Hewlett Packard 3438A (Rev A) Mains voltage configuration - information request

[Alyk]

Hello All

I have recently purchased a used, tested HP 3438A multimeter via ebay from the US. At this point I would expect the AC configuration to  the 120VAC and I want to set it to the maximum voltage range for use in Australia.

I have found, downloaded and read the service manual for this model. The problem being - the manual shows a resistor configuration of two columns of placements where the revision 'A" board in the meter has only one column of configuration for the resistors.

Are their any users that have the correct resistor configuration for the higher voltages? either a picture or good description to enable me to reconfigure my unit.

Many thanks in advance - I am a new member to this forum.

Alyk

[coromonadalix]

Welcome here

You can easily find documentations and service manual to help you

this link will open a pdf,  see section 5-24  page 52

Its an old copy version  From Keysight   sorry

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiQ0q7J56TsAhXhRd8KHTykAe0QFjAAegQIBhAC&url=https%3A%2F%2Fwww.keysight.com%2Fmain%2Fredirector.jspx%3Faction%3Dref%26cname%3DEDITORIAL%26ckey%3D1908773%26lc%3Dkor%26cc%3DKR%26nfr%3D-33186.709732.00&usg=AOvVaw0pYT_--7AG991DVeCZ9P3c



EDIT  added an operation manual     "file attached"

[wn1fju]

In case you can't find a schematic/picture, you should be able to figure this out without them.  First, remove all of the jumper resistors.  There are typically two coils in the primary of the transformer, one with an additional tap.  You want both coils to be in series and you want to not use the tap.  Either follow the traces on the board from the transformer, or use an ohmmeter to verify that you have identified both coils and they have maximum resistance (the tap is bypassed).  Then simply add jumper wires to configure it that way.  You shouldn't need to actually use resistors.

Typically, one side of one of the primary coils goes directly to the line plug.  You typically need one jumper to connect the other side of that coil to one side of the second coil and a second jumper to connect the other side of the second coil back to the line (or fuse).

[Alyk]

Thank you 'coromonadalix' for the information, the two references I had found and read before asking for assistance, but it does go to confirm there is not much information on this device in the searchable wilds. Thanks again.

I have now power tested the meter and the transformer is quite hot to touch but the meter does not show any issues so far.

[Alyk]

Thank you 'wn1fju' for your suggestion, I did analyse the connections to the transformer and connected it so that the maximum length of the taped coil and the other coil are in phase and in series. So far so good, though the transformer does get quite warm to the touch. I do not know how warm these meters normally run at, it certainly is hotter than I had expected after being powered on for three hours.

At the moment I am awaiting some GPIB cables to do more testing. I will also test its DC acuracy against my Aliexpress voltage standard.

[Alyk]

In case you can't find a schematic/picture, you should be able to figure this out without them.  First, remove all of the jumper resistors.  There are typically two coils in the primary of the transformer, one with an additional tap.  You want both coils to be in series and you want to not use the tap.  Either follow the traces on the board from the transformer, or use an ohmmeter to verify that you have identified both coils and they have maximum resistance (the tap is bypassed).  Then simply add jumper wires to configure it that way.  You shouldn't need to actually use resistors.

Typically, one side of one of the primary coils goes directly to the line plug.  You typically need one jumper to connect the other side of that coil to one side of the second coil and a second jumper to connect the other side of the second coil back to the line (or fuse).

This was the action I did, and it was successful however the transformer and rear of the meter was extremely hot as I reported before.
Since then my GPIB cables and a HP 59401A Bus System Analyser arrived and I was able to perform further testing. What I found was the GPIB was not responding to any signals.

The cause of my new problems was found to be a bypass capacitor that developed the same characteristics as a short length of wire, ie. it when dead short across the supply rails for the GPIB interface and thus an overload for the voltage regulator and the transformer.  With the capacitor fixed the instrument works and is close to the same voltage as my other DMM meter. So I am quite happy I have two items working on the GPIB, and can now make the other items I have live correctly again.

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