[TechAssist] Re: Diode testing
- From: "majorthom@xxxxxxxxxxxxx" <majorthom@xxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Fri, 27 Aug 2004 21:30:06 -0700 (PDT)
Hi-Finally an answer
Pete
J Silverman <greentron@xxxxxxx> wrote:
If light can get to the diode junction, it will generate a voltage. For
silicon diodes, up to about 0.6 volts. It will deliver current to a load. If
you apply an external reverse biasing voltage greater than the generated
voltage, a reverse current will flow proportional to the light intensity.
These are the effects that let you make photovoltaic battery chargers and
lightmeters. You can hook a transparent diode across your scope input to
view the output pulses from a remote control handset.
Also will drive you crazy if you are troubleshooting a circuit with diodes
in certain places in the circuit. I recall one such case with transparent
glass diodes back to back as clamps across the input of an op amp. Symptoms
kept changing as I moved around. Replaced them with diodes in opaque cases
and then I was able to go on with the troubleshooting.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
Fax/Phone 864 232 3889
mail to: greentron@xxxxxxx
----- Original Message -----
From: "walter wood"
To:
Sent: Friday, August 27, 2004 11:03 AM
Subject: [TechAssist] Re: Diode testing
> I've seen that happen in circuit, but never out of
> circuit.
> Maybe someone smarter than me can explain it.
> Walter
> --- Wayne Vanaman
> 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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>
> =====
> 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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Neal Electronics
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