On Mon, Dec 30, 2024 at 01:47 PM, Adam wrote:
L101 (the one on the 5V board) gets very hot
No this is not normal.? It gets only warm during normal operations, including transmit.
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Note: it is dangerous to operate the QMX without D108, especially if there is a short on the output of the 5V supply somewhere.? This is because the CPU tries in vain to raise the voltage to 5V, increasing the output of the switching supply, which (without D108) puts 12V on the 5V VCC rail, significantly increasing the current being sourced into the short - that is likely why your L101 is getting hot.? The added current may burn through whatever is shorting, and suddenly put 12V on all the 5V parts.
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So something must be partially shorted/failed on the 5V board, or on the 5V components on the main board to cause this.? If your receive is working properly, it's probably not a component on the main board - most of the receive section components are on Vcc.? Does receive still work?? On one of my units, I inadvertently shorted 12V to Vcc, and in additions to causing failures on the 5V power supply, it damaged IC403 to have an internal near short to ground.? I isolated it by lifting the Vcc pins of the ICs one at a time until the short disappeared.? But this IC being damaged also destroyed all signal receive functionality.
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I would measure the main-board resistance between the 5V rail and gnd, without the power supply in place.? This should have several Kohms of resistance, if not, there is a failure somewhere on the main board.? Hopefully it is OK and the only failure is in the 5V supply.
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An option to consider is to order a set of the little power supply boards from qrp-labs (on their spare parts page) - they are very inexpensive, and may save you some troubleshooting and repair.
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Stan KC7XE
