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Getting ready to wind T501 on a revision 1 QMX+ I picked up at FDIM earlier this year.? I'm checking ahead on the steps to wind T501 based on page 26 and 27 of the manual, plus using the info for making it a 3 to 2 winding for 12 volts from page 4.

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Just for grins I checked the test points called out on page 27 for checking for no short at any of the points marked "A".? I'm finding the center tap point of T501 on the board is showing a dead short to ground.? Looking at the schematic this should not be the case, especially since the T501 coil has not yet been installed.

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Do I have a defective main board?? If I wind the coil and install it I will be seeing a short at all of the points marked "A" on page 27 of the manual.

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Anyone else seen this problem?

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Gary A. - W0MNA

The center tap position of T501 should not be shorted to ground, before or after installation of the transformer.? It should only be connected to the hole for one of the L502 wires (the one marked as point A) before installation.

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The hole just outboard of the center tap (toward the edge of the card) is grounded (this is one leg of the secondary - noting that the position of the center tap on the board is adjacent to the secondary winding, not the primary).

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But it would be exceedingly rare to have a bad board - they all go through fabrication tests.? So I would check carefully to make sure there are no external reasons you are seeing a ground here.? And verify that the center-tap hole is connected to that point A hole.

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Stan KC7XE

Are the BS170's installed?? I assume they are not blown if you have not yet finished building the transmitter part of the board, but there could be a solder glob from drain to ground somewhere.

Is L502 installed?? Could be a short to ground on the far side of L502.

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On Sat, Dec 7, 2024 at 08:41 AM, Gary - W0MNA wrote: