Fluke77 stopps booting after battery replacement - Page 1
Forum section: electronics / repair

author: wodipo
author_rank: Newbie
timestamp: January 29, 2022, 11:32:03 am
content: Hello all,after more than 30 years of using the Fluke77 I now have an issue that it doesn't boot anymore:The defect appears in the following manner :- Turn on the DMM- Self-test screen with all segments appears- Self-test screen does not go away and it stops and keeps the display reading.No "beep" from the buzzer that probably indicates finishing of booting.This just happened after replacing the battery.Checked the two IC's for poor soldering, but all looks fine. Is there any chance to find out what could have happenend?

author: orbanp
author_rank: Regular Contributor
timestamp: January 29, 2022, 01:04:16 pm
content: There is a 20 pages long service manual for the Series I DMM, it has a table with various fault scenarios and tests.The SM is somewhere on the net. That should help you finding the problem.Regards, Peter

author: wodipo
author_rank: Newbie
timestamp: January 29, 2022, 05:16:19 pm
content: Hello Peter,thanks for the feedback. I own the manual, but it is not much of help. The repair flow chart mentiones only defects on some discrete capacitors or issue with the rotary switch. All this is fine. There should be a clock-crystal, 32 kHz, but I still wasn't able to find that cystal on the board.

author: mqsaharan
author_rank: Regular Contributor
timestamp: January 29, 2022, 06:14:00 pm
content: Quote from: wodipo on January 29, 2022, 05:16:19 pmWelcome to the forum.I don't know if my reply will be of much help. But here it goes.The clock crystal is right above the battery under the part of the shield that is at the lower right side of the switch.I repaired mine back in 2017 by re-flowing the front end chip, AP75, the one behind the battery on the backside of the board. The soldering did appear OK to me as well (except for one leg that I found un-soldered) and re-soldering fixed my meter. After that I re-flowed the microprocessor, upper chip, the one behind the display as well. It is working great since then.And it is a good idea to follow the fault guide. Speaking of which it does say to follow the overall system check (paragraph 4-16) in case the display hangs up in power-up self test as you are experiencing. It also says that the possible components at fault could be R14, R8, R15, R16, VR1, C7, C8, Z1, CR2, U1.Good luck with your repair. Its not a bad meter.

author: wodipo
author_rank: Newbie
timestamp: January 30, 2022, 01:46:51 pm
content: Feedback from myself:- Thanks for the location of the well hidden clock crystal. The clock works fine- I have very carefull resoldered all pins of the two flat pack IC's- also resoldered the rotary switchResult: No change of the fault. Looks like that that is the end after 30 years. "Only" because the battery was replaced.. Unbelievable. Seems like sh... happens.

author: mqsaharan
author_rank: Regular Contributor
timestamp: January 30, 2022, 02:58:45 pm
content: I'm sorry it didn't work out.There are way more knowledgeable and experienced people than i am on this forum. Hopefully, someone will chime in and suggest you a better course of action.

author: mqsaharan
author_rank: Regular Contributor
timestamp: January 30, 2022, 03:07:33 pm
content: From the following thread, what I have gathered is that others are suggesting to find a donor meter if you suspect Ap75 has failed.https://www.eevblog.com/forum/repair/prestine-fluke-75-is-it-worth-searching-for-a-new-u1-chip/

author: wodipo
author_rank: Newbie
timestamp: January 30, 2022, 10:18:15 pm
content: Yes, interessting. I also had to fix the rotary switch mechanic too several years ago.https://www.mikrocontroller.net/topic/503332#newThere's another sudden death of the Fluke, including mine.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 01, 2022, 02:46:07 pm
content: Check the reset line if it's external to the IC's.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: February 01, 2022, 07:23:24 pm
content: Good Morning Wodipo, You said:"This just happened after replacing the battery." Just for the devil of it, put the old batt. back in, (unless it is totally dead).Did you put in an 'Ultimate Lithium'? Try another 'regular' 9v batt.

author: charlyd
author_rank: Frequent Contributor
timestamp: February 02, 2022, 09:50:25 am
content: Here you have the service manual with Schematics.for the complete manual please DM me

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 03, 2022, 12:54:05 am
content: CPU reset is U2-pin35 (check C2) also check clock output from U1-pin56.