Electronics > Repair

HP 34401A Repair/ restoration

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scenz:

--- Quote from: factory on May 28, 2022, 09:01:28 pm ---Your list is missing the PCB shield plates, or whatever they are called.
Internal picture of mine below, same Rev as your early one, but s/n about 8000 later.

David

--- End quote ---

Hi David, I'm not missing the shield. For the first picture i just took it off. You can see the shielding in the third picture.


--- Quote from: Paceguy on May 29, 2022, 03:52:36 am ---My advise, for what it's worth: I would keep this unit as a parts donner unit and look out for another defective unit at a reasonable price that has all of it's parts and a good display and see if you can make one good one from the two. It will take time and money to find everything that's missing on this one and you are taking a chance to ever get it up and running. I suggest checking ebay seller Surplus2d to see if they have any scrap ones that they haven't listed. Emailing them is the best.

--- End quote ---

Nah, I'm having fun fixing this unit. We will see how far i will take this this. Everyone please remember I'm doing this for fun. It does not interest me much if I have payed 50€ or 100€ to much for such a unit at the end. If I need to measure something I have my Keithley 2700 at home and a alot of Keithley 2000s and Keysight 34461As at work.


--- Quote from: HighVoltage on May 28, 2022, 09:49:30 am ---I also have an older VFD, if you are interested.
Probably perfect to play around with.

--- End quote ---

Hi HighVoltage, all the parts have arrived today. Thank you very much. The VFD looks good enough for me. I will probaly stick with it  :-+.

I will now begin to check the unit and check if the self test will past. I assume it will probably not  ;)

HighVoltage:

--- Quote from: scenz on June 01, 2022, 01:07:50 pm ---
Hi HighVoltage, all the parts have arrived today. Thank you very much. The VFD looks good enough for me. I will probaly stick with it  :-+.

I will now begin to check the unit and check if the self test will past. I assume it will probably not  ;)

--- End quote ---

Wow, that was a fast delivery and you installed the VFD already.
Looks nice !

It seems you have fun.
Enjoy the ride.

scenz:
Now that i have a better ribbon cable for the LCD and had the time to solder everthing together i was able to test the unit a bit more.

The basic funcionality of the unit is available but the DC voltage measurement does not work at the moment and the culprit is also already found!

The resistor R104 is/was cracked so that the unit was working while i put pressure on it. I have now ordered a replacement 13k resistor in 2512 package. Ordered some more than i need to match it to the other resistors used.

This could also be a reason why the unit was giving me sometimes the error codes 612, 613, 615, 617, 618, 619 and sometimes not when i used pressure on R104.

But to be also on the safe side i have also ordered U153 as these also can break and cause these errors.

Once the resistors arrive I will post if now everthing works.

strawberry:
K103, K104, current source, : selftest measure 10M

scenz:
Have now replaced the R104 resistor and the self test passes :). Now I need to contact Keysight to get a new cover, frontpanel and button panel. I probably need to print myself a new rear/front switch as the old one will probably not fit with the new panel.

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