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Bryan, What is the current draw of the amp when transmitting?? Does it change when it acts up? 73 Evan AC9TU

Scott from the QMX manual PLEASE READ THE BASIC ASSEMBLY AND USE INSTRUCTIONS IN THIS MANUAL VERY CAREFULLY BEFORE APPLYING POWER TO THE BOARD! SUPPLY VOLTAGE: 12.0V maximum is recommended,

Thank you Stan, that is most helpful and a very clear explanation. I hadn’t appreciated that Q507 was switched on during receive. Cheers Nick

Good evening, I understand the WMX’s voltage sensitivity, and especially the fact that most Lithium batteries have a nominal “12v” of 13.5vdc +/-. The power source I’m looking at runs at

Chris, I've not known that way of removal to have been described before for SMD! I'd have thought it the best way to ruin a board but you succeeded:-) To me your "tricky bit" is fairly easy, but

Nice job replacing that tiny thing! What a strange fault.? Very glad itnis working for you now. Stan KC7XE

Here are some waveforms of Q507 from a working QMX+.? All are of the transmission of a single 30wpm 'dit'. My supply voltage was about 11.7V, scales as labeled, with zero baseline one line up from

thank you for the link Stan...73 S

I hit the 510s with circuit chiller while it was acting up.? No luv. Hit the rest of the amp parts as well.? Nothing. -- regards, Bryan, N0LUF

Thanks Ron. I will do that. :)

For some time (several months) I had what I thought was some intermittent QRM, where the band was covered in spikes spaced exactly 100 Hz apart. Here's how it presents itself in the WSJT-X (there

Okay Nick. I appreciate the quick response. I need to put the radio away for the night anyhow but i think if i find the source of the transmit problem, i may find the source of the receive problem as

Now take this with a pinch of salt, but looking at the component values in the QMX+ a DAC output of 1.92V into the base of Q513 should turn the TX hard on. ?However it’s late in the evening here

Hi Joel, with your measurements the VGS of Q507 is -1.3V, which is not enough to turn it on. The specs for the FET are -1.5 minimum and -2.5V typical. The modulator circuit is to my understanding for

Would love to be part of a group buy. 72/72 de OZ1ES Erik

BTW, one more thing....What sort of signal and p.p. voltage should i see on either the base or emitter of those transistors? thanks. VY2KW wrote:

Hi nick. I have tested and yes, R506 and R507 coincide with the source and gate voltages at Q507. The next step i guess, will be to check the gate of Q507 with my scope and see if i am seeing a

I should add that when installing the new pads, test for shorts and reset the bias. Too much bias can cause excessive heat.

Bryan, I suspect that the connection to the heatsink is the problem.? It should be getting warm.? Try resetting the IRF510s on the heatsink.? I also suggest switching to AlN (Aluminum Nitride)

Thanks for confirming Gus, I've been waiting to hear back from you. I've now got a new PCM1804 chip and I'm plucking up the courage to have a go at replacing it.