Fluke 87V wont turn OFF - Page 1
Forum section: electronics / repair

author: AngraMelo
author_rank: Regular Contributor
timestamp: October 31, 2018, 10:08:02 pm
content: Hey guys, got a cheap 87V from a dude over the internet.Came with both fuses blown but the fusible resistor was fine.When I try to power it off it just goes to uA mode.I tried everything, cleaning the contacts, measuring all the capacitors and diodes... I though it was an allignment thing on the selecting weel but it seems more than that.I do have a working 87V here and I check all the measurements and they are very close besides one smd diode.The diode right above the battery jack reads 30Mohm on the good 87 and 3Mohm on the bad.Im a bit lost, is that a function that I ahve to turn off? What else should I check?I dont have the option to send it back to fluke because I live in Brazil and when the meter gets through customs they will simply charge me a insane ammount of money as if I were importing it.any tips?

author: lowimpedance
author_rank: Super Contributor
timestamp: October 31, 2018, 10:49:00 pm
content: Your best bet would be to down load the original 83-85-87 series service manual, now this is of course not the 87V (which has no available schematic.) but will be better than nothing.Compare the 87 schematic for the power supply section and the 87V PCB to see any similarities and hopefully there are.The 87 manual has a power supply test section for faults that might shed some light. Particularly as you have a good 87V to compare against.The Fluke web site has the service manual for the 83,85,87 series.

author: retiredcaps
author_rank: Super Contributor
timestamp: October 31, 2018, 11:12:43 pm
content: Quote from: AngraMelo on October 31, 2018, 10:08:02 pmThat is pretty standard with my ebay experience despite seller advertising meters as working. When I tell them the fuses are blown, they don't believe me saying the meter turns on. Obviously, they don't understand what the fuse does in a meter and probably shouldn't be using a Fluke.QuoteDoes the lcd on the meter show the correct annunciators in all positions other than off? Does DCV rotary setting show DC on the lcd?QuoteDid you look under the selector wheel? Seehttp://mrmodemhead.com/blog/fluke-83-dmm-repair/What is the current draw when the broken 87V is on DCV and off? Are they comparable to the working 87V?

author: retiredcaps
author_rank: Super Contributor
timestamp: October 31, 2018, 11:20:26 pm
content: Quote from: lowimpedance on October 31, 2018, 10:49:00 pmModemhead's Fluke 83 blog entry that I referenced above goes through troubleshooting and measuring the 83 power supply.

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 01, 2018, 12:14:42 am
content: Quote from: lowimpedance on October 31, 2018, 10:49:00 pmI will look for them and check them out!Quote from: retiredcaps on October 31, 2018, 11:12:43 pm

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 01, 2018, 12:18:18 am
content: You meant the current when the selector is over OFF? If yes, than the current is 1.28mA

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 01, 2018, 12:20:34 am
content: I also looked under the selecting weel, both the good 87 and bad 87 look identical, from their spacing to their hight.

author: lowimpedance
author_rank: Super Contributor
timestamp: November 01, 2018, 02:25:04 am
content: Quote from: retiredcaps on October 31, 2018, 11:20:26 pmNice practical walk through the procedure.@AngraMelo, follow the linked blog above rather than the manual to start with.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 01, 2018, 03:03:46 am
content: Quote from: AngraMelo on November 01, 2018, 12:20:34 amWhen I mean look under, I mean to remove it and look under. Seehttp://mrmodemhead.com/blog/fluke-83-iii-rotary-switch/

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 01, 2018, 02:12:29 pm
content: I took it all apart, including the weel and cleaned it. I was not clear on the previous reply, I meant to say that I detached the weel from the board and check the contacts against the good 87 and they were identical, I also rubbed them with isoalcohool as well.

author: lowimpedance
author_rank: Super Contributor
timestamp: November 01, 2018, 10:20:59 pm
content: If the meter functions correctly when actually switched to various modes but cannot be turned off then go through the external components associated with the power supplies for shorted or leaky parts.It has to be one of those, and the 87V will probably be similar to the earlier series in respect to the supplies and how its turned on and off.

