Fluke 87-I repair

[retiredcaps]

Also with the unit off, and no battery, the two MOVs register as OL both directions (getting somewhere).

I take the battery out because I might commit an oops and short something out.  It looks like removing the battery made change in the readings of the varistors.

R2 still shows as 0.8517M (which seems wrong),

My R2 definitely reads 909K in circuit (both ways).  R2 is supposed to be +/- 1%.

Could you test C20 in circuit and let me know what you get? I get about 0.136nF.

I get 0.115nF (no relative mode used) in circuit both ways.

Interestingly, it is drawing a very small amount of current when turned off... about 9.80uA.

This is consistent with modemhead's finding on the Fluke 83 (8.85uA)

http://mrmodemhead.com/blog/fluke-83-dmm-repair/

Same for this Fluke 87 post (at very bottom - 7.5uA)

http://www.edaboard.co.uk/fluke-87-flat-batteries-t268153.html

My own test also shows 7.5uA when in the off position.

[retiredcaps]

Give the PCB another good clean with IPA and check again.

Modemhead doesn't always document all his repairs, but I have firsthand knowledge that he sometimes gives multiple IPA baths to clean the PCB.  Sometimes a stiff clean toothbrush is required and lots of drying time.

I, too, have sometimes needed to give pcbs multiple IPA baths to get rid of contamination that was causing leakage current.

[staze]

okay, just cleaned it again, and again... same result. ~9.8uA when switched off. Interestingly, and maybe I'm being oblivious here, but I'm seeing 9V between the negative side of the battery (VDD/GND?) and the COM jack when the unit is switched off. That, to me, seems... wrong.

[staze]

Modemhead doesn't always document all his repairs, but I have firsthand knowledge that he sometimes gives multiple IPA baths to clean the PCB.  Sometimes a stiff clean toothbrush is required and lots of drying time.

I, too, have sometimes needed to give pcbs multiple IPA baths to get rid of contamination that was causing leakage current.

Okay, I'll give it another one tomorrow... but yeah, obviously something is leaking somewhere. Either that, or the switch is toast...

[retiredcaps]

Okay, I'll give it another one tomorrow... but yeah, obviously something is leaking somewhere. Either that, or the switch is toast...

If you read the Fluke 83 repair blog, it goes into great detail how the code switch works including diagrams on how to take the code switch off and check for contamination.

[retiredcaps]

Just a couple of other measurement suggestions?

1) What is the resistance between Z1 pin 1 and the left side of R29?  Mine is 0.2 ohms.  I'm curious if the pcb track is damaged?

2) What is the resistance of R2 out of circuit?

[staze]

I got the back switch all clean... I don't see anything dirty anymore (there wasn't really before). I'll just have to dunk the whole thing again tomorrow (once I pick up another bottle of 99% IPA) and let it soak a bit. But from what I see in the description for the 83, it sounds like when the switch is off, it's just shorting Vss to ground... so shouldn't there be SOME draw when off (only 9uA, or about 1/100th of what it draws when on).

That said, Vss and Vdd appear to be out of spec when the unit is on... which is probably due to whatever has failed. But I really don't know at this point.

[retiredcaps]

I'll just have to dunk the whole thing again tomorrow (once I pick up another bottle of 99% IPA) and let it soak a bit.

A bit of a long shot, but I also take a sharp multimeter probe or dental pick and carefully drag it between the pins of the main IC during the IPA bath.  The alternative is to use a stiff toothbrush and give the pins a good scrub.  After it dries thoroughly, I then inspect it with a 10x jewelers loupe.

Right now, I'm out of ideas, but if you are taking voltage readings, please post them so we can see.

[staze]

Just a couple of other measurement suggestions?

1) What is the resistance between Z1 pin 1 and the left side of R29?  Mine is 0.2 ohms.  I'm curious if the pcb track is damaged?

2) What is the resistance of R2 out of circuit?

1. 0.03R after zero'ing out the leads/probes.
2. 850K. Damn. Means I have to find a replacement. Gar.

So just tested Vss and Vdd again. Vss is perfect at -3.20V. Vdd is at 2.99V. So, Those are dandy. So it's not power supply, seemingly. Vref checks out at 1.2324V. VBT+ is 3.5948, VBT- is -5.794V. So I think all the various PS measurements are right on. My leakage is somewhere else, it would seem.

Doing the calculation, to get only 9.805uA of leakage (on a brand new, 9V battery at 9.473V) there's a good >1Mohm resistance the battery is being shorted through...

[staze]

Scrubbed... nothing, no change. And all the pins look good.

If you have the unit apart, could you tell me what R61 measures as (in circuit)? I ask because the reflow process for this meter and that resistor appears to have gone wonky, since it's at a diagonal. Probably not a real issue, but it has drawn my attention the whole time. It's supposed to be a 2.2M resistor (and that's what it's marked as (225), but in circuit, it measures only 7.2K, and it's the only SMT component that's crooked.

Thanks!

[retiredcaps]

If you have the unit apart, could you tell me what R61 measures as (in circuit)?

I see R61 on modemhead's picture here

http://mrmodemhead.com/blog/wp-content/gallery/f87_00/F87FR_009.JPG

but my board doesn't have R61.

My board is Rev H.

[staze]

lol! Crooked! Weird... it's like the pick and place for that one was misaligned.

My board is rev P in sharpie on the back, or rev K by the "silk screen" (looks more like solder mask covered trace).

I get about 1Meg between the battery terminals in the off position. Do you get OL/Open?

