Author Topic: Fluke 8020B Teardown - 30yo DMM Technology  (Read 30956 times)

0 Members and 1 Guest are viewing this topic.

Offline ModemHead

  • Frequent Contributor
  • **
  • Posts: 680
  • Country: us
  • No user-serviceable parts inside.
    • Mr. ModemHead
Fluke 8020B Teardown - 30yo DMM Technology
« on: October 06, 2012, 04:33:36 am »
Thanks to a tip from EEVBlog forum member retiredcaps, I recently picked up a Fluke 8020B DMM for $5 + postage from the usual auction site. This model dates from somewhere in the early to mid-80s and is an updated version of the 8020A, Fluke's first handheld DMM. The seller's description said this one "would not power up". However, when I installed a battery, it worked perfectly. Overall, the unit is in very good cosmetic shape, especially after a thorough cleaning. Unfortunately the button for the AC/DC selector switch is missing.

So for those who may be interested in 30 year-old DMM technology, let's take it apart!


The case is held together by 3 self-tapping screws. I deem myself qualified to remove the screws.


Accessible (barely) from the battery compartment is a 2A glass fuse, with a spare thoughtfully provided in a plastic clip. The battery cover fits tightly and is a major pain to remove and re-install.


Flexible shielding material wraps around most of the circuit board assembly, bonded by a small screw to a metal stand-off. The shield is permanently attached to the case bottom half with melted-over plastic studs. The 3A HRC fuse is not accessible until the meter is disassembled to this point. Also accessible is a DC cal adjustment, AC cal adjustment, and a "high-frequency" compensation adjustment. The meter is spec'ed to 5KHz bandwidth with reduced accuracy from 1kHz to 5kHz.


The circuit board layout is dominated by the push-button switches. The daughter board on the right contains the continuity beeper circuitry and piezo noisemaker. The fuse block is quite firmly attached at that angle.


Double-sided board. All through-hole components. Wrinkly solder mask, which is common for PCBs of this era. The PCB artwork is dated 1981.


The LM358 op-amp on the main board is the AC converter and is factory-selected for 600kHz GBW. The continuity piezo noisemaker is on the little daughter board, triggered by an LF442 op-amp comparator and a 74C00 quad nand gate as oscillator and driver. The JFET-input LF442 is selected for 100pA input bias current. The continuity buzzer is supposed to be used with the 2K-ohm range which results in a 115-ohm threshold. But since the buzzer is driven by a comparator from the voltage divider, the buzzer also operates in other resistance ranges at non-useful thresholds.


The 3A fiber tube HRC fuse is in series with the 2A glass fuse, providing 10kA interrupting capability in case of a serious fault. Series varistors, a thermistor(obscured) and a 1K 2W fusible resistor provide over-voltage protection. The two beefy 2A diodes limit voltage across the current measurement shunt.


All through-hole components, no SMD in sight. The large gray-black tapped resistor is the current shunt for measuring up to 2A. The blue resistor network behind it is the primary voltage divider. The input thermistor is fully visible in this shot beside the 1W 100K resistor.


External power input jack is under the display. Not usually found on modern DMMs due to the safety hazard. The power rails are not isolated from the meter's input jacks, and thus could raise the 9V input to hazardous voltages.


The 4030 quad exclusive-OR gate is used to drive the LCD decimal points and lo-bat annunciator, gated with the LCD backplane clock. The rectangular orange components are resistor arrays.


Those are some sturdy-looking switches.  They consume a lot of space, but there are no extra components hidden underneath.


This meter is 3-1/2 digit, 2000-count. The display is a fairly generic "1888" with decimal points, leading minus sign and a "BT" low-battery annunciator.  There are no bar graphs or units indication.


The black elastomeric connector is tall and thin and held in place with a removeable plastic piece.  The protective transparent lens is 2.4mm thick Perspex.


The A/D converter/LCD driver is a 40-pin DIP Intersil chip marked with Fluke p/n 429100. Probably very similar to the ubiquitous ICL7106. Looks like a 1985 date code. The device in the TO-18 metal case below the trim-pot in the upper left is a 1.22V bandgap voltage reference. The clock crystal is 3.2MHz.


Measuring an 806-ohm 0.25% precision resistor mounted on a dual banana plug. The tilt stand is a bit short, but the display is already angled, so the net result is a good viewing angle. Note the external power jack at top right.


Measuring a 5.000V reference voltage. I never touched the trim-pots. It arrived this way. Not knowing this unit's history, I have no idea if it was ever in a calibration program. But in any case it's still perfectly useable.


