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New QDX Hi band 9v build. Powering on and quickly testing voltage with a multimeter, on GND and input of L8 toroid (15-17m band) shows ~7.5v and falling smoothly no matter which band selected.

Is it an SMD part that is bad or possibly something else? I tried my best to figure it out myself with all the documentation out there but I'm stumped at this point.

Hello William,

If I understand your description correctly, the banded side of D6 does not go close to 0 volts when the 15 or 17-meter band is selected.? The most likely cause is the toroid enamel has not been burned through.? The toroid is needed to conduct the forward bias current for D6.

If L8 is not the issue, either L7 is open or Q4 is not turning on.? A quick check of D2's operation will show if those devices are working correctly.

73
Evan
AC9TU

Voltages are ~0.04v when selected, and 8.2v when not selected at the corresponding points of D1, D3, D4, and D6.

D2 and D5 voltage falls when powered up from 8v to about 0.93v over time, like a few minutes. Just like L8 input point.

All measurements are taken from the pads on top side of board. All the relevant points have continuity and measure 0 ohms.

I made a 2 minute youtube video with a demonstration.

https://www.youtube.com/watch?v=GRMA4vYuthQ

The voltages taken from the 15/17m chain fall over time when QDX is connected to power.

Hi Wiliam,

Can you verify if the drain of Q4 goes low when selected?



If so, check that the junction of L# and L8 also goes low.

Have you tried resoldering L3 and L8 leads???

73
Evan
AC9TU

I reflowed the hell out of L8, and then tested the drains of Q3, Q4, and Q5, and they checked out when testing the bands.

So I did the L6,8,10 check it it all passed!

Getting 3-4w with around 900ma consumption on all bands, time to tweak toroids!

Thanks for your time and expertise!