Is joule thief circuit gets overunity?

[hoptoad]

snip...
I can currently only go 5MHz with 16bit resolution, above that, I have to go analog.
PW

May Anna Log never die ! .... KneeDeep

[poynt99]

@poynt99,

For Board 80, 0.38V just managed to turn the LED ON - dimly and flickering.

I shorted the Probes on CH1 and CH2 and the screen pictures are attached.  Ch2 turned out to be the more quiet channel.

There is something wrong with that noisy channel Lawrence. There shouldn't be such a large difference in noise between the two. I'd suggest you get those probes checked out, and if they are OK, then the scope.

[ltseung888]

There is something wrong with that noisy channel Lawrence. There shouldn't be such a large difference in noise between the two. I'd suggest you get those probes checked out, and if they are OK, then the scope.

@poynt99,

Thank you for your suggestion.  Mr. Zhou is an ATTEN DSO retailer.  I shall get him to check all my ATTENs sometime next week.  I shall ask him to focus on the "DC Offset" puzzle.

I just came back from the Tektronics Dealer in Hong Kong.  He said that there is sudder interest in the high end 4-CH versions.  At least one customer has placed an order.  He does not have these high end versions in stock.  Seeds turning into ......

[TinselKoala]

A rather obvious test would be to swap the probes between channels. If the noise follows the probe to the other channel, then you know the probe is bad. If it doesn't, then you know the scope's noisy channel is bad.

Yet again I ask. How was the large voltage discrepancy noted during the probe compensation discussion resolved? What caused it, how did you correct it, and can we be assured somehow that it is in fact now corrected?

[TinselKoala]

Is there some reason why the DC offset issue can't be tested right now, at home, using a known low-voltage source?

For a first test, take a 10 megohm resistor and a 100K resistor and connect them in series. Hook both scope probes from one oscilloscope to the junction of the two resistors. Hook up a AA battery,  positive pole to the 10 meg free end and negative pole to the 100K free end. All probe references to the negative pole. Use an accurate DMM to measure the voltage between the junction of the resistors and the negative pole.

Now look at the voltages seen by each probe/channel combination. Obviously they should all be the same, and the same as the DMM measures. If there is an offset problem it should show up as a difference in the readings of the channel vs. the DMM. Mark your probes and swap them around on the scopes and channels..... 4 probes and 2 channels per scope means 12 tests per scope.  This might actually take you half-an-hour to perform the whole series.

(Check all probes are at 10x attenuation and that all channels are also set for 10x attenuation probes. Do not use the "default setup" or "auto" functions of the scope; set each channel for DC coupling, no BW limit, zero baseline on the center graticule (overlap both traces so that you can see any differences) and the appropriate vertical amp setting (20 mV/div if possible). The timebase setting shouldn't matter since you are measuring DC here. Set the trigger at the zero baseline.)