Author Topic: Modding a Keithley 197  (Read 15696 times)

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Offline akabek

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Re: Modding a Keithley 197
« Reply #25 on: February 03, 2021, 04:43:14 pm »
I just realized I had the wrong model number mentioned.  I have the 197a.

I was looking at those EL panels.  Were you able to cut yours to size?  I thought I read somewhere the panel in your link could not be cut.

Is your Keithley a 175a?  I wonder if the driver may be the issue.  To be honest I am not sure how bright the backlight should be in a 197a.
« Last Edit: February 03, 2021, 04:45:33 pm by akabek »
 

Offline don.r

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Re: Modding a Keithley 197
« Reply #26 on: February 03, 2021, 05:10:26 pm »
Never got to the stage of cutting since I discovered it was the driver. Mine was a 175A. Measure the voltage going into the panel. It should be somewhere between 70 and 90V (AC?). Mine was 25V. I used a driver similar to this but not sure what the input voltage was (12V or 5V): https://www.aliexpress.com/item/1005001977407178.html
 

Offline akabek

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Re: Modding a Keithley 197
« Reply #27 on: February 03, 2021, 06:05:14 pm »
Never got to the stage of cutting since I discovered it was the driver. Mine was a 175A. Measure the voltage going into the panel. It should be somewhere between 70 and 90V (AC?). Mine was 25V. I used a driver similar to this but not sure what the input voltage was (12V or 5V): https://www.aliexpress.com/item/1005001977407178.html

Excellent, I will do some checking tonight.
 

Offline akabek

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Re: Modding a Keithley 197
« Reply #28 on: February 04, 2021, 12:21:33 am »
I checked the AC voltage going into the backlight panel and it is 44.8v.  Just curious how you know the AC voltage should be between 70 and 90v?  Were you able to locate the schematics for the 197a? 
 

Offline don.r

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Re: Modding a Keithley 197
« Reply #29 on: February 04, 2021, 05:31:02 pm »
I checked the AC voltage going into the backlight panel and it is 44.8v.  Just curious how you know the AC voltage should be between 70 and 90v?  Were you able to locate the schematics for the 197a?
Can't remember where I saw the voltage but I think it was the standard of EL panels. They light at 50V and get brighter as voltage increases. Mine was the 175A and has schematics in the user manual. I think the feed voltage to the driver circuit could have been 5V but you can measure that. Its the black box on the back of the front panel.
 

Offline rwzahora

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Re: Modding a Keithley 197
« Reply #30 on: August 02, 2022, 01:22:26 pm »
My 197A had a very weak backlight so I thought I'd look into replacing it.  The old panel was a Loctite LSI 37269-1 as shown in an earlier reply.  It is 19mm x 86mm.  I purchased a panel from eBay (https://www.ebay.com/itm/393103760354?var=662007375026) and cut it down on three sides and nail-polished the edges.  It works and the light is much better than the original unit although I would have liked it even brighter.  The voltage to the panel is 76Vac measured with a multimeter and the drive is triangleish at about 370 Hz.
 
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Offline jupiters_spot

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Re: Modding a Keithley 197
« Reply #31 on: November 12, 2022, 05:14:40 pm »
Reading through this thread it seems that:
- the 197A has a backlight, and some here have needed to replace the inverter driver to supply the correct voltage to the electroluminescent backlight
- there aren't any posts about adding a backlight to a 197 (as opposed to 197A) display.  Did I miss such a post?

Adding a backlight to a 197 appears to involve two primary steps: install appropriate inverter to drive EL strip, and trim/seal/install EL strip behind LCD display.  All of the EL drive inverters I see either require 12V DC or 120V AC, and I'm not sure I see a convenient source of switched power of either sort in the base 197.  I'd want the backlight to turn on/off with the meter's power button so I'd need to power the inverter somewhere after the meter's power switch.  If anyone has installed an inverter and EL backlight in a base 197 (not the 197A), please share with us how you powered the EL drive inverter and where you managed to stuff the inverter into the meter's case.
 

Offline tookiTopic starter

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Re: Modding a Keithley 197
« Reply #32 on: November 12, 2022, 05:52:38 pm »
A 197 display upgrade has been a project on my to-do list for a few years. :p

I don’t think there’s much sense in using EL these days, since LED is so much easier to drive.

Long-term, an entire replacement display board, using a microcontroller to decode the original display signals and reformat them for some modern display, is likely a smarter way to go. (The work to decode the original display signals is already complete.)
 

Offline jupiters_spot

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Re: Modding a Keithley 197
« Reply #33 on: November 12, 2022, 06:23:31 pm »
Quote
Long-term, an entire replacement display board, using a microcontroller to decode the original display signals and reformat them for some modern display, is likely a smarter way to go. (The work to decode the original display signals is already complete.)
I'm intrigued.
Looks like someone has done it: https://www.reddit.com/r/electronics/comments/pkknvk/keithley_197_with_oled_display_upgrade/
 


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