Author Topic: Repair HP 3467A - Showing No Display  (Read 327 times)

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Online VK5RC

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Repair HP 3467A - Showing No Display
« on: December 09, 2018, 09:47:44 pm »
As a bit of an old HP gear fan, and the small boy in me likes moving parts - I bought an "As Is"  HP 3467A a 4 1/2 digit 4 channel recording DMM with Maths and Time stamping on the thermal paper printer.

On arrival - it had not clearly been used for some time - it worked for a minute until a command to print was requested - the printer moved a little then the display (LED) vanished . On repeat switch on - nothing. Checking DC PSU voltages for values and ripple were OK, the microprocessor clock was active and but the micro appeared to be rebooting every few seconds or so.

Manual Issues. An original manual took some months to find as the one on the Keysight website is borderline readable - I have scanned the Letter sized pages, but the schematics are beyond my scanning abilities - if you need a section let me know and I can send a copy and or photo.
The manual indicates the micro can reboot if it isn't happy with power voltages etc. They appeared OK but it all went pear shaped at the time of using the printer - so I looked there first.
Printer Unit  Access - to get to the printer you need to unclip the front plastic face - this is achieved form the top of the unit by pushing down carefully. the 3 lugs (see photo below) and then the face hinges forward. The printer unit is held in by 4 screws on the side, 2 power cables and a large signal harness.
This printer uses a small motor (metal cog in photo below) driving an intermediate cog (indicated below in photo) and this intermediate cog had perished and a large chunk had broken off, With quite a bit of care and luck I was able to make another from plastic stock I had, the completed unit below. Took me three goes to get it right mind you. (Mini lathe, rotary table and small mill) Cog 10.0mm diameter 30 teeth.

Rewinding the printing head unit back to its 'returned' position and a bit of dry lubrication was applied.  Replacing the unit initially resulted in the paper feed being a bit erratic, cleaning the 2 drive rollers with a bit of water then a very gentle sandpapering to get a bit of friction and all is working again!

Results below
« Last Edit: December 09, 2018, 09:50:15 pm by VK5RC »
Whoah! Watch where that landed we might need it later.
 
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Offline Floopy

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Re: Repair HP 3467A - Showing No Display
« Reply #1 on: December 10, 2018, 05:57:59 am »
Very nice, :-+ when I find physical manuals I always make sure that they have been scanned. Hp gear is always a pleasure to work with. At least the old gear. Easily servicable, clearly layed out.
-Floopy
 

Online VK5RC

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Re: Repair HP 3467A - Showing No Display
« Reply #2 on: December 10, 2018, 11:12:37 am »
Thanks, I enjoy these challenges - I know my limits :)
Whoah! Watch where that landed we might need it later.
 

Offline xrunner

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Re: Repair HP 3467A - Showing No Display
« Reply #3 on: December 10, 2018, 12:01:28 pm »
Very cool job. Must be nice to be able to make your own gears.  :-+
I am a Test Equipment Addict (TEA) - by virtue of this forum signature, I have now faced my addiction
 

Online VK5RC

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Re: Repair HP 3467A - Showing No Display
« Reply #4 on: December 10, 2018, 03:29:24 pm »
First time and in plastic! Was quite a steep learning curve, I had never heard of a gear's modulus before! Still a bit vague really.
I couldn't find any gear even close on eBay etc
Whoah! Watch where that landed we might need it later.
 


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