Hi Don, Thanks for your suggestions. I disconnected pin 2 of MAX534 and applied external control voltage there (simulating a healthy channel "A" of the DAC). Fortunately, now I can control the power output from the transceiver from 0 to MAX. The sine wave looks undistorted and exactly on the desired frequency (but to be honest, initially I also thought like you that the PA could be oscillating).
The current consumption is now much better - between 0.8 and 2.1A for output power values 1-10W. The power indication on the display also shows meaningful values during TUNE. The strange thing to me is why the DAC pin was outputting 0V, but the ALC circuit still drove the BFO attenuator gain to the max... There's a remote chance that the damaged output was somehow in HI-Z state and the solder flux residual on the PCB was leaking some tiny amounts of current into the non-inverting input of this sensitive CMOS opamp (datasheet states that the input leakage current is 2fA!). Looks like MAX534 just made it into my shopping list for the next week... Thanks for your comments. I'll drop a line here when I have some more progress with the PA ALC. 73, Nikolay (LZ1NRD) ------------------------------------- Mail.bg: Безплатен e-mail адрес. Най-добрите характеристики на българския пазар - 20 GB пощенска кутия, 1 GB прикрепен файл, безплатен POP3, мобилна версия, SMS известяване и други. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
