Been working on this 29" TV and cannot work out why the voltage on the
one of the driver transistors is low. Drive transistors located on the
CRT neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB
IC and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across
it before.

Thanks

TEX

TEX wrote:
Been working on this 29" TV and cannot work out why the voltage on the
one of the driver transistors is low. Drive transistors located on the
CRT neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB
IC and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across
it before.

Thanks

TEX

You need to provide the rest of the troubleshooting voltage and
waveform measurements at the crt for anyone to help.

From the spartan information available, the blue bias or drive is way
too high.

Are you saying the Blue driven at too a high a voltage? I would have
thought it was too low, or the others too high, causing the imbalance.
I have measured these with the CRT connected to the board and
disconnected with same findings.

wrote:
TEX wrote:
Been working on this 29" TV and cannot work out why the voltage on the
one of the driver transistors is low. Drive transistors located on the
CRT neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB
IC and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across
it before.

Thanks

TEX

You need to provide the rest of the troubleshooting voltage and
waveform measurements at the crt for anyone to help.

From the spartan information available, the blue bias or drive is way
too high.

Blue drive to the video output device may be too high, causing the item to
conduct too heavily, that will eventually lower the voltage because of the
current draw.Check the condition of the video drive and output devices, the
voltages at each device, and the voltage at the video processor ic. Also
check the video signals at each device. Post the diagnostic results so we
can evaluate those parameters and attempt to supply additional relevant
information
"TEX" wrote in message news:1154261584.506828@ftpsrv1...
Are you saying the Blue driven at too a high a voltage? I would have
thought it was too low, or the others too high, causing the imbalance.
I have measured these with the CRT connected to the board and disconnected
with same findings.

wrote:
TEX wrote:
Been working on this 29" TV and cannot work out why the voltage on the
one of the driver transistors is low. Drive transistors located on the
CRT neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB
IC and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across
it before.

Thanks

TEX

You need to provide the rest of the troubleshooting voltage and
waveform measurements at the crt for anyone to help.

From the spartan information available, the blue bias or drive is way
too high.

TEX wrote:
Are you saying the Blue driven at too a high a voltage? I would have
thought it was too low, or the others too high, causing the imbalance.
I have measured these with the CRT connected to the board and
disconnected with same findings.
snip

No I did not say the voltage was too high. I said the bias or drive to
the blue was too high.

" writes:

TEX wrote:
Are you saying the Blue driven at too a high a voltage? I would have
thought it was too low, or the others too high, causing the imbalance.
I have measured these with the CRT connected to the board and
disconnected with same findings.
snip

No I did not say the voltage was too high. I said the bias or drive to
the blue was too high.

What he's trying to say is that high cathode voltage reduces brightness, all other
factors being equal. But you need all the other readings.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Worst case scenario ,,,,cut the trace to the pin and start adding 2M
resistors,,,,a pot would be nice .I've done it on the screen voltage on
monitors and corrected a BUNCH of them,,,,second thought 2Mohm might be a
little excessive,,,,,,,)) start w/whatever you have. Good Luck
joe.

This, however, is not fault finding. It is fault condition correction by
bodging ...

( or botching if you prefer )

Arfa

I am trying to locate the actual drive circuit, but makes it quiet
difficult without a schematic and if you don't know wtf you are looking for.

I have done some more testing and found that although i initial get low
readings of Blue = 120VDC, Green =195VDC and Red =195VDC at the
cathodes, if i leave the unit on for about 5mins the voltages are all
the same. But still has a slight red tinge and green is still low.

Now these are the reading from the collector of the drive transistors
and basically and cathode pins to the CRT. On readings i get on the
otherside of the resistors for each gun is about 217VDC constant and
equal between them all.

Now in this unit it looks like the main guns are red and green for
intensity setting and the blue gun separate, as it has a slightly
different circuit layout and components.

TEX


Art wrote:
Blue drive to the video output device may be too high, causing the item to
conduct too heavily, that will eventually lower the voltage because of the
current draw.Check the condition of the video drive and output devices, the
voltages at each device, and the voltage at the video processor ic. Also
check the video signals at each device. Post the diagnostic results so we
can evaluate those parameters and attempt to supply additional relevant
information
"TEX" wrote in message news:1154261584.506828@ftpsrv1...
Are you saying the Blue driven at too a high a voltage? I would have
thought it was too low, or the others too high, causing the imbalance.
I have measured these with the CRT connected to the board and disconnected
with same findings.

wrote:
TEX wrote:
Been working on this 29" TV and cannot work out why the voltage on the
one of the driver transistors is low. Drive transistors located on the
CRT neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB
IC and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across
it before.

Thanks

TEX
You need to provide the rest of the troubleshooting voltage and
waveform measurements at the crt for anyone to help.

From the spartan information available, the blue bias or drive is way
too high.

"TEX" wrote in message news:1154258261.420666@ftpsrv1...
Been working on this 29" TV and cannot work out why the voltage on the one
of the driver transistors is low. Drive transistors located on the CRT
neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB IC
and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across it
before.

Thanks

TEX

You can see if it may be a driver problem by switching color drive feed
wires to the crt board. As in switch the red with the green and see how
bright the color is driven. This may eliminate the problem from the color
output from the chassis and you can concentrate your effort to the neck
board. If the green is bright after switching with red driver, then you
will know the green driver is weak (not the output on the neck board). Jtt

Confirmed it is not a color driver feed issue. Found a schematic for
another model TV and from that worked out which wires were the
control/drive lines. 5 wire connection RBG gnd and 12v. All the input
drives give value of around 3.1v. Swapped drives and confirmed they working.

So confirmed it is either a CRT fault or neck board fault. I was hoping
that since the voltages i was getting at the driver transistors are the
same weather the board is connected to the CRT or not, then it is board
board.

