Products > Test Equipment

Rigol DS2072 vertical problem

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battlecoder:

--- Quote from: tautech on November 12, 2023, 04:16:31 am ---Don't discount someone hasn't hurt both inputs = oh that doesn't look right, let's look at it on the other channel = both channels zapped.  :bullshit:

--- End quote ---
That's...true  :-\ Hopefully it's not the case. I'm at my lab now and will see if I can find faulty caps or suspicious voltages. With nothing to compare against it will be hard, but since the other thread contains the part numbers for several components I can at least check if the voltages make sense.

As much as I love tech equipment I've mostly repaired old stuff (for which schematics are available) and simple supply issues (where the device isn't even powering ON, and the supply is not delivering power), so this kind of issue is a first for me. Will take me a while to fix it, IF I'm ever able to.

battlecoder:
Alright, so I couldn't check much today because it's suddenly very late, but I checked some voltage regulators right outside the CH1/CH2 "cans", next to Rigol's branded chip (FPGA? custom IC?), and they were reading 3.26V instead of 3.3V. A similar voltage regulator in a different area of the board was reading 3.3V spot on, so I'm not sure if this is an actual problem or if that's within reasonable accuracy.

Anyway, I did manage to find two test points on the board (right outside the cans, near the corner of the scope) where the vertical offset of the traces on screen manifest as a voltage:


With the trace at the center of the screen my multimeter was reading approximately -635mV, with the trace at the bottom -550mV, and with the trace at the top around -750mV. All "negative" (relative to global GND, but maybe I should test against the VGND_1 pin that's in the corner). I'm not an expert but I would have expected a swing that has 0V at either extreme or at the center. Not sure if this is where the problem lies, but this area is where I'll probably be poking around a bit more tomorrow.

EDIT: Additionally, the testpoint labeled "OS_2.5V" does indeed read 2.5V on my multimeter.

battlecoder:
I know this is a bit of a long shot, but anyone here owns this oscilloscope and is willing to give me some reference values for the test points?

OR, alternative, is there a chance that this is just a matter of some missing calibration values and it's just software and not hardware?

TurboTom:
The OS_CH1 and OS_CH2 are the offset (bias) voltages for the two channels. The circuitry is a smaple-hold with a single channel 16 bit DAC (Texas DAC8560) and an analog multiplexer (HC4051) to distribute analog signals to several hold circuits consisting of the two quad CMOS OPAMPs TLC274 and the RC "chickenfood" around. This provides all the analog control voltages that are required in different places in the trigger / analog input circuitry.

I've still got an MSO 2000A that's currently not in use --  I can take some measurements if you like, but the festive season will still keep me busy for a few days, so if you're not in a hurry, I'll be prepared to tear mine down to do some comparisons...

battlecoder:
I would really appreciate that. Thanks for the insights on the overall circuit structure btw, I'd be a pity to throw this scope away or sell it "for repairs", when the issue could be (potentially) easy to repair. Everything else works fine so it could be just a bad voltage reference (fingers crossed).

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