Old Fluke Multimeters

[blue_lateral]

The third one is 4681912.

[Dave Wise]

Just following up on the 8060A C19 RMS cap.  My main board is Rev H and assembly Rev H.

My C19 is installed matching silkscreen and schematic, that is, plus facing the display and connected to U2 pin 6.  Measuring voltage using a hi-Z meter, I see -2mV in DC mode, +5mV in AC mode with a non-overloading 1kHz sine, and +0.5V with 2x overload.  So polarity matters but leakage won't be an issue.

I checked my C19 candidates at room temperature.  I only tested one sample of each type.  Charge one hour at 10V, measure leakage with a 10 Meg meter, discharge 10 seconds, record peak voltage to estimate DA.
Nichicon UKL1E470KEDANA is 9nA and 0.19V (1.9% DA), Chemi-Con ELE-350ELL470MF11D is 5nA and 0.27V (2.7%), Murata ceramic RDEC71E476MWK1H03B is 25nA and 0.70V (7%) - to my surprise, it's the worst as well as the most expensive.  Of these three parts, I would use the long life Chemi-Con aluminum electrolytic.

And my beeper boards are on their way!

[blue_lateral]

I've had one of the polymer contenders for 8060A C36,  Kemet A759, connected to 10.5 Volts for about a day and a half now measuring leakage current at room temperature to see how bad the polymer capacitor leakage really is under the conditions it would probably see in an 8060a laying on my bench. It is connected across the 9 volt battery. If I remember correctly, drtaylor mentioned earlier in this thread that he expected polymer cap leakage to be negligible in the places where electrolytics were originally used in the 8060a. That tracks with these capacitors as C36. Leakage at 10.5 Volts at room temperature is below my ability to accurately measure. It appears to be less than 20 nanoamps, maybe a lot less. I'll probably check a couple more of these as time goes on.

Spec is 120 microamps at 20C, not to exceed 120 microamps at 20C after damp heat or surge testing (see datasheet). Kemet A759 22uf/35VDC , Mouser 80-A759BQ226M1VAAE80 , datasheet here: https://www.mouser.com/datasheet/2/447/KEM_A4072_A759-3316694.pdf

These are almost too tall but do clear the processor board.

[blue_lateral]

I checked my C19 candidates at room temperature.  I only tested one sample of each type.  Charge one hour at 10V, measure leakage with a 10 Meg meter, discharge 10 seconds, record peak voltage to estimate DA.
Nichicon UKL1E470KEDANA is 9nA and 0.19V (1.9% DA), Chemi-Con ELE-350ELL470MF11D is 5nA and 0.27V (2.7%), Murata ceramic RDEC71E476MWK1H03B is 25nA and 0.70V (7%) - to my surprise, it's the worst as well as the most expensive. 

Could you go into a little more detail about your testing method? Thanks.

[Dave Wise]

I don't see what I left out, except possibly the well-known trick of using a voltmeter with known resistance to measure small currents.  I put the meter in series with power supply and DUT and let the meter's input resistance be the ammeter shunt.  With a 10 Meg meter, 10mV is 1nA.  Since I had three DUTs in play, I used three meters, a Fluke 8000A, a Fluke 8100B, and a Monsanto 2000.  After measuring the leakage, I shorted the meters.  Then I turned off the power supply, which has a few kilohms of bleed at the terminals, and after 10 seconds I pulled off the meter shorts and watched the readings go negative, level off, and fall.  This isn't exactly like the IEC standard since the meters load the recovering caps, but since all I wanted was a comparison it doesn't matter.  It was quite a surprise to see the ceramic cap perform worse than the electrolytics!

I see that the typical leakage of the polymer caps, like that of the regular caps, is far below the spec sheet limit.

[Dave Wise]

D.R. Taylor, if you're listening, there's text missing from your Hidden Features paper.  At the end of page 1, you write, "The accuracy loss is due to a".  At the beginning of page 2 you write, "out in the normal 10 megohm volts mode".  I'd love to know what went in between.

And it seems to me that one can only get hi-Z by having the MAC disconnect the OREF- pin, because otherwise there's a sneak path to ground through R2, RT1, Z1.2-4, Z5.7-6, OREF-, OREF+, and Z5.8-10.

UPDATE: In normal 10-Meg mode, DC goes through a voltage divider with R2 (1K) on top and 10 Meg on the bottom.  Hi-Z mode disconnects the 10 Meg so we read 0.01% high.  But I can't figure out how to word that to fill in the missing text.

