EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: thefatmoop on December 22, 2020, 04:36:06 pm
-
Hi,
I bought a used Fluke 8845A recently. Has an odd issue where the display shows menus and I can interact with the menus. The issue is the system displays no measurements and has the high voltage icon. None of the measurements work at all (AC V, DC V, DC I, AC I, continuity, resistance). But if i tap on the unit, it'll spring to life and work as normal.
So my thought is that there's likely a micro just driving the display that's not getting data from the micro that's sitting on the ADC.
Here's a video i sent to the seller
https://www.youtube.com/watch?v=CK8SGAhLSvw (https://www.youtube.com/watch?v=CK8SGAhLSvw)
I paid ~1/2 the cost of a new unit - i paid a bit higher than used because it just had it's calibration checked. Is this worth troubleshooting? I can still return this unit.
-
Could be switch contacts for front rear input jacks.
This has been common problem with these units.
Check on forum for 8846A issues.
https://www.eevblog.com/forum/repair/fluke-8846a-repair/msg1456474/#msg1456474 (https://www.eevblog.com/forum/repair/fluke-8846a-repair/msg1456474/#msg1456474)
-
Put a shorting plug in it and or connect the test leads--don't leave it as an open circuit. Then test all the ranges. If you still have a problem, cycle the front/rear switch a few times.
Get used to that flickering lightning bolt and the OVERLOAD warning, you will see a lot of it with this meter. It's just the way they work and it is simply reading noise from the open terminals.
-
I did make a discovery - When the issue is occurring, i can fix it by gently pushing on the backside of the pcb where the front/rear input selection switch is at.
The problem now is the switches are on the bottom side of the PCB, and the whole unit really looks like there was a LOT of effort to prevent someone from removing the main pcb. Does anyone know of any photos/videos of removing the main pcb or taking the front display build off? I've been trying to figure out removing the main pcb for an hour now. I don't have good desoldering tools, so i don't want to unsolder anything.
Video of my issue
https://youtu.be/CdH7jRZIMjU (https://youtu.be/CdH7jRZIMjU)
-
You don't have to desolder anything.
TIN worked on an 8846A a while back.
https://www.eevblog.com/forum/repair/fluke-8846a-repair-shenanigans/msg1758920/#msg1758920 (https://www.eevblog.com/forum/repair/fluke-8846a-repair-shenanigans/msg1758920/#msg1758920)
-
How the hell did he get the mainboard+front display out?! Did you look at my second video link?
-
Those white rectangular pins behind the input jacks come out first.
That stud in the middle of the board stays in but you have to lift the board over it and everything slides out to the front of the unit.
-
This is what it looks like at the switch pins.
-
Thanks for the pictures, do you know/remember if the sliding 'sled' module is somewhat loose on the pcb? Mine wiggles quite a bit
I'm certain it's in the front/rear selector brush assembly. It just doesn't look like it's well designed... Returning the unit and likely going with an Agilent 34401A?
https://youtu.be/klm0b-3O8mY (https://youtu.be/klm0b-3O8mY)
-
Yes that sliding unit is a bit loose.
Maybe why everyone has problem with it.
Great videos by the way.
Great camera, good sound.
Maybe you should make a few more teardowns?
-
I'm certain it's in the front/rear selector brush assembly. It just doesn't look like it's well designed... Returning the unit and likely going with an Agilent 34401A?
I think it is more of an environmental issue rather than looseness. All the more reason to buy cosmetically nice equipment--like many instruments, these meters are electrically robust, but environmentally sensitive to humidity and dust. If the 34401A works for your needs, there are still some NOS ones on eBay.
https://www.ebay.com/itm/NEW-Agilent-34401A-Digital-Multimeter-6-5-digits-New-in-The-Box/393044731082?epid=710140765&hash=item5b834aa4ca:g:3S8AAOSwjN5fsGs3 (https://www.ebay.com/itm/NEW-Agilent-34401A-Digital-Multimeter-6-5-digits-New-in-The-Box/393044731082?epid=710140765&hash=item5b834aa4ca:g:3S8AAOSwjN5fsGs3)
-
I would return it and try to get another meter, thoses meters can be a nightmare to repair, and after seeing many meters 8845 and 8846 having interfaces communications problems, i would not hesitate to return it
no schematicas available, getting parts is problematic
-
I would return it and try to get another meter, thoses meters can be a nightmare to repair, and after seeing many meters 8845 and 8846 having interfaces communications problems, i would not hesitate to return it
no schematicas available, getting parts is problematic
But those that work are amazing! ;D I have one that I repaired.
That being said, I’ve seen two of those with the switch broken, but that’s easy to diagnose. And if you don’t need to use the rear terminals, you can eliminate it by bridging it in the front position.
-
That being said, I’ve seen two of those with the switch broken, but that’s easy to diagnose. And if you don’t need to use the rear terminals, you can eliminate it by bridging it in the front position.
Do you have photos of what terminals you bridged? I'd hate to make a mistake if I end up trying this.
-
Do you have photos of what terminals you bridged? I'd hate to make a mistake if I end up trying this.
Unfortunately not, that wouldn’t be acceptable in an ISO manufacturing environment. One was replaced by the calibration lab and I repaired the other one using epoxy. I’m sure you can figure out by measuring the distance between the spring contacts in the plastic and matching them with the pads on the PCB.
-
Maybe asking fluke if this part is orderable ??
-
Hi Guys,
So I think I purchased this very multimeter from ebay the label on the front left is the same as in the video on thefatmoop post and according to the ebay listing pictures.However I noticed that the label has been removed on the unit when it arrived today.
Anyway I unboxed and flipped the line voltage around to 240 volt and powered it up as I'm in the UK. The seller listing mentioned it was temperamental on the reading and required tapping. This was confirmed when I powered it up. So I took it apart to investigate.
To do this you need to do the following.
1) Remove front and rear grey rubber protectors.
2) Spread bail carefully just enough to remove.
3) Remove outer case screws 4 on bottom and slide case off.
4) Remove IEEE488 connector hex standoffs and RS-232 hex standoffs.
5) Remove Power transformer screws on right side as seen from the front
6) Remove forward and rear input connector plastic keeper ( pull away slightly at the top and pull up)
7) On the top of the instrument near the front aft of the display front pane remove two screws then remove the side Screws on the same plate
8) Remove the two Dome head screws going through the front bezel
9) Carefully remove the front panel complete and set aside.
10) remove the screws on the main board one under the transformer, one front right and one on the front left
11) Gently slide the board out though the front, it gets a bit tricky with the rear input connectors as some tilting is required to clear the riv-nuts for the front bezel.
So with the board now release from the the case. I went straight to the front/rear input switching on the bottom of the main board. I then pulled off the board by disconnecting the input rod screw and removing the two screws through the slide/contact assy. There is a plastic stop that runs in a slot cut into the PCB, this limits the slide movement to prevent the slide/contact assy from getting to the removal/installation cut outs on the side of the PCB. I gently lift this and slide back to the cut outs, once in this position lift straight up and then shes out!
Bingo! all the wipers that make contact with the board pads were different heights compared to one another.
So with a watch makers screwdriver gently straightened them so all were level and a bit of contact cleaning performed in all affected areas. I also greased the button assy with some Dow Corning DC4 as i found it was a little tight. I then reassembled everything, powered it up and now she is fixed!
Now I have a good bench multimeter for the workshop.
I hope this helps anyone with a similar issues with the Fluke 8845A/8846A
Keep a look out on the forum for the noisy power supply issues on my Tek 2440 scope, I intend to use the 8845A to check the voltage rails for ripple as the scope has a noisy trace.
https://www.eevblog.com/forum/repair/tektronix-2440-a16-power-supply-issue/msg3497888/#msg3497888 (https://www.eevblog.com/forum/repair/tektronix-2440-a16-power-supply-issue/msg3497888/#msg3497888)
Many thanks all.
regards
eevblognut2021
-
Congrats, that’s a good 6.5 digit meter.