Is there any way to adjust this?

[micky]

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

Is there any way to adjust this?

Or, is there ever a way to adjust this?

No schematic is available, I'm pretty sure but its guts look like most
of them. .

 

[Phil Allison]

micky wrote:

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

** So all the other ranges are OK ?

If so, it sounds like manufacturing error.



..... Phil

 

[pfjw@aol.com]

On Thursday, February 9, 2017 at 11:35:54 PM UTC-5, micky wrote:

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

Is there any way to adjust this?

Or, is there ever a way to adjust this?

No schematic is available, I'm pretty sure but its guts look like most
of them. .

Some few types have an internal adjustment process. Short the leads, push a sequence of buttons, it zeros out for ohms. For DCV, it will require a battery of known voltage within the range required.

Peter Wieck
Melrose Park, PA

 

[Phil Allison]

The Peter Fuckwit Wieck Troll spewed:

Is there any way to adjust this?

Or, is there ever a way to adjust this?

No schematic is available, I'm pretty sure but its guts look like most
of them. .

Some few types have an internal adjustment process.

** Fuck off, you retarded pile of bat manure.

No-one needs to see your brain dead, autistic crap.



..... Phil

 

[pfjw@aol.com]

On Friday, February 10, 2017 at 7:43:18 AM UTC-5, Phil Allison wrote:

No-one needs to see your brain dead, autistic crap.



.... Phil

Off your meds again?

Fluke 73III True RMS meter. Set to ohms. Cross leads. Hold Down Yellow (range) Button. Meter adjusts to 0 ohms. Proceed from there. I have been using this meter for almost 20 years now, and go through this when either switching leads or changing the battery, or if it has been sitting for a while.

I guess quality equipment (along with quality meds) is not available in your cave?

 

[pfjw@aol.com]

On Friday, February 10, 2017 at 2:48:59 PM UTC-5, Robert Roland wrote:

On Thu, 09 Feb 2017 23:35:45 -0500, micky <NONONOmisc07@bigfoot.com
wrote:

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

Is there any way to adjust this?

Or, is there ever a way to adjust this?

It seems to me, the cheaper it is, the higher the chance of finding a
calibration pot inside.

But the calibration is only for the voltage reference, so, as Phil
comments, if only one range is off, then it is not a calibration
problem.
--
RoRo

Or, the rest of the range is OK, with the error only at the lowest end of the scale (and how Fluke does it in my case for Volts) as noted by the OP. If measuring in dozens or hundreds of volts. a 0.5 V error ain't much. 0-2 V, quite a bit. About anyone can make a meter that is +/-1% at 500V. Not so many at 2% at 2V.

Peter Wieck
Melrose Park, PA

 

"It seems to me, the cheaper it is, the higher the chance of finding a
calibration pot inside."

Your theory is blown out of the water, sorry. Those $0.000 ones from Harbor Freight have no pot.

>"But the calibration is only for the voltage reference, so, as Phil
comments, if only one range is off, then it is not a calibration
problem.
--
RoRo "

Kinda is and kinda ain't. Seriously, I only recently learned how these things work and truthfully I could not design a worse circuit. Unfortunately I can't seem to design a better one either so I guess I understand why they did it the way they did it.

However one thing is common to almost all voltmeters. The lowest voltage range IS the reference and all the others are divided down by a precision resistive divider. therefore when that low range is off, all ranges should be off by the same amount, if it is indeed in the main calibration.

The only time I have had the lower ranges bad was in a Fluke. That unit had batteries that had leaked onto the PC board so it is logical to assume that there was a leakage path and that was causing the error. That unit would zero with the probes crossed, but uncrossing them would result in a reading of a couple of volts. That was not resolved at the 200 volt range of course.

The resolution must be considered, for example if you have a fifty volt supply and this thing reads 50.17 volts and every other meter you have reads 49.91, that is significant and needs to be noted. It is the same problem, but partly masked by the resistive divider.

Instrumentation is a PITA, which is why alot of techs will not touch it. Back in the TV days many would just send meters and scopes in, not even take the cover off. I learned some lessons on it myself, like on Tek scopes. When they say 50 volts it is not like a TV where anything between 35 and 75 will be fine, it means 50 volts within a volt. Maybe even tighter than that.