Thanks for looking.

Edit 1-July-2017: Photobucket sucks.
« Last Edit: July 02, 2017, 02:33:26 am by ModemHead »
 
The following users thanked this post: TechieTX, Eduardosky, thermistor-guy

Offline robrenz

  • Super Contributor
  • ***
  • Posts: 3036
  • Country: us
  • Real Machinist, Wannabe EE
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #1 on: October 06, 2012, 04:43:15 am »
Nice review, great pictures

Offline Amarbir[Lynx-India]

  • Frequent Contributor
  • **
  • Posts: 431
  • Country: in
  • Indian Dealer
    • Lynx-India - Visit Us For Not So Boring Electronic Instruments
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #2 on: October 06, 2012, 04:43:57 am »
Well,
    beautiful mind blowing review  ,just curious how old is the hrc fuse technology is btw
Regards

Amarbir Singh Dhillon [ Lynx-India ] , Chandigarh [ India ] - > www.lynxdealerstore.com , www.lynx-india.com
Indian Distributor For  [ Autoelectric , Sofitech , IDEOfy ,Peak Electronic Design [UK ] , Anatek And Creatronica ]
My Electronics Blog - > www.lynxchandigarh.com
 

Offline robrenz

  • Super Contributor
  • ***
  • Posts: 3036
  • Country: us
  • Real Machinist, Wannabe EE
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #3 on: October 06, 2012, 04:55:53 am »
@ Amarbir 

This is the kind of review I am talking about in your meter thread.  Great pictures, Lots of detail, Nothing left out, some basic accuracy checks, good commentary.

Offline david77

  • Frequent Contributor
  • **
  • Posts: 788
  • Country: de
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #4 on: October 06, 2012, 05:09:27 am »
Very nice tear down, lovely photos.

Have been looking for a 8060 for some time, I like these old Fluke meters.
Just one thing: It is not Flukes first hand held DMM, they introduced the 8030 and the 8040 in about 1974. Very different technology and form factor but hand held and portable none the less.
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4784
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #5 on: October 06, 2012, 05:15:24 am »
Nice, very good restore job.  You could easily get another one on eBay and cannibalize a keycap.  This model made Fluke famous for DMMs back in the late 1970s.  It set a trend for a style that was heavily copied.  I lusted after that and could only afford a kit copy, and it doesn't look half as good as the 8020a 30+ years later, but its still calibrated [ one feature was it was manually self calibrating] and working.

http://www.fluke.com/Fluke/usen/community/fluke-news-plus/ArticleCategories/RD/25-Years+of+DMMs.htm

A pdf history of the Fluke DMM:

http://support.fluke.com/find-sales/download/asset/2386856_a_w.pdf



« Last Edit: October 06, 2012, 05:48:22 am by saturation »
Best Wishes,

 Saturation
 

Offline Excavatoree

  • Frequent Contributor
  • **
  • Posts: 824
  • Country: us
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #6 on: October 06, 2012, 06:21:34 am »
Unfortunately the button for the AC/DC selector switch is missing.


PM or e-mail me your address - I'll send you one that, hopefully, will be up to the rest of the meter's appearance.

I've got several of these, most are in pretty bad shape, but many of them still work and still meet specs.

I don't have any in that nice of a condition.
 

Offline ModemHead

  • Frequent Contributor
  • **
  • Posts: 680
  • Country: us
  • No user-serviceable parts inside.
    • Mr. ModemHead
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #7 on: October 06, 2012, 06:38:21 am »
Nice, very good restore job.  You could easily get another one on eBay and cannibalize a keycap.  This model made Fluke famous for DMMs back in the late 1970s.  It set a trend for a style that was heavily copied.  I lusted after that and could only afford a kit copy, and it doesn't look half as good as the 8020a 30+ years later, but its still calibrated [ one feature was it was manually self calibrating] and working.
As for restoration, I didn't do much but clean off some grime. It worked right off the bat. Even the fuses are good. I think this unit had an easy life somewhere, it obviously has not been abused. I was only a little disappointed that I missed the opportunity to fix it or go off in search of something made of unobtainium.

When this unit was new, I was a junior engineer who got assigned the beat-up old Simpson 260. The senior engineers got the new stuff.  So it's fun for me to get this so cheaply and play with it. And share the pix.
 

