Thanks everyone. This has given me a lot of things to check as I further investigate over the next few evenings. I'll let you know what I find.
Chris > On Aug 5, 2017, at 3:07 PM, Charles Steinmetz <csteinm...@yandex.com> wrote: > > Arthur wrote: > >> I’d say it would be an MMIC amp similar to this device [Avago MGA-87563] > > If a chip similar to the Avago part Arthur referenced is what is installed, > which seems plausible, the 0.749v on the RF input (Pin 3) is a fault and is > caused by an external source of voltage (3.417v) imposed on the RF output > (Pin 6) through the internal feedback resistor to Pin 3, attenuated by the > gate resistor. > > Avago says this particular chip needs to have 0vDC at Pins 3 and 6, so if the > connected parts would impose any DC voltage on those pins, external blocking > capacitors must be used on Pins 3 and 6. You might check to see if there are > blocking caps (at least at Pin 6), and if they are good. (Alternatively, the > internal output capacitor from Pin 6 back to the output FET source may be > bad.) > > Of course, don't expect a bad external cap to be the only other problem -- if > it is bad, the 6-pin amp may well be bad, as well as whatever is connected to > the other side of the cap. > > Best regards, > > Charles > > > <Avago_MGA-87563_equiv_circ.png> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
