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FLUKE 8810A Display Blinking

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peterkos2:
Greetings.
 I got my hands on this older Fluke 8810A multimeter.
 Of course, I immediately turned it on and the display just flashed and it was dark. But when I opened it, I couldn't believe my eyes - the switch was in the 115V position.  Of course, farted insurance.
 A normally prepared spare inside, I replaced it, the multimeter started up, the numbers are just running around, but even when measuring it fluctuates quite a bit, it depends on the ranges - the bigger the more it fluctuates.
 I found the service manual and checked the voltages on the test points, on some it holds perfectly +18V - OK
                     -18V- so there is -24V
                    -13V - there is -19V
                     +7V - OK
                      -7V -OK
                     +35V and -35V are standard
 The problem is probably in the circuit of the CR30 bridge. The power supply of the U18-NE5534N is -26 and +16, I don't really understand it - like +16V, I understand there is a 10V zener, but -26V goes directly from the bridge...
 I tried everything I could, but I can't figure out what the problem is
 I will be glad if you direct me if possible.
 Thank you all for the answers 😀

J-R:
I am not familiar with this specific model, but as a general comment did you check the capacitors and clean the front panel switches?

peterkos2:
I checked the capacitors and they are fine, just the capacitor on the 9V branch is instead of 4700uF a little over 6000uF and the ESR is excellent, I don't understand that.  I sprayed all the buttons

yo0:
For the op, check the 1 mhz crystal oscillator, seen similar behaviors in the past twice,


best regards


Pio

floobydust:

--- Quote from: peterkos2 on March 31, 2024, 08:36:25 pm ---Greetings.
 I got my hands on this older Fluke 8810A multimeter.
 Of course, I immediately turned it on and the display just flashed and it was dark. But when I opened it, I couldn't believe my eyes - the switch was in the 115V position.  Of course, farted insurance.
 A normally prepared spare inside, I replaced it, the multimeter started up, the numbers are just running around, but even when measuring it fluctuates quite a bit, it depends on the ranges - the bigger the more it fluctuates.
 I found the service manual and checked the voltages on the test points, on some it holds perfectly +18V - OK
                     -18V- so there is -24V
                    -13V - there is -19V
                     +7V - OK
                      -7V -OK
                     +35V and -35V are standard
 The problem is probably in the circuit of the CR30 bridge. The power supply of the U18-NE5534N is -26 and +16, I don't really understand it - like +16V, I understand there is a 10V zener, but -26V goes directly from the bridge...
 I tried everything I could, but I can't figure out what the problem is
 I will be glad if you direct me if possible.
 Thank you all for the answers 😀

--- End quote ---

I would guess U18 is damaged from the overvoltage, you have NE5534 rated 44V and old service manual gives rated max 36V for '301.
Fix the -18V rail before you damage parts. Not sure about 10V zener CR34 1N961A or Q63 PNP 2N4890 TO-39 if they are OK.
U17 - Fluke 313106 Motorola MC723CG for the +18V rail, it also requires the +7V REF.
U18 - Fluke 363515 AD301A, LM301AN but OP has NE5534 for higher voltage.
U19 - Fluke 355107 Motorola MC7805CT

The +18V is the reference for the -18V rail, so they are dependent.
The -13V rail is 5V above the -18V rail.

If you ran it at 2x mains input, uh the filter caps might be damaged as well.
edit: redid post, it was out.

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