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 03, 2018, 06:43:30 pm
content: To keep you guys updated:Ive found a shorted transistor, it is a 3904 in smd format with the letters 1am over it.As soon as I order a new one and get it fixed I will post pics for future reference if anyone has the same problem.

author: lowimpedance
author_rank: Super Contributor
timestamp: November 03, 2018, 11:07:34 pm
content: Thanks for the update. Had to chuckle at the bit in your sentence "1am over it".Sounds like you are well 'on it' now.

author: ElecSeb
author_rank: Regular Contributor
timestamp: November 04, 2018, 07:14:46 am
content: 1AM MMBT3904L General Purpose Transistor NPN Siliconhttp://www.onsemi.com/pub/Collateral/MMBT3904LT1-D.PDF

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 04, 2018, 10:33:00 pm
content: hahahahahhaha I did not see that! I guess I was so glad Ive found something that Im making jokes without even noticing!

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 08, 2018, 03:57:11 am
content: Well friends, I changed the smd transistor and it still continues. I can still measure the short between base and emitter. I look at everything around it but I cant figure it out.The meter still wont power off

author: Psi
author_rank: Super Contributor
timestamp: November 08, 2018, 06:32:41 am
content: Fluke sometimes will replace their meters even if you don't have any documentation.Could try contact them.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 08, 2018, 10:35:37 am
content: when the transistor was removed the meter did come off ? you may have something failed who always drive the transistor on ?could you take a picturs on the transistor section ?what is the transistor pcb markings location ?There is the model 87 service manual: i think it sould be similar to the 87V serie in some ways.http://assets.fluke.com/manuals/83_85_87smeng0500.pdfCheck section 5-10 page 83, you have theQ3 transistor mmbt3904 who drives Q8, maybe you have something like the mosfet (Q8) who can be shorted out

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 09, 2018, 01:12:19 am
content: Thank you for the schematic!The 87V is rather different but Im found some similarities.Here is a picture of the bad transistor that funny enough was replaced and is still bad...

author: coromonadalix
author_rank: Super Contributor
timestamp: November 09, 2018, 01:21:42 am
content: okWhen you removed the shorted transistor, have you tried the meter ? is the meter stayed off ? or on ?I would remove it again, and check the other nearby sot-23 transistor for short ?Not sure about the 5 pins sot, maybe one is an regulator and the other an protection device, could you write their markings ?

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 09, 2018, 01:31:40 am
content: Both the 5 pin smd's seem to be regulators.The small one is marked: AQIthe larger one PCYIThe other transistors on upper left corner of the picture do not appear faulty.I did not try the meter without that transistor. I will do that tomorrow and get back to you!Thank you so much for helping me!

author: coromonadalix
author_rank: Super Contributor
timestamp: November 09, 2018, 02:56:43 am
content: I think the AQI is an LDO regulator like :AQI smd marking gives this :TPS71533DCKRMAX6745XKLD3BQ71533DCKRand PCYI gives this : TPS77050DBVT, TPS77050DBVR, TPS77050DBVRG4, TPS77050DBVTG4I maybe wrong but ? they are regulators in sot 23-5 packages

author: ElecSeb
author_rank: Regular Contributor
timestamp: November 09, 2018, 05:49:16 am
content: Also something to check are the resistors around.Found last weekend one in a fluke near a Q which was unlimited, preventing the Q from closing and thus one reason for problems.

author: AngraMelo
author_rank: Regular Contributor
timestamp: November 09, 2018, 11:37:27 pm
content: Exactly, I got the same results as your for the Q`s.I will also check the resistor. I have a crazy pain in my neck from keeping my head down on the bench for too long. Ill take a look as soon as I get better!thanks guys

author: ElecSeb
author_rank: Regular Contributor
timestamp: November 10, 2018, 06:57:02 am
content: Sometimes it is difficult to distinct values, so you might need to desolder from the board.In my case it was an 1MOhm...IN your case I would start with the 01E, O1D and 01C around it.Currently waiting for my orders to continue my repairs...