Tek never made multimeters. They are escort designs
The Tc chip is an old Teledyne design. Microshit borged that when they acquired the semiconductor division from vishay. It included telefunken, teledyne and i believe a division of harris.
Teledyne was a big competitor for intersil a/d multimeter chips. The teledynes are really good chips
The fluke scopemeter was designed by philips of the netherlands. They sold their T&M group to fluke in early 90'
You can fix the tds220s like missing button and broken cal outputs with
Arts from the redtagged one. They use a stupid 7404 as buffer for cal output. The redtagged out of cal is unrepairable as the reference has gone off. It sits inside the big national semiconductor asic and that is unobtainium.
The tds3000 series : get the latest software from tek (if you cant grab it, i have it) you need 4 floppy disks. It updates to latest firmware and unlocks all options so you dont need those plugin modules. Tek released all options for free in the latest release firmware when they discontinued that series,
The three channel one probably has the center pin broken off the hybrid. Ive seen dat before. The mechanical construction is a bit flimsy on those.
To open the machine: look at the handle left and right. The round pivot point: pop the disk off. There is a black and white block in there. Look carefully for a little metal pin. It looks like a little rivet. Using nippers ( pliers cant grab it) pull that pin out. Its about 2 cm long.
Then take the black and white plastic block and rotate it 1/4turn(hold handle steady). The bloack can now be removed.
The handle will now be off. Remove 3 screw in back (one around power plug, two on gpib module) and lift case off.
Pop the metal lid off the analog inputs (you need to remove fan assembly. 2 cables and 2 screws.)
Take a look at the center pin of the bnc . It connects using a tabto the maxtek hybrid. Most likely sheared off there.
Opening the tds 220: take the handle , put it vertical, now pull the two vertical pieces outward. Thes removes the handle. There are two hidden screws under there.
There is a screw in battery compartment too i believe.
Pull out the power button ( you risk breaking off the switch if you dont do this) then remove back panel. Easy peasy