Author Topic: Fluke 8200A read problem.  (Read 7278 times)

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Offline neo

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Re: Fluke 8200A read problem.
« Reply #25 on: September 29, 2017, 11:52:48 am »
Oh, and neo, mine is a baby compared to yours.  I haven't found a date stamp anywhere on the chassis, but the component date codes range from the late 70s to mid 1980, so I'd assume that it was made late in 1980.  I'm curious - does yours use LEDs for the mode indicator lights, or incandescents, or...?

-Pat

Wait - belay that previous date estimate - a closer look at the ohms converter board reveals trim pots with 1981 production dates (light blue ones on the right), (and a big honkin' 6.99M precision resistor with a mid '79 date - Fluke must have bought things in big lots!), so I now guess mid 1981 for a build date?



Near as i can tell its all neon or regular incandescents, so then i take it i got an old one and that explains the switches.
I had my hopes up last night an hour after spraying the switches but now in the morning they are back to being the same gummy mess.

EDIT:
Once in a range it is fine even after the contact cleaner dries its "dry switching"  that is the problem.
« Last Edit: September 29, 2017, 01:31:45 pm by neo »
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Offline neo

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Re: Fluke 8200A read problem.
« Reply #26 on: September 29, 2017, 12:58:48 pm »
It sounds like you're starting to scratch the surface, as it were, on the contacts in the switches. When the cleaner evaporates, the goo settles and causes problems. If the cleaner can't dissolve the muck and nothing will come out of the switches, it may not improve without disassembly or replacement of the switches. Perhaps, as Pat implied, a different cleaner may work better to dissolve the old lubricant.

i'm open to suggestions on what i should use, though i should note 50 dollar bottles of chemicals are out of my current price range.

It is actually all of the range switches not just one or two now and the best way into any of them with contact cleaner is just to pop the front off and spray the springs.
« Last Edit: September 29, 2017, 06:55:47 pm by neo »
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #27 on: September 29, 2017, 11:53:54 pm »
Wonderful teardown photos, Pat! I was also appalled at seeing those switches soldered on both ends between PCBs. That's just evil! By the way, in the 8200A manual, is there any info on disassembling the switch modules?

neo, I'm not sure what's the best option since we don't know what kind of gunk is in there. On the 8100A, the switch shaft and contacts can be removed by sliding it out the rear of the switch module. I don't know if that's the case with the 8200A. If you can get the shaft out, then you can clean the contacts directly.

Update: The 8100A manual says to clean with alcohol. Then lubricate the switch contacts with a thin coat of Rykon 2EP grease (American Oil Co.) or equivalent. Most contact cleaners have alcohol in them, but you could also try to fill the switches with IPA (not beer) and work them if you can't remove the shaft and contacts.
« Last Edit: September 29, 2017, 11:59:23 pm by bitseeker »
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Offline neo

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Re: Fluke 8200A read problem.
« Reply #28 on: September 30, 2017, 12:32:59 am »
So i guess it all comes down to whether or not the switches come apart without breaking the thing.

The way i see it is i have three options, either;
A) Leave it in DC or \$\Omega\$
B) Take the switches apart and clean them.
C) Bathe them in a lot of chemicals.

I would rather have it fully functional.
Pat, could you kindly look in the manual for information on this?
IPA = isopropyl correct?
« Last Edit: September 30, 2017, 12:35:16 am by neo »
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Offline Cubdriver

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Re: Fluke 8200A read problem.
« Reply #29 on: September 30, 2017, 02:09:08 am »
IPA is isopropyl, yes.

I looked in the manual and there are instructions on the switches; I've taken photos and will post them as soon as I get a computer keyboard issue fixed.  Give me an hour or so...

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #30 on: September 30, 2017, 03:40:24 am »
That's great news, Pat. I'm optimistic that the switches will be similar and be able to be disassembled without desoldering.
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Offline Cubdriver

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Re: Fluke 8200A read problem.
« Reply #31 on: September 30, 2017, 04:53:02 am »
Ok, it took a bit longer than an hour to get the photos taken, marked up, uploaded, and captioned, but I'll have something posted showing my take on the procedure shortly.  (shortly being however long it takes me to type it up and insert the pics.)  Meanwhile, here are photos of what I was talking about last night regarding securing the display assembly to the interconnect board so that the ribbon cable doesn't get buggered up after dismounting it to gain access to the switches...

I wound up getting some of that evil plastic that everything is blister packed in these days - you know, that impossible to tear stuff that you can barely cut with bolt cutters and that will slice you open if given half a chance.  Anyway, I found a flat piece about 1.5 x 3", and folded it into a four layer accordian shape.  I burned a pair of holes through all four layers with a soldering iron (ahh, the smell brought back memories of melting holes in Rat Shack P-box kits back in the days of my misspent youth), then cut them in half to wind up with two folded plastic pieces with a pair of holes.

After first removing the five screws securing the display assembly and bulkhead to the interconnect board (two short in front, three longer across the back), I used the short screws from the front to secure the bulkhead to the outer pair of short rear standoffs on the display board.

The plastic pieces were then used to bridge the upper bulkhead holes to the rear brackets on the interconnect board, and hold them nicely secure relative to one another giving you one thing to work with, rather than two tied together with a potentially delicate ribbon cable.  The photos should explain what my rambling probably did not.   :P

Display/bulkhead removed from interconnect; bulkhead secured with front mounting screws to outer rear standoffs (I put the screws that held the bulkhead and interconnect board rear to the enclosure sides back into their respective holes when I disassembled the meter to help keep them organized and to reduce the chances that my furry lab assistants might decide to play with (AKA lose) the loose hardware.):


Detail of screw holding bulkhead to standoff:


Plastic 'brackets':


Detail of assembly with bracket in place:


Overall front oblique:


Overall rear oblique:


-Pat

If it jams, force it.  If it breaks, you needed a new one anyway...
 
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Offline Cubdriver

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Re: Fluke 8200A read problem.
« Reply #32 on: September 30, 2017, 04:55:15 am »
That's great news, Pat. I'm optimistic that the switches will be similar and be able to be disassembled without desoldering.

Alas deslobbering will be necessary to service them.   |O

The good news is that the board that must come off is single sided without through hole plating, and there are only 14 connections to desolder.  The switches themselves can remain on the main interconnect board.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline Cubdriver

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Re: Fluke 8200A read problem.
« Reply #33 on: September 30, 2017, 06:30:02 am »
Ok, now for the fun one.  Fluke 8200A mode/function and/or range switch repair.  As bitseeker suggested, dismantling and cleaning the switches is pretty easy.  Easy like replacing the pilot bearing in a car with a manual transmission is easy.  Once you get there, it should be cake - the getting there part is the issue...   |O |O

To begin with, the meter must be torn down to the point that the display board/interconnect board assembly is out and in your hands, and from there the display board must be dismounted from the interconnect board, as it sits directly above the switch gangs.  I'd suggest securing them to one another somehow (such as the method using plastic tie straps as shown in my earlier post) to make handling them easier and reduce chances of damage due to movement between them.

Interconnect/display assembly with display board secured out of the way of ganged switches on interconnect board:




The RANGE switch (on the right) may be worked on at this point as it is accessible, however if the FUNCTION switch gang (Vdc, Vac, ohms, etc.) needs attention, then the additional step of removing the function indicator PCB atop these switches must also take place.  At a glance, this doesn't look like it should be too terribly difficult to do, as it is a single sided board (no through hole plating to worry about) and there are only 14 connections to deal with.  A solder sucker and/or solder wick should permit removal to be accomplished with a minimum of foul language and hair loss.

Function indicator daughter card.  Desolder switch connections (in rows, front to back - do not desolder indicators or resistors).  Older versions will likely look at least somewhat different as they may be incandescent (most likely) or neon, rather than LEDs.  Regardless, removal should be the same:




Once access to the switches has been obtained, the rear support bar must be removed from whichever gang of switches is to be repaired.  The support bar is a three sided aluminum channel that is affixed to the switches by a combination of 'L' shaped slots that engage posts on the switch bodies and retaining tabs that are bent inwards and bear against the switch body sides, preventing the bar from shifting laterally and disengaging from the posts:

Front and rear support bars (range switches shown here):


Support bar and switch parts (range switch):


This image of the range switch as an error in the markup; the small top left tab is NOT a locking tab - they are on the bottom of the rear bar on the range switch:


Support bar on function switch assembly:



First off, prior to removing the support bar, ALL of the switches in the gang must be in the off (out) position, as when they are on, the rear of the actuator extends out through the support bar.  Pushing a different switch in far enough to release the 'on' one, but not far enough to latch it will accomplish this.