Offline ModemHead

  • Frequent Contributor
  • **
  • Posts: 680
  • Country: us
  • No user-serviceable parts inside.
    • Mr. ModemHead
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #8 on: October 06, 2012, 06:39:51 am »
Unfortunately the button for the AC/DC selector switch is missing.
PM or e-mail me your address - I'll send you one that, hopefully, will be up to the rest of the meter's appearance.
...
Thanks! That's very kind of you.
 

Offline retiredcaps

  • Super Contributor
  • ***
  • Posts: 3044
  • Country: ca
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #9 on: October 06, 2012, 10:02:35 am »
Have been looking for a 8060 for some time, I like these old Fluke meters.
Initally, I alerted ModemHead with this auction, but was too slow in typing

http://www.ebay.com/itm/130773179911

$6 for a potentially working 8060A with a faded lcd.  From what I read, the old Fluke 8060a has insanely wide AC bandwidth (100kHz for some ranges)

Even if it didn't work, I would pay $6 for it because the manual has full schematics and with all through hole components I might have a decent chance of learning a lot.


 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 25875
  • Country: au
    • EEVblog
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #10 on: October 06, 2012, 12:20:46 pm »
Great photos!
The ducks guts of old Flukes is the 8060A. Still has potent specs by today's standards.

Dave.
 

Offline firewalker

  • Super Contributor
  • ***
  • Posts: 2160
  • Country: gr
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #11 on: October 06, 2012, 04:11:46 pm »
30 years old and still safer than many new DMMs...

Alexander.
Become a realist, stay a dreamer.

 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 25875
  • Country: au
    • EEVblog
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #12 on: October 06, 2012, 06:15:18 pm »
 

Offline Salas

  • Frequent Contributor
  • **
  • Posts: 291
  • Country: gr
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #13 on: October 06, 2012, 06:26:35 pm »
Make cheap or make proper is older policy than merely 30 yrs old. ;)
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 1571
  • Country: us
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #14 on: October 06, 2012, 06:40:00 pm »
I know a lot of people who still swear by these things.  Particularly if you need manual ranging these meters can be operated one handed and are much nicer than the typical rotary switch with 20 positions.
 

Offline Flávio V

  • Regular Contributor
  • *
  • Posts: 63
  • Country: pt
  • Capacitor lover
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #15 on: October 06, 2012, 07:56:53 pm »
Might teardown my 8060A to show...i have recently fixed the battery connector so it is not 100% original...
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4784
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #16 on: October 06, 2012, 08:48:44 pm »
That's a great buy.  Older Fluke's had an issue with debris collecting under the elastomer of the LCD, all it needs is a cleaning and it likely will work as good as new.  Many old Flukes make great lab and home DMM; they are all pre-CAT rating, do not have built in transient protection and if used in a professional setting could incur some liability.


Have been looking for a 8060 for some time, I like these old Fluke meters.
Initally, I alerted ModemHead with this auction, but was too slow in typing

http://www.ebay.com/itm/130773179911

$6 for a potentially working 8060A with a faded lcd.  From what I read, the old Fluke 8060a has insanely wide AC bandwidth (100kHz for some ranges)

Even if it didn't work, I would pay $6 for it because the manual has full schematics and with all through hole components I might have a decent chance of learning a lot.

« Last Edit: October 06, 2012, 08:51:49 pm by saturation »
Best Wishes,

 Saturation
 

Offline david77

  • Frequent Contributor
  • **
  • Posts: 788
  • Country: de
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #17 on: October 07, 2012, 06:44:20 am »
Thanks for the heads-up, but shipping costs from the US are insane. I'll wait until one shows up here in Europe. It's not something I need urgently, just one piece of kit I'd like to have.

Have been looking for a 8060 for some time, I like these old Fluke meters.
Initally, I alerted ModemHead with this auction, but was too slow in typing

http://www.ebay.com/itm/130773179911

$6 for a potentially working 8060A with a faded lcd.  From what I read, the old Fluke 8060a has insanely wide AC bandwidth (100kHz for some ranges)

Even if it didn't work, I would pay $6 for it because the manual has full schematics and with all through hole components I might have a decent chance of learning a lot.
 

