Re: Video circuit working but dark

["Keith Doxey" <ukha@xxxxxxx>]

To save traffic on the list and to make sure we solve this one, I=20
will build the circuit tonight then fix it.

Keith


--- In ukha_d@xxxxxxx, "Dan" <dtoma@f...> wrote:
> Hi Paul,
>=20
> Have you checked the form of the sugnal with an oscyloscope?
> The black level can be to low comparing with the original or the=20
signal is
> attenuated in your circuit.
> In my opinion, R8 and R9 are to big for this circuit.
> They must be maximum 1K.
> You must have an output impedance of the circuit near 0 in order to=20
increase
> it at 75 ohm using the R10-R12 resistors.
> Try to decrease the value of R8 and R9 to 1K and see what's happen.
>=20
> BR,
> Dan
> ----- Original Message -----=20
> From: "Paul" <groups@s...>
> To: <ukha_d@xxxxxxx>
> Sent: Saturday, May 24, 2003 12:38 PM
> Subject: [ukha_d] Video circuit working but dark
>=20
>=20
> > Having played a lot with the resistor values - I've got a
working=20
circuit
> but it still lacks overall brightness (has a 'greyish' quality to=20
the
> picture). Increasing the gain washes out whites but the overall=20
picture is
> still reasonably dark. Saturation of colours is good though.
> >
> > Any ideas - Keith?
> >
> > Paul.
> >
> > > -----Original Message-----
> > > From: Paul [mailto:groups@xxxxxxx...]
> > > Sent: 23 May 2003 22:35
> > > To: ukha_d@xxxxxxx
> > > Subject: RE: [ukha_d] Heeeeeeeeelp! - got somewhere!
> > >
> > > Got a picture but it's quite 'grey' and needs to be
brighter.=20
How much
> of
> > > this might be down to long lead lengths (as it's on=20
breadboard)? The
> > > capacitors between the power supply pins of the op amp and
GND=20
are close
> > > to the IC but have quite long leads to GND - would this make
a
> difference?
> > >
> > > As to shielding of the incoming/outgoing signal cables -
should=20
they be
> > > connected to AC GND or the common of the PSU?
> > >
> > > Should they also be shielded as close to the PCB as
possible?
> > >
> > > Ta,
> > >
> > > Paul.
> > >
> > > > -----Original Message-----
> > > > From: Frank Mc Alinden [mailto:fmcalind@xxxxxxx...]
> > > > Sent: 23 May 2003 22:20
> > > > To: ukha_d@xxxxxxx
> > > > Subject: Re: [ukha_d] Heeeeeeeeelp! - got somewhere!
> > > >
> > > > Hi Paul
> > > >             What exactly are you making ?? sounds=20
interesting.. (nosey
> > > > frank) ;-))
> > > >
> > > > Frank
> > > > ----- Original Message -----
> > > > From: "Paul" <groups@s...>
> > > > To: <ukha_d@xxxxxxx>
> > > > Sent: Saturday, May 24, 2003 7:17 AM
> > > > Subject: RE: [ukha_d] Heeeeeeeeelp! - got somewhere!
> > > >
> > > >
> > > > Ahhh - I did have one of the transistors connected
wrong - the
> datasheet
> > > > from RS was the wrong one!
> > > >
> > > > Now I need to fine tune the output which is a bit
odd=20
brightness and
> > > > colour
> > > > wise.
> > > >
> > > > I've got a tant cap on the input side and a 5K
trimmer=20
instead of
> 2K5 -
> > > > will
> > > > this make a difference?
> > > >
> > > > Thanks Keith and Dan!!!
> > > >
> > > > Paul.
> > > >
> > > > > -----Original Message-----
> > > > > From: Paul [mailto:groups@xxxxxxx...]
> > > > > Sent: 23 May 2003 21:34
> > > > > To: Dan
> > > > > Cc: ukha_d@xxxxxxx
> > > > > Subject: RE: [ukha_d] Heeeeeeeeelp!
> > > > >
> > > > > When I disconnect pin 1 (pin6 on the old part)
(output) -=20
it's at
> > > 10.5V
> > > > -
> > > > > is this what you'd expect?
> > > > >
> > > > > Paul.
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Dan [mailto:dtoma@xxxxxxx...]
> > > > > > Sent: 23 May 2003 21:11
> > > > > > To: Paul
> > > > > > Subject: Re: [ukha_d] Heeeeeeeeelp!
> > > > > >
> > > > > > Hi Paul,
> > > > > >
> > > > > > It seems to be a problem with the
transistors.
> > > > > > Disconnect pin 6 of the CI and check if then
it is at 0V.
> > > > > > If yes, then you must check the two
transistors.
> > > > > > Usually they must be pairs (the same beta
factor and  the=20
same
> > > > > > characteristic in order to correctly balance
the push-
pull output.
> > > One
> > > > > > good
> > > > > > indication that something is wrong with them
is that the
> resistance
> > > > > > bewteen
> > > > > > E-C is measurable (it must be allmost
infinite if the=20
base is not
> > > > > > connected).
> > > > > >
> > > > > >
> > > > > > BR,
