BK Precision 886 Erratic Readings - Page 1
Forum section: electronics / repair

author: sirloin
author_rank: Newbie
timestamp: October 10, 2020, 03:44:10 pm
content: Hi Guys,I bought a BK Precision 886 LCR/ESR meter many months ago. I was using it to test some old capacitors etc, I quite honestly don't know if it ever worked right.I am trying to do some diagnostics on removed parts etc but what I am finding is that I can't seem to get it to work.For example, when I do the CAL0 (open) calibration with DCR selected the meter finishes the CAL and then the resistance continuously jumps around from 10-90Mega Ohms, sometimes showing OL.If I do the same procedure with CALS (shorted) with DCR selected the meter then jumps around usually from 2-4K Ohms, sometimes hitting 0 and sometimes going even higher (This is with the shorting bar still in place).I am using the external power adapter for the unit, without any batteries installed. Although previously I did try using the 2 AA batteries, with and without the wall adapter with the same results.Does anyone have any suggestions on where I could start looking/measuring? I saw another forum post with a lot of helpful details on the various ICs and regulators. My current plan is to start here.

author: sirloin
author_rank: Newbie
timestamp: October 10, 2020, 07:58:50 pm
content: I started just visually inspecting things. Mainly focused on the input board.I noticed a 01A resistor (100 Ohm, 1%) and it had a bubble on it... Measuring it I was not getting anything close to 100 Ohm, so I figured it was blown. I replaced it with another (don't have 1%, but fine for now). I am now able to measure things like 330uh inductor.If I try measuring smaller values it still does not work. I will check for more bad parts.I am able to measure from 1uH to 330uH (all I have tested so far)... so maybe fixed?So after calibrating with this resistor fixed, I can get a stable 0 ohms in the DCR setting with the shorting bar inserted. With the bar removed, I still get wonky results ranging from 150MOhm to OL (more common 150MOhm to 400MOhm)

author: sirloin
author_rank: Newbie
timestamp: October 12, 2020, 02:57:08 pm
content: I ordered some 1% resistors.Also attached a picture to show more context on where R317 is, it is at the bottom of the board next to the 3 large contacts for the probes.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 12, 2020, 07:26:40 pm
content: maybe you put an charged capacitor and it blew some parts of the lcr ?

author: sirloin
author_rank: Newbie
timestamp: October 12, 2020, 09:11:58 pm
content: Very possible I did.I think the problem was trying to get right into measuring ESR and finding "bad" caps. I think I should have used it to verify a few known good components first. I do know to discharge the caps first, but of course, I could have forgotten to do one.

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2020, 09:27:12 pm
content: You may already know this, but just for reference, if you do CAL OPEN, then CAL SHORT and leave the shorting bar in in DCR mode, you should get 0.000R, or really close to that. When you remove the shorting bar, you should get more than 100M.

author: sirloin
author_rank: Newbie
timestamp: October 12, 2020, 10:07:32 pm
content: Thanks, I saw another thread here with the full calibration document (I don't have all the required resistors though).The first clue I had was after calibrating with the shorting bar in place it was not reading 0 ohms. Once that resistor was replaced, it is now reading 0 when shorted. The open resistance does still jump around, but it is over 100M Ohm.Not sure if anyone is interested in trying to read the code on the Atmel chip to convert their 885 (think it might just be a firmware change?) but I would be willing since the unit is still in pieces waiting on the new 1% resistor.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 12, 2020, 11:26:34 pm
content: could be interesting

author: Luzbel
author_rank: Newbie
timestamp: October 20, 2020, 06:30:08 pm
content: hi, do you have a backup firmware? I have a mt4080A.I hope you can fix the lcr.