Products > Test Equipment
[SOLVED]HP/AGILENT/KEYSIGHT 34401A 2W Ohm Problem
coldframe:
Problem has been solved
This is a complicated problem, Quick summary about it
First : Front/Rear Select Push Switch mechanical Falut (ie, oxydized contacts..)
Pic 1. New Part (C&K Components Silver Plate Push Switch)
Alternate Part# 51902 (F8UEE)
http://www.mouser.com/ProductDetail/CK-Components/51902-F8UEE/?qs=%2fha2pyFadujTidtN1Llg9KzbODfiX9eD%252bMABDo%2f5rXk%3d
Agilent Part# 3101-3162
http://www.home.agilent.com/myagilent/faces/partDetail.jspx?partNumber=3101-3162&imageStatus=YES&_afrLoop=688445535652000&_afrWindowMode=0&_afrWindowId=null#%40%3F_afrWindowId%3Dnull%26_afrLoop%3D688445535652000%26imageStatus%3DYES%26partNumber%3D3101-3162%26_afrWindowMode%3D0%26_adf.ctrl-state%3D1220ztkopw_13
--- Quote from: Dr. Frank on February 24, 2014, 08:08:47 am ---If nothing helps, order a spare switch from agilent.
PS: The "old" HP 34401A are still good, but switches are always a problem.
--- End quote ---
Second : H/L Sense Seriese Resistor Fault
Pic 2. I can't see the problem with the naked eye
Pic 3. Desolder them and Check one by one(3 defect of the 12 resistors, 25 percent :palm:)
Pic 4. Soldered the circuit boards (72Kohm Seriese resistor temporarily)
Test : Function : 2W, Resolution : 6 Digit Slow Mode, Hi/Lo Shot and NULL function
Pic 5. Benchvue
Pic 6. Multimeter
CRCW251224K0JNEG 24K 1W 2512 Chip Resistor
http://www.mouser.com/Search/Refine.aspx?Keyword=CRCW251224K0JNEG
Agilent Part# 0699-3406
http://www.home.agilent.com/myagilent/faces/partDetail.jspx?partNumber=0699-3406&imageStatus=YES&_afrLoop=52685776462000&_afrWindowMode=0&_afrWindowId=2irg93od1_19#%40%3F_afrWindowId%3D2irg93od1_19%26_afrLoop%3D52685776462000%26imageStatus%3DYES%26partNumber%3D0699-3406%26_afrWindowMode%3D0%26_adf.ctrl-state%3D2irg93od1_31
--- Quote from: free_electron on January 24, 2014, 06:52:18 pm ---another thing to check while you got the machine open is the big 2512 resistors close to the big switch. i have seen those develop cracks on the electrodes. simply resolder them.
--- End quote ---
After many complications the matter was settled But,
At the moment still has corroded solder joint problem but expected that
To Do.
Find Potential Problems in PCB(ie, Corroded solder joint, Cracked Joint, Pad Contamination..)
Ordering new parts
Calibration
Thank you again to Dr. Frank, free_electron for a work knowledge :-+, and everyone who helped me out on this forum.
coldframe
razberik:
Hello. I am writing to contribute to repair logs of 34401A.
I received cheap, broken 34401A with missing mains switch push rod, that plastic part holding front terminal in place and rear plastic frame.
1. problem - not booting
Multimeter was not starting properly. When switched on, it illuminated all display segments, then two beeps and then nothing. Shift was working.
Exact behaviour like this:
Turned out to be bad connection between front panel and mainboard. Here is what I found. Broken connector. Somebody torn off that plastic part holding ribbon cable in place. Temporary fixed with wires extension. Not very clean solution, but it works until I receive proper replacement.
After this repair, multimeter starts properly.
2. problem - measuring wrong numbers on some ranges
After ribbon cable fix, multimeter was showing something, but nonsense numbers. When switched to 100V, 1000V range, everything works. All DC amperes OK. 4W Ohms OK. Random errors from selftests.
Then I realized that 2W sometimes work innacurately, sometimes dont work at all.
So I started to trace the signal path when some little voltage applied to input. And then it suddenly started to work.
Turn out to be bad connection on R104 2512 13K resistor. When I was touching that place, results were changing randomly. Resolved by applying flux and reflowing solder joints on R104.
Therefore I am confirming this:
--- Quote from: free_electron on January 24, 2014, 06:52:18 pm ---another thing to check while you got the machine open is the big 2512 resistors close to the big switch. i have seen those develop cracks on the electrodes. simply resolder them.
--- End quote ---
and indirectly this (from this thread):
--- Quote from: zucca on May 15, 2014, 04:10:29 am ---I then started to follow the sense tracks and, hello 24K resistors... why when I press you the sense line goes from open circuit back to good?
So I reflowed all those six 24K bastards. Actually it looks like three of them had a bad joint (they were invisible to me, I could spot nothing with my naked eyes).
--- End quote ---
After repair, multimeter passes all tests and seems to be working properly. Compared to another two 34401As.
I hope it might help somebody.
Now I should sketch up missing plastic parts for 3D printer. We will see... :)
bitseeker:
Nice hunting to a successful repair. Having 3D models for replacement plastic parts would be great as more and more of them become unavailable from Keysight's parts inventory.
coldframe:
hello razberik,
I congratulate you on your success :-+
I'm sure great help to someone.
coldframe.
HighVoltage:
Nice repair and good price!
I had a broken 2512 resistor before as well and it is an easy fix.
This seems to happen more often than expected.
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