Electronics > Repair
Fluke 5440B repair
Rax:
I landed a 5440B at my bench that's exhibiting some confusing symptoms.
The unit came to me in pristine form - Fluke original stickers everywhere, original manuals and cables. Even the registration form was enclosed.
The unit exhibits no signs of life, other than the green power LED lighting (next to the turn on knob). Nothing else seems to be alive, including the fan. I opened the unit (tearing all those cal stickers...) and checked the rails, both unreg and reg on A10 and A12, and they seem reasonably close. Definitely "alive."
Upon checking A19 though, there's no DCV present on it. Which makes some sense, given the fan is also off (they feed off of the same 120V VAC line). Upon checking for continuity between J2 (13/26; 14/28) and J8 (12/24; 11/23), I see that the lines on the motherboard seem to be OK.
Other checks:
* I see 116VAC between 9F and 9S on A11
* The line switches (S1, S2, S3) seem to show correct continuity between their poles
* I measured all "full winding" taps of the GUARDED XFMR and they all show reasonable ohmic values
I'm not sure how to explain the presence of the line VAC between 9F and 9S, and no VAC at the fan and UNGUARDED XFMR... Particularly as CR2 is lighting. Not sure if I should suspect the E1 spark arrester or what else could be going on here.
Thanks for all input.
picburner:
with the 120V mains one reason for the failure of the instrument and the fan to turn on could be one of the switches s1-s3 which has/have false contacts. Although you have measured them (in circuit) the presence of the transformer windings may have distorted the measurement. Try exercising the three switches several times.
The green LED CR2, connected to a secondary winding of the transformer (by cr1/r1), could light up dimly even with a small flow of current and this contributes to confusion.
Check that s4 is also working properly of course.
Also, to be safe, I would also check the fan itself by unplugging it from the instrument.
leighcorrigall:
You probably want to start by reviewing the following documentation from the service manual:
Overview:
Figure 3-1 module locations
Fan-related diagrams:
Figure 2-7 power supply simplified schematic
Figure 7-6 A3 (motherboard)
Figure 7-14 A11 (guarded transformer termination)
Specific to the outside regulation that is connected with the fan:
Figure 7-20 A17 (outside guard regulator)
Figure 7-22 A19 (outside guard terminator)
Assuming the fan is working and unable to receive power, you should look at the switch (Figure 5-25), the mains input and guarded transformer (Figures 7-6 and -14), and all of the fuses (Figure 7-14).
EDIT: Believe it or not, you should also remove the fan filter. Sometimes it gets stuck in the fan and prevents free movement. I have seen a video somewhere on YouTube with this problem. Might as well rule out the really simple things first.
EDIT: If you are to remove the front panel to access the switch, pay extra attention to the DIP plug. It is extremely fragile and should be handled with great care. The front panel can be removed after both clam-shell covers are removed and the rack handles.
EDIT: To remove A19, the fan must be removed and both of the large mounted capacitors. The large filter capacitor should eventually be replaced as it can cause overheating of A17 and A19 boards, resulting in a 'check guarded power supplies' fault. C7 36DX343G015AF2B (CAP, AL, 34000uF, +/-10%, 15V) should be replaced by CGO343M020L or MAL210116333E3. I use the Vishay capacitor even though it is much shorter than the original.
leighcorrigall:
Attached is a picture of the guarded transformer (A11) with a lot of the fuses.
EDIT: This module is connected to the frame from the adjacent side with a set of screws. You will have to remove the clam-shell covers to access them.
Rax:
--- Quote from: leighcorrigall on July 09, 2024, 05:51:28 pm ---You probably want to start by reviewing the following documentation from the service manual:
Overview:
Figure 3-1 module locations
Fan-related diagrams:
Figure 2-7 power supply simplified schematic
Figure 7-6 A3 (motherboard)
Figure 7-14 A11 (guarded transformer termination)
Specific to the outside regulation that is connected with the fan:
Figure 7-20 A17 (outside guard regulator)
Figure 7-22 A19 (outside guard terminator)
Assuming the fan is working and unable to receive power, you should look at the switch (Figure 5-25), the mains input and guarded transformer (Figures 7-6 and -14), and all of the fuses (Figure 7-14).
EDIT: Believe it or not, you should also remove the fan filter. Sometimes it gets stuck in the fan and prevents free movement. I have seen a video somewhere on YouTube with this problem. Might as well rule out the really simple things first.
EDIT: If you are to remove the front panel to access the switch, pay extra attention to the DIP plug. It is extremely fragile and should be handled with great care. The front panel can be removed after both clam-shell covers are removed and the rack handles.
EDIT: To remove A19, the fan must be removed and both of the large mounted capacitors. The large filter capacitor should eventually be replaced as it can cause overheating of A17 and A19 boards, resulting in a 'check guarded power supplies' fault. C7 36DX343G015AF2B (CAP, AL, 34000uF, +/-10%, 15V) should be replaced by CGO343M020L or MAL210116333E3. I use the Vishay capacitor even though it is much shorter than the original.
--- End quote ---
Thank you, Leigh. Very thoughtful, insightful input.
I am pretty intimately knowledgeable of the 5440 series: https://www.eevblog.com/forum/metrology/fluke-5440a-datasheet/, which I think you've seen.
I am currently suspicious of the card edge connectors (bad contact?...) and maybe the E1 spark arrestor. Also, picburner's recommendation to closer examine the line switches. I may either condition them and try again on board, or pull them off the board and properly test them.
I suspect once I figure out why the 120VAC line going to the outboard supply and fan is fixed, the unit may just go back to operation. But why that's offline is currently a mystery to me.
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