Fluke 87V shows dashes also - Page 1
Forum section: electronics / repair

author: srmahaffy
author_rank: Contributor
timestamp: August 26, 2021, 03:41:43 pm
content: Hi everyone, I’m new here.I followed another post by Multiple Cheese Slices, who had a Fluke 87V showing dashes, which he repaired with the great assistance here.I wanted to share my related problem with my Fluke 87V that I recently purchased for repair, that displays the same dash - - - - issue. Here’s some baseline of my meter:- It came without the plastic selection knob (which I replaced)- damage to the J1 connector with the common port broken (I suspected this with eBay pics showing this port misaligned)- the battery cover/area on one side looks partly melted. (PCB inside is fine, not burned) I suspect it was near a soldering iron or something- looks like meter got hit, or dropped which caused the J1 connector damage.After opening the meter, the PCB at the COM was also stressed, and was bent up, and started to crack. When I removed the J1 connector, it is much better aligned, more flat, and I don’t see any trace cracks/opens as a result, and checked continuity in those areas. Also found solder joints cracked near J1 lower right of PCB which I re-soldered. I reviewed the 8X V series schematic and inventoried all the components, and which ones that aren’t installed for an 87V. Everything looks correct, except found U8 is missing ( I could see the solder flow pads that the part used to be there). I have a replacement part on order. I also found R2 sticking up on one side which I re-soldered. Regarding J1, I have a new replacement, but was holding off on soldering it in, as I want to solve the dash problem first. After I get the new U8 replacement (LT1790-2.5) I’ll post +2.5 / +.0.8 voltage readings. So far though, I confirmed U6 output, and U10 input voltages are correct with ground reference as BTM. COM port as reference, is currently not okay. I was hoping the open R2 repair would correct that, but it didn’t.

author: Manul
author_rank: Super Contributor
timestamp: August 26, 2021, 08:58:37 pm
content: Nothing will work normally if there is no LT1790. I would say you better not even run the meter without it. Hopefully, that is all that meter needs.And what is that bubble wrap? It does not look like an ESD safe bubble wrap. Jeez, you are asking for trouble.

author: srmahaffy
author_rank: Contributor
timestamp: August 27, 2021, 04:18:49 am
content: Thanks for your feedback Manul.Regarding the bubble wrap, it is ESD safe, but only used it while taking the pic.

author: srmahaffy
author_rank: Contributor
timestamp: September 02, 2021, 03:49:33 pm
content: Hi everyone,I received my replacement LT1790-2.5 for U8. (I used P/N LT1790BIS6-2.5#TRMPBF which has .1% accuracy and 25PPM deg/C according to the Linear Circuits data sheet on the Mouser website. Maybe someone can provide input here… on the Fluke BOM, in the 87V/AN service manual, it looks like Fluke is calling out the “B” grade specs but listing the “A” grade part number (??). The A grade spec on the data sheet lists .05% accuracy and 10PPM deg/C). I would have purchased the “A” part, but couldn’t find it in stock anywhere, so went with the “B” part.Regardless, I’m happy to report with the U8 part installed, my meter is now working. Here are my voltage readings with the “COM” port as my reference:- TP17 (U10-5) is +2.495V- U6-5 is +0.823V- BTM is -2.498VOnce I verified these voltage levels, I soldered in my new replacement J1 connector and re-verified the voltages again, then put my meter back together. All mode selections work, and made resistance, capacitance, Vac/dc measurements and compared them to another working fluke meter. I checked the temp mode, by putting my probes together, so didn’t do an accurate check there, and didn’t make any current readings.This forum and information provided in it was a big help!! Thank you!!

author: Manul
author_rank: Super Contributor
timestamp: September 02, 2021, 04:20:45 pm
content: Good job! Regarding the LT1790, I always thought that they use "A" grade (I saw it in the part list). I don't know, maybe check manuals of other comparable fluke multimeters (they likely use same IC). Unfortunately you also cannot judge from IC marking, because both "A" and "B" are marked "LTPZ", so PCB images from web wont help.

author: srmahaffy
author_rank: Contributor
timestamp: September 03, 2021, 05:16:08 pm
content: Thanks for your feedback Manul, I appreciate it. Regarding the “A” grade of the LT1790-2.5, it does make sense that Fluke would use that for their more precision meters, which I think the 87V is. I will check other manual BOMs, as it has me curious.Thank you again