[blue_lateral]

I don't see what I left out, except possibly the well-known trick of using a voltmeter with known resistance to measure small currents.  I put the meter in series with power supply and DUT and let the meter's input resistance be the ammeter shunt.  With a 10 Meg meter, 10mV is 1nA.  Since I had three DUTs in play, I used three meters, a Fluke 8000A, a Fluke 8100B, and a Monsanto 2000.  After measuring the leakage, I shorted the meters.  Then I turned off the power supply, which has a few kilohms of bleed at the terminals, and after 10 seconds I pulled off the meter shorts and watched the readings go negative, level off, and fall.

That did occur to me. Years ago I often used that trick to measure leakage with a HVPS and a VTVM in tube based equipment. After posting I tried it with the power supply and DMM (Tektronix TX-3). I wondered at the time if you were timing self-discharge somehow, but now I see. It never occurred to me to also check for dielectric absorption until I read your post. Now I probably will.

It seems to have stabilized at around 3.4 mv, give or take a few counts as it drifts. It's been there most of the day. It does get a little worse if you heat it up with your fingers, but we are down where it shouldn't matter for C36.

I just got an email from Mouser that the Kyocera caps ( RPF0509220M035K ) have finally shipped. I'll post a comparison when I get them.

It was quite a surprise to see the ceramic cap perform worse than the electrolytics!

I bought some of those same series Muratas in 22uf as a possible C36, but they have a huge capacitance rolloff with voltage according to the datasheet, about half of it at 10 volts as I recall. I've not tested it. It occurred to me that maybe 47uf would be closer to a 22uf electrolytic when connected to a 9V battery, but I sort of gave up on that idea. I too am surprised they were the worst performers of the 3 you tested. Can you see anything about them (other than cost) that is bad enough to kick them out as a possibility for C19?

[Dave Wise]

If my instrument is representative, C19 sees only a few millivolts in normal operation and did not have to be a special low-leakage part.  Although its leakage and DA is worse than basic aluminum electrolytics, a Type II ceramic should do fine, and outlive your great-grandkids besides.  I won't bother; a 10000-hour electrolytic would outlive me and that's plenty.

[Dave Wise]

I finished my 8060A beep frequency mod.  Works great.  See topic "Low Frequency Continuity Beep for Fluke 8060A".

[kblue]

Greetings! Scored some 8060A's myself and yes, i know it's an old topic!

Just a single, simple question: Someone here wrote, they dumped the PCB into an ultrasonic cleaner and it survived. So it's okay to do so? Was about to do the same, because reaching every corner just with a isoprop-bath and a brush wont gonna work. The board is rather dirty (just sticky dirt, no burned stuff)

Best wishes!

/edit: Dumped it now into the ultrasonic cleaner (with leaking caps removed and display ofc) ... after i dealt with the corrosion (which was okay'ish no IC was hurt ). It's now superclean ... like you-could-eat-from-it clean. Sadly the display is a bit broken (there's a small impact spot). Apart from that, it's good damn accurate! Tested the meter with some DMMCheck References and its spot on.

[adinsen]

I hope noone will resist that I'm posting to this old topic, but I'm still trying gluing this part, now using epoxy 2C glue. But I frankly do not think it will hold. Anyone here who has an unrepairable 8060a with one of these to spare that I can buy?

[AVGresponding]

For delicate but strong things like that, I've had some luck using tissue-paper grade glass-fibre. A single layer with just enough resin to cover it, or indeed any medium-hard setting glue, on each flat surface you can get to that doesn't interfere with another part. UV cure nail varnish would probably do it too, that stuff sets as hard as resin, and it goes on thin.

[EE-digger]

I've repaired many plastic parts by hot air welding with my SMT station.  Plastics that could not be glued were fixed, strong and sturdy.  Repaired many Bausch and Lomb stereozoom microscope zoom mechanisms that way.  They were prone to cracking.

[adinsen]

Thanks for all the good suggestions for perfecting the repair  Fortunately it looks like the 2c epoxy is holding up better than I expected

Unfortuntately I still have missing segments, and it must be the zebra strip causing it. My instrument has one of the old round ones and the strip is clearly deformed. I can rotate it, and the segments come back for a few days, but the strip seems to rotate back to the default shape and the segments starts to go away again.

The cutout in the LCD holder is 54.9mm x 3.2mm. But what is the correct height? Measuring the compressed, originally round rubber, I get 2.75mm min, 3.2mm max. So I'm thinking it was Ø=3.0mm originally.