Anyway, this PITA better be worth it, take and see if you are just not noticing the error on the higher ranges. It is off 14 on the low range, go up a range, is it off 1.4 % ? Go up another range, is it off 0.14 % ? Now for that you might have to get a really high end other meter. Personally I can borrow a high end Fluke that will do it and it has been check every way to Sunday and back. I mean money was spent.

We did have some fun restoring a few old time meters, one of them is the job from HP that had four light bulbs in it. The next step is electrometers, like Keithley etc. Maybe. I still have yet to get used to these junk ass LCD scopes, preferring my CRO always.

Bottom line though, when a meter gets that kind of problem it is probably time to ditch the bitch. It is very unlikely to be an easy fix no matter what.

Fess up with the brand and model. If it is an old nixie tube job it is a novelty and worth fixing maybe, even that old B & K job, LED and with the zero control you set to make the "-" blink on and off. I used to have one of those and it was not a bad meter, I am still wondering what happened to it. Never sell a house folks, let me tell you. You lose more stuff than you ever knew you had and then spend the next twenty years wondering where this and that went. If you sell a house, just go get a lobotomy, you'll be much happier.

Bottom line, when it comes to DVMs, only the bestest and bounciest are really worth fixing. Some of the ones in the middle are worth sending to the factory if you got a warranty. Fewer are worth paying their out of warranty rates. but they do have the special equipment to fix and calibrate them, but really most of it is just change the main board and check the calibration. If it flies, ship it.

Good luck, but really it sounds to me like you simply need a new meter. Maybe this one could monitor line voltage or whatever, but that is about it.

 

[Phil Allison]

The Peter Wieck Fuckwit Troll spewed

No-one needs to see your brain dead, autistic crap.



.... Phil


Off your meds again?

** Fuck off, you retarded pile of bat manure.

No-one needs to see your brain dead, autistic crap.

Fluke 73III True RMS meter. Set to ohms. Cross leads. Hold Down Yellow (range) Button. Meter adjusts to 0 ohms.

** ROTFL - wot brain dead crap.


** Fuck off, you retarded pile of bat manure.

No-one needs to see your brain dead, autistic crap.



..... Phil


Proceed from there. I have been using this meter for almost 20 years now, and go through this when either switching leads or changing the battery, or if it has been sitting for a while.

I guess quality equipment (along with quality meds) is not available in your cave?

 

[Phil Allison]

Robert Roland wrote:

But the calibration is only for the voltage reference, so, as Phil
comments, if only one range is off, then it is not a calibration
problem.

** Of course not, have to be brain dead to think that.



..... Phil

 

[Phil Allison]

The Peter Wieck Fuckwit Troll spewed:

Or, the rest of the range is OK, with the error only at the lowest end of the > scale ....

** Complete CRAP !!!

Fuck off, you retarded pile of bat manure.

No-one needs to see your brain dead, autistic crap.



..... Phil

 

[Robert Roland]

On Thu, 09 Feb 2017 23:35:45 -0500, micky <NONONOmisc07@bigfoot.com>
wrote:

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

Is there any way to adjust this?

Or, is there ever a way to adjust this?

It seems to me, the cheaper it is, the higher the chance of finding a
calibration pot inside.

But the calibration is only for the voltage reference, so, as Phil
comments, if only one range is off, then it is not a calibration
problem.
--
RoRo

 

[Ralph Mowery]

In article <8450e28b-2764-4217-9d2a-a8f875ab8d21@googlegroups.com>,
jurb6006@gmail.com says...

"It seems to me, the cheaper it is, the higher the chance of finding a
calibration pot inside."

Your theory is blown out of the water, sorry. Those $0.000 ones from Harbor Freight have no pot.

I hae opened up 3 of the 'free'or about $ 6 if just bought ones and they
all have an adjustment pot. They all seem to be close enough compaired
to my Fluke that I did not do any adjustment to that pot.

Have you actully opened up any ?

 

[Phoena Greene]

"micky" <NONONOmisc07@bigfoot.com> wrote in message
news:cjgq9cpbgkls3mmjbfj8t622auumn86f4o@4ax.com...

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

So give it back to him

 

[micky]

In sci.electronics.repair, on Thu, 9 Feb 2017 21:04:57 -0800 (PST), Phil
Allison <pallison49@gmail.com> wrote:

micky wrote:

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.



** So all the other ranges are OK ?

I checked since I first posted and the 20 and 200 volt DC scales have
the same problem. They give the same reading of 1.7 on a AA battery, a
battery that is probably dead since it's 3 years old and the camera two
of them are in was dead, and isn't now that I replaced the batteries.

And the AC volts is good,
I don't have a handy way to messure milliamps
The continuity buzzer is dead (and I checked both leads).
And none of the resistance scales work.

So it's probably not worth keeping a battery in it with ohms scales, but
I am still interested in calibration so I'm glad I asked.

The story is more complicated than it was yesterday. Yesterday I
replaced some other battery and measured the old one and it was 1.4.
then I measured the two from yesterday and instead of 1.74, it said
0.6!!
But later today I measured again and it was up to 1.7!!! A dirty
pot?

Hmmm.

Hmmm.

Okay, my final paragraph today: I figured that out, but only by
fildding with it. How many of you figured it out from a distance?
(It's another serious problem.)

If so, it sounds like manufacturing error.

It may have worked well at one time. Actually my friend died and this
was among his things. So eEven though I have other, better, and similar
meters, I'm reluctant to throw it out.

The fuse had been blown and was missing, so he took it apart. The shine
is off a tiny bit of circuit board by the fuse, so it was a big blowout.
And there are two holes in the PCB with nothing in them right near the
burned spot, but the first two times I looked there, I thought they were
just extra holes, since there is no evidence of a part, and I though
there was no copper trace. There were parts in the way so I couldn't
see everything.

But now I see that there is a trace headed in the direction of each
hole. I guess the blowout took the part and part of the traces with it,
that there was nothing holding the part to the PCB but the solder
attachment to the traces. That's why the holes are so empty and clean.

With this added knowledge, I'll look it up again. (I looked it up
yesterday and found how big the fuse should be.)

Just $15 at Amazon.
https://www.amazon.com/Velleman-DVM850BL-Hold-Function-Backlight/dp/B00068U24A
http://www.vellemanusa.com/products/view/?country=us&lang=enu&id=350297

And manualslib.com has the manual but it's only 9 pages and has no
schematic.

The missing part seems to be connected to the ground on one side and one
pin of an 8-pin IC at the other. I suppose it's either a cap or
resistor. Since the ohms scales don't work, is it reasonable to guess
it's a resistor???

I have a resistor-substitution box, bought at a hamfest and only used
once. Wait, that time I decided it was easier to use a pot. I could do
that now too.

Unless one of you knows what the part would be, or where to get a
schematic for a Vellaman DVM850BL

the only other idea is to buy a second one and see what part is in that
spot. Then I could give away the new one.

>.... Phil

 

[Robert Roland]

On Fri, 10 Feb 2017 12:53:43 -0800 (PST), jurb6006@gmail.com wrote:

"It seems to me, the cheaper it is, the higher the chance of finding a
calibration pot inside."

Your theory is blown out of the water, sorry. Those $0.000 ones from Harbor Freight have no pot.

You did not read what I wrote, did you?

I spoke of chance, and you refute my claim based on one single sample?

Not exactly solid statistics.
--
RoRo

 

[John Robertson]

On 2017/02/09 8:35 PM, micky wrote:

My friend gave me an digital VOM, and DC voltages in the 2 volt range
read 14% high.

Is there any way to adjust this?

Or, is there ever a way to adjust this?

No schematic is available, I'm pretty sure but its guts look like most
of them. .

Did you try a new battery in the meter? Weak batteries will give odd
readings...

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

>"I hae opened up 3 of the 'free'or about $ 6 if just bought ones and they
all have an adjustment pot. They all seem to be close enough compaired
to my Fluke that I did not do any adjustment to that pot.

Have you actully opened up any ? "

About three of them, no pots.

Of course that does not mean they're all the same, I have encountered two distinct types at least, one has a power switch and the other simply has an "off" position on the range switch. (which I do not prefer)

Perhaps they were well hidden. At any rate, one pot for the whole thing would adjust all the ranges, so if only certain ranges are off then something else is wrong.

There are probably many different versions of these things. At work I stumbled across a Craftsman meter which is about the spitting image of one of these, but then we know Sears stuff is built by the lowest bidder. However I haven't taken that one apart, it works, I will see the inside when the battery dies I guess. It could be totally different but really I do not see the reason why. When they work right they seem to really work right, they agree with my decent Fluke and they agree with my buddy's even better Fluke.

I had one that would not zero on any range, they said don't even bother to send it back, they just sent a new one. Throwaway test equipment, ever thought you'd see it ?

But then a $300 guitar can be throwaway as well, really. My buddy bought an Ibanez acoustic with the electronic pickups. Sounded great actually, like a miced guitar and not much feedback. But the electronics quite. He calls and they gave him a full refund and said not to even bother sending it back. I bought it thinking maybe I would fix the pickup but never got to it, so I have me a decent acoustic. And that prick made $100 off of me. It does play really well though. He should have sold it to me for $50 though. But really, I started taking that guitar apart and the way they put the pickup in pretty much precluded any type of repairs. I swear, it should be illegal for electronics manufacturers to be in possession of any type of glue, and I mean death by slow torture for thee board of directors.

 

>"I spoke of chance, and you refute my claim based on one single sample? "

No, several. Unless the pot is well hidden somewhere.

I have changed the batteries in a few, and one I wanted to somehow revamp and make it read like a benchtop DVM but once I saw the ubiquitous zebra strip I figured the chances of that were slim and none and slim has a bullethole in his head.

Thing about these tings is it is almost not worth changing the battery, depending on where you go it might cost you more than the whole meter.

But anyway, using this Google groups is getting to be a drag, no tree view so you have a hard time seeinf where your post goes, as in who it appears you are responding to. And now it doesn't like my old Firefox so I am in IE again. I used to have Thunderbird set up opn this thing but lost it somehow due to a system restore or something. I might just shoot the thing and be done with it.

 

[Ralph Mowery]

In article <c22213e5-34e4-46c9-aba6-dcc113c9e530@googlegroups.com>,
jurb6006@gmail.com says...

I had one that would not zero on any range, they said don't even bother to send it back, they just sent a new one. Throwaway test equipment, ever thought you'd see it ?

But then a $300 guitar can be throwaway as well, really. My buddy bought an Ibanez acoustic with the electronic pickups. Sounded great actually, like a miced guitar and not much feedback. But the electronics quite. He calls and they gave him a full refund and said not to even bother sending it back. I bought it thinking maybe I would fix the pickup but never got to it, so I have me a decent acoustic. And that
prick made $100 off of me. It does play really well though. He should have sold it to me for $50 though. But really, I started taking that guitar apart and the way they put the pickup in pretty much precluded any type of repairs. I swear, it should be illegal for electronics manufacturers to be in possession of any type of glue, and I mean death by slow torture for thee board of directors.

Most anything under $ 500 is a throw away now unless you can fix it
yourself. With companies charging $ 50 to $ 100 per hour labor, the
cost to ship it back, especially if it is big or heavy, all tht ammounts
up fast. Sort of like the socket sets from 40 years ago with the
lifetime warrenty. The whole set was about $ 5. If you sent the broken
part back and $ 4.50 for retrun postage and handling, they would send
you a replacement for the broken part.

 

"Most anything under $ 500 is a throw away now unless you can fix it
yourself."

That is more a socioeconomic issue almost. how did it get that way ?

>"With companies charging $ 50 to $ 100 per hour labor,"

In the old days I had a TV shop, the rent for 3,500 square feet was $350 IIRC, the elctric bill was low, and beer was like two bucks a sixpack. Gas was cheap, food was cheap.

"the
cost to ship it back, especially if it is big or heavy, all tht ammounts "

Have you tried to drive lately ? Back then we bought a hundred dollar car, threw whatever plates we had on it and just drove. there were no problems because we did not hit the other cars. Never even heard of seat belts either..


>"up fast. Sort of like the socket sets from 40 years ago with the
lifetime warrenty. The whole set was about $ 5. If you sent the broken
part back and $ 4.50 for retrun postage and handling, they would send
you a replacement for the broken part. "


Sears started this shit where if your ratchet screwed up they handed you a kit to fix it. Do that to me and I will hand it back and say, well ? You fix it, it is not my job. Having known someone who worked there, actually they do it for you. If the customer asks anything just fix it for him, when you first go to work there it is in your training.

That is actuially alright but I stil don't buy their shit. I wanted wrenches that were Xrayed, not made so cheaply you can replace then fifty times and still show a profit on the books. When I am underneath a car with the tranny on my chest I need that tool not to break, not to have to drive (my transmissionless car) 25 fucking miles to see if your store is open to get a replacement Chinese piece of shit I oculd have gotten for a tenth of the price over at Harbor Freight.

Rant over.