Help with Fluke 175 repair - Page 1
Forum section: electronics / repair

author: MC2Short
author_rank: Contributor
timestamp: November 24, 2024, 11:32:36 pm
content: Hey guys, I'm new here, and got suggested to post this here from a good dude on discord who was trying to help me figure this out.So I accidentally blew up my Fluke 175 on a MOT like an idiot, and I've been trying to fix it. The ohms and continuity modes especially were messed up. The resistance testing didn't work at all, and the continuity setting would beep with or without the leads, or the fuses. I figured out I had some bad MOV's. I replaced them with good ones from another dead older fluke. I checked the diode bridge and that tested fine, I tested the green resistor it tested at 1K ohm. The grey one on the left is 1 ohm. I now have it to the point where measuring ACV and DCV is accurate, and my resistance setting works somewhat now, but it's reading wrong. The continuity setting doesn't continuously beep when on continuity, and it was beeping when I shorted the leads, but it still also gave me wrong resistance numbers. So at this point I'm trying to figure out what I need to do or check or replace to get the ohms/continuity reading right. Thank you for your help. *Update* My 175 is now apparently not reading AC voltage now for some strange reason. [ Specified attachment is not available ]

author: MC2Short
author_rank: Contributor
timestamp: November 24, 2024, 11:36:19 pm
content: I should also add I tested all those and resistors all were 123.6K ohms. Battery is brand new, I also used different leads I had. I'm not sure what else to do or check at this point.

author: MC2Short
author_rank: Contributor
timestamp: November 25, 2024, 01:12:28 am
content: Lol I seen this cal point on the back of the 175[ apparently it's not going to do me any good as it seems I need a multifunction calibrator which used at cheapest I've seen is roughly $500 all the way up to $80,000!! Good Lord.attachimg=1]

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2024, 04:56:03 am
content: Unfortunately I'm not aware of a schematic being available for this, but here's a guess (and what I would try next).If you have hot tweezers or another way of easily removing and reinstalling SOT-23 packages, look at the photo I've attached and locate the six three-terminal devices that I've drawn a red line around. Just remove them all and set them aside and try the meter again and see if it works properly. Make sure you keep them organized so they go back where they came from in case this turns out to be a dead end.

author: Ugur
author_rank: Regular Contributor
timestamp: November 25, 2024, 05:38:50 am
content: There are the transistors mentioned by "bdunham7" in the previous message. 4 of them side by side. Take them out and check. Probably at least one or two of them are broken.

author: MC2Short
author_rank: Contributor
timestamp: November 25, 2024, 05:51:56 am
content: Thanks guys I'll give it a shot

author: MC2Short
author_rank: Contributor
timestamp: November 25, 2024, 08:08:57 pm
content: Well, I got all those SOT-23's off, and I think at least a couple were broken, but I may have broke a couple more just trying to remove them. I tried to start the meter up once they were off, but it seems to be totally dead now.Those SOT-23's were so small and cooked I couldn't read the numbers on them to find replacements for them, and I have no idea if they're all just transistors, or voltage regulators, etc.. so until I can find that out, it looks pretty much like I'm out of luck for now. As far as I know there's not a schematic to be able to easily figure that out either. Thanks for the help though guys. I do appreciate it.

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2024, 09:44:54 pm
content: Do you mean physically broken? How did you remove them?

author: MC2Short
author_rank: Contributor
timestamp: November 25, 2024, 10:11:26 pm
content: Yeah, physically.. I desoldered them using my soldering iron and desoldering wick. I might have had the heat up a bit too high on my iron. I thought I'd be able to pull it off, but I really need some better equipment like the hot tweezers and even a digital microscope soldering station. With a lot of stuff from being a mechanic to doing this type of stuff, a lot of it really does come down to having the right tools and equipment. I'm probably going to buy both those things, but I still have no idea what those sot-23's actually are, so until someone with a fluke 175 can tell me I'm stuck. I believe it's a revision 15 board as when it turned on prior it used to quickly display F175 on the screen which the older versions don't do apparently from what I've read. I can just look at the board and read it to be sure but I'll need a few hours before I can do that. Fortunately I didn't break any of the copper traces off the board.

