Sick Fluke 89 IV (Fluke 189) - Page 1
Forum section: electronics / repair

author: jchw4
author_rank: Regular Contributor
timestamp: April 26, 2021, 05:28:18 am
content: I got a sick Fluke 89 IV which turns on, but displays stable 0 in all modes. No fluctuation, nothing. Exactly 0.After disassembly the only suspicious part is area around tantalum (?) capacitor next to the Fluke IC. I am tempted to wash it with IPA, but I don't see any sources for this leak.Do SMD capacitors leak? I thought they do not.In-place the capacitor measures 47uF and ~21Ohm ESR. The supercap above seems to be intact, no corrosion. There are also less flakes around it.Could this black SMD electrolytic capacitor be the source for this mess?(The second photo is full size and very large.)

author: Falkra
author_rank: Regular Contributor
timestamp: April 26, 2021, 08:01:18 am
content: Hi, a bit of cleaning around the main IC with IPA (or first compressed air) can't be a bad thing, it seems dirty (some... dust maybe ?), there is a bridge or two on the main IC, but it may not be conductive, anyway, cleaning is fine.The cap has high ESR (21 ohms), but this should be measured out of circuit for better results, to be sure : it may be ok in fact. I would first clean and test again (no risk, except spending some time reassembling)

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 26, 2021, 12:24:31 pm
content: As Falkra said: Some mess between pins 11-12 and 38-39-40.A few other ideas... Power it from a lab PS and check the power rails. (There's one topic around with photos that give test points for power.)Check backup capacitor voltage.Next may be a defective 93C46 EEPROM, I've posted dumps in another post but if you do have to replace it you'll likely need to go through the readjustment procedure.Edit:No, usually tantalums don't leak they short and given enough power go up in flames.What condition is the battery compartment in?The PCB has plenty of flakes that look like battery leakage crystals.

author: jchw4
author_rank: Regular Contributor
timestamp: April 28, 2021, 12:59:07 am
content: Quote from: Falkra on April 26, 2021, 08:01:18 amIt's not a bridge. I don't have a better photo, but it looks like a transparent jelly. It's actually not on the board, it's "up in the air" attached to the other side of the IC leads.QuoteYep, this is what I thought too.Quote from: shakalnokturn on April 26, 2021, 12:24:31 pmI did. I suspect that there is missing -3.3V rail, but I haven't traced it yet. Will post later when I find some time to work on it.It's difficult to see on the photo, but there is some green rust on a few traces just above the Fluke IC. It does not look too bad though.Quote3.3V. Seems fine.QuoteThe battery compartment is bright and clean, and so are the battery contacts.I was very surprised to see these chips, after I removed the shield (this area is covered with shield). But what puzzles me is that the shield is totally clean and no spots on it.So the chips do look like a battery damage, but everything else inside is very clean.Under different angles I can see that there was something spilled on the board in this area (there are very tiny drops of something all around like the transparent jelly mentioned above).This way I am trying to find the source of this gunk before cleaning, because otherwise I may never find it.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: April 28, 2021, 03:08:24 am
content: Probably the supercap is at fault.https://www.eevblog.com/forum/testgear/fluke-189-with-leaking-surface-mount-coin-cell/

author: retiredcaps
author_rank: Super Contributor
timestamp: April 29, 2021, 12:28:13 am
content: Quote from: jchw4 on April 26, 2021, 05:28:18 amDid you check the input protection like fusible resistor, PTC, and MOVs?

author: Black Phoenix
author_rank: Super Contributor
timestamp: April 30, 2021, 02:20:22 am
content: Quote from: feedback.loop on April 28, 2021, 03:08:24 amThe supercap have absolutely no influence on this error that OP is reporting. The only thing the supercap is used is for RTC and keeping the settings/logs then changing batteries. Other than that, you can remove the supercap from the mainboard that the DMM will work without any problem in any function, except that his memory will be reset as soon you remove the batteries.Plus if you look at the pictures the user published, his supercap is in excellent condition, without any visible damage. It doesn't mean it could be dead, but it is not leaky, that's for sure.

