Power output lost

[PA4VA (Arjen)]

Dear om's

Since a few days my power output slowly decreased and now I've left around 1/2 watt.
First I thought that Q1, Q2, Q3 could be the problem so I replaced these.
Unfortunately that wasn't the solution, the problem is still the same.

Does any of you have an idea?

Kind regards and 73
Arjen PA4VA

[LILO]

How did you measure it?

[PA4VA (Arjen)]

Hi Lilo,

I measured it with a power (watt) meter and a dummy load...
In CW mode ofcourse

[dl6sez]

Hello Arjen,

measure at 74ACT00 with Oscilloscope if it still works as squarewave signal provider to PA FETs.

73 de Chris

[PA4VA (Arjen)]

Thanks for the reply Chris.

That would be the next on my list .
Unfortunately I don't have an oscilloscope to measure.

Because there is still some (0.5 watts) output I tried to receive my signal on another receiver.
It turned out to be on the right frequency so there is RF. CW gave a clear signal however in SSB the audio seemed to be distorted. Hope this helps to find a solution?

73 de Arjen

[dl6sez]

Hello Arjen,

no this is what i have expected
I don't think it is more distorted than normal. Nearby control of ssb modulation without high attenuation, let's say more than 60dB, sounds not good with (tr)uSDX as tx.
So just no other chance only measurements...

73 de Chris

[KN4OK]

I lost all my output power and did a reset with still no output power. Everything else works fine. I did have a burnt cap in the power supply section and replaced it.

Dave KN4OK

[dl6sez]

Hello OM,

why is there a burnt capacitor?
You must have done something
No Power is 100% a PA FETs reason.

73 de Chris

[KN4OK]

Hello Chris, When I was hooking up my battery power, I suspect at the connection of the external adapter the plus and minus touched. I opened it up and saw C-3 fried. So I replaced it and the radio works fine in RX only. Well, I just found C2 bad.

[PA4VA (Arjen)]

So just no other chance only measurements...

73 de Chris

Or just replace the 74act00 anyhow
(they are not very expensive)

[dl6sez]

Hello OM,

i don't understand why there C2 and C3 are blown up with your described error, makes totally no sense.
You must have done something different, maybe you changed + with -....too high input voltage, but this should kill more.
We can not really conclude if it is 74ACT00 or PA FETs but must be one of these if you receive and don't get power output at tx.

73 de Chris