Fluke 8845A repair

[Big Dog]

I picked up a fluke 8845A from government surplus in condition code A, however it was in F condition.

The meter starts to come up, displays a menu but nothing else, no readings, keyboard does nothing, not even the soft power switch.

All voltage regs are good, see data across the optical links, but get lost trying to trace data to and from the front panel.

Any help or ideas would be welcome, including a schematic.

Jim

[Jacek_Paw]

In this case I would check cristal oscillators, maybe one of them is dead and system doesn't start?

[Big Dog]

all micro's have bus activity and their crystals are at the right frequency.

Sorry, should of had that in the first post.

[Jacek_Paw]

OK, so I have another idea: are you sure that this meter is broken? Maybe it is in some kine of remote state? That could explain that the keyboard doesn't work and lack of readings.

[Big Dog]

No idea on that one, would not a power cycle clear any state like that.
Not read the manual to this meter, but I would hope a power cycle would clear this.

[alank2]

You said you get a menu, what type of menu?  On my 8845A it will briefly display the menu at the bottom before displaying measurements during power up.  On mine it:

Immediately says "INITIALIZING" when power is applied and the rear power switch is turned on.  [a few seconds]
Then it display the bottom menu items that go with the soft keys [a second]
Then it clicks and starts showing measurements.

You might lookup 8845 or 8846 on youtube to see what the normal startup looks like to compare yours to.

[Big Dog]

Mine comes up with the following;

FLUKE DMM
WWW.FLUKE.COM INITIALIZING...


then it comes up with a menu as follows;

Ratio    D.Fltr  A.Fltr  2nd meas

D.Fltr is highlighted, also about every 12 seconds this is blanked or refreshed,
as you can see the info disappear for a 10th of a second.

no clicks, keyboard locked up.

[Jacek_Paw]

I have tested today SYST:REM and  SYST:RWL on my 8846A, first turns the meter into remote state and second locks the keyboard, but after cycling the power meters turns on in normal(operative) mode. So my gues about remote state is definitely wrong.

[Big Dog]

It's a good thing it was wrong, as I have no other way to talk to this other than the keyboard/display interface.
But it would be a mistake that Fluke would not make, that being said, I've seen HP do it.

[Big Dog]

No one has schematics for this unit?

Jim

[t-17]

I have another 8845A here, also defective. Mine boots up correctly, but always states "overflow" no matter what is at the inputs. 440mA input fuse was blown and somebody had already a go at the 3.3V rail regulation for the analog part. But all voltages check out fine, reference is fine, no error messages are displayed, clocks are running. But without documentation, this is going to be very hard to trace. Next thing is to check all the opamps (going to take a while).

The reason I'm writing this is: Maybe we can exchange our findings and help each other with the repair?

[crasyboye]

same problem: http://bbs.38hot.net/forum.php?mod=viewthread&tid=753281&extra=page%3D1

[coromonadalix]

I dont think well never see an "leaked" or official schematics of the 8845 8846 .. 


Thats why i went to buy 34401a instead with limited functionalities, the 8846 was my first choice of meter at least they have services manuals.

I saw some of their rebranded models landing on ebay this year,  lots of them had internals problems, hang ups, lan problems, stuck on boot    etc ....

If you translate the bbs38 thread it may give you some hints, they talk about memory corruption and usb interface problems / busted parts, but it doesn't go far ??
http://bbs.38hot.net/thread-753281-2-1.html

I hope there is a FW available ??

Or maybe some one is able to make some ic / memory dumps ??

[Johnny10]

You should read the 8846A thread.

These units have the peculiar problem you describe.

I now have three 8846 units with same problem and one wonderfully working unit.

Have never been able to trace problem.
Unit fires up digital side but something is amiss on analog side.

[t-17]

I have managed to get my unit back into working state. Have a look at this thread. I tried to gather everything I could find out back then (most importantly, IC designators and their function in the circuitry):

https://www.eevblog.com/forum/repair/fluke-8845a-(8846a-like)-6-5-digit-multimeter-showing-_overload_-at-all-times/

Perhaps it is helpful to you.

[Miti]

You should read the 8846A thread.

These units have the peculiar problem you describe.

I now have three 8846 units with same problem and one wonderfully working unit.

Have never been able to trace problem.
Unit fires up digital side but something is amiss on analog side.

Check inguard/ outguard IR LED/ sensor. There are two pairs for two way communication, RX side covered by two small metal shields. One was very weak on mine but it was showing an error related to inguard/outguard.

[jerry_gao]

My 8845 have the same issue,  Have you solved this issue?