Successfully repaired high-pressure differential probe

[pzil]

Hi guys

       I bought a bad high voltage differential probe?Yesterday I decided to repair it?I spent half  day, found the fault?

[HighVoltage]

So, what was the fault?

[Armadillo]

This is a poor copy of the original.
The high voltage input section should be segregated from the differential input section. 
It don't even have isolation slots cut into the board.

But good repair from you, though.
Appreciate your sharing but it would be best for you to also relate the faults and the repair, yeah.
 

[pzil]

This is Yokogawa's product ?But when I teardown it?I was surprised that it is OEM products made in Taiwan?Now let's talk about what is wrong with this product:When the power switch is turned on, the power LED and overrange LED are ON?So I measured the output (BNC) voltage value?voltage value is only 0.018V ?I suspect there may be a problem with the circuit's power supply?I continue to teardown?I found the power supply is a DC / DC circuit, and there is a transformer?I guess the circuit structure (but I can not know the circuit Schematic )?

[pzil]

DC / DC circuit works?Transformer input should be PWM?I use an oscilloscope to measure the circuit here?It is found that it is a 0V DC signal level?So I continue to measure the IC's output signal, which is also a 0V DC level?I suspect IC is bad?But I did not  teardown IC ?Because I think the IC connected circuit may be bad?So I measure the transistor connected to the transformer?Found that the resistance between the transistor B C is 96 ohms?I suspect the problem is here?So I changed the transistor?After turn on the power again?Measuring transformer input circuit?
It is a beautiful PWM signal?overrange Led does not work