Fluke 5700a repair

[TiN]

veedub565
Upload to my FTP server, I'll give you web-page with all links automatically. I still have some 180GB on storage available, should be enough 

I meant to make a huge article about all 5700-related shenanigans (and photos, I have lot of gigabytes of photos of all different 5700/5720 and even 5730 variants), but easier to say than done.

That's useful to know, so looks like all of them came with the rear terminals, but only wired up as an option.

Not all of them, but most. And yes, you could order rear terminal option which means Fluke would disconnect front terminal cable and route it to rear instead. There is little different guarding as well in that configuration. The procedure is briefly outlined in SM, as user can do that swap too.

Yes, when I replaced resistors I went for bigger size instead of matching BOM to the letter. E.g. in many cases I've replaced 1/4 or 1/2W resistor with 2W or so, given other specs match or exceed. Also I liked to use MF resistors instead of thin/thick film, where possible, except high power resistors.

[veedub565]

Looks like I'm going to have to re-order some of these resistors. At least they aren't too expensive.

[veedub565]

So after measuring the CC resistors from the A18 board there seems to be a general pattern. And I would imagine its the same for all the boards.

All measurements are approx

0.125w =
0.25w = 2.3x6.5mm
0.5w = 3.5x9.5mm
0.75w = (don't think there are any)
1w = 5.7x14.5
2w = 7.9x17.7mm


So I'm just going to have to re-order the resistors, and pick a size close to the originals, that obviously matches or exceeds the original wattage rating.


Just the A18 board is a lot of work, a lot of measuring component sizes, measuring the pitch, picking correct spec etc. Quite a bit to think about really. It looks nice with all new electrolytics fitted though

[MegaVolt]

Also to replace the carbon composite resistors, especially the 1W ones which are to be replaced with 3W ceramic.

Can you tell me which resistors you consider to be carbon? The ones in the picture are of different sizes, I think they are wire-wound.
And judging from other Fluke instruments, some of them are used in precision circuits and are specially selected.

[Kleinstein]

The larger resistor in the size comparison is a typical small carbon comp resistor. The smaller one is a film based resistor, likely metal film.

The carbon composite resistors usually have the brown plastic body with smooth surface (no wire visible). The come in different sizes but usually very similar optics.
The carbon resistors usually are with 5,10 or 20% tolerance - hardly ever better than 5%. Precision wire would are often better than 5% (except for low values).  The component list should state the type of resistor they are. They would not replace a corbon with a precision wire wound - a power wire wound or metal film maybe. The carbon resistors were never meant to be stable. It was know from the start they are poor stability.

[picburner]

Board A18 for example: all resistors circled in red are carbon composite resistors.

[MegaVolt]

Board A18 for example: all resistors circled in red are carbon composite resistors.

Why do you think so?
According to the documents these are IRC BWH resistors. Wirewound.
https://www.tedss.com/LearnMore/Failsafe-Moulded-Wirewound-Resistors

They are also used in the Fluke 5440 in the voltage divider circuits (after the special selection). That is, they can provide accuracy and matching.

Where did you get the idea that these resistors are carbon?

[picburner]

Why do you think so? According to the documents these are IRC BWH resistors. Wirewound.

Simple: the value of resistance.
The resistors in the board go up to 560Kohm while those of your link reach 2.4Kohm max

[MegaVolt]

The resistors in the board go up to 560Kohm while those of your link reach 2.4Kohm max

Do you have a datasheet for these resistors?

So far I see in the Fluke 5440:

The resistors are in the output divider and provide 5ppm instability. These can't be carbon resistors. Fluke are not stupid.

Their resistance is 99kOhm and 18kOhm

[MegaVolt]

The ratings on the schematic are different from what is on the board. This may be the difference between the A and B version.
The ratings on the board are really less than 2.4kOhm.
I'm confused... how do I distinguish one resistor from another?

[picburner]

I dissected a resistor of this type that I had in the junk drawer.

1: insulating body (bakelite or ceramic)
2: resistive material (mixture of coal, talc and other binding compounds).

[MegaVolt]

I dissected a resistor of this type that I had in the junk drawer.

What is the brand of these resistors? Perhaps a datasheet?

[Kleinstein]

It us rather difficutl to so if they are carbon composite or the linked high power wire wound ones with overmold.
The resistor value gives a hint as the wirewound are low resistance only. The molded carbon compasite type was quite common.

Anyway the wire wound version linked is not a precision type, but one to work at relatively high temperature and thus high power for the given size. It may be a good choice for those resistors that get quite hot. There may be a few in those case actually be such wire wounds, but is hard to tell from the look.

For the precision it would not make that much difference (except that the cabon ones usually have a negative TC (some -200 ppm/K) while the wire would are more likely to have a postive TC like + 100 ppm/K.  So in theory one could test (usually out of circuit): postive TC is likely carbon and negative TC is not carbon.

[MegaVolt]

Anyway the wire wound version linked is not a precision type, but one to work at relatively high temperature and thus high power for the given size.

The Fluke 5440 uses them for an accurate output divider. They promise 5ppm.

[MegaVolt]

What is the brand of these resistors? Perhaps a datasheet?

The carbon resistors are from Allen-Bradley. In order to distinguish them you need to read the BOM sheet carefully.

[MegaVolt]

Datasheet

[veedub565]

Board A18 for example: all resistors circled in red are carbon composite resistors.

Why do you think so?
According to the documents these are IRC BWH resistors. Wirewound.
https://www.tedss.com/LearnMore/Failsafe-Moulded-Wirewound-Resistors

They are also used in the Fluke 5440 in the voltage divider circuits (after the special selection). That is, they can provide accuracy and matching.

Where did you get the idea that these resistors are carbon?

because it says so in the service manual parts list

[MegaVolt]

because it says so in the service manual parts list

Yes. I already figured it out. Externally, the same resistors can be both good wire resistors. They can also be bad carbon ones. And you can tell by their rating if they are greater than 2.4 kOhms.

[TiN]

These can't be carbon resistors. Fluke are not stupid.

Fluke came to senses and in newer A18 boards they replace all CC resistors to better types already. This is also confirmed by comparing old 5700A BOM and new 5720A BOM.

Here's how newer (year 2001) board look like:



Here how old one looked like during repair, when I cut all carbonized FR4 out and before install and air-wire all broken connections on 4 layers.



 

[MegaVolt]

Everything I said about the 5440 and the divider in it was wrong. I was looking at the wrong board. The divider is made correctly with anobtanium resistors.

[veedub565]

The new extender boards arrived, I had them made up by JLCPCB and they look pretty good (I went for blue)




It's a shame they don't actually fit the connectors 

[veedub565]

Images won't embed for some stupid reason. Here you go

https://flic.kr/p/2mn7aQo

https://flic.kr/p/2mmYusc

https://flic.kr/p/2mn3n5s

[TiN]

Oopsie, sorry about that 

Forgot about that, I used Panduit DINs and they are not same as usual ones from Digikey.

You can file the excessive PCB allow connector fit.

[veedub565]

Doh! I used Panduit ones too (100-964-053) same as Fluke used.

Yes I wondered if I could file the PCB down a little to make them fit. I didn't want to risk damage any internal tracks which may be there. Looks like it should be ok though

[TiN]

You can cut freely, nothing to worry about. Edge plane, including inner layers not even connected to anything.