Keithley 175A Manual with Schematic - Page 1
Forum section: electronics / repair

author: Leuams
author_rank: Contributor
timestamp: February 24, 2024, 08:44:27 pm
content: I picked up a sick Keithley 175A that I am trying to repair, the meter measures zeros for any input or OL for resistance. I searched for a manual with schematic but so far all the manuals I can find are missing the schematic. The manual fromKeithley (Tek)is missing the schematic section. I also found a few more downloads but they too are missing the schematic.I did find thisthreadfrom someone repairing a 175A with a few screen shots of the schematic but if possible I would like the full schematic.Thanks in advance for any help.

author: J-R
author_rank: Super Contributor
timestamp: February 24, 2024, 11:51:52 pm
content: I believe the differences between the 175 and 175A are small enough that the schematic in the 175 manual should get you pretty far:https://download.tek.com/manual/175_901_01A.pdfBut just in case you aren't aware, before doing anything to the DMM be sure to properly clean all the switches with contact cleaner. Remove the PCB from the case, remove the front panel, hold the PCB vertically with the switches facing down, then spray the switches from the open end as well as on the pin contacts while working them all a few dozen times.Beyond that, the typical repair procedures sound reasonable, such as checking power supply voltages and capacitors.

author: Leuams
author_rank: Contributor
timestamp: February 25, 2024, 01:23:59 pm
content: Thanks for the suggestion to use the 175 schematic, I will give that a try.Cleaning the switches with Deoxit D100 is my usual course of action, I "repaired" a 179A that the seller claimed didn't power up with a few drops in each switch. I'm out of Deoxit right now so while I wait for it to be delivered I was going to have a poke around and check voltages.

author: tooki
author_rank: Super Contributor
timestamp: February 25, 2024, 04:55:18 pm
content: Quote from: Leuams on February 24, 2024, 08:44:27 pmFYI, if you look closely at those screenshots, you’ll find they’re taken from the 175 schematic J-R linked to. (For example, the revision notes. I would expect those to get reset on the schematic of a new model.)The 175 is the little brother of the 197 (they’re basically identical except for the number of digits), and I know that in the 197A, the only difference over the is the addition of the display backlight (and the change in case color from brown to gray). So I’d be quite surprised if there are any other differences in the 175A.

author: J-R
author_rank: Super Contributor
timestamp: February 25, 2024, 11:04:59 pm
content: I buy my stuff locally because I seem to run out at inopportune times. Lowes has the "CRC QD Contact Cleaner 11oz" and the "CRC Lubricant, multi-purpose 5 oz".

author: Leuams
author_rank: Contributor
timestamp: February 25, 2024, 11:32:52 pm
content: Thanks for the advice tooki, I will look at the family of schematics if I need to dig deeper into the device.Quote from: J-R on February 25, 2024, 11:04:59 pmI believe the last time I looked locally the auto parts store also had the "CRC QD Contact Cleaner" but I haven't found the Deoxit dropper bottle locally and that was what did the trick for the 179A where the CRC temporarily fixed it.Thanks everyone, I will update here if I get it working.