Electronics > Repair

Dead LeCroy 9414

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You may have to draw out the area around the switcher to gain some understanding.
Often in the cheap SMPS's a 10-22 uF E-cap is between the VDD pin and GND and sometimes the supply for it comes from a high value resistor from rectified main for startup, then a "running" supply comes from a feedback winding. Normally a diode in series from the feedback winding.
Others rely on the feedback winding and the voltage feedback loop to "kick" off.

Grab a few datasheets for switcher IC's and look at various applications for clues to the LeCroy switcher operation.

Well my guess was a capacitor with decreased value....reminded me when in good old times I repaired a Panasonic VCR with couldn't be switched on....the owner told me I could keep it if I could repair it...as the TV shop wasn't capable off....turned out to be a bad capacitor lost his value over time...which was responsible to filter peaks of detected load current for the overcurrent protection.

Anyway....biggest problem is now to get hands on a transformator to galvanically isolate it from main line to hook up a DSO...
Just have a big one here...when powering on the whole basement gets dark (o;

Another problem is that the schematic in the service manual is barely readable....


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