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[SOLVED!!] DSO4072C Both channels BAD.

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Post time 2018-7-11 19:10:23 | Show all posts |Read mode
Edited by X-Blade at 2018-8-26 06:24

Hello.

I bought an hantek DSO4072C from a seller from ebay.
It was working good but after few days both channels went bad.
Seller dont answer my  messages and left me alone with the scope.

When I press Autoset button both channels turn on with a lot of noise, specially the CH2.

I can solder and replace components, just tell me what to replace and part numbers, if you can.
Can anybody help me, please?

Thank you.


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Post time 2018-7-13 08:08:31 | Show all posts
Hello  you can try this :Remove the probe    Press Utility button----Self Calibration---Confirm  then wait for a monent,  Restart  the machine. Good luck for you.

Sorry for my bad English

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 Author| Post time 2018-7-14 05:35:10 | Show all posts
Thank you for your help Newbee.
Unfortunately I tried it but if hangs on 13/38 forever.
I will try to send it to somebody who represents Hantek.
This cheap chineese oscilloscopes are more a toy than a tool.
My hitachi V212 analog one resists to ervery abuse I subject it.

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Post time 2018-7-19 09:07:24 | Show all posts
X-Blade replied at 2018-7-14 05:35
Thank you for your help Newbee.
Unfortunately I tried it but if hangs on 13/38 forever.
I will try t ...

Sir, in your picture, did you input any signal to the channel?

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 Author| Post time 2018-7-20 05:16:52 | Show all posts
Hello amy.
Yes is connected to the internal 1khz output on the panel.
It acts like there is no ground connected.
Very strange.
It started to do this after i was measuring an inductor SRF  without caution or some problem related to the common ground.

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 Author| Post time 2018-8-1 02:45:33 | Show all posts
Edited by X-Blade at 2018-8-1 03:12

Hello friends.
Thank you for all your support.
I was searching another forum and I found the schematic (not official / Reverse-engineered) of the both Channel inputs:



In another thread I saw someone reporting a similar problem , so I replaced all the 5 sot-23 components of each channel:


BAV99 (marked A7), MMBTH10 (marked 3EM), MMBF4393 (Marked 6G) and the 2 x BC846B (marked 1B)

Now both channels are working but still not working correctly but exactly in the same way:
I connected the probe to the front calibration output (5v @ 1KHZ), probe at 1X and channel with 1x setting:


Looks good and accurate, but when I try to change the vertical position the amplitude of the waveform decreases and signal get distorted:


Interesting thing: I AM NOT ABLE TO BRING THE WAVEFORM BELOW THE  CENTER HORIZONTAL LINE FROM THE GRID BUT ABOVE IT MOVES CORRECTLY, expept the variation on the amplitude.
Both channels behave the same.
I have another oscilloscope (analog) I can perform some measurements.
Any suggestion?

Thank you all.




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 Author| Post time 2018-8-2 01:18:30 | Show all posts
Hello people.

I found that -5V rail from 79M05 is putting out -7,4V (-5V Testpoint) . It looks like the regulator is gone, I will try to get a new one, replace and retest.
Cheers.

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 Author| Post time 2018-8-26 06:23:07 | Show all posts
FINALLY it was solved.

Everyone can check my steps on
https://www.eevblog.com/forum/re ... -both-channels-bad/

Thank you.
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