Author Topic: [Repair] Keithley 2015 THD - THD not working  (Read 922 times)

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Offline usagi

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[Repair] Keithley 2015 THD - THD not working
« on: May 22, 2017, 11:17:59 pm »
Picked up a used Keithley 2015 THD, everything works except the THD measurement - it never shows anything, just shows a blank.

All other DMM functionality passes full calibration, and functions perfectly.

The OCD in me wants to get the THD working. Sadly there does not appear to be any schematics or service manual for the THD module. Also the 2015 THD has basically zero self test functionality.

Anyone with a 2015 THD have suggestions where to start? Or maybe pointers to 2015 THD module schematics or 2015 THD service manual?

Offline MadTux

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Re: [Repair] Keithley 2015 THD - THD not working
« Reply #1 on: May 22, 2017, 11:43:23 pm »
K2015 THD board usually isn't too difficult to fix, I fixed a couple of broken ebay cheapies some time ago.

Find the data sheet for all chips (AD9850, OPA275 and a couple more, follow the signal from AD9850 towards the BNC, the area with the analog switches is a bit confusing, those 2x4 opamps on the bottom are used to buffer the signal on each BNC, each opamp has 200Ohms on output to get 50Ohms on BNC).

One of mine had a bad OPA275 and another magically fixed itself after swapping a couple of chips. It's also very helpful to have another working K2015 next to broken one, so you can compare signals, exchange those 17AT65 EPROMs to confirm data integrity and swap suspect chips, so you don't have to buy them only to realize the problem is somewhere else ;-)

I have uploaded 17AT65 firmware here on forum, in case you need it.


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