HP 3488A

This will be a long association chain. Just follow!
It is started with a picture on facebook about a Kenwood analog two channel AC voltmeter. It can be nicely used to check stereo audio equipment channel differences. I love the concept, but still I'm not an analog meter guy.
I was thinking. What if I pickup one of my digital bench meters and develop some desktop software around my own (still in development) GP-IB USB adapter, and add an uncontrolled MCU based channel switch. Uhh, this sound ugly, in addition, this is not the post where I will explain it. Just get it, I'm developing it, and publishing soon.
So go back: I chosen one of my HP 3478A 5.5 digit multimeter for this. And here come a few things.

• I need a switch for the project
• The display of the 3478A is a heap of crap without backlight
• I don't want to kill the original display on those unit, so get something similar, cheaper.

As usual I was looking around the eBay. And look what I found. Two HP 3488A. those are loaded with cards (usually you can find it empty), for €102 delivered. So I bought it immediately.
It is a good practice for the display modifications, if they work (the seller didn't guarantied it), can be used as a switch for the project above, and also for other purposes. Also, it nicely fit into my test equipment collection.
So here they are:

First of all, I removed all of the cards, cleaned the units (get rid of all of the stickers, dirt)
Let see the inventory:

• Two HP3488A units. One of it miss its power button. No stands.
• Two 44471A General Purpose relay cards. One of it even has the connector block, the other don't
• Two 44470A Matrix relay cards. Both of them with connector block, just from one of the blocks the plastic insert was missing

One misterious, HP branded, and hacked - some (not even nice) modifications are made by one of the previous owners.
This is the mysterious card, I would appreciate, if somebody can give me any info on it:

After a bit cleaning, I tried out the units. for the first smoke test, both looks like working, the self tests are succeeding, I can hear the relay click from console, and from remote GPIB commands.
As you know, I'm in the 3D design, and printing for a while.
Here I needed two missing plastic parts. One for the power switch replacement

And one for the connection block insert.
I designed both, in my regular OpenSCAD:

 Here they are printed:

Left is the original, right is the printed:

Now, the power button in its place:

Project of getting in shape the HP 3488A units now completed.