Electronics > Repair
Fluke 5440B repair
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TheDefpom:
Sounds similar to an issue I had on my 5200a, one of the output transistors were breaking down under high voltage, causing it to short out and drag the output down.
Rax:

--- Quote from: TheDefpom on July 14, 2024, 05:59:10 pm ---Sounds similar to an issue I had on my 5200a, one of the output transistors were breaking down under high voltage, causing it to short out and drag the output down.

--- End quote ---

Trying to see trough the weeds of the troubleshooting steps and the eclectic results they return, one thing stands out from my symptoms, namely the fact that the output plateaus at about 60V regardless of setting, which I think seems to point to a hard level-related failure like I think you're describing, Scott. I don't think the issue is the "level-composing" logic, or even the monitoring/protection systems, but a simple hard stop at 60V out.
Rax:

--- 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 tried to contact him to no avail. Having the possibility to use such a board would be fantastic. I'm sure there's others like me that would appreciate such a board. Though I can't imagine this was/is a large market for their board.
Rax:

--- Quote from: leighcorrigall on July 12, 2024, 01:15:02 pm ---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.

--- End quote ---

Thank you for this pointer. I have not run into this with the 5440A, I assume because of the entirely different readout.

In my unit this seems to be adjusted to 24.1V, so I assume this was the Fluke techs lowering it to what it should actually be. As a reminder, this unit came to me with all original Fluke stickers everywhere (and in pristine condition at that).
Rax:

--- Quote from: leighcorrigall on July 11, 2024, 05:13:31 pm ---If you have another 5440B that you do not mind opening, I would suggest swapping those cards, including the transformer, to see if you can isolate the problem.

--- End quote ---

This may be my shortest path to success, as I do have my 5440A, and they're very very similar, if not outright identical (other than the display board). In fact, I seem to recall I identified a couple other less know differences going by just the SMs, which may be documented in my 5440A thread.

In any case, I need to collect some guts to begin such an endeavor, as maneuvering two behemoths like these guys are are not for the faint of heart (or people liking theirs backs working OK). I need to wrestle them in a way where I could have both open side by side, and this in my cramped workshop will be tough.
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