Author Topic: Fluke 8808A Question  (Read 10896 times)

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Offline GAD

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Fluke 8808A Question
« on: January 07, 2016, 08:04:40 pm »
Hello all,

I recently bought a used Fluke 8808A after being supremely disappointed with the Siglent SDM3055.

I love everything about the Fluke and it seems to work well with one apparent quirk, and I'm hoping you can tell me if this is normal.

With the Fluke powered on and stable it defaults  to auto-range and DCV. It reports something like 3.2mV with the probes laying on my desk. I then put the probes on a 9V battery and it reports something like 142.345mV (it does not auto-range). If I then push DCV again, the meter auto-ranges and reports correctly. Is this normal?  It seems counter-intuitive to have a meter require that I take my hands and eyes off of what I'm testing in order to initiate a test, but the manual seems to indicate that this is normal.

Any help is appreciated.

 

Offline retiredcaps

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Re: Fluke 8808A Question
« Reply #1 on: January 07, 2016, 08:22:07 pm »
Hmm,I don't have any Fluke bench meters nor have I used any, but the behaviour you describe doesn't sound right to me?

According to the instructions, snapshot included, you just select DCV and the meter autoranges.

If you bought it from ebay, can you list the auction number so we can see who the seller is and how it was listed (used, parts, new, etc)?
 

Offline retiredcaps

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Re: Fluke 8808A Question
« Reply #2 on: January 07, 2016, 08:24:50 pm »
After the meter autoranges correct to show the 9V battey voltage, what happens if you measure an AA 1.5V cell right away afterwards?  Does it still autorange correctly to read 1.5V?  What happens if you re-measure the 9V battery again after this?  Does it work properly without you having to hit the DCV button each time?
 

Offline jpmkm

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Re: Fluke 8808A Question
« Reply #3 on: January 07, 2016, 08:44:36 pm »
That is not normal.  Have an 8808A on my bench and the default state is indeed DCV autorange.  If I measure 12VDC, it shows it without me having to push any buttons.  You might check the manual(I know it's floating around somewhere online) to see if there is a factory reset.  Perhaps there is some setting that I don't know about that is giving you that behavior.

FWIW, though, I hate the autoranging on this meter.  Too slow for repeated measurements when I know what I am expecting.  I set up the custom modes(S1-S6 buttons) to switch between the modes and ranges I want - a couple DC voltage ranges, a couple resistance ranges, and the continuity checker.  I know that doesn't exactly solve the problem you're having, but it makes life easier for me, at least.
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #4 on: January 07, 2016, 09:02:10 pm »
Hmm,I don't have any Fluke bench meters nor have I used any, but the behaviour you describe doesn't sound right to me?

According to the instructions, snapshot included, you just select DCV and the meter autoranges.

If you bought it from ebay, can you list the auction number so we can see who the seller is and how it was listed (used, parts, new, etc)?

Right, but look at the steps - #1: connect leads, #2: push button. That's the only way it works for me. 
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #5 on: January 07, 2016, 09:03:27 pm »
After the meter autoranges correct to show the 9V battey voltage, what happens if you measure an AA 1.5V cell right away afterwards?  Does it still autorange correctly to read 1.5V?  What happens if you re-measure the 9V battery again after this?  Does it work properly without you having to hit the DCV button each time?

Great idea!

No, it does not. If I push DCV while the probes are connected, the relays click and it reports the voltage. As soon as I remove the probe the relays click again and it goes back to mV. Testing a AA thereafter repeats the same behavior.
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #6 on: January 07, 2016, 09:05:35 pm »
That is not normal.  Have an 8808A on my bench and the default state is indeed DCV autorange.  If I measure 12VDC, it shows it without me having to push any buttons.  You might check the manual(I know it's floating around somewhere online) to see if there is a factory reset.  Perhaps there is some setting that I don't know about that is giving you that behavior.

FWIW, though, I hate the autoranging on this meter.  Too slow for repeated measurements when I know what I am expecting.  I set up the custom modes(S1-S6 buttons) to switch between the modes and ranges I want - a couple DC voltage ranges, a couple resistance ranges, and the continuity checker.  I know that doesn't exactly solve the problem you're having, but it makes life easier for me, at least.

Thanks. I may end up doing the same, but I want all the functions to work.

I've never had a bench meter before, but I've had way too many handhelds and I've never experienced this before. It almost seems to me like it's a triggering problem (from the point of view of someone who's never used triggering) but that feature is set properly.

The meter can be set to Fluke 45 mode, and I did that which resets the meter. It works exactly the same way in regards to auto-ranging.
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #7 on: January 07, 2016, 09:08:22 pm »
BTW this is the auction: http://www.ebay.com/itm/221985999159?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

It's got 14-day return so I've got that going for me. It is absolutely not the unit pictured, so that's disappointing, but we're just talking some minor sticker residue so that's not the end of the world.
 

Offline retiredcaps

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Re: Fluke 8808A Question
« Reply #8 on: January 07, 2016, 09:27:35 pm »
You bought this from a seller in Ireland?  Were there no sellers in the USA?
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #9 on: January 07, 2016, 09:37:52 pm »
Why is that relevant? I got a fairly good price and it got here in three days.
 

