Best way to clean multimeter PCB to illiminate offset errors? - Page 1
Forum section: electronics / repair

author: R_G_B_
author_rank: Frequent Contributor
timestamp: December 03, 2015, 08:24:57 pm
content: Hi I have a millimeter is shows offset DC voltages e.g 0.2V, sometimes 00.04 for example. They should be 0.0000 for example there is no Rel button or setting for this.I located the DC amplifiers place a hpas140i across the output and was able to identify where the problem is.I cleaned each ampler first with flux cleaner then with IPA the problem got worse the offset increased. I decided to use 0.25mil solder on the legs of the amplifier IC then used flux cleaner on its own this seemed to work very well and the offset error was down to 0.0005 volts. However after time the problem had come back. Are there any techniques to eliminate this problem? look forward to seeing how others go about solving this problem.ThanksR_G_B_

author: DmitryL
author_rank: Regular Contributor
timestamp: December 03, 2015, 09:06:19 pm
content: I have cleaned my multimeter board in IPA ultrasound bath. Helped very well.

author: VK5RC
author_rank: Unknown
timestamp: December 03, 2015, 10:54:09 pm
content: How high is the input impedance? If very high, a non-zero reading might be better than a zero one, an absolute zero reading often means there is lower impedance between the inputs, a non zero reading may indicate it can pick up static, ie very high impedance.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: December 04, 2015, 06:55:16 am
content: What I'm going to do is remove the components and clean under thenm and any excess solder try resoldering with out flux clean the board using just iPA see how that method worksR_G_B

author: DmitryL
author_rank: Regular Contributor
timestamp: December 04, 2015, 09:58:17 am
content: That's just silly.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 04, 2015, 04:11:10 pm
content: Usoldering parts meas quite some stress to the parts and the board too - so I would avoid this if possible (no defect).Usually cleaning with IPA should work. It may need to be done several times. Also some heating / bakeout is helping - though no need to go to 100 C, something like 50 - 60 C should be enough.Voltmeters with a very high input impedance (> 100 M) may have an offset in open circuit mode - this can go alle the way up to overrange and still be in specs. The more measingfull parameter is the bias current, or voltage measured with something like 10 M between the inputs.Sometimes leakage currents can compensate und thus a low open circuit reading may be just coincidence and thus rather unstable.What DMM is it ?

author: R_G_B_
author_rank: Frequent Contributor
timestamp: December 05, 2015, 09:15:37 am
content: I must have tried to clean the board at least 40 times. With not much luck. So as a last resort I removed the components and cleaned under them. There was quite a lot of contaminates. IPA is not effective for some strange reason it increases the DC offset quite a bit in my situation.ThanksR_G_B

author: R_G_B_
author_rank: Frequent Contributor
timestamp: December 05, 2015, 09:23:15 am
content: The input impedence is 10 megohmsIts a graphing multimer.R_G_B

author: dacman
author_rank: Frequent Contributor
timestamp: December 06, 2015, 01:13:31 am
content: Try IPA followed by compressed air. If you had an air compressor it would need a dryer and a filter (dryer for humidity and filter for oil).