Bad DLP Ballast?
 

Me again with this miserable Zenith DLP TV. I made a post about this about
a month ago regarding lamp replacement, I was able to do it successfully and
returned it to the customer. A few weeks later the customer brought it back,
this time with a different symptom; the set tries to power but makes a
buzzing sound, and shuts off.
With the front cover removed, I soon saw the source of the buzzing sound.
A small round white component off the HV transformer (looks something like a
large diode) lights up bright blue appearing to arc internally. The lamp
does not power up at all. I checked the lamp and it is fine, so at this
point I'm suspecting a bad ballast...... but with replacements costing up to
$200, I sure hope it isn't.
Thanks for any advice.

Bad DLP Ballast?
 

Chris F. wrote:

Me again with this miserable Zenith DLP TV. I made a post about this about
a month ago regarding lamp replacement, I was able to do it successfully and
