Hi all, thanks for all the suggestions. I am starting to think this is a feature not a bug. I tinkered with the FS710 a bit today. It shows about 600mVpp 100Hz sawtooth on the +/-13.9VDC input to the voltage regulators. I changed the big electrolytic caps and the smaller tantalum caps around the 7805/7905 regulators - but no change to the sawtooth. With a 1M 10x probe and a cheap scope there is no visible 100Hz ripple on the +/-5V regulator outputs. some new pictures in my blog: http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/
Maybe my earlier result with strong spurs was a result of a ground loop between REF-distribution-amp, 3120A, and this F710-distribution amp. They were probably plugged in to different AC outlets... Anders On Thu, Oct 1, 2015 at 1:52 PM, Bob Camp <[email protected]> wrote: > Hi > > It can also be a blown diode in the bridge. When that happens the ripple > goes > way up. A quick check with a scope should tell you what’s happened. 50 Hz > triangle > wave = blown diode. 100 Hz triangle wave = blown cap. > > Bob > > > On Oct 1, 2015, at 4:04 AM, Esa Heikkinen <[email protected]> wrote: > > > > Anders Wallin kirjoitti: > > > >> I seem to get very strong spurs at 50Hz and harmonics with an old > >> second-hand SRS FS710: > >> http://www.anderswallin.net/2015/09/srs-fs710-noise-measurement/ > >> feature or bug? Anyone looked at the powersupply and figured out what > parts > >> to change? > > > > If you live in a country with 50 Hz mains network then this sounds like > a dead capacitor in the power supply. Usually this means that it has old > fashioned linear power supply (with classic iron transformer). In that > case, replace the secondary capacitors after the rectifier bridge(s). Check > voltages with oscilloscope if you wanna see which ones, but it might be > good idea to replace them all (there should't be many of them). > > > > Should be very easy to fix. > > > > -- > > 73s! > > Esa > > OH4KJU > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
