fried transistors?
 

Invoking PayPal is extremely unfriendly and unnecessary. You can email me. There are certainly no scams here.?

If they are kits it probably just means you built it wrong. If assembled units, they're all tested but of course something could be intermittent. It happens. We can work through it. Since you didn't give your name I can't check your order(s).


73 Hans G0UPL


On Tue, Aug 15, 2023, 4:11 AM kourampies <djkourampies@...> wrote:
Well, it seems I got scammed since both QDXs are faulty. Hopefully PayPal will cover me.

The v3 doesn't transmit any measurable signal, so I didn't bother into researching any more.

The v5 seemed to work, but it was way too hard to complete a QSO compared to my G90 on 5w, even on 1w. After spending two days trying to do POTA activations with it, severely frustrated and disappointed I visited a friend with a SWR bridge that can measure even mWs.

There it was, power output was 7mW on all bands. Enough to make contacts if you tried a lot, but not something I could tolerate. Nothing obvious wrong with the board, and the basic continuity tests shows no problems. Power draw was 0.3A at all times, nothing changed when transmitting.
?
I won't spend any more time with these, hopefully PayPal will refund me and if the seller wants he can have them back.

But asking out of curiosity, does the v5 seem like a case of fried transistors?
 

Like I said in my first post those were bought used from I private seller, not new. My Paypal transaction has nothing to do with you, but with the seller who sold me two non working transceivers. If you want to check something on the supposedly assembled by QRP Labs unit, I can give you some photos or the sellers name etc in private, just to confirm if this actually bought assembled or he did it himself.
 

No problem if you want me to check something let me know... From my point of view it's not very useful info if we don't know what the builder did between receiving it from QRP Labs and selling it to you. But happy to check it helps you.?

73 Hans G0UPL


On Tue, Aug 15, 2023, 1:31 PM kourampies <djkourampies@...> wrote:
Like I said in my first post those were bought used from I private seller, not new. My Paypal transaction has nothing to do with you, but with the seller who sold me two non working transceivers. If you want to check something on the supposedly assembled by QRP Labs unit, I can give you some photos or the sellers name etc in private, just to confirm if this actually bought assembled or he did it himself.

 

Thanks, I will email you some pictures of the board so you can give me your opinion if the assembly looks something done by QRP Labs soon.

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