Electronics > Repair
Fluke 87-1 Constant beeping, stuck in V AC and no measurement possible
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Wildsau96:
Hi everyone,

i got a problem with my Fluke 87-1. When i turn it on, it just beeps and the meter is stuck on V AC. No matter what i select on the rotary switch. In the mA/A position the meter crashes. And there are no measurements possible.

At first i suspected the rotary switch. I cleaned it and the whole board with IPA. The ptf section seems to be in good condition (I attached some pictures of the board). There are no shorts in the banana jacks.
I also inspected the board for damaged traces or components. I couldn‘t find anything.
It fails the rotary switch test (0000 in every position and crashes at the mA/A positions) (The switch shaft is not reversed).

So i dug deeper into the whole thing. Modemheads guide on his blog already helped me understand the workings behind the mode selecting.
All my values for the power supply section of it are correct, except for AP6 (U4P87). When the meter is turned on, it reads -2.8 V.

P03 (U4P66) starts at -0.468 V in the OFF position and 0V in the V AC position and then goes down to -2.8 V (AP6) in about -0.45 V increments with every switch position. Between the switch positions it blips down to -4.4 V (Vbt- is -5.35 V).
May that be a indicator of the problem?

I really hope U4 is not cooked, because otherwise the meter is in good condition.

I also checked various other aspects of it:
- The varistors RV1 and RV2 both measure OL.
- The fusible resistor R1 measures 1.011 kOhm
- The thermistor RT1 measures 1.469 kOhm
- The spark gap E1 measures OL
- The bridge rectifier U1 shows good results in a diode test
- The fuses F1 and F2 are still good
- The input impedance measures OL in the V AC position and 11.10 MOhm in the V DC position with a battery installed. Without a battery installed it measures about 22 MOhm in V DC
- The meter draws 9.3 μA from the battery, when the rotary switch is in the OFF position and 1.2 mA in the ON position
- I resoldered some pads that looked suspicious
Wildsau96:
It also seems like i get a ghost reading in the V AC mode. The reading seems to be unaffected by the range setting.

Here is a link to a video, where you can se the problem with the meter:
https://youtube.com/shorts/WHH5sR39Y2c?si=ev4wmNNqIr8c1dWH
Paceguy:
Hi, I would check the 4 input jack block. One appears to have cracked plastic. The 87 beeps when leads are installed in wrong jacks in respect to the rotary switch settings. Also check the spark gaps.
Wildsau96:

--- Quote from: Wildsau96 on May 07, 2024, 06:58:44 pm ---
At first i suspected the rotary switch. I cleaned it and the whole board with IPA. The ptf section seems to be in good condition (I attached some pictures of the board). There are no shorts in the banana jacks.

- The spark gap E1 measures OL


--- End quote ---
Louis_C:
Have you checked the resistor network chip. It's the large white SIP on the side of the board. Cold solder or broken connection can cause this to occur.
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