Author Topic: Fluke 8845A repair  (Read 4061 times)

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Offline Big Dog

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Fluke 8845A repair
« on: May 07, 2016, 01:50:46 am »
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
 

Offline Jacek_Paw

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Re: Fluke 8845A repair
« Reply #1 on: May 07, 2016, 06:54:54 am »
In this case I would check cristal oscillators, maybe one of them is dead and system doesn't start?
 

Offline Big Dog

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Re: Fluke 8845A repair
« Reply #2 on: May 07, 2016, 12:38:04 pm »
all micro's have bus activity and their crystals are at the right frequency.

Sorry, should of had that in the first post.
 

Offline Jacek_Paw

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Re: Fluke 8845A repair
« Reply #3 on: May 08, 2016, 08:56:33 am »
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.
 

Offline Big Dog

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Re: Fluke 8845A repair
« Reply #4 on: May 10, 2016, 07:07:29 pm »
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.
 

Offline alank2

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Re: Fluke 8845A repair
« Reply #5 on: May 10, 2016, 07:35:58 pm »
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.
 

Offline Big Dog

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Re: Fluke 8845A repair
« Reply #6 on: May 10, 2016, 08:18:03 pm »
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.

 

Offline Jacek_Paw

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Re: Fluke 8845A repair
« Reply #7 on: May 11, 2016, 06:32:37 pm »
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.
« Last Edit: May 12, 2016, 06:38:21 am by Jacek_Paw »
 

Offline Big Dog

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Re: Fluke 8845A repair
« Reply #8 on: May 12, 2016, 12:32:43 am »
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.
 

Offline Big Dog

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Re: Fluke 8845A repair
« Reply #9 on: May 16, 2016, 11:07:12 pm »
No one has schematics for this unit?

Jim
 

Offline t-17

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Re: Fluke 8845A repair
« Reply #10 on: July 08, 2016, 05:35:11 pm »
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?
 


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