[TechAssist] Re: Diode testing
- From: "Wayne Vanaman" <Wayne@xxxxxxxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Fri, 27 Aug 2004 16:56:11 -0500
For most meters, the reading on the diode test function is actually a
voltage. That is, if you took a current limited power supply and applied a
forward biased voltage to the diode, measuring it with another meter you
should obtain the reading of a meter using a "diode" test. So a
theoretically perfect silicon diode would measure about .6V, a germanium
diode about .2V.
Wayne Vanaman
Omega Electronics
6904 W Fairfield Dr
Pensacola, Fl. 32506-3310
Wayne@xxxxxxxxxxxxxxxxxxxxx
WWW.PensacolaTVRepair.Com
850-456-5995 voice
850-458-6369 fax
----- Original Message -----
From: "Paul" <dntwntv@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, August 27, 2004 12:46 PM
Subject: [TechAssist] Re: Diode testing
> I don't know how you can read voltage on the diodes test function. But
then I don't know all the meters and there capabilities. I have a fluke and
a beckman and they both read about the same in this instance. I did notice
that if put on the 200ohm scale that with one of these diodes, the reading
will change like a charging capacitor in the negative direction. If that
makes any sense. Here is the kicker. The new diode that just came in checks
much like the old ones.I am really confused now. I am going to change them
when I get both of them in. Supplier only had one.
> Paul
> Wayne Vanaman <Wayne@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Wendsday I pull CR4401 pn 242907 from an RCA 169 chassis, and it
> measured -1.2 volts on the diode check setting with a fluke 77 series 3.
> Minus volts out of circuit on a
> diode? What the heck? Changed the battery in the meter, same thing.
> Changed the diode and the set worked.
>
> How the heck do you get minus volts? That means that
> there was some sort of capacitance/pn junction problem with that diode.
>
> Minus ohms.
>
> Wayne Vanaman
> Omega Electronics
> 6904 W Fairfield Dr
> Pensacola, Fl. 32506-3310
>
> Wayne@xxxxxxxxxxxxxxxxxxxxx
> WWW.PensacolaTVRepair.Com
>
> 850-456-5995 voice
> 850-458-6369 fax
>
>
> ----- Original Message -----
> From: "walter wood"
> To:
> Sent: Thursday, August 26, 2004 9:24 PM
> Subject: [TechAssist] Re: Diode testing
>
>
> > It seems to depend on the meter, as to what the
> > diode check position will read.
> > I have a Micronta(inexpensive radio shack) that
> > reads 820 t0 840 consistantly on good diodes.
> > I have two Fluke meters, ond old (series 73) but
> > great, and an expensive Model 83 series three.
> > They both consistantly read 460 on the diode scale.
> > I think you diodes are leaky.
> > You have enough evidence that I would certainly
> > replace them.
> > Check the new ones out of circuit before installing
> > them, and if weird make a note of it.
> > There are some odd ball things out there.
> > i've got a large spiral notebook full of such
> > measurments.
> > ALWAYS, use the same meter though, for comparaison,
> > or note the results with the different ones.
> > Another thing I like to do is take resistance
> > measurements on key components, such as convergence
> > ic's, regulators, outputs etc. on common products,
> > on a set that is working correctly.
> > I note this, and it helps more often than not.
> > SAMS used to provide this.
> > HTH
> > Walter
> > --- Paul wrote:
> >
> > > When checking diodes for leakage, what range on
> > > the ohm meter do you use and is there an
> > > acceptable amount? Sounds like electronics 101
> > > but I have a couple of diodes that are flat case
> > > diodes mounted on a heat sink. They read 160
> > > front to back on the diode check. No reading back
> > > to front. However they read 20k on the ohms
> > > scale. If heated this reading goes down to 2 or 3
> > > K. I normally set my meter on 100k ohm for
> > > leakage. I thought they must be leaking. But
> > > wondered if there are some big diodes that test
> > > this way normally? Someone said that 10X the back
> > > to front was normal. These are in the secondary
> > > of a SMPS + & -- 25v to convergence amps.
> > >
> > > Paul
> > >
> > > Paul ,B
> > > Central TV&Video
> > > 911W Grand Ave
> > > Grover Beach Ca.
> > > (805)481-8084
> > >
> > >
> > >
>
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> >
> > =====
> > Walter Wood
> > Future Tech Home Center
> > 2786 Hwy. 43 N.
> > Lawrenceburg Tn. 38464
> > 931-829-3337
> > Fax 931-829-4044
> > mailto:wwood_38478@xxxxxxxxx
> >
>
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> Paul ,B
> Central TV&Video
> 911W Grand Ave
> Grover Beach Ca.
> (805)481-8084
>
>
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