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Re: Video circuit working but dark
Hi Paul,
Have you checked the form of the sugnal with an oscyloscope?
The black level can be to low comparing with the original or the 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
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.
BR,
Dan
----- Original Message -----
From: "Paul" <groups@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Saturday, May 24, 2003 12:38 PM
Subject: [ukha_d] Video circuit working but dark
> Having played a lot with the resistor values - I've got a working
circuit
but it still lacks overall brightness (has a 'greyish' quality to the
picture). Increasing the gain washes out whites but the overall 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. How
much
of
> > this might be down to long lead lengths (as it's on breadboard)?
The
> > capacitors between the power supply pins of the op amp and GND
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
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
interesting.. (nosey
> > > frank) ;-))
> > >
> > > Frank
> > > ----- Original Message -----
> > > From: "Paul" <groups@xxxxxxx>
> > > 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
brightness and
> > > colour
> > > wise.
> > >
> > > I've got a tant cap on the input side and a 5K trimmer
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)
- 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 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 base is not
> > > > > connected).
> > > > >
> > > > >
> > > > > BR,
> > > > > Dan
> > > > > ----- Original Message -----
> > > > > From: "Paul" <paul@xxxxxxx>
> > > > > To: "Dan" <dtoma@xxxxxxx>
> > > > > 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 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 (without
> > any
> > > > > input
> > > > > > > signal)
> > > > > > > - direct voltage on each of the two
diodes(D1 and D2)... it
must
> > > be
> > > > > around
> > > > > > > 0.6V
> > > > > > > - check if one of the R6 or R7 resistors
is not 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 compatible with
> > > > CA3100
> > > > > ?
> > > > > > > The rest of the substitutions are not
important.
> > > > > > >
> > > > > > > BR,
> > > > > > > Dan
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > > From: "Paul"
<groups@xxxxxxx>
> > > > > > > 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 opamp
> > > package)
> > > > > > > > Q1 2N3053 (Gen purpose NPN
transistor) changed to BC182L
> > > > > > > > Q2 2N4037 (Gen purpose PNP
transistor) changed to BC212
> > > > > > > > D1 1N914 (small signal Diode)
changed to 1N4148
> > > > > > > >
> > > > > > > > R3 is a 5K trimmer rather than 2K5
specified (is this a
> > > problem?)
> > > > > > > >
> > > > > > > > I'm using an ATX PC PSU as the +12V
and -12V source with the
> > > > common
> > > > > > > connection connected to the ground
points on the circuit (is
> > this
> > > > > right?).
> > > > > > > The PSU has slightly different voltages
(+12V is something
like
> > > > +11.4V
> > > > > > > and -12V is actually -11.04V).
> > > > > > > >
> > > > > > > > When I connect up the circuit, it
doesn't work and 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@xxxxxxx>
> > > > > > > > > To: <ukha_d@xxxxxxx>
> > > > > > > > > Sent: Friday, May 23, 2003
7:46 PM
> > > > > > > > > Subject: [ukha_d]
Heeeeeeeeelp!
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > > Anyone with electronics
experience – I need help
(please!)
> > > > > > > > > >
> > > > > > > > > > My transistors are
cooking!
> > > > > > > > > >
> > > > > > > > > > Anyone?
> > > > > > > > > >
> > > > > > > > > > Paul.
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > ** UKHA2004 BE THERE! **
- start planning now.
> > > > > > > > > >
> > > > > > > > > > http://www.automatedhome.co.uk
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ukha_d@xxxxxxx
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> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > ** UKHA2004 BE THERE! ** -
start planning now.
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