DSO4254B channel 2 Damaged?!?

Rob_ITA

I see on p3 differences between channels, does it mean something?

CH1 0,6 Pk-Pk
CH2 1,48 Pk-Pk
CH3 1,36 Pk-Pk
CH4 1,98 Pk-Pk

Rob_ITA

I've discovered this interesting behaviour.
I've set 500mV/div and 5Vpp/1kHz in all 4 channel. All 4 probe are x1.
If I test p7 on channel 1 and p7 on channel 2 I see a difference (violet waveform = ch yellow 1 - ch blue 2) in amplitude.
If I test p7 on channel 1 and p7 on channel 3 there's no difference (violet waveform is flat).
Also no difference in amplitude between p7 on channel 3 and p7 on channel 4.

The same behaviour when I test p8 between channels.

Could be the IC [U203] below p7 and p8?

Rob_ITA

When performing the calibration I notice that for each channel a line is positioned in the center, top and bottom of the screen for each volt/div in testing.

The blue line [channel 2] always reaches the others with difficulty and after a certain number of attempts it goes into error. I always get different errors depending on the vol / div it is calibrating. If I connect to the serial interface, can I get other useful information?

Rob_ITA

Waiting for your answer, I inverted U203 between ch2 and ch3.  The problem remained on ch2.  I'll try to see the resistance values.  I later tried to do a reset and at the end I can only choose between French and German.  Could you tell me how to make English appear again?

Rob_ITA

Reset = recover system with f2 after a failure startup

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?

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

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?