DSO4254B channel 2 Damaged?!?

Rob_ITA

I measured the resistance values and they are correct.

Since in point 3 of channel 2 (AD8510 U201 output) the waveform is not stable compared to the other channels I could try to invert it with channel 3. If the problem moves to channel 3 then I have found the faulty component. You say it could be a valid test?

amy

Rob_ITA replied at 2021-1-12 04:48
I measured the resistance values and they are correct.

Since in point 3 of channel 2 (AD8510 U201  ...

Yes. It can be tested like this.

It is suggested to exchange 8370 of the two channels to try first.

Rob_ITA

I did another 2 tests.

I first inverted between channel 2 and 3 AD8510 and the waveform remained unstable on channel 2. Then I inverted between channel 2 and 3 AD8370 and the unstable waveform is always on channel 2.
I can try to swap the 3 transistors (marked 3EM) between channels 2 and 3 to see if anything changes.
They all look the same and could they be MMBTH10?

Rob_ITA

I swapped the 3 transistors but nothing has changed (between ch2 and ch3).
I reversed the 2 mosfets (w6g) and nothing has changed (between ch2 and ch3).
Every time I do the calibration the blue line (channel 2) has difficulty in reaching the others and goes into error. What else could I reverse? The switching diode marked A7?

Rob_ITA

Can I verify anything in this area?

This should be the offsets for the 4 channels (pin2 of the AD8510s of each channel).
With a 5Vpp / 1Khz input signal on ch1, ch2, ch3 and ch4 and setting 500mV / div here I measure with a DC voltmeter:

Ch1: -2.37V
Ch2: -2.29V
Ch3: -2.37V
Ch4: -2.37V

amy

Rob_ITA replied at 2021-1-16 00:49
Can I verify anything in this area?

This should be the offsets for the 4 channels (pin2 of the AD8 ...

Please do not input any signal to the four channels, and put the four channels in the middle of the vertical direction.And then test the voltage of the four points marked in your diagram and the corresponding points of the four channels marked in my diagram.

Rob_ITA

No input signal (probes disconnected).

500mV/div and GND symbol in the middle of the screen for all 4 channels.

md = my Diagram
yd = your Diagram

ch1 -2,37v(md) , -2,37v(yd)
ch2 -2,29v(md) , -2,29v(yd)
ch3 -2,36v(md) , -2,36v(yd)
ch4 -2,36v(md) , -2,36v(yd)

Did you think there was some signal loss in the tracks?

Rob_ITA

I was thinking of something. If I remove this resistor can I isolate the AD8510 pin2 input?
If yes, I could do this for all 4 channels I could isolate the 4 points of my diagram.
If there is still voltage difference there then the anomaly could be in the area of my diagram.

Rob_ITA

disconnected the "cuttingResistor" for ch2 and ch3.
Same values as post #27.
I think that the problem is the area of my diagram.

On hex Inverter U33(?!?) :
I=input, O=output

p1 2,39v I
p2 1,41v O -->ch2
p3 2,35v I
p4 1,46v O -->ch1
p5 0,94v I
p6 4,97v O
p7 gnd
p8 0v O
p9 4,97v I
p10 1,46v O -->ch3
p11 2,35v I
p12 1,45v O -->ch4
p13 2,36v I
p14 4,97v (vcc)

Rob_ITA

I've reconnected the 2 resistor.
This is the serial output from some calibration (ended with errors).
(Remove zip extension and open with notepad.)