[retiredcaps]

lol! Crooked! Weird... it's like the pick and place for that one was misaligned.

I can open another 87 to take a look, but it is getting late so I don't want to make any mistakes.

I get about 1Meg between the battery terminals in the off position. Do you get OL/Open?

I get around 1.04Mohm.

This will be my last post (early AM).  I can take more tomorrow.

[staze]

well, then the 9.6uA when the unit is off makes sense. =P

At this point, I have a bad R1, bad R2, and a bad R29. Doesn't explain the voltage on the front end, but I actually haven't checked that since I removed those parts (will tomorrow).

What timezone you in (I see Canada, but not haven't looked where). =)

[PedroDaGr8]

Scrubbed... nothing, no change. And all the pins look good.

If you have the unit apart, could you tell me what R61 measures as (in circuit)? I ask because the reflow process for this meter and that resistor appears to have gone wonky, since it's at a diagonal. Probably not a real issue, but it has drawn my attention the whole time. It's supposed to be a 2.2M resistor (and that's what it's marked as (225), but in circuit, it measures only 7.2K, and it's the only SMT component that's crooked.

Thanks!

I just tore apart my working 87-I and the only resistor I could find marked 225 near u6. For some reason, I don't see r61 on the board diagrams in the service manual pdf I have. Anyways, when I measure across it in circuit (no battery, set to off) I get 8.554K.

Sent from my EVO using Tapatalk

[SoundTech-LG]

Don't know if this helps at all, but on my 79II , when I removed R1 (1K fusible) there is a trace connected to the via on the inner layer that leads to RT1 that broke off. Easy to happen as R1 comes out of the board. Might be good to check. Good luck.

[staze]

I'll check that.... but from what I could tell looking at the 87-I, it only seems like it's a front/back board. It's thick enough to be a multi-layer, but I don't see any evidence of traces on the inside of the board when holding it to a light... =/

[staze]

Checked with those components removed, and there's no voltage on the inputs (which, makes sense since they're basically completely disconnected from the rest of the meter at this point).

So, one question that comes up is...

Anyone know where I can get this: GS-3-100-9093-F-LF (3W, 909K 1% 100ppm resistor). Digikey is out of stock. http://www.digikey.com/product-detail/en/GS-3-100-9093-F-LF/989-1215-1-ND/

Can't say I've ever dealt with them having to order something. Anyone have experience? Or should I just call/email Fluke and see if they can send me replacements? Can't imagine that'll be cheap.

For now, might just try to add some resistors together to get ~909K and see what I get. Though I would think all that would lead to would be way out calibration rather than anything really strange. R29 is just jellybean.

Also need a replacement Fusible... looks like Mouser carries a 1K 2W 5% fusible which should work just fine.

[Vgkid]

It looks like I will need to follow this thread, my meter reads accurately on vollts/ resistance, not so well on mv range. The Input impedance is 10M on the DCV range, and 3M+/- .4 on, with an open circuit on the AC scale.

[SoundTech-LG]

The other thing you can do is buy a parts only Fluke on ebay, and harvest what you need.

[staze]

True, but those parts can often be bad... burned out by overvolting the meter.

Really, this meter is probably a parts unit itself... =/

I did just email Fluke asking for pricing for R1 and R2... guess we'll see.

[staze]

Ouch, got back to me. Lead time for the parts is nearly 6 weeks, and about $20. =/

Might have to see if Digikey can get them.

[lowimpedance]

 For the 909K , if space permits you could try the 1M ohm gs-3 in parallel with this 10M (High voltage and pulse withstanding 1/2W)
 http://www.digikey.com/product-detail/en/HVR3700001005FR500/PPCHF10MCT-ND/720093.
Both are in stock at Digikey. Should get you close enough to the 1%.

Have you checked R12 (most likely fine, but..).

Bodging in close enough values to test the overall function and fault find further is the way to go until your confident the meter is fully operational then get the Fluke parts to finish off.
 But if something major has gone  (IC!) then well nothing much lost, and you have a parts unit and motivation to get another one 

[staze]

For the 909K , if space permits you could try the 1M ohm gs-3 in parallel with this 10M (High voltage and pulse withstanding 1/2W)
 http://www.digikey.com/product-detail/en/HVR3700001005FR500/PPCHF10MCT-ND/720093.
Both are in stock at Digikey. Should get you close enough to the 1%.

Have you checked R12 (most likely fine, but..).

Bodging in close enough values to test the overall function and fault find further is the way to go until your confident the meter is fully operational then get the Fluke parts to finish off.
 But if something major has gone  (IC!) then well nothing much lost, and you have a parts unit and motivation to get another one 

Yeah, think I'm just going to wack in some 1/4W resistors for now to get 900K or so (since that'll be within 1%). Then a 1K 1/4W for R1... and a 100K 1/4W for R29...

I haven't done the math (since, I'm not sure how to start), but it would be curious to see if the combination of R29 reading 170K, plus R2 reading 850K, and R1 being open, combined would lead to how far out the DC volts is. I'm kind of guessing it would explain it.

R12 I haven't checked. It's on the back, so I hadn't even tried. =P

[staze]

bodged some 1/4w 1% resistors in to replace R1, R2, and R29. No change at all. Voltage on the input jacks in the DCV setting seems to be coming from the R1 side of things (lower voltage on the input jack side of R1). I need sleep, but I think I'll hook the scope up tomorrow and see if it's just a constant voltage, or if there's something obvious about where it might be from.

One of the transistors seem like an obvious, or something still wrong with the rotary switch, but I've cleaned that thing so many times at this point...

Thanks!