Where to next??

TEX

James Thompson wrote:
"TEX" wrote in message news:1154258261.420666@ftpsrv1...
Been working on this 29" TV and cannot work out why the voltage on the one
of the driver transistors is low. Drive transistors located on the CRT
neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the complementary
color to produce the hue. Or are the other two guns over driven????

Since there is green am i to assume there is nothing wrong with the RGB IC
and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come across it
before.

Thanks

TEX

You can see if it may be a driver problem by switching color drive feed
wires to the crt board. As in switch the red with the green and see how
bright the color is driven. This may eliminate the problem from the color
output from the chassis and you can concentrate your effort to the neck
board. If the green is bright after switching with red driver, then you
will know the green driver is weak (not the output on the neck board). Jtt

After checking the CRT neck board again and found no obvious faults. I
checked the driver signals and found that the Blue drive is double of
that of the other two guns.
As previously stated I am sure i noticed that the cathode voltage had
equalised after a few minutes of running, but coloured hue was still
present.

Will trace back further and see what else I can find. So maybe it isn't
a CRT output drive board then...


TEX



TEX wrote:
Confirmed it is not a color driver feed issue. Found a schematic for
another model TV and from that worked out which wires were the
control/drive lines. 5 wire connection RBG gnd and 12v. All the input
drives give value of around 3.1v. Swapped drives and confirmed they
working.

So confirmed it is either a CRT fault or neck board fault. I was hoping
that since the voltages i was getting at the driver transistors are the
same weather the board is connected to the CRT or not, then it is board
board.

Where to next??

TEX

James Thompson wrote:
"TEX" wrote in message news:1154258261.420666@ftpsrv1...
Been working on this 29" TV and cannot work out why the voltage on
the one of the driver transistors is low. Drive transistors located
on the CRT neck board.

Blue =120VDC
Green =195VDC
Red =195VDC

Green does show up on the screen but very dull. Red/magenta hue. Am i
correct to say that the blue it under driven causing the
complementary color to produce the hue. Or are the other two guns
over driven????

Since there is green am i to assume there is nothing wrong with the
RGB IC and it is still just a driver circuit problem

Where to diagnose from next??? Just stuck on this cos never come
across it before.

Thanks

TEX

You can see if it may be a driver problem by switching color drive
feed wires to the crt board. As in switch the red with the green and
see how bright the color is driven. This may eliminate the problem
from the color output from the chassis and you can concentrate your
effort to the neck board. If the green is bright after switching with
red driver, then you will know the green driver is weak (not the
output on the neck board). Jtt

"TEX" wrote in message news:1154356295.483649@ftpsrv1...
After checking the CRT neck board again and found no obvious faults. I
checked the driver signals and found that the Blue drive is double of that
of the other two guns.
As previously stated I am sure i noticed that the cathode voltage had
equalised after a few minutes of running, but coloured hue was still
present.

Will trace back further and see what else I can find. So maybe it isn't a
CRT output drive board then...


TEX



TEX wrote:
Confirmed it is not a color driver feed issue. Found a schematic for
another model TV and from that worked out which wires were the
control/drive lines. 5 wire connection RBG gnd and 12v. All the input
drives give value of around 3.1v. Swapped drives and confirmed they
working.

So confirmed it is either a CRT fault or neck board fault. I was hoping
that since the voltages i was getting at the driver transistors are the
same weather the board is connected to the CRT or not, then it is board
board.

Where to next??

TEX


Perhaps it has developed a small short do to oxidation in the picture tube.
If you can find an old shop around with a picture tube rejuvenator, or if
you might have one, hook up the tube and do a short test and zap the grids
with it. Might not take much to get it back to good shape, since you say it
work fairly well and only has a slight dulling to the green.

Sam Goldwasser wrote:

" writes:


TEX wrote:

Are you saying the Blue driven at too a high a voltage? I would have
thought it was too low, or the others too high, causing the imbalance.
I have measured these with the CRT connected to the board and
disconnected with same findings.
snip

No I did not say the voltage was too high. I said the bias or drive to
the blue was too high.


What he's trying to say is that high cathode voltage reduces brightness, all other
factors being equal. But you need all the other readings.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
Worst case scenario ,,,,cut the trace to the pin and start adding 2M
resistors,,,,a pot would be nice .I've done it on the screen voltage on
monitors and corrected a BUNCH of them,,,,second thought 2Mohm might be
a little excessive,,,,,,,)) start w/whatever you have. Good Luck
joe.

--
Posted via a free Usenet account from http://www.teranews.com

James Thompson wrote:
"TEX" wrote in message news:1154356295.483649@ftpsrv1...
After checking the CRT neck board again and found no obvious faults. I
checked the driver signals and found that the Blue drive is double of that
of the other two guns.
As previously stated I am sure i noticed that the cathode voltage had
equalised after a few minutes of running, but coloured hue was still
present.

Will trace back further and see what else I can find. So maybe it isn't a
CRT output drive board then...


TEX



TEX wrote:
Confirmed it is not a color driver feed issue. Found a schematic for
another model TV and from that worked out which wires were the
control/drive lines. 5 wire connection RBG gnd and 12v. All the input
drives give value of around 3.1v. Swapped drives and confirmed they
working.

So confirmed it is either a CRT fault or neck board fault. I was hoping
that since the voltages i was getting at the driver transistors are the
same weather the board is connected to the CRT or not, then it is board
board.

Where to next??

TEX


Perhaps it has developed a small short do to oxidation in the picture tube.
If you can find an old shop around with a picture tube rejuvenator, or if
you might have one, hook up the tube and do a short test and zap the grids
with it. Might not take much to get it back to good shape, since you say it
work fairly well and only has a slight dulling to the green.
Also check that the filament supply resistor has not gone high.