| Electronics > Repair |
| Fluke 87-I repair |
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| retiredcaps:
--- Quote from: staze on February 19, 2014, 07:14:42 am ---Hmm... so resistor network, or those varistors, or.... Could you check those, and see if you get infinite in both directions? --- End quote --- As you probably guessed, after I took the photo, I went to sleep. I have to run a bunch of errands today, but I took some quick measurements using a Fluke 187 (500Mohm capacity). I can take more measurements later tonight and read your replies more fully. For now (all readings in circuit - both directions), R2 = 909k E1 = infinite RV1 = infinite RV2 = infinite R29 = 99.5k R1 = 0.9971k Z1 = to come later, but a quick measurement shows they all match values shown in Figure 5-3 (I didn't measure the 9.996M as it wasn't "obvious" to me which pins to measure) Since your RV1 and RV2 are reading in the 100Mohm area, I suggest you remove (desolder) RV1 and RV2 and see if that fixes the problem. If you are correct about the 87 getting blown out, it is likely the varistors are defective even though they don't measure shorted. |
| staze:
Cool. I'll remove those MOVs and try that. I did clean everything up, and not seeing anything indicating the damage to the PCB is causing issues. R29 still looks physically damaged. One other question... could you take a picture of the top and bottom rotary switch in the "off" position? I'm not 100% sure I didn't screw something up there. =P Those MOV's shouldn't be leading to voltage on the input side of things, would they? Anyway, at this point, guess I'm looking at at least replacing R1, and R29. But also figure it's RV1 and RV2. |
| retiredcaps:
--- Quote from: staze on February 19, 2014, 06:56:52 pm ---R29 still looks physically damaged. --- End quote --- Since my R29 measures close to the 100kohm in the schematic, yours is definitely bad. --- Quote ---Those MOV's shouldn't be leading to voltage on the input side of things, would they? Anyway, at this point, guess I'm looking at at least replacing R1, and R29. But also figure it's RV1 and RV2. --- End quote --- Here is a thread where bad varistors was causing Robomeds to have incorrect voltage readings. https://www.eevblog.com/forum/testgear/fluke-87-v-mystery-low-impedance-input/ PS. Did you measure E1? If you did, I do not see the measured value? |
| retiredcaps:
--- Quote from: retiredcaps on February 19, 2014, 06:08:42 pm ---Z1 = to come later, --- End quote --- Pin Z1 is closest to input jacks. Measured with Fluke, unknown calibration status, 187 and in both directions. Figures in the brackets are from Figure 5-3 of service manual. Z1 to Z2 = 10.012M (9.996) Z3 to Z7 = 1.1117M (1.1111) Z4 to Z7 = 101.11k (101.01) Z5 to Z7 = 10.014k (10.010) Z6 to Z7 = 1.0008k (1.0001) edit: typos |
| staze:
Was this with the 87 on or off? |
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