> > > > > > Dan
> > > > > > ----- Original Message -----
> > > > > > From: "Paul" <paul@s...>
> > > > > > To: "Dan" <dtoma@f...>
> > > > > > Sent: Friday, May 23, 2003 10:55 PM
> > > > > > Subject: RE: [ukha_d] Heeeeeeeeelp!
> > > > > >
> > > > > >
> > > > > > > Oh, and I'm not sure what you mean by
" check if one of=20
the R6
> or
> > > R7
> > > > > > resistors is not interrupted"?
> > > > > > >
> > > > > > > Paul.
> > > > > > >
> > > > > > > > -----Original Message-----
> > > > > > > > From: Dan [mailto:dtoma@xxxxxxx...]
> > > > > > > > Sent: 23 May 2003 19:40
> > > > > > > > To: ukha_d@xxxxxxx
> > > > > > > > Subject: Re: [ukha_d] Heeeeeeeeelp!
> > > > > > > >
> > > > > > > > Hi Paul,
> > > > > > > >
> > > > > > > > Check the following points:
> > > > > > > > - IC1-pin 2, 3 and 6 to be as near
as 0V as possible=20
(without
> > > any
> > > > > > input
> > > > > > > > signal)
> > > > > > > > - direct voltage on each of the two
diodes(D1 and=20
D2)... it
> must
> > > > be
> > > > > > around
> > > > > > > > 0.6V
> > > > > > > > - check if one of the R6 or R7
resistors is not=20
interupted
> > > > > > > > - check the polarity of the two
diodes.
> > > > > > > > If something different, send me a
mail.
> > > > > > > >
> > > > > > > > I don't know EL2244C... you're sure
that it is=20
compatible with
> > > > > CA3100
> > > > > > ?
> > > > > > > > The rest of the substitutions are
not important.
> > > > > > > >
> > > > > > > > BR,
> > > > > > > > Dan
> > > > > > > >
> > > > > > > > ----- Original Message -----
> > > > > > > > From: "Paul"
<groups@s...>
> > > > > > > > To: <ukha_d@xxxxxxx>
> > > > > > > > Sent: Friday, May 23, 2003 8:39 PM
> > > > > > > > Subject: RE: [ukha_d] Heeeeeeeeelp!
> > > > > > > >
> > > > > > > >
> > > > > > > > > I'm building the following
circuit:
> > > > > > > > >
> > > > > > > > > http://home.maine.rr.com/randylinscott/jan98.htm
> > > > > > > > >
> > > > > > > > > But with the following
substitutions:
> > > > > > > > >
> > > > > > > > > IC1 CA3100 (single opamp)
changed to EL2244C (dual=20
opamp
> > > > package)
> > > > > > > > > Q1 2N3053 (Gen purpose NPN
transistor) changed to=20
BC182L
> > > > > > > > > Q2 2N4037 (Gen purpose PNP
transistor) changed to=20
BC212
> > > > > > > > > D1 1N914 (small signal Diode)
changed to 1N4148
> > > > > > > > >
> > > > > > > > > R3 is a 5K trimmer rather than
2K5 specified (is=20
this a
> > > > problem?)
> > > > > > > > >
> > > > > > > > > I'm using an ATX PC PSU as the
+12V and -12V source=20
with the
> > > > > common
> > > > > > > > connection connected to the ground
points on the=20
circuit (is
> > > this
> > > > > > right?).
> > > > > > > > The PSU has slightly different
voltages (+12V is=20
something
> like
> > > > > +11.4V
> > > > > > > > and -12V is actually -11.04V).
> > > > > > > > >
> > > > > > > > > When I connect up the circuit,
it doesn't work and=20
the
> > > > transistors
> > > > > > and
> > > > > > > > IC
> > > > > > > > get very hot!
> > > > > > > > >
> > > > > > > > > I'm treble checking the
circuit. Any thoughts?
> > > > > > > > >
> > > > > > > > > Thanks,
> > > > > > > > >
> > > > > > > > > Paul.
> > > > > > > > >
> > > > > > > > > > -----Original
Message-----
> > > > > > > > > > From: Dan [mailto:dtoma@xxxxxxx...]
> > > > > > > > > > Sent: 23 May 2003 18:14
> > > > > > > > > > To: ukha_d@xxxxxxx
> > > > > > > > > > Subject: Re: [ukha_d]
Heeeeeeeeelp!
> > > > > > > > > >
> > > > > > > > > > Hi Paul,
> > > > > > > > > >
> > > > > > > > > > Transistor from what???
> > > > > > > > > > Or ...just a simple
transistor?
> > > > > > > > > > :-)
> > > > > > > > > > Dan
> > > > > > > > > > ----- Original Message
-----
> > > > > > > > > > From: "Paul"
<groups@s...>
> > > > > > > > > > To:
<ukha_d@xxxxxxx>
> > > > > > > > > > Sent: Friday, May 23,
2003 7:46 PM
> > > > > > > > > > Subject: [ukha_d]
Heeeeeeeeelp!
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > > Anyone with
electronics experience =96 I need help
> (please!)
> > > > > > > > > > >
> > > > > > > > > > > My transistors are
cooking!
> > > > > > > > > > >
> > > > > > > > > > > Anyone?
> > > > > > > > > > >
> > > > > > > > > > > Paul.
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > ** UKHA2004 BE
THERE! ** - start planning now.
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