JVC AV-28WR2EK with blue gun stuck on
 

Hi,
I have a JVC widescreen TV AV-28WR2EK which has a fault with the blue gun,
or its driver. I searched the NG and found some good posts about similar
problems which suggested it was probably a short in the tube (and to try
floating the heater).
Well, I tried a few diagnostics:
swapped the blue and red cathode drives at the final resistor, fault still
on the blue gun.
lifted the drive transistor collector on blue so that the cathode voltage
rises to the supply, fault still there on blue.
'floated' the heater using 3 turns of wire around the HT transformer core,
and fault is still there!

So I begin to think there isn't a heater to blue cathode short, but maybe a
blue to something else short.

Then I tried disconnecting the blue cathode completely, by lifting the final
resistor, and the blue gun turns off! So is it shorting to something or not?
If I stick my DVM on the blue cathode and ground to measure its 'floating'
voltage it turns on strongly, so its being pulled down by the DVM. If I
measure voltage between blue cathode and supply I get the blue gun very
faintly on and a voltage reading of about 15-20 volts (blue gun more
positive than supply).

The supply voltage is 201V and before I started fiddling I saw at all 3
cathodes I was seeing voltages of 150-170 volts depending on the picture.

I would have decided the tube had a short except for the behaviour when the
cathode is left floating, which suggests to me that the blue gun would
probably turn off if it was driven to a higher voltage than 201V.

Has anyone seen a similar problem? And if so, was there a fix? Or, does
anyone have any further ideas for things to try?

Dave.

Right at the cathode and control grid of the blue tube, if you swapped it
with another colour channel, and the blue still stays bad, I would strongly
suggest that it is defective.

From my interpretation, I am convinced that you have a bad tube. This is not
uncommon.

How old is the set?

--

Jerry G.
======


"Dave Gostelow" wrote in message
...
Hi,
I have a JVC widescreen TV AV-28WR2EK which has a fault with the blue gun,
or its driver. I searched the NG and found some good posts about similar
problems which suggested it was probably a short in the tube (and to try
floating the heater).
Well, I tried a few diagnostics:
swapped the blue and red cathode drives at the final resistor, fault still
on the blue gun.
lifted the drive transistor collector on blue so that the cathode voltage
rises to the supply, fault still there on blue.
'floated' the heater using 3 turns of wire around the HT transformer core,
and fault is still there!

So I begin to think there isn't a heater to blue cathode short, but maybe a
blue to something else short.

Then I tried disconnecting the blue cathode completely, by lifting the final
resistor, and the blue gun turns off! So is it shorting to something or not?
If I stick my DVM on the blue cathode and ground to measure its 'floating'
voltage it turns on strongly, so its being pulled down by the DVM. If I
measure voltage between blue cathode and supply I get the blue gun very
faintly on and a voltage reading of about 15-20 volts (blue gun more
positive than supply).

The supply voltage is 201V and before I started fiddling I saw at all 3
cathodes I was seeing voltages of 150-170 volts depending on the picture.

I would have decided the tube had a short except for the behaviour when the
cathode is left floating, which suggests to me that the blue gun would
probably turn off if it was driven to a higher voltage than 201V.

Has anyone seen a similar problem? And if so, was there a fix? Or, does
anyone have any further ideas for things to try?

Dave.

The user manual is copyright 1997 and I guess the TV is probably that old.
I've only had it a few days. I don't want to believe the tube is bad, but
I'm probably going to have to accept that it is, and its not going to be
worth replacing it. I'm going to try one more thing tomorrow before I give
it up: try adjusting the G2 (screen) setting to see if that makes any
difference. I found something about that adjustment on another posting which
was about fixing single colour visible flyback faults.

"Jerry G." wrote in message
...
Right at the cathode and control grid of the blue tube, if you swapped it
with another colour channel, and the blue still stays bad, I would
strongly
suggest that it is defective.

From my interpretation, I am convinced that you have a bad tube. This is
not
uncommon.

How old is the set?

--

Jerry G.
======


"Dave Gostelow" wrote in message
...
Hi,
I have a JVC widescreen TV AV-28WR2EK which has a fault with the blue gun,
or its driver. I searched the NG and found some good posts about similar
problems which suggested it was probably a short in the tube (and to try
floating the heater).
Well, I tried a few diagnostics:
swapped the blue and red cathode drives at the final resistor, fault still
on the blue gun.
lifted the drive transistor collector on blue so that the cathode voltage
rises to the supply, fault still there on blue.
'floated' the heater using 3 turns of wire around the HT transformer core,
and fault is still there!

So I begin to think there isn't a heater to blue cathode short, but maybe
a
blue to something else short.

Then I tried disconnecting the blue cathode completely, by lifting the
final
resistor, and the blue gun turns off! So is it shorting to something or
not?
If I stick my DVM on the blue cathode and ground to measure its 'floating'
voltage it turns on strongly, so its being pulled down by the DVM. If I
measure voltage between blue cathode and supply I get the blue gun very
faintly on and a voltage reading of about 15-20 volts (blue gun more
positive than supply).

The supply voltage is 201V and before I started fiddling I saw at all 3
cathodes I was seeing voltages of 150-170 volts depending on the picture.

I would have decided the tube had a short except for the behaviour when
the
cathode is left floating, which suggests to me that the blue gun would
probably turn off if it was driven to a higher voltage than 201V.

Has anyone seen a similar problem? And if so, was there a fix? Or, does
anyone have any further ideas for things to try?

Dave.

"Dave Gostelow" wrote in message
...
The user manual is copyright 1997 and I guess the TV is probably that old.
I've only had it a few days. I don't want to believe the tube is bad, but
I'm probably going to have to accept that it is, and its not going to be
worth replacing it. I'm going to try one more thing tomorrow before I give
it up: try adjusting the G2 (screen) setting to see if that makes any
difference. I found something about that adjustment on another posting
which
was about fixing single colour visible flyback faults.


If disconnecting the pin turns the blue off there's still hope. Are you
*sure* you swapped the blue with something else right at the tube socket?

I definately swapped the right connections.

I'm very happy tonight because just over 1/4 turn of the 'screen' trimmer
has solved the problem. It has got the blue to turn off properly in black
parts of the picture, but the blue gun is still extremely strong compared to
the other two. I have been able to get a reasonable colour balance by
changing the engineer settings with the remote.

My conclusion: the tube is not dead yet, but how long it lasts is anyones
guess.

Thanks for the replies, and also to those whose archived posts I found via
google which gave me the hints that fixed the problem!

"James Sweet" wrote in message
news:db42e.54875$hA3.37942@trnddc09...

If disconnecting the pin turns the blue off there's still hope. Are you
*sure* you swapped the blue with something else right at the tube socket?

I'm very happy tonight because just over 1/4 turn of the 'screen' trimmer
has solved the problem. It has got the blue to turn off properly in black
parts of the picture, but the blue gun is still extremely strong compared
to the other two. I have been able to get a reasonable colour balance by
changing the engineer settings with the remote.

My conclusion: the tube is not dead yet, but how long it lasts is anyones
guess.

Update: how long did it last? Until mid-august. After making the adjustment
the picture was
OK until it suddenly started getting an overall blue tint again about the
end of July. I tried another adjustment of the 'screen' trimmer but this
only made the picture very dark and contrasty.

Conclusion: I only extended the life of the TV by about 3 months.

How I have fixed the problem: I bought another TV!

Dave,

I recently bought a similar TV (secondhand) and noticed that there is a green cast/noise at the darker area of the picture. there is a limitation on the colour adjustment from the remote control and cannot solve the green noise situation. Can you advise what should proceed from here?

cheers,
keng