The HP A is capable of making highly accurate measurements. In order to .. you should use manual range to get to the lowest range possible for the. Hp A Pdf User Manuals. View online or download Hp A User Manual. View and Download HP A user manual online. A Multimeter pdf manual download.
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Following recent trend with Hewlett-Packard equipment repair, welcome new article for more popular bench DMM repair worklog. In this article initial diagnostics, repair attempt and calibration will be covered. Redistribution and use of this article or any images or files referenced in it, in source and binary forms, with or without modification, are permitted provided that the following conditions are met:.
All information posted here is hosted just for education purposes and provided AS IS. In no event shall the author, xDevs.
Keysight A Digital Multimeter — Datasheet. Agilent A Multimeter — Product overview. HP A front and rear. DMM is very dirty outside, and definitely need good deal of scrubbing with alcohol and cleaning. Meter does power on, VFD screen lit up and keypad working normally. HP A after cover removed. That is likely due to absence of fan or vent holes anywhere in the chassis.
Removed front panel, to get easier access to mainboard. HP A front panel removed, front and rear.
Front panel board REV. HP A mainboard, top and bottom side photographs. All the magic and active parts are located on single mainboard. Banana input terminal jacks are custom-made parts, with big solid copper tube sockets bent and soldered directly to motherboard. This is one of best connections, and look really clean. These are often a problem on old instruments, if contacts got contamination and unable to maintain low resistance connections.
Not this time though, no problems detected with a switch, probed input 1. LM is socketed, just like more recent xA instruments. Some of hobbyists were even upgrading reference to LTZ circuit for better A stability.
HP A power supplies. Removed remnants, cleaned and repaired PCB using copper foil and installed fresh capacitor of same size and spec. This means all electrolytic capacitors must be replaced, no questions asked. I had some left from other repairs, so you can see already new caps on photo above. Now thinking about possible cause and overvoltage on this rail, I checked 3.
And yes, some were dead short, and some were missing, likely due previous owner repair attempts. I did not have SOT packaged type, so used leaded ones instead. No function impact anyway.
HP A local 15V zener regulator. Cause for this was again bad tantalum capacitors, C, C, C, C Replacement of bad tantalums with new ones 22uF 25VDC specification, D-size package fixed local voltage supplies.
HP A more zener regulators and capacitors. Now all voltages are fine, but meter still not working, with exactly same test results, wrong DCV readings and failure on any other function. There were some cases of input protection resistors in size failure on A, but check revealed no problem with input circuitry as well. Overall signal path is rather simple to read on board, even without reference to service manual or schematics. Layout is tidy and nicely done for this instrument, thumbs up to HP engineers.
Switching to different gains and DCV ranges had input adjusted properly. HP A current source for resistance function test. All currents were stable and spot on expected values.
HP A resistor network U and references test. As you may already guess, all resistances were fine. U ASIC resistor network measurement results. U multiplexer 74HC was replaced as well, but issue was same.
Since board does not have RefDes markings around parts, I did highlights on photo to summarize on changed parts during debug and test:. HP A Replaced components locations. Shift registers on AC circuitry and few other opamps were replaced as well, but that was actually unnecessary.
HP A Firmware revision 1. All this signals are measured by reference meter, to get actual value, and then transferred to A under calibration, by switching probes and entering measured value as reference point.
After calibration, values are compared to Keithley meter to ensure they agree on readings.
HP 34401A Manuals
Calibration was referenced hl34401a measurement results of my Keithley which was calibrated in February by Tektronix, and is most accurate meter I currently have up to date.
Few photos of calibration steps for better understanding. First step — zero calibration with 4W short. HP A Zero calibration with 4W short. Bad parts from meter.
File:HP 34401A User Manual.pdf
Total man-hours spent on this project around 8 hoursgive manal take few. Especially considering, that I never had A before. Credits to EEVB log member sonicyang which own this meter, for making this repair article possible. Hope we can see more stuff later this year!
| HP A repair and calibration worklog
If you like the article or have any questions, jump in comments! All feedback is valued at xDevs. Disclaimer Redistribution and use of this article mankal any images or files referenced in it, in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Repair workflow Image 4: As usual, every repair should start from local power supply diagnostics and debug.
Since board does not have RefDes markings around parts, I did highlights on photo to summarize on changed parts during debug and test: Calibration was referenced to measurement results of my Keithley which was calibrated in February by Tektronix, and is most accurate meter I currently have up to date Few photos of calibration hp34401a for better understanding. First step — zero calibration with 4W short Image Final test with 10VDC: Time worklog summary Image July 19,6: HP a, what to worry about when buying used?
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