开云体育

I recently acquired a second TDS-380 that was "working" - meaning with an signal at the output it displayed a trace on the screen. But the 'scope displays an offset with no input signal. With no input to either channel, Channel 1 measures a mean voltage of about -1.95 volts on the 2 volt scale, and Channel 2 a mean voltage of about -2.55 volts on the 2 volt scale. These measurements vary with the vertical scale setting.

I ran through the calibration procedure, and then measured the 5 volt calibration signal. For sweep rates of 25 uSec per division and slower (not fit to screen mode) the amplitude measures about 5 volts. When I increase the sweep speed to 10 uSec per division the displayed waveform and measured amplitude almost doubles.

I have replaced U402, the acquisition RAM, as that has been found a problem elsewhere, including my other TDS-380 which had similar problems that were corrected by replacing that RAM. No change for this 'scope.

I have the manual with schematics and layouts, but there is no circuit description in the manual. Is there a circuit description available somewhere? This would certainly be helpful in trying to isolate the problem to a block. on the Root Sheet - block diagram.

I don't believe there are any surface mount electrolytics on the mainboard. On the other hand, I have software to communicate with the 'scope over the RS232 port, and discovered eleven open traces on that board that required jumpers before the computer would communicate with the 'scope.

Any assistance will be appreciated.

Gary Appel

After studying the limited circuit description in the manual and the schematics, I think I have a basic understanding how how the Sampler works.

With a constant square wave into channel 1 I have observed the data out of the Sampler in both the fast, and the slow acquisition modes. It appears that I have a vertical problem occurring in the fast mode. The amplitude and offset of the data is very different in the two modes, with the amplitude greater (and too large) in the fast mode, which is also what I am seeing on the screen at sweep rates of 10 uSec / division and greater. After calibration the amplitude in the slow acquisition mode is accurate, although there is still an offset from zero. I have verified that the input signal to the Sampler is not changing between modes.

Unfortunately I don't know enough about the Sampler to determine whether the sampler is bad, or if there is some other problem. It does not appear to me that there is any offset or gain inputs to the Sampler. I don't know what the four bit address bus, and four bit data bus are for.

Does anyone have enough experience with the sampler in the TDS 380 to know if something external can be changing the gain and offset, or has the Sampler failed?

Thanks,

Gary Appel