Electronics > Repair

Keithley 6517A Electrometer: dead voltage source; Replacment for 2SK1412 MOSFETs

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DB4UCH:
Hello together,

I recently took on repairing a Keithley 6517A Electrometer with a broken voltage source. When I got this unit, some components in the voltage source section were already missing, including one 2SK1412. I then checked the remaining large MOSFETs and two of the three 2SK1412 had failed (low resistance between Gate and Drain). So, I will need to replace those MOSFETs (2SK1412). I will also replace most of the semiconductors around those FETs, because I can't really be sure what exactly killed what. (the supply voltages for ±1200V and ±, 120V seem to be in range according to the service manual, so most likely not those)

Is there any "trusted" source for those MOSFETs or for the possible replacement (NDFPD1N150CG, which is EOL as well and seems even harder to source)?

Are there any other (available) FETs that might work in this application?

Thanks!

Greetings,

Simon

Jetecnet:
Last time i bought these 2SK1412 I got them from Radwell, price has gone a bit crazy though.
https://www.radwell.com/Buy/SANYO/SANYO/2SK1412
JC

voltsandjolts:
Not trusted but cheap!

https://www.ebay.co.uk/itm/226356193374

squadchannel:

--- Quote from: voltsandjolts on October 29, 2024, 01:28:32 pm ---Not trusted but cheap!

https://www.ebay.co.uk/itm/226356193374

--- End quote ---

TO220, but the shape of the molding is very unique.
for fake parts, most of them are just re-marked with a laser. is not possible to change the shape of the package.
legs are oxidized and solder plated.
I think it is genuine.

Kleinstein:
There are other high voltage MOSFETs available. The problem seems to be finding small ones with a low gate capacitance - no problem with 1 or 2 A types (e.g. STW3N150 or IXTH1N200). It depends on the circuit how well it would handle the higher capacitance.

If one can accept a slightly lower voltage rating, the IXTP02N120P could be an option. Still a little higher capacitance, but not that much.

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