Looking at Ali, I found this: https://www.aliexpress.com/item/1005011800555853.html

It's only 2mm wide but stands 3mm tall. Hopefully it will not trip over. The length can be cut down, I think 

Anyone here who have replaced the zebra's on the 8060? Apart from this project involving a total replacement of the LCD, I have not come across anyone dealing with zebra strips: https://hackaday.io/project/185306-fluke-8060a-custom-lcd

The LCD is fine on my instrument 

[blue_lateral]

I have successfully repaired broken 8060A case parts like screw towers with Dichloromethane. The plastic is completely unresponsive to Acetone and MEK, so it can't very well be ABS. I suspect the plastic is Polycarbonate or some sort of blend, but I know very little about plastics. Does anyone here know what plastic it really is? Dichloromethane does not just work by painting over a dry crack like it does on some other plastics. One needs to keep soaking the bond area and get it softening before final gluing. It does work. This assumes the broken area is not contaminated with some other glue, so it might pay to try Dichloromethane first.

[drtaylor]

I'm sorry I didn't see your post. What I left out is that the high impedance mode will give a slightly different result than the normal 10Mohm load. This is due to the fact that there is a 1kohm protection resistor in front of the precision 10M divider. This drop is calibrated out. So if the meter reads 1.0000 Volt in the normal mode, it will read 1.0001 when you disconnect the divider by popping out both the Ohms button and the Volts button. So there will be a 1mV positive error. The actual voltage that the A/D is seeing is 0.9999. So in the high impedance mode it will read 1mV higher. Negligible +0.01% additional error, so hardly worth mentioning. I suspect that's why I dropped the ball at the time. I advise just getting rid of R3, the 100Meg resistor. It's only function is to lower the input impedance slightly which really is the wrong thing to do, but marketing thought keeping the input impedance as close to 10M as the somewhat novel input structure would allow was important. This input divider structure is the reason the 8060 outperformed all handheld meters in audio band frequency voltage measurements. Still more accurate AC frequency range than most modern handheld DMMs.

[Dave Wise]

Coming in late, Dave, sorry.  In what configurations is R3 keeping input resistance equal to 10Meg?  If a low voltage range, it could be important to play correctly with the high voltage probes (80K6, 80K40) that expect exactly 10Meg.

[drtaylor]

Regarding the 8060A and how the divider works:

In the 2V range, the input divider is in divide by 10 mode. This is 10M over 1.1111M. This divider is not used in DC, only AC. In DC the input is not divided for the 200mV and 2V ranges. However, in AC, the signal used is divided by 10 and has variable capacitors to adjust the response as flat as possible. So if the 2V range button is pushed, the input impedance is sitting at 11.1111M. So the 100M is switched in to bring it back to 10M. Only the 2V range is modified by the 100M resistor. I should note that the impedance is not exactly 10M in any range. The 2V, because of the 100M resistor comes the closest. In most ranges the input is slightly higher than 10M. In the 200mV range, the input impedance is 10.010M. In 2V, 10M (but the 100M resistor might be a 5%). The 20V range (divide by 100) has the biggest 10M variation; 10.101Mohms, ~1% high. The 200V and 1000V ranges use divide by 1000. The input impedance is 10.010M, the same as the 200mV range.

Whoops, I forgot the input protection resistor R2 adds 1kohm ±5% to all the above calculations. So the numbers should be: 200mV, 2V, 200V and 1000V ranges are 10.011M, 2V 10.001M (without counting the tolerance of the 100M resistor, R3), 20V is 10.102 Mohms.

These impedance variations are within the usual specified range of ±1% of most High Voltage probes. Ironically, many of the more modern Autoranging Fluke meters jump to 11.111M on their 3 or 4V ranges, so I guess the marketing group didn't care anymore. The instruction manual for the Fluke 80K-40 probe suggests a correction factor for those Multimeters. There are also high voltage probes that are for high impedance DMMs. These would work with the 8060A in its high impedance 200mV and 2V ranges (both function switches popped out) but if it is a divide by 1000 probe, you'd only be able to measure to 2000V.

[adinsen]

I got the 3.0mm zebra strips yesterday and now have a working multimeter with a working LCD 
I ruined one cutting it a bit too short, but I have 8 strips to spare. If anyone in Europe needs one (or two), let me know and I can mail it.

My plastic repair with 2 component epoxy also holds on. So whatever the type of plastic is, epoxy appears to bind well to it