Re: No TX #ubitx


And the input Z of your vom is? (Ohms per Volt) ..and the reading was  ? ...Just possible the vom was providing enough bias to turn on Q90 due to its loading


On Monday, February 18, 2019, 9:54:14 AM PST, Ted via Groups.Io <k3rta@...> wrote:

The bias controls do make the expected adjustments in current for the finals.

Interestingly enough, I was repeating some voltage readings yesterday and when I put my VOM lead into Pin 1 of Q90, the bottom of my hand - which was touching the IRF510 heat sinks- started to get warm.  A glance toward the wattmeter told me there was RF out!

The TX output quit when I removed the lead and returned more or less when touching the Q90 pin again. After touching the side points for 2cm around in all directions with nothing to show for it, I went and threw in, a 2N2222 as an upgrade, taking care to bend the gate backward betwixt the other two leads so that the E., B., and C. were on the circuit board pads they need to be on.  In firing the rig on, the '2222 gets nice and toasty, as does the pre driver pair (as they did before).

So, did that fix the problem? Actually, no. Still no RF out, now.  I put a 2N3904 back in and still nothing, though, being as the pre drivers are warm as well, I'd suspect the problem comes after them. An RF "sniffer" loop shows that RF fields diminish quickly, downstream of Q90 toward the rest of the transmitter power stages. 

I spent the time believing in a Q90 stage solution because of the sporadic full-strength output while taking measurements. It defies explanation how simply making metallic contact can restore seemingly full output, in a way that a re-solder and/or Q90 replacement didn't fix.

I'm sure that reading this report makes no sense. Well, neither did it make sense being there at the time so we're in the same place on that count.

Diving back in after the day job is done with.


On Sat, Feb 16, 2019 at 6:00, Raj vu2zap
<rajendrakumargg@...> wrote:

does the bias control pots change the idle current ? if it does then finals are fine and final circuit is fine!


At 16/02/2019, you wrote:
>On Sun, Feb 10, 2019 at 11:11 PM, Raj vu2zap wrote:
>Your finals are blown. Check if you have TX 5V at the output of regulator, if yes
>then replace IRF510's.
>Nope, new finals made no difference, surprisingly enough.  Have put this aside for a few days to get a fresh start next time diving into this. It's interesting how such a seemingly simple thing gets complicated. 
>See my update above for the latest readings, if you like.  I'd love to see this back on line before my V5 package shows up next week :)

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