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2024, 10:55:15 pm
content: If you couldn't read the markings on the components prior to desoldering them and the physically fell apart when you took them off, I'd suspect that they got blown up and toasted. Unfortunately I cannot fnd any 175/177/179 or 77IV teardown photos with enough resolution to read the markings. However, removing them shouldn't make the meter completely dead either unless one or more of them is actually part of a different circuit and not input clamping. Hopefully someone somewhere can eventually provide a hi-res photo of that board.

author: MC2Short
author_rank: Contributor
timestamp: November 26, 2024, 01:18:11 am
content: Again I appreciate the help. If anyone can find it, or happens to have the same board, it's stamped FLUKE 17X-3021 REV 004 at the top of the board. Thanks again.

author: cardosoluis
author_rank: Newbie
timestamp: November 26, 2024, 07:49:55 am
content: Hi! i don't know it his might be helpfull but i have a fluke 77 iv that i'm repairing myself, here's the pictures of the components.my board seems a bit different than yours, if you look for Fluke 77 iv erratic behaviour you have thare a full picture of my board to compare

author: mqsaharan
author_rank: Regular Contributor
timestamp: November 26, 2024, 12:01:08 pm
content: Hi MC2Short,I am not aware of any rules/guidelines that component manufacturers follow for labeling SMDs. You need to be careful while working with these. They are not always easy to figure out.In the picture posted by cardosoluis, out of six sot-23 devices marked by bdunham7, marking for the first one from top is readable. And a quick search suggests that it is MMBT6429 NPN Transistor.I am attaching here a picture where the markings for the last 4 as well as the 2nd one from top is readable. I am not sure what device it is. Hopefully, someone knows about it and helps you figure it out.The last 4 devices have the same markings and look like they are being used as clamping devices. I am not sure exactly what devices these are, but I think they'll be NPN transistors of some sort.I hope it helps.EDIT: Please see the message in the following link for the 2nd device.https://www.eevblog.com/forum/repair/fluke-77-iv-repair-no-backlight-or-continuity-buzzer/msg3265012/#msg3265012

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2024, 05:05:14 pm
content: If I had been able to see those markings I probably would have suggested only removing the bottom 4 devices marked "JC". I wasn't able to definitively find what any of them are as those markings and package could be either transistors or dual-diode packages. There are a few members that seem to be really good at identifying SMD packages so hopefully one of them will spot this thread--or perhaps the OP can post another thread specifically on that subject.Removing the protection components, whether transistors or diodes, won't cause the meter to stop functioning.

author: MC2Short
author_rank: Contributor
timestamp: November 26, 2024, 06:35:15 pm
content: I found a picture I had of those top two sot23's, but I can't figure out what they are.. The top one especially is hard to read to me. I also found a pretty good picture of the bottom four. Looks like 6B> or something along those lines. I think the 6B> might possibly be a BC817-25, but I'm not sure.After doing a lot of reading I think the CXQPI is a IRLML6302And I think the M1L one is a NSVMMBT6429LT1G but if anyone else has a opinion on what it might be please let me know

author: Ugur
author_rank: Regular Contributor
timestamp: November 28, 2024, 08:20:22 am
content: This is true.

author: bdunham7
author_rank: Super Contributor
timestamp: November 29, 2024, 06:57:27 am
content: Quote from: MC2Short on November 26, 2024, 06:35:15 pmNow that you have them off, can you verify that pin 1 and 2 (base and collector) pads on the board are connected where the "6B" components go? From another picture it looks as if pin1 is NC on these, but if there is a trace under the body of the device then everything makes sense and BC817-25 will work just fine as will many other NPN transistors.You've done some pretty good part number research. I think your conclusion on the M1L is correct. Your ID of the CXQPI is interesting and a plausible reason for the meter to stop functioning. What did you read and how did you come to find the IRLM6302 number?

author: MC2Short
author_rank: Contributor
timestamp: December 13, 2024, 08:22:26 pm
content: I apparently got them right because I ordered those sot23s and now my fluke 175 works perfectly again. I'm amazed really.

author: MC2Short
author_rank: Contributor
timestamp: December 13, 2024, 08:25:17 pm
content: I used this for identification for the CX sot23

author: MC2Short
author_rank: Contributor
timestamp: December 13, 2024, 08:30:04 pm
content: I might have just got lucky, but I was searching forever to try and figure out what those codes might have been for.