DSO4254B channel 2 Damaged?!?

amy

Customer Consultation

Hi, I bought the DSO4254B and I think there is a problem with channel 2.
When I press the AutoScale button it gives me an incorrect value (about 100V). On the other channels it works correctly.
Product purchased on November 29, 2020 from aliExpress.

amy

Reply

Do you swap probes to test ch1 and CH2? Does the oscilloscope still show CH2 abnormality?

Please warm up for half an hour and perform self calibration. Do not connect any test line or probe during self calibration. Then test again.

amy

Judging from the problem, it should be a hardware failure. Let's do some hardware tests. If you can solder, please follow these steps.

1. Open all channels, switch the volt/div between 200mV and 500mV, and check whether there is relay sound.
2. Input 1kHz/10Vpp square to four channels at the same time, their voltdiv is set to 100mV, their probe ratio is consistent. Compare and test the waveforms of several points marked in the figure below.


If you can't weld, please contact the seller for repair.

amy

Please set the volt/div of the four chanels to 500mV, and compare and test the waveforms of 8 points.

amy

Please remove these resistors in CH2 area and test their resistance value.

If the resistance values are OK, then can probably judge that U203 is broken.

The model of U203 is LMH6552SD/NOPB.

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.

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.

amy

Please heat the scope for 30 minutes, then short circuit the signal terminal of CH2 to the ground (connect the core of BNC to the metal ring, like the picture), and then perform the calibration. Is it possible to pass the calibration?

amy

Please setting the four channels to 500mV/div, and use a scope to view the voltage curve of these four points CH1/CH2/CH3/CH4 on above picture. Is the voltage at CH2 changing?

In addition, without inputting any signal, check whether the line can be seen in all volt/div of CH2, or whether the line can be seen when move CH2 up and down.

amy

That's great. You're awesome. we didn't help much.