Fluke 177 multimeter repair

[manojsoorya]

Hi all
My Fluke177 is not working suddenly..... Its not show nothing in display....Battery is a new one with the voltage of 8.7 v. No corroded track in PCB. There is an IC AD737 is in PCB and it need a negative supply. But all positive voltage and regulator IC's are giving correct voltage. The negative voltage is missing, I think. Please check the uploaded image. There are two marking and I have question about this point....
1. What is the voltage in this point with respect to ground?
2. Which component is this?
I think its a voltage conveter stage and produce the negative supply.... the marking is "C5P5E" on this component. No datasheet available.....

Please help me to bring back to life...

 

[manojsoorya]

Check this image too..

The 4th pin of the AD737 need negative voltage....

Track not corroded and its connected the above point 1.

 

[tronitech]

A new battery would be over 9.0V and 8.7V doesn't sound good?

 

[rjenkinsgb]

A new battery would be over 9.0V

Yes; but the valid voltage range for dry cells is 1.5V new down to 1V per cell when exhausted.

Anything [properly] designed to operate from a "9V" battery (6 x 1.5V cells) should be able to work down to 6V so 8.7 is well up within the range.
It's certainly not the cause of this problem.

 

[manojsoorya]

Hi
Now I am figerout the details about voltage at the AD737, its ground.

Now its only the matter of "C5P5E".....

 

[rjenkinsgb]

The only references I can find to a component starting C5 are either a PNP transistor or a dual schottky diode..

I don't see enough components in that board area alone (the original photo) to create a charge pump.
It would need either two transistors and capacitors or one plus inductors, then plus a rectifier either way.
(plus resistors etc.)

What do the other heavy tracks connect to? The vias left of 1 and right of 2 in your photo?

Edit - one of my meters is a fluke 187, which does not seem too far away from yours.
I've just taken that apart to see if the circuit board is similar, but it does not have anything that looks like the areas in your photos.

It does have a very obvious miniature transformer at the top, with an LT1307 switched mode PSU DC-DC converter IC at the side of it - I think it's safe to say that will be the supply source in this one.

 

[rjenkinsgb]

Found better pictures of the overall 177 circuit board here:
http://www.eevblog.com/forum/testgear/fluke-77iv-and-179-differences-with-teardown-photos/
Look at this photo:
http://www.eevblog.com/forum/testge...n-photos/?action=dlattach;attach=181113;image

Note bottom centre - the CD4069 with chained pins, two resistors and a cap above it.

That immediately looks like some version of a classic logic inverter oscillator, eg:
**broken link removed**
or
http://www.talkingelectronics.com/ChipDataEbook-1d/html/images/4069-fig3a.gif

I believe that's the AC source that should feed via a cap to a rectifier and regulator.

I'd trace the connections from there to the other part of the circuit & also check you can see oscillation on some pins of the 4069.

That may also have two or more sections in parallel to boost the output drive to the rectifier.

 

[manojsoorya]

Thank you so much for your effort to help me...Thank you.

Finally I figerout that the controller M430F437 are faulty...Clean the pad of disply and selector switch throughly...No chane.

I allready change the LT10327, LT1070...
But no progress...

I am trying to findout the firmware for this model.....If it get, the controller available at ebay store...

If not success, I really dont know what i do next.....

 

[manojsoorya]

I think the CD4069 used forbuzzer to check the continutity. Will uplload a schematic later....