Offline tautech

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Re: Fluke 8808A Question
« Reply #10 on: January 07, 2016, 10:05:12 pm »
Hello all,

I recently bought a used Fluke 8808A after being supremely disappointed with the Siglent SDM3055.......

In what way?

I've checked your previous posts to see if you'd sought help on EEVblog but obviously you hadn't.
Care to share more on your disappointment in this thread:
 https://www.eevblog.com/forum/testgear/siglent-technical-support-join-in-eevblog/
(not wanting to hijack this thread  ;) )
Avid Rabid Hobbyist
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #11 on: January 07, 2016, 10:42:06 pm »
Hello all,

I recently bought a used Fluke 8808A after being supremely disappointed with the Siglent SDM3055.......

In what way?

I've checked your previous posts to see if you'd sought help on EEVblog but obviously you hadn't.
Care to share more on your disappointment in this thread:
 https://www.eevblog.com/forum/testgear/siglent-technical-support-join-in-eevblog/
(not wanting to hijack this thread  ;) )

Done. The best way to describe it is a "feel" thing. I like the Fluke better in almost every way.
 

Offline tautech

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Re: Fluke 8808A Question
« Reply #12 on: January 07, 2016, 10:54:10 pm »
Hello all,

I recently bought a used Fluke 8808A after being supremely disappointed with the Siglent SDM3055.......

In what way?

I've checked your previous posts to see if you'd sought help on EEVblog but obviously you hadn't.
Care to share more on your disappointment in this thread:
 https://www.eevblog.com/forum/testgear/siglent-technical-support-join-in-eevblog/
(not wanting to hijack this thread  ;) )

Done. The best way to describe it is a "feel" thing. I like the Fluke better in almost every way.
Thanks for sharing your views.  :)
Avid Rabid Hobbyist
 

Offline jpmkm

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Re: Fluke 8808A Question
« Reply #13 on: January 07, 2016, 11:01:37 pm »
Dumb question, but have you tried different test leads?

Does the autoranging work when measuring resistance? 
 

Offline ManateeMafia

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Re: Fluke 8808A Question
« Reply #14 on: January 08, 2016, 02:02:34 am »
I wonder if something is wrong in the input protection circuits? I also have an 8808A that was defective when I bought it. It was too cheap to turn down ($75) and the only two problems were an open trace to a 5V regulator input and a missing fuse on the bottom of the meter.

Are any of the other functions working? AC/DC Current, resistance, etc..

If you do open it up, I would appreciate it if you could make sure I have my repair connected properly  :o I can also help if you need any comparison testing.
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #15 on: January 08, 2016, 02:23:04 am »
Dumb question, but have you tried different test leads?

Does the autoranging work when measuring resistance?

That's not a dumb question at all! I grabbed another set of probes and the behavior is identical.

I got permission from the seller to open it up. Nothing obviously wrong inside aside from dust, though I do see a SM resister that looks like it may have been resoldered at some point. I cleaned the soft button contacts and the meter is SO much nicer to use now. It's still not auto-ranging properly.

This sucks because it seems to do everything else well. I can store settings as described by a previous poster and it works perfectly. I can measure ACV and Hz at the same time and the dual display works great. I can min/max, delta, etc., and it all works.

I tested auto-range on resistance, and it does work better than on ACV or DCV, but it's still not right.
 

Offline jpmkm

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Re: Fluke 8808A Question
« Reply #16 on: January 08, 2016, 02:40:48 am »
If you set the manual range on DCV to the smallest range and then measure your 9V, does it display 0L(overload)?  Try stepping through the ranges and see what measurements you get.  Perhaps there is an issue with a particular range such that the meter isn't even registering a voltage to begin with, and therefore would have no reason to autorange since it isn't measuring anything.
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #17 on: January 08, 2016, 02:51:21 am »
I wonder if something is wrong in the input protection circuits? I also have an 8808A that was defective when I bought it. It was too cheap to turn down ($75) and the only two problems were an open trace to a 5V regulator input and a missing fuse on the bottom of the meter.

Are any of the other functions working? AC/DC Current, resistance, etc..

If you do open it up, I would appreciate it if you could make sure I have my repair connected properly  :o I can also help if you need any comparison testing.

I took detailed pics of the guts that I'm happy to post.

Both bottom fuses are intact and test good.
 

Offline ManateeMafia

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Re: Fluke 8808A Question
« Reply #18 on: January 08, 2016, 02:54:27 am »
Thanks. I will open mine tomorrow and post a photo of my bodge wire. I need to confirm I stole power from the right place. I can't see any burnt traces so it must be on an inner layer or a bad via. I can post other photos too if you have a different rev board.
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #19 on: January 08, 2016, 03:19:26 am »
If you set the manual range on DCV to the smallest range and then measure your 9V, does it display 0L(overload)?  Try stepping through the ranges and see what measurements you get.  Perhaps there is an issue with a particular range such that the meter isn't even registering a voltage to begin with, and therefore would have no reason to autorange since it isn't measuring anything.

