Electronics > Repair
Fluke 5440B repair
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Rax:

--- Quote from: TheDefpom on July 11, 2024, 11:38:48 pm ---hmmm, just did a quick search and found this....

https://www.adret-electronique.fr/fluke_5440B/fluke_5440B_display.html

--- End quote ---

Very interesting, but I'm not sure I get it - is there a board and BOM available to do this upgrade? They say this much, but I couldn't find a link to a storefront. I'm reading this with google translate, my French speaking days in school are long gone.

The other thing interesting to find out is whether this upgrade can be applied to the 5440A. I know the display module is completely different between the two.
picburner:
The person who made that board, if I remember correctly, is a user of this forum: jfphp
The board in the link is a prototype, a long time ago he sold the assembled board in his eBay shop but now I can't find it.
leighcorrigall:

--- Quote from: Rax on July 11, 2024, 10:06:56 pm ---
...

The only downside is that, as much as the unit is just about pristine, the display is really dim (and some digits are brighter than others, which I think I've seen before). A bit of a disappointment, as one thing I was looking forward relative to my 5440A is a legible display, as the 5440A's is very inconvenient to use in practical terms. The 5440B was probably on for years and years in a system environment where it was probably never turned off.


--- End quote ---

You reminded me of something very important. The Outside Guard Regulator (A17) should be operating TP4 at 24.0 V, not the specified value in Tables 3-4. This supply is for the VFD. R18 on A17 can be adjusted to lower this voltage.

In your case, the VFD is dimming because of age, or, if you are really lucky, the voltage is too low.
leighcorrigall:

--- Quote from: picburner on July 12, 2024, 04:33:46 am ---The person who made that board, if I remember correctly, is a user of this forum: jfphp
The board in the link is a prototype, a long time ago he sold the assembled board in his eBay shop but now I can't find it.

--- End quote ---

I remember this being true. The user might be willing to help out.
leighcorrigall:

--- Quote from: Rax on July 11, 2024, 11:00:27 pm ---
...

As soon as I try to go over about 40V (>= 50V), the unit fires an "OUTPUT LIMIT FAULT. OUTPUT UNDER VOLTAGE" and resets itself. Per SM (p. 4-14), I'll need to do some A8 (possibly A9 and A4) investigations... Back to pulling up the sleeves!

--- End quote ---

Glad that you have fixed the line voltage issue. Now, it is onto more problems! :horse:

Although I have not experienced this fault before, I highly recommend that while you are removing boards, you replace all of the thermal paste on each of the heat sinks. A common problem with overheated regulators is that they tend to produce undervoltage. These calibrators run very hot, and this type of maintenance will greatly improve the performance and lifespan of the unit.

You should also continue to clean the card slots as well. A4, A8, and A9, according to Table 4-1.

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