toggle quoted messageShow quoted text
if touching Q90 make the power amp oscillate then probably the whole
chain is ok. This is quite normal for a
high gain PA.
now check L1/2/3/4 for continuity, there could be a bad solder on one of
There is a spreadsheet in a folder called vu2zap in the file section with
static voltages of uBitxv4 if you want
At 18-02-19, you 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
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
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
- >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