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Tektronix DM5120 - a Keitley 196 brother

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coromonadalix:
The RT1
[/quote]
According to the ANSI reference designators, RT is a Thermistor (NTC or PTC).
[/quote]

I just dont understand it's purpose in the circuit ??

Neomys Sapiens:
I did not see whether it is a PTC or a NTC. If it is a PTC, it is probably a sort of overload protection, while a NTC might be used as a temperature compensation for other parts.

texaspyro:
I've seen several of these with a bad AC input channel.  The problem was a blown resistor... I don't remember which one or the value.  It was around 2W size and brown in color.

coromonadalix:
thks for the tip

Ill try to fit   the two bottom tektronix frame locks into a switch lever ???  I could keep the look intact ??  the hardests parts to find would be the keypad switches if they break.

coromonadalix:
It liiiiives !!!          outside the frame, some photos

The 196 xformer secondary is almost a perfect fit,  you have to cut a small top portion of the white mta156 connector (the analog meter section plug)

You have to cut and remove some pcb traces on the component side after drilling new holes for the primary section of the xformer, i used a twist drill wth 1mm bit for the holes, the xformers pins are very short in lenght, i had to put wires on the primary side.

Build a small rectifier board with the 10000uf capacitor for the 5vdc digital section (cpu rom sram etc..), i use the idc connector to hold it and thru it transfert the xformer rectified 10vdc to the main 5vdc regulator (huge heatsink)

All the patchs i've made must not exceed the height of the main 5vdc regulator heatsink,  because the analog meter will go over it,  it will have around 1/2 inch of clearance, the regulator get warm.

I've kept the 5vdc reulator 1 amp pcb fuse and socket (photo),  removed the ac fuse pcb socket

Added an 115v 230vac selector switch, and a ac socket with 2 included fuses, I changed ideas for the Emi rfi filter due to space contraints.

I'll simply use a main ac powerbar with included protections,  the Keithley 196 did not have emi rfi protections ...

My only problems left are the power switch,  i'll try to keep the vintage look, or remove a bnc connector on the front  ??? The two Tektronix levers frame locks aren't easy to adapt ... and make a new rear aluminum plate with the needed holes for the voltage selector switch and ac socket.

I dont think i'll ever use the gpib port on the board.

For the keen  eyes  you see a green wire going into the xformer,  i replicated the Keithley 196 wiring for the earth ground, the xformer seems to have a ground shield inside it, and i'll add the final green wire to the metal casing once the project is completed.

EDIT: the case is at ground supply level already, the front panel and the logic panel give it thru the metal mounting spacers.

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