I've built a QMX HB and 2 QMX+ units.
In all three I found the screw head to be too close for comfort to that nearby chip.
I simply filed a flat on the screw head right down to almost the ends of a pair of the Phillips head slots. Used a hand file for two then remembered I had a nice Dremel tool and used a medium coarse sanding drum for the third. That last one took about 2 minutes going carefully.?
You can also shift the screw body a bit away from the IC when doing the final snug down of the screw/washer/nut. Hold the screw head with a screwdriver and tighten the nut carefully with your fingers or a small pair of pliers while adjusting the position of the washer over the BS170's. No need to use a lot of torque!?
On Thu, Oct 3, 2024 at 6:23 AM, Ronan Cantwell
<ronancantwell@...> wrote:
My mid-band QMX (rev 4) is finally back up on its feet and running nicely after a few repairs. I posted a thread a while back with the initial fault(s) and progress with its diagnosis / repair.
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To cut a long story short, a fault on one of the PSU boards took out a few of the ICs on the main board. After fixing the PSU board (faulty zener), I went about ordering replacements for the 5351 and IC's 501, 502 and 503. These were all fitted, along with a fresh set of BS170's and a quick rewind ?of transformer T501, just in case. The end result is a fully working radio that puts out a minimum of 5W on all bands running on a 12V supply.?
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Now for a quick heads-up:
There was one small issue in the repair. The 74ACT08 chips that I ordered from Farnell were a tiny bit too long for the tight space on the board. The metal screw for the BS170 retaining washer prevented the IC from aligning properly with its pads. I ended up having to sand the body of the chip down very slightly in order that it would fit the space. The chips I ordered were manufactured by ONSEMI - part number MC74ACT08DG. They are the correct package and pin spacing but the chip body is just that tiny bit too long for the available space without modification.
Here's a photo of the shortened chip in place, showing the clearance between it and the screw.?
Hope this helps someone who may have similar issues with their radio. It's a great little box and I'm glad it's back in action!?
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Cheers,?
Ronan
MM0IVR?
