Fluke 8050A -- Received it today

[JenniferG]

It was to be my first decent multimeter.  I guess I get what I pay for.  ($20 plus $10 shipping).

Despite the guy saying it is in "great condition" (which the photos he took seemed to depict), there was a big lump in the front panel that I saw immediately, that you just don't see from the angle he took.  Don't know what could of caused that.. but it was damaged some how.

Also, I just now notice he took photos of every side but the back.  Well the seal is off the back, so it must have been tampered with.

It turns on... the display works fine.  But wow it's hosed lol.

6.00V reads around 6.5V.

a 22 ohm resistors reads 30 ohm.   But interestingly the ohms keeps dropping over time.  Over about two minutes it dropped down to 25 ohm and pretty much stayed put or was just at a crawl so slow downwards to 22 ohm .. I dunno.

With my VERY limited experience of electronics, I am guessing it is electrolytic capacitor related? It reminds me of measuring a cap as it is turned on or off.

[technogeeky]

No pics? For shame!

[JenniferG]

No pics? For shame!

This is the photo he took of it:



I didn't even notice that lump below the DB label and he didn't point it out in the description nor took special photo of it at alternate angle.. described it as great condition lol.  If I was selling that I would of pointed that out to the buyer.  Seems deceptive.   Well it turns out to be quite a dimple protruding out .. I don't get it.. what could of caused it.  Some force from within or someone tampering with it.  EDIT: Again it looks like nothing in this photo, from this angle.

[retiredcaps]

6.00V reads around 6.5V.

a 22 ohm resistors reads 30 ohm.

The above may be fixable.  First, post clear focused pictures of the pcb.  Multiple shots will help.  We are looking for something obvious like a blown or bad component.

If the inside is dirty a simple IPA bath of the pcb might correct the above problem.  Otherwse, we can check the input protection components like the PTC, MOVs, etc.

[JenniferG]

Do I need to be concerned about battery back up or NV RAM calibration data? I don't want to lose the calibration data messing with the pcb.   I have to take it apart a bit because the display board is in the way

[james_s]

I'm not familiar with the 8050A, but I wouldn't expect there to be NVRAM in such an old meter, it's probably just some old fashioned trimpots. This should be an interesting project, see if you can find schematics and have a look inside. You'll probably need another meter to diagnose this one but it never hurts to have two meters anyway.

[Andy Watson]

Do I need to be concerned about battery back up or NV RAM calibration data?

No. The calibration is "hardware coded". 
Besides, you've obviously got calibration standards that are much more accurate than the meter is presently reading - so there's nothing to lose.

I have to take it apart a bit because the display board is in the way

Take is slowly - understand what you are doing. Do not tweak any pots or other adjustments in an attempt to correct the reading. The symptoms that you describe indicate a fault (probably leaky caps); not a calibration issue. Once you have identified and corrected the fault I wouldn't be surprised to find that the meter returns to "calibration".

P.S. http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Fluke/Fluke_8050A

Edit: Also, search this forum for the writings of Dr Taylor and note the efforts taken to ensure that PCBs are clean, clean, clean.

[james_s]

Unless somebody has already gone in there and tweaked every adjustment there is. That's the classic noob error, makes it so much less fun to repair something when you can't tell whether it's still broken or just way out of whack because the last person who worked on it adjusted everything they could find to adjust.

[JenniferG]

Again, I am upset with the seller who took photos of all sides but the back, hiding that it was tampered with.  He probably knew it didn't work and was way out of whack and was selling it cheap for that reason.

THere are 10 electrolytic caps on the board (took it apart).  4 of which are larger (one of them read 460uf).  None look bulged.

[james_s]

Welcome to eBay.

The capacitors are probably not the problem, although it may make sense to replace them due to age but I wouldn't worry about that much yet. This meter was made long before the bad capacitor plague.

[JenniferG]

I guess I'll try and get $10 knocked off from the seller because it wasn't fully as he described.  And then part it out and try to get some money back.  I imagine I could get $10-15 for the working lcd / display board -- lcd is quite decent. That way a person has a spare LCD to use and a spare display board they can play with to make a custom LED display for it.  (BTW, this PCB mounted transformer looks pretty useful for another project maybe.)

EDIT: Of the four larger caps one pair is 470uF 16v and the other pair 220uF 25v.  They'd be easy for me to replace -- I have a local electronics shop (Mom&Pop) like 1 mile away.

EDIT #2: Put an offer in on Instek GDM-8251a.  I also want an HP 3478a.

[Andy Watson]

Again, I am upset with the seller who took photos of all sides but the back, hiding that it was tampered with.

If it helps, consider it as $30 worth of education. However, I would not give-up hope of resurrecting this meter. Look for contamination on the PCB - cap leaks ? - battery leaks ? - just water ingress ?

I have had some minor success in shrinking bumps on plastic panels using a hot-air soldering iron. Keep the temperature way down low and be patient - plastic does not conduct and it takes a while for the heat to penetrate - let the surface tension pull it flat - experiment in an area of no significance. Note it's not my fault if you end-up with a homogeneous lump of squiggy grey plastic

[Cubdriver]

Before you go and part it out, at least give repairing it a shot!!  Can you post pics of the innards?