The rear support bar is removed by carefully bending the locking tabs flat with the face of the bar so that they will clear the switch bodies (there are multiple locking tabs, likely one between each switch).  On the range switch assembly, they are on the bottom, closest to the interconnect board, and on the function switch assembly they are on the top.  Once the tabs are bent flat, the support bar is slid in the appropriate direction (towards the outside of the unit, to the right for the range switch and to the left for the function switch) far enough to permit the retaining posts to disengage from the 'L' slots that they are in.  It is then removed by pushing it to the rear.  I have not taken a meter apart this far, so I cannot comment on the force needed to move and remove the support bar, but would not be surprised if gently prying with a screwdriver in one of the slots is needed.  If the bar is reluctant to move, recheck to ensure that all the tabs are bent clear of the switch sides.



Beyond this, the procedure shown in the following manual page photos should be followed to disassemble and clean the switches, and then reassemble everything.  The gist of it is that once the rear support bar is off, the buttons, retaining clips, and springs are removed, then the actuator and contacts may be pushed out through the rear of the housing.  The contacts are cleaned and the mechanism relubricated, then the whole mess goes back together.  I have no idea what a modern equivalent to their suggested grease might be, but I would use a small amount of white lithium grease if I were doing it.  Key being small amount, not a huge glob.



First page -
Sections 4-20, 21, 22, and 23 apply to ALL switches in the unit.  Note that section 4-24 applies only to the 'function' switches (for extra confusion, there are two sets of 'function' switches) on the small daughter board that has the AC mains switch on it.  These are push on - push off switches, NOT the ganged switches used in the 'function' and range assemblies we're interested in here.




Second page -
Figure 4-2 applies to the push on push off switches, NOT the ones we're interested in.  I believe that 4-3 shows something similar ot what our switches will look like internally, but am not 100% certain.  Our part starts at section 4-25:




Third page -
Now we're getting into the meat of the procedure.  the illustrations combined with the picures above should hopefully make the procedure clear:




Fourth page -
Hopefully section 4-26 or 27 will not be necessary, especially as I've no idea where one might find a replacement switch...:




Fifth page -
The remaining instructions on installing a replacement switch:
\]


And as always, assembly is the reverse of disassembly.

Hopefully this helps - good luck with it, and let me know if I can try to dig anything else out to assist.

-Pat

<edit to add note about ensuring all switches are 'off' before attempting to remove rear support bar>
« Last Edit: September 30, 2017, 05:49:49 pm by Cubdriver »
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Offline neo

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Re: Fluke 8200A read problem.
« Reply #34 on: September 30, 2017, 02:43:03 pm »
https://www.amazon.com/WD-40-Specialist-White-Lithium-Grease/dp/B0083V8KBE/ref=sr_1_10?ie=UTF8&qid=1506780343&sr=8-10&keywords=white+lithium+grease

Would that be a good choice for the lithium grease?

Great  pictures and instructions, armed with those i might be able to manage disassembly and reassembly of the switches.
My board looks exactly the same only with little incandescent glass bulbs as opposed to red LEDs, in my opinion the white light is more fitting than the red.
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Offline Le_Bassiste

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Re: Fluke 8200A read problem.
« Reply #35 on: September 30, 2017, 03:25:27 pm »
can't comment on that lubricant, really.
 you want to avoid any mineral stuff, because it might deteriorate the pushrod and may have undesired creeping behavior. others may have better recommendations than i have here. i've been using white teflon grease, extremely sparingly applied to avoid any contact with the contactor elements to avoid creepage paths. see picture of dismantled keithley 200x input selector prior to cleaning, for the fun of it.
re-assembly went really smooth, and instrument passed keithley calibration lab without problems.
mind your carpet monster, though.
 

Offline Cubdriver

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Re: Fluke 8200A read problem.
« Reply #36 on: September 30, 2017, 05:35:46 pm »
If it jams, force it.  If it breaks, you needed a new one anyway...
 