I think you're onto something there. I cannot get it to report an 0L condition.

If I manually cycle down to the lowest DCV range with nothing attached, the display reads, say, -0.259 mV. When I attach to the battery it reports around 138.663 mV. When I remove the probes, it goes up to 151.219 mV. Weird. If I reconnect, I get 138.x mV again, but if I hit DCV it ranges, but not correctly! I get about 1/2 of the proper voltage. Looking at the manual, it's reporting 4.7VDC in the 20V range and 8.x in the 200V range.

On ACV, I get a similar behavior.

Doing some further testing, it appears as though the meter *will* auto-range DOWN, but not UP (unless I force it by hitting the DCV/ACV buttons). If I set to ACV auto-range and put the probes into an AC outlet, I get 54.011 mV. If I hit ACV, it auto-ranges to whatever the wall outlet is putting out. If I pull the probes, it drops back to 55.x mV. If I put the probes back in, nothing appears to happen.

I recreated this with my function generator where I can create voltage up to about 7VAC. When it knows the voltage, it will auto-range down, but it will never auto-range up. Same with DC. If I hook it up to my DC power supply, I can see it auto-range down but never up.

No matter what I've done, I cannot get the meter to display 0L in any range.

« Last Edit: January 08, 2016, 04:22:56 am by GAD »
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #20 on: January 08, 2016, 06:18:40 am »
Some pics of the guts.

Before and after dust:






Control board:






Power:




The only funky solder (R14):




With the front reassembled:


« Last Edit: January 08, 2016, 06:20:53 am by GAD »
 

Offline GAD

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Re: Fluke 8808A Question
« Reply #21 on: January 08, 2016, 07:04:09 am »
Decided to get some known data and work from there.

The meter has five ranges in DCV. They are:

200 mV
2 V
20 V
200 V
750 V

With a 9V battery fresh out of the box, here are the readings in each range (meter set to "slow"):

200mV: ~139.75mV
2V: 1.568V
20V: 4.59V
200V: 8.245V
750V: 8.25V

My Fluke 175 reads 9.15V from the same battery using the same probes.

The same deal for AC (Ranges are the same) with the probes mashed into an AC outlet:

200mV: ~55.18mV
2V: 0.48744V
20V: 0L (yay!)
200V: ~107.695V
750V: 109.52

My Fluke 175 reads 118.2V in the same outlet using the same probes.

I think this meter needs help.

« Last Edit: January 08, 2016, 07:14:11 am by GAD »
 

Offline retiredcaps

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Re: Fluke 8808A Question
« Reply #22 on: January 08, 2016, 07:46:08 am »
Why is that relevant?
There are a number of reasons, but at 12:46AM, I will be brief and focus more effort into interpreting your data results in subsequent posts.

The biggest reason is we don't the history of the meter and how it was used or treated by the seller.  Questions that come to mind are (which you don't have to answer right away).

1) Did you buy it from Ireland due to some communications with the seller that we don't know about wrt to its condition/performance, etc?

2) Did the seller tell you some history and how it was used?

3) ....
« Last Edit: January 08, 2016, 08:03:19 am by retiredcaps »
 

Offline retiredcaps

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Re: Fluke 8808A Question
« Reply #23 on: January 08, 2016, 07:56:46 am »
With a 9V battery fresh out of the box, here are the readings in each range (meter set to "slow"):

200mV: ~139.75mV
2V: 1.568V
20V: 4.59V
200V: 8.245V
750V: 8.25V

My Fluke 175 reads 9.15V from the same battery using the same probes.
A quick search shows no service manual or schematic for the 8808A.

There could be a number of reasons for the above results.

1) Relay to switch ranges is not operating correctly.

2) Input protection (MOVs, PTC, fusible resistor, current limiting resistors) are damaged, but not visible to eye.  Coming from Ireland where mains voltage is 220-240VAC and depending on the user environment, perhaps this meter had an oops moment?

3) There is contamination (dirt, debris, flux, etc) on the pcb affecting the readings.

4) Main IC is damaged and won't auto range correctly.

Depending on how the seller wants to handle potentially costly return shipping (you pay or seller pays) will dictate on whether you try to repair this or send it back.  If you have to pay shipping to Ireland, you probably want to send it with tracking number and require a signature.  This may not be cheap.  This is another reason why I asked earlier about buying from Ireland vs USA.
 

Offline retiredcaps

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Re: Fluke 8808A Question
« Reply #24 on: January 08, 2016, 08:02:43 am »
I suggest the following tests.

1) Put the 8808A in the DC mV range.  Using the Fluke 175, measure the input impedance of the 8808A.
2) Put the 8808A in the DC 2V range.  Using the Fluke 175, measure the input impedance of the 8808A.
3) Repeat for the 20V, 200V and 750V range.
4) Report all 5 readings.

Your readings/results should match what is in the 8808A manual below with the Fluke 175 reporting 0L for the mV and 2V range (unless note 1).
« Last Edit: January 08, 2016, 08:34:07 am by retiredcaps »
 


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