-Pat

[JenniferG]

I don't see anything obvious -- but I'm a newb.  Images are 1024 pixels wide if you open them up in another window they would probably be bigger.

[DimitriP]

Again, I am upset with the seller who took photos of all sides but the back, hiding that it was tampered with.  He probably knew it didn't work and was way out of whack and was selling it cheap for that reason.

THere are 10 electrolytic caps on the board (took it apart).  4 of which are larger (one of them read 460uf).  None look bulged.

Sounds like "not as described" to me. Ask for  $10-$15 credit and if he declines, leave negative feedback and let us know his ebay ID.

Do it now,  before you  forget and  the  feedback windows lapses

[ModemHead]

The advice in this thread is spot-on, especially the part about not messing with the trim pots just yet.

ADC input stages are very high impedance.  Tiny leakage currents along with inherent parasitic capacitance can cause faulty ramp-up or ramp-down type readings.  Tiny leakage currents can be caused by contamination on the PCB, possibly even inside the switches.

Get yourself a good supply of strong isopropyl alcohol (IPA) and brush the board with it, both sides.  Allow drying time of course.  If the fault gets any better, do it again.  Dunk the whole board, if necessary.

[JenniferG]

The advice in this thread is spot-on, especially the part about not messing with the trim pots just yet.

ADC input stages are very high impedance.  Tiny leakage currents along with inherent parasitic capacitance can cause faulty ramp-up or ramp-down type readings.  Tiny leakage currents can be caused by contamination on the PCB, possibly even inside the switches.

Get yourself a good supply of strong isopropyl alcohol (IPA) and brush the board with it, both sides.  Allow drying time of course.  If the fault gets any better, do it again.  Dunk the whole board, if necessary.

Yeah, I had no intentions of touching those 4 adjustment pots.  Was hoping that whoever had it before didn't either, but it was tampered with.. bunch of sticky residue all over the back of this unit , over the case screw hole.. large rectangle about 2 inches wide even, of old label goo.  The seller didn't snap a photo of this, but all other sides interestingly.

[JenniferG]

THat upper left switch.  Copper sitcking on the outside.  doesn't seem right.  That's the only thing I noticed anyways.

[ModemHead]

THat upper left switch.  Copper sitcking on the outside.  doesn't seem right.  That's the only thing I noticed anyways.

Normal.  Part of the push-in/push-out mechanism.

[JenniferG]

Some of those DIP are socketed.  I suppose I could try to re-seat them all.  But it seems more like an analog problem not digital. Many of those 4016 chips.  Quad Bilateral switches.  Interestingly they go for like $1 a piece, in case I part it... might be useful for a project.. dont' have any yet.

I am not sure what isopropyl alcohol would do?  I mean it's all soldered and alcohol only cleans the outer surface?  I'm newb sorry for my questions.  EDIT: oh are you saying stuff accumulated on the surface that is conductive?

[Cubdriver]

You can try reseating the chips.  For now, though, rather than pulling them and risking pin damage, I'd just give each of them a push down while supporting the board beneath it.  You may hear/feel a slight 'click' as the chip moves in the socket.  If just pushing yields no clicks or movement, perhaps pry them up *just a touch* with a small screwdriver - just till it moves.  Either end should do it, it's not even necessary to lift both as just the movement should shift all the pins slightly.  Then reseat them.    If there's oxidation, this may break it.

Does yours have the battery, or not? 

What does it indicate on, say, DC volts with no input and/or the input connections shorted together?

-Pat

[Cubdriver]

Some of those DIP are socketed.  I suppose I could try to re-seat them all.  But it seems more like an analog problem not digital. Many of those 4016 chips.  Quad Bilateral switches.  Interestingly they go for like $1 a piece, in case I part it... might be useful for a project.. dont' have any yet.

I am not sure what isopropyl alcohol would do?  I mean it's all soldered and alcohol only cleans the outer surface?  I'm newb sorry for my questions.  EDIT: oh are you saying stuff accumulated on the surface that is conductive?

On some hi-Z meter circuits, even invisible deposits of crud can cause issues - yes, the stuff can be conductive.  Perhaps megohms, or tens of megohms, but even that can throw things off.

-Pat

[ModemHead]

On some hi-Z meter circuits, even invisible deposits of crud can cause issues - yes, the stuff can be conductive.  Perhaps megohms, or tens of megohms, but even that can throw things off.

+1

[JenniferG]

Does yours have the battery, or not? 

What does it indicate on, say, DC volts with no input and/or the input connections shorted together?

Model without the battery it says on the back label anyways.  Don't see a battery.

Set the volts to DC, 2V range.  Turned it on and observed .003.  A few seconds later it was .0115.
Then over time:
.0104 (15 sec)
.0098 (30 sec)
.0093 (1 min)
.0090 (1:15 min)
.0086 (1:30 min)
.0084 (1:45 min)
.0083 (2 min)
.0080 (2:15 min)
.0077 (2:30 min)

I suppose it might slowly keep going down but I turned it off at this point.  This is with no probes plugged into the unit.

[Cubdriver]

Just for grins, leave it plugged in and on for a while.   Who knows how long it's been off - perhaps the power supply filter caps need to re-form.

-Pat