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #37 on: September 30, 2017, 06:46:10 pm »
Pat, nice job on the modern switch disassembly docs and the custom servicing brackets. It does appear that, apart from the number and location of switches, the 8100A and 8200A switches are essentially the same.

Fortunately, Fluke didn't solder every pin of the switches to that upper PCB. What a relief!
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Offline Cubdriver

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Re: Fluke 8200A read problem.
« Reply #38 on: September 30, 2017, 08:39:03 pm »
Pat, nice job on the modern switch disassembly docs and the custom servicing brackets. It does appear that, apart from the number and location of switches, the 8100A and 8200A switches are essentially the same.

Fortunately, Fluke didn't solder every pin of the switches to that upper PCB. What a relief!

Thanks!  I suppose it's not surprising that they'd try to use common parts when possible.  They are certainly a PITA to service, though, thanks to their location.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #39 on: September 30, 2017, 10:42:06 pm »
Yeah, I guess they're close enough in age to be able to share parts. I was afraid that the switches might be newer and, hence, less serviceable.
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Offline neo

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Offline Cubdriver

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Offline neo

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Re: Fluke 8200A read problem.
« Reply #42 on: October 01, 2017, 02:29:30 am »
I'm having a hard time disassembling the switches, i got the rear clip off as well as the button and spring but i have no clue how to get the shaft out.

EDIT: I got one.
« Last Edit: October 01, 2017, 02:36:41 am by neo »
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #43 on: October 01, 2017, 02:35:09 am »
Some of the switches have a front bar that is part of the mechanism that causes only one switch at a time to be engaged. You'll have to disengage the shaft from that front bar in order to get the shaft to come out of the back of the switch housing.
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Offline neo

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Re: Fluke 8200A read problem.
« Reply #44 on: October 01, 2017, 02:41:52 am »
What does it mean if they are actually clean inside?

and what would i look up to buy a new key? Not a shaft just the little square key you push one of mine is slightly melty.
« Last Edit: October 01, 2017, 02:46:59 am by neo »
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #45 on: October 01, 2017, 02:51:33 am »
It doesn't matter much what it looks like. Start with the switch that exhibited the worst connectivity. Clean the contacts and reassemble the switch. Did it fix the continuity of the switch? If not, compare the metal contacts of that switch with the switch that works fine. Is the badly behaving one misshapen or have visible damage to the contact surface? Does swapping the metal contacts move the problem from the bad switch to the good one?

If the metal contacts of the bad switch are bent (more compressed than in the good switch), then they're bad. The manual says not to bend them back (i.e., replace the switch).
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Offline neo

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Re: Fluke 8200A read problem.
« Reply #46 on: October 01, 2017, 02:53:43 am »
It doesn't matter much what it looks like. Start with the switch that exhibited the worst connectivity. Clean the contacts and reassemble the switch. Did it fix the continuity of the switch? If not, compare the metal contacts of that switch with the switch that works fine. Is the badly behaving one misshapen or have visible damage to the contact surface? Does swapping the metal contacts move the problem from the bad switch to the good one?

If the metal contacts of the bad switch are bent (more compressed than in the good switch), then they're bad. The manual says not to bend them back (i.e., replace the switch).

The only real way to test these is reassembly, continuity testing each one is a bit of a circus.
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #47 on: October 01, 2017, 02:55:19 am »
and what would i look up to buy a new key? Not a shaft just the little square key you push one of mine is slightly melty.

I doubt that you'd be able to buy just the keycap unless you can find someone who happens to have a stash of parts. Usually with old equipment, donor units are acquired to replace parts. The manual would have the part number, which you can then search for. Sometimes you'll get lucky and hit a site for vintage test equipment that has it.
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Offline neo

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Re: Fluke 8200A read problem.
« Reply #48 on: October 01, 2017, 02:59:46 am »
I may have a small problem, one of the springs went flying and it flew right into obscurity. I was trying to be careful and i managed to get 5/6 but the 6th, as i said, went ping.

I really feel kinda dumb right about now.

EDIT:
The 6th shaft won't come out due to board standoff.
« Last Edit: October 01, 2017, 03:32:07 am by neo »
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Offline bitseeker

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Re: Fluke 8200A read problem.
« Reply #49 on: October 01, 2017, 03:35:44 am »
Uh, oh. Keep the pets, if any, away until it's found.
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