Hello Tek experts:
Recently I bought a Tek SG5010 oscillator from eBay. The seller claimed it worked normally. Yesterday I checked its functionality against an AA5001 distortion analyzer.
It's wave form looked O.K., distortion figure was at 0.0056% @ 4.088kHz, 514mV; no filter. With 400Hz HI pass, audio band pass filter in, THD+N was down to 0.0021%.
When I plugged its output to a DC5009 frequency counter, their readings were not agree with each other. Then I realized the PLL LED was lit, indicating oscillator was not phase locked!
Carefully tune the frequency dial, it appeared to phase locked only to bands of frequencies:
The following were frequency range this SG5010 would not phase locked
...........1.638-1.890kHz, 2.063-3.760kHz, 4.112-5.542kHz, 6.160-7.143kHz, 7.184-7.423kHz, 8.208-9.025kHz, 10.288-10.304kHz, 10.320-10.368kHz, 10.384-10.498kHz .......
Among them certain sharp peaks, e.g. 8.459kHz, 8.709kHz, could be phase locked. When PLL red LED on SG5010 did not light, it's frequency agreed with that from DC5009.
THD+N figure was at similar range, either the oscillator was phase locked or not.
I did not have the service manual for SG5010. Any one experienced the same symptom for signal oscillator in general? Why there were bands of frequencies which can e phase locked? Is this problem digital in nature?
Thank you in advanced.
Yeun-Jung Wu
