Agilent 34401A repair method
MY customer claim that 34401A burn on testing .
He said that he has tested Vacuum amplifier plate voltage about 500V DC.
34401A has a low sound then no measure and bad smell.
Why do it easy broken ??
Any body know why do it occur ? |
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Black area is R122 disappear and no curcuit pattern .
One resister R122 was burned by High Voltage&Current.
Relay K104 was Three point contact.
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Input is left side. Front Panel HI is connect HI.
DCV is route to two input range DCV_LOW,DCV_HIGH by K103,104 .
Problem was made by K104(Lower relay) Pin9,11,13 3point contact.
High Voltage through R122 to ACGND.(Analog Circuit Ground)
For detail circuit Please Down load this photo. |
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Range DCV_LOW is protected R104-R111 13Kohm*7 total 104Kohms.
DCV_HIGH has 1/100 divider U102 9.9Mohm and 100Kohm.
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R122 is CHIP resister and Circuit pattern is burn up.
So R122 was set K103 Pin9 to K104 pin9 on Back plane .
K104 is replaced as OMRON G6AK-274P.
And remove black area by scrach because it change carbon . |
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DCV_LOW has about 200mV offset after repair .
It could not recovery by software calibration.
U101 Analog Switch IC will be broken by High Voltage .
I is 4.8mA (500V/103Kohm). I do not know absolute rate.
Agilent can't support this IC . Board replace only by JPY60,000 .
I got from China chip dealer. Thank you . |
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This is PLCC44 SOT187 made in Korea.
Fuction is Input Buffer Analog switch (DCV,ACV,OHM) & Current Source for OHM.
Removing is easy but setting is hard because no legs . |
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Self Test Again "PASS "
ReCalibration is needed on CAL menu. |
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