author: jchw4
author_rank: Regular Contributor
timestamp: May 17, 2021, 02:35:17 pm
content: Quote from: feedback.loop on April 28, 2021, 03:08:24 amI did desolder the supercap, but it seems to be OK. No liquid damage.Quote from: retiredcaps on April 29, 2021, 12:28:13 amYes, I did. The all seem to be OK.Quote from: Black Phoenix on April 30, 2021, 02:20:22 amI would guess that feedback.loop was answering my original question "where this stuff has come from". But you are right, the supercap was OK.

author: jchw4
author_rank: Regular Contributor
timestamp: May 17, 2021, 02:55:14 pm
content: There was a very nice 189/89 IV repair manual once published on the forum (see the links to the posts):Quote from: daisizhou on August 26, 2020, 12:18:59 pmQuote from: kripton2035 on August 26, 2020, 02:49:16 pmWhich was very helpful, but did not help much. All the voltages seem to be OK. Input path is OK, ceramic resistor network is fine.I actually have another 189 (this time a a real 189) that I could compare.(It was also sick, but soaking the PCB in IPA for a day as suggested by the manuals above seem to have fixed it.)So after much poking around, I found 6 traces going from the measurement IC to the uC (see the image below).(Luckily these signals have accessible vias (and wire-wraping wire nicely fits in), so these is no need for fancy grabbers to grab the data.)My 189 has pulses on five of them (the one remaining I marked "SPI GND(?)").The "READY (?)" pin has double pulses synchronized with the SPI.So you can see that 189 has "fancy" bus with a lot of data, while 89 IV has a very short repeating pattern.And 89 IV has no signal on the mysterious "READY" pin!I also dumped the SPI Flash initialization sequence, and it seems that both meters read mostly identical addresses and values.I can use settings, switch modes and ranges, turn on the backlight, etc. So it seems that everything works except that the value is always 0.Unless I am missing something, I guess that the measurement IC is blown. Could you suggest other ideas?Upd: Added another photo to show that uC is on the other side of the board and it's not the TIR1000.

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 17, 2021, 04:58:39 pm
content: The TIR1000 your coloured lines seem to go to is a IrDA interface encoder / decoder not SPI flash.The closest to SPI flash (but not SPI) is the 93C86 next to it, I previously mentioned this although stating the wrong capacity.They do fail. It could be as simple as the 93C86 not responding on the bus, calibration values are not loaded to RAM the DMM refuses to go any further.Good luck I'll keep reading...

author: jchw4
author_rank: Regular Contributor
timestamp: May 17, 2021, 09:21:30 pm
content: Quote from: shakalnokturn on May 17, 2021, 04:58:39 pmIf you look closer, the traces do not go to the TIR1000. The uC is on the other side and is not shown here. The lines shown go somewhere in the middle layer till the via, and then continue on the other side (see below).(Please also note that this photo is mirrored to match the layout.)

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 17, 2021, 09:30:10 pm
content: The new photo makes things clearer.You could be right about the analog IC, still there's plenty more to look at before coming to that conclusion.

author: Shock
author_rank: Super Contributor
timestamp: May 18, 2021, 12:50:41 am
content: Quote from: jchw4 on May 17, 2021, 02:55:14 pmJust curious what the symptom of the 189 you soaked was.

author: jchw4
author_rank: Regular Contributor
timestamp: May 18, 2021, 01:25:50 am
content: Quote from: Shock on May 18, 2021, 12:50:41 amIt is actually described in the "unofficial repair manuals" from above. Basically it was off by ~10%.It also had visible battery damage, battery contacts corroded to pieces, damaged the case, the PCB...So it was pretty obvious it needed some cleaning(And luckily the damage area was only around the input jacks and the protection circuit, otherwise it could be totally dead now.)After brushing and finally soaking for a day, it seems to behave more reasonable now. I did not have time to verify it, because the case is still damaged, but it seems to work.

author: jchw4
author_rank: Regular Contributor
timestamp: May 22, 2021, 11:26:40 am
content: As I don't have more ideas now, I'll probably share what I traced.Here are power and "some" of ground lines of my the Fluke 189.Battery(-) seems to be global ground.Digital part has separate +3.0V line that is also held by the supercap.