Offline lowimpedance

  • Frequent Contributor
  • **
  • Posts: 932
  • Country: au
  • Watts in an ohm?
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #18 on: October 08, 2012, 12:32:52 pm »
 Nice clear full detail pics., and in nice condition -  good score.
The main chip is indeed an Icl7106!. I own 2 8020A 's which had stuffed LCD's so I 'hard wired' repaired them with modern displays easily and cheaply available. A small amount of fitting mechanically and the meter is good to go. The thread is in the blogs archives under Fluke 8020a with bad LCD.
low Z
You call that current ?.......
I'll show you current !
 the odd multimeter or 2 or 3 or 4...or........never mind
 

Offline amyk

  • Super Contributor
  • ***
  • Posts: 5529
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #19 on: October 08, 2012, 08:10:47 pm »
Does anyone else find it interesting that Fluke used the same ADC chip that's now found in the cheapest Chinese DT-830 series DMMs?
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4784
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #20 on: October 08, 2012, 11:23:46 pm »
It was state of the art at the time, DMMs that flooded the market thereafter in the early 1980s used the same chip, how the chip has survived in panel meters today and such is a testament to good chip design.  Note the 8020 is occupied mostly by the switch assembly rather than electronics; the 7106 made it possible to make DMMs affordable to most everyone.
Best Wishes,

 Saturation
 

Offline ModemHead

  • Frequent Contributor
  • **
  • Posts: 680
  • Country: us
  • No user-serviceable parts inside.
    • Mr. ModemHead
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #21 on: October 09, 2012, 12:11:23 am »
Yes, it's very interesting that my 30 year old $5 meter shares the same basic technology as today's $5 Harbor Fright meter.  A testament to good chip design, but the fact that this one is still here and working is also a testament to good solid product design.  I'm not so sure anything made today will still be around in 30 years.

@low-Z: That was a great thread! I learned about removing the polarizing film from an LCD there, plus the inspiration from seeing someone hack old equipment back into use.
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4784
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #22 on: October 09, 2012, 02:14:10 am »
Yes, they are made very well, while there are a few DMMs from that era are also good, they are not as prolific as Fluke from top brands: HP had a few DMMs as well as Tek.  Functionality and practical accuracy came out of the 1980-1990 period pretty much based on Fluke's models, while HP set the standard for bench DMMs.  By 1987, the Fluke 80 series came into the catalog and has been there ever since, and what's new with different generations are higher IC integration, CAT and Pollution rating, increase toughness and IP ratings, but the accuracy ratings, design and features  [ capacitance, frequency counter etc.,] are unchanged.  Can the Chinese or lesser brand DMMs, endure?  They probably can but a typical Fluke is made to survive desert heat, Alaskan cold, humidity of a seagoing vessel, military applications helped its reputation. The original Fluke's weren't IP or Pollution Degree rated but they empirically survived and created its reputation.  So for home labs and consumers, this level of toughness is overkill, but if you can get a used Fluke DMM cheap on eBay, its most likely will last a lifetime compared to a newer meter from lesser brands because Fluke has a legacy, while the other's still have to make theirs.



Yes, it's very interesting that my 30 year old $5 meter shares the same basic technology as today's $5 Harbor Fright meter.  A testament to good chip design, but the fact that this one is still here and working is also a testament to good solid product design.  I'm not so sure anything made today will still be around in 30 years.

@low-Z: That was a great thread! I learned about removing the polarizing film from an LCD there, plus the inspiration from seeing someone hack old equipment back into use.
Best Wishes,

 Saturation
 

Offline free_electron

  • Super Contributor
  • ***
  • Posts: 6848
  • Country: us
    • SiliconValleyGarage
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #23 on: October 09, 2012, 05:07:22 am »
Don't diss the 'lowly 7106. The technology in that device is still the most accurate way of measuring a voltage as it is completely self adjusting and self-nulling. These machines are a voltage to time-interval converter ( and not an 'ADC' like we know it in the traditional sense like a SAR or a thermometer system ). The conversion mechanism is dual slope. Even the Agilent 3458 8 1/2 digit machine uses that technique. that's how accurate it can be made.
Can't get there with any other known a/d convertor technique.

The fluke parts are probably a bit 'selected'.

my first digital multimeter ( 1984) was a hung-chang clone of the 8020 .
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 14704
  • Country: za
Re: Fluke 8020B Teardown - 30yo DMM Technology
« Reply #24 on: October 09, 2012, 05:38:57 am »
7106 only has a few needs for accuracy. A short term stable clock, it only has to be stable over under 5000 cycles, nothing more. A reference voltage of the desired accuracy, and you have a built in one good enough for room temp operation right on the chip, which will give accuracy of 199x at least. You need one good film capacitor to store charge, and all it needs is low leakage and no voltage dependance, easily met by most modern polyester film units.

Not terribly sensitive to supply voltage. Can work with a lot of noise on the input, and if you select the clock right it ignores mains hum completely. Very god for ratiometric use, which can be done totally without any trim at all needed if you use precision resistors. Robust device as well, and easy to interface to the LCD displays.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf