Vintage multimeter repair - Page 1
Forum section: electronics / repair

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: February 24, 2020, 02:22:59 pm
content: I have a Kaise SK-60 Multimeter that has been giving me incorrect readings so I took it apart and started test all resistors an this one seems to be blown.It's connected directly to the com port so my guess is it was acting as a fuse and burnt as i cannot get a resistance reading on it.It's marked as 0.887 F. Can I assume this is the resistance value in? What should I replace it with?

author: ArcticGeek
author_rank: Regular Contributor
timestamp: February 24, 2020, 06:58:38 pm
content: This looks to me like a standard wirewound 1% resistor - wirewound resistors were common in the "old days" for use in multimeters.My thinking is just get a replacement 887 ohm resistor from Digikey or Mouser (or anywhere else for that matter). 887 ohm is a standard 1% resistor value so that should be fine. You can likely get a 0.25% tolerance or even 01% tolerance in the same value if you are concerned about precision.Good luck

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2020, 07:18:41 pm
content: ^ That should be 0.887 ohm (not 887 ohm), presumably a current shunt. That's going to be rather harder to find (based on a quick search).The other approach would be to purchase a 1 ohm resistor and then pad it down to the correct value by tacking on higher value resistors in parallel.

author: floobydust
author_rank: Super Contributor
timestamp: February 24, 2020, 07:31:49 pm
content: It looks like that is the shunt resisotr for 500mA current-range and should be 0.867ohms. The SK-70 uses 0.8 ohms and attached is schematic, hopefully a similar circuit but it is only 30kohms/V and yours is 50kohms/.V.Maybe try parallel 1R with 6.52R or so?

author: mzacharias
author_rank: Frequent Contributor
timestamp: February 26, 2020, 12:47:29 am
content: And by the way, a burned out shunt resistor would not affect AC or DC voltage readings.Not directly, anyhow, but the same mishap that took out the shunt might have caused some other damage.This type of damage is common - could be the Rx1 and/or Rx100 resistors could be bad as well.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 26, 2020, 05:16:43 pm
content: For the shown schemeatics a burnt shunt would actually effect the voltage readings too - leading to a higher indicated voltage. However it depends on the circuit.For a first test one could try a value one close by - even 1 Ohms / 1K (less likely) should give a nearly working meter if this was the only defect.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: February 26, 2020, 07:49:55 pm
content: Thanks for the replies.I tried replacing it with a 1 ohm 1 % resistor and the Voltage readings where almost spot on. This will do for the meantime until I find myself a 0.887 Ohm resistor to replace it with.Prior to changing it, I was not able to read any voltages as the needle would shoot all the way right regardless of the range selected.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: February 29, 2020, 12:27:06 pm
content: I am not able to find any 887 mresistors so I wanted to ask if I could make my own using some nichrome heating wire wrapped in heatshrink so that the wire doesn't short itself by accident.I could also straighten the entire thing in case the coil may affect the measurement somehow and place it at the bottom of the case covered with hot glue.Please let me know if this might work or am I better off using an 820 ohm resistor?

author: tunk
author_rank: Super Contributor
timestamp: February 29, 2020, 01:14:35 pm
content: You could, but it will not work as a fuse.Or, as several has suggested above, use two resistors in paraliel:E.g. 1 and 8.2ohm will give you around 0.89ohm.

author: Gyro
author_rank: Super Contributor
timestamp: February 29, 2020, 02:10:55 pm
content: Don't forget solderability - there's no point in winding your own resistor, only to find that you can't solder the nichrome wire into the board.Go with the parallel resistor approach...http://www.pmillett.com/rescalc.htm

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: February 29, 2020, 02:52:07 pm
content: Quote from: Gyro on February 29, 2020, 02:10:55 pmI was thinking I'd cross the bridge when I get to it.Makes more sense to use parallel resistors now that I think of it that's what I'll do thanks!

author: pcmad
author_rank: Regular Contributor
timestamp: March 01, 2020, 01:01:35 am
content: have you check the correct voltage on power source my old mulit meter shows out of cal reading if the battary in low