In sci.electronics.repair, on Thu, 9 Feb 2017 21:04:57 -0800 (PST), Phil
Allison 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-DVM8.../dp/B00068U24A
http://www.vellemanusa.com/products/...=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