Fluke77 stopps booting after battery replacement

[wodipo]

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?

[orbanp]

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

[wodipo]

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.

[mqsaharan]

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.

Welcome 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.

[wodipo]

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 switch

Result: 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.

[mqsaharan]

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.

[mqsaharan]

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/

[wodipo]

Yes, interessting. I also had to fix the rotary switch mechanic too several years ago.

https://www.mikrocontroller.net/topic/503332#new

There's another sudden death of the Fluke, including mine.

[shakalnokturn]

Check the reset line if it's external to the IC's.

[BILLPOD]

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.

[charlyd]

Here you have the service manual with Schematics.

for the complete manual please DM me

[shakalnokturn]

CPU reset is U2-pin35 (check C2) also check clock output from U1-pin56.