« Reply #11 on: October 20, 2016, 07:56:42 pm »
Time for an update on my 3457 repair.
I looked over the forum for information on this multimeter and a forum member whose posts came up quite often was cncjerry. I decided to try a PM to the member to see if he had any insights.
Fortunately he was more than willing to look over my shoulder, so to speak, which gave me the confidence to dig right in to this repair.
I got down to the A2 board much easier than anticipated and started measuring and comparing voltages that cncjerry suggested.
Johnny10, Get the schematic page 8-77/78 and check the voltages on the input hybrid. There are a number of them called out:
From Schematic My Measurements
Pin 4 10V 10.19
Pin 8 8V/5.6V 3.16
Pin 21 12V/8.4V -0.430
Pin 17 8.4V 0
Pin 18 8.4V 1.905
Pin 31 +5 5.05
Pin 22 -15 -15.04
My measurements were being brought down by something in that constant current circuit.
I then went back to schematic on Pg 8/69-8-70
it shows:
U212 Pin 7 Should be +15v I have -0.359 .
I did have correct supply voltages on U211
+15, -15.
U213 correct supply voltage.
I seemed to have proper voltages at other locations except around U212 and Q211
I unsoldered the U212 chip.
and got 5.6V on Pin 8. Good sign!
I then did a trick that Ronald over at Dos4ever taught me .
Threw in a 741 OPamp to see if I could get something on Ohms range.
Everything worked!
Ohms function began displaying for the first time.
I still get errors :Hardware Error: 1 Calibration error.
Ohms measures 20% low but I decided before I calibrate unit I will order and replace the proper 1826-1381 chip.
Will keep you informed of progress once proper U212 chip is installed.
cncjerry was most gracious and helpful and gave me the confidence to tackle this repair. Thank you Jerry! A truly great forum member.
« Last Edit: October 20, 2016, 10:48:22 pm by Johnny10 »
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