Fluke 725 and 726 schematics or service doc. - Page 1
Forum section: electronics / testgear

author: PA4TIM
author_rank: Super Contributor
timestamp: February 15, 2015, 08:30:56 pm
content: Is there someone who has the schematics for these proces calibrators.I have both here for repair. I'm in the process of drawing the front-end schematics because these will not be the only ones I get here for repair. But that is a lot of work because many traces are hard to follow because the pcb is rather crowded and the leftover space covered with silkscreen.The 725 was fried by 230V on the right input. It was shipped to a dealer for repair but came back as not repairable. The result was a relais mounted the wrong way, a wrong model TVS, damaged pads and traces, a damaged resistor, wrong connected 4053 (-5 tied to the gnd pin (because it misses 7 solder pads) and a through hole solid state relais with cut pins soldered ( cut for desoldering ? ) It costs a lot of time but it is for my best customer who has a dozen or so.So possible more things are done wrong and that way my schematics will be wrong too. If I hold the pcb against the light it looks like there is an innerlayer too. At the moment I'm stuck with a few components I can not find where they are connected to.At this moment It powers up, swtiches from V to mA and to loop. It measures V and mA but about 10 times to low. The OP297 opamp has no output but works. The fault must be somewhere after the opamp but I can not find where most of it it gets lost. Probably somewhere between the opamp and the ADC. A lot of my repairs come without schematics and most times I get them back to work again but this one is a nasty little sucker

author: yuckinus
author_rank: Newbie
timestamp: October 16, 2015, 05:37:42 am
content: hello PA4TIMhave a fried 726 also. Connected to 400V on the right input. It's a mess inside but still powers on and some functions work. Everything next to the right red jack was blown up and a schematic would be great to figure out what is missing. Did you get a schematic?

author: PA4TIM
author_rank: Super Contributor
timestamp: October 16, 2015, 06:33:54 am
content: No, I could not find a schematic. The 725 and 726 are not repaired. I repair a lot without schematics but trouble shooting these guys is not easy. From the top of my head: The 725 had a dead LT chopperamp, ADC, DAC, a few mux's, a fet switchs and some opamps and mosfets. Parts alone would be over 80 euro and it would never be as good it was with all te damage to pads and traces.I was a bit supprised to see so much damage in a Fluke. The protection seems to be of no help. But these Flukes are not made by Fluke. They are rebranded.

author: kaz911
author_rank: Super Contributor
timestamp: April 19, 2016, 12:45:16 pm
content: i know this is an old thread - but if any of you still have old 725/726 broken - I'm looking for some for donor parts. I have one where some moron tried to take it apart - so display plastic lock's are broken so won't hold display in place.Apart from that it uses 400mA when off - and does not turn on at allso right now I'm debugging. So far it seems like it might be the LT1373 or related to it anyway.

author: PA4TIM
author_rank: Super Contributor
timestamp: April 19, 2016, 03:18:21 pm
content: Sorry, no parts, they are back to the owners.

author: kaz911
author_rank: Super Contributor
timestamp: April 21, 2016, 07:42:33 am
content: if anyone needs an "x-ray" image of Fluke 725 - one is attached.Both sides photographed - "rear" side scraped so only (mostly - i'm lazy) pads and traces are left.Rear image the rotated - and put on top of top side of board - and aligned so top pads align with bottom pads.If you need original PSD file - shoot me a PM. It is 100+ MB. But here it is in "low res" png format. Helps a lot in figuring out where things go

author: PA4TIM
author_rank: Super Contributor
timestamp: April 21, 2016, 10:14:08 am
content: That is real handy. I have done this years ago in the Gimp but the result was not very good. Tried it a year ago again but I could not get the layers over each other and see-through.I would like to do it myself because I do a lot of repairs on gear without schematics and like you do it, it is so much more easy to follow traces and I love the fact that you see the vias very well. Ik is very hard on some smd boards to follow a trace to a via and find that one on the other side to continu. Also handy when there are BGA's.Can you tell or maybe share in a youtube video how you make them.

author: yg89
author_rank: Newbie
timestamp: July 05, 2016, 06:32:46 pm
content: Please, I need the value of the resistor R114, the Fluke 725.Tks.

author: Andrey66
author_rank: Newbie
timestamp: January 08, 2017, 09:54:03 am
content: Quote from: kaz911 on April 21, 2016, 07:42:33 amHello,Sorry to trouble you, and my English.Currently I repair FLUKE 725 Service manual or the circuit I have not found.I would really appreciate if you send me the original PSD file in any file hosting.Thank you Andrey

author: Nexis
author_rank: Newbie
timestamp: September 17, 2017, 10:56:28 pm
content: Hi KazIs it possible to send me the PSD file?Best regardsNeil

author: giacomo
author_rank: Regular Contributor
timestamp: December 28, 2020, 03:05:39 pm
content: Hi, guys i have just received a broken 725, the electronics seem untouch but one plastic clip that should hold the display was brooken.I quick hooked it to my power supply and when i turn it on it drows 400mA, the voltage drop to 2,5v and it does not want to turn off when i push the power button again. No display, but i hear a buzz, probably from the transformer.The small transformer in the middle immediatly becomes hot, so i disconected it from the power and start by checking at the diodes and tantalum capacitors around it. Now I suspect the LT1373.I just started but since there is no schematic i would glad to hear the experiences from other people.