Fluke 8060a reading low before True RMS chip - Page 1
Forum section: electronics / repair

author: BullyFreeBear
author_rank: Contributor
timestamp: March 18, 2025, 08:01:12 pm
content: Hello I would like to start by saying I have already gone through and recapped and cleaned the nasty electrolytes off the board. This was my grandfathers meter when he worked for IBM that's dated 26th week of 1982.I have brought this meter back from the dead, getting a steady 5+ and -4.9v. Now I've got an issue when I apply AC voltage to the meter it reads a little low, and that the decibels counter reads -43 DB. I used some of MrModemHeads advice from a different post, where you apply .190 MV at 200Hz to the input of the meter and then read pins 5 and 10 on the RMS chip, and all I got on pin 5 was .171MV and on pin 10 I got -.175MV DC which is what was displayed on the meter. I have been trying to wrap my head around what could be going on but for the life of me I can not figure out what is wrong.Now I should mention that ohms, DC and HZ seem to be fine. I will upload the schematic that MrModemHead provided.EDIT: I would like the add that I am waiting for a new 22meg resistor to come in the mail, as I cracked the old one while trying to remove the old 47uf capacitor near the True RMS chip.

author: BullyFreeBear
author_rank: Contributor
timestamp: March 18, 2025, 08:08:07 pm
content: It looks like I posted this in the wrong forum. Sorry about that. Can I move this to Repair?

author: tautech
author_rank: Super Contributor
timestamp: March 18, 2025, 08:49:49 pm
content: Quote from: BullyFreeBear on March 18, 2025, 08:08:07 pmAs the OP you can.Use the Move Topic feature at the foot of your page.

author: BullyFreeBear
author_rank: Contributor
timestamp: March 18, 2025, 08:52:39 pm
content: Thank you! I had no clue I could just move it.

author: Andy Watson
author_rank: Super Contributor
timestamp: March 18, 2025, 11:46:29 pm
content: Quote from: BullyFreeBear on March 18, 2025, 08:01:12 pmAre you sure that you cleaned off all the electrolyte ? Meters of this calibre can be very sensitive to leakage currents in the wrong place. There is a thread on this forum in which Dr Taylor describes the steps he took to decontaminate the PCBs.I think it's this thread:https://www.eevblog.com/forum/testgear/old-fluke-multimeters/(! OMG - it 39 pages long - but worth reading.)

author: BullyFreeBear
author_rank: Contributor
timestamp: March 19, 2025, 04:11:34 am
content: Wow that was a long read. I learned a lot more about that meter.One thing that I noticed, is that I have the worst leakage out of all the meters in that long thread. I mean most of the solder joints around those caps pop and bubble when I heat them up. I'm going to take Dr.Taylor's advice and then some. Ive had to take out a few ceramic caps just to clean the legs of the cap and remove the grayish dull solder from the through hole.Right now I'm going to let that board soak overnight again and try cleaning it, this will be attempt number 2.I marked with yellow where I get lost when I comes to the low AC Voltage, and I marked in blue where I found corrosion on the legs C16 and tried to clean the C18 while I was there, I'm worried that there may be corrosion under Z3 because it seem like the electrolyte wicked into the traces them selves because I've had to run jumpers on the input and output of U4.

author: bdunham7
author_rank: Super Contributor
timestamp: March 19, 2025, 04:34:24 am
content: Measure on both pins 2 and 3 of Z1 and if the drop is occurring there, look for leakage or contamination in the area I've circled in red.

author: BullyFreeBear
author_rank: Contributor
timestamp: March 20, 2025, 06:15:48 am
content: I traced the voltage drop back to R13, I found that the voltage drops by 15mv between that resistor. From what I've read from this post (https://www.eevblog.com/forum/testgear/fluke-8060a-calibration-service/25/) that's a little high.Now I don't want to assume that the resistor is bad, but it sure seems odd that the voltage dips that much. If I ohm out that resistor it seems to read 103k which is in tolerance. As of right now I'm a little stumped.EDIT: I couldn't fall asleep, so I went back to the meter and tested negative voltage pin on the chip, and it came up as -4.31v which is much lower then I would expect when everywhere else its -4.98. I also checked pin 6 and it reads 190mv. In the morning I'm going to run a jumper wire from VSS near the negative voltage generator to the RMS chip and see if that fixes my issue.EDIT 2: The -4.31 is the drop across the 100uf cap coming from the VSS, so nothing to worry about.

author: BullyFreeBear
author_rank: Contributor
timestamp: March 23, 2025, 05:08:19 am
content: Thank you bdunham. I measured there and unfortunately that wasn't my problem.But I have found an issue, TP3 and TP8 test points are reading 2v when they're supposed to be 3.5v, I'm not sure how I overlooked that. Any tips on what to check would help as I only see C12 and Z1 creating that voltage.I might check the C21 I put into the meter, as I don't trust the Microcenter bundle of no name caps that I got to have the best ESR. Im also planning on buying nice low ESR nichicon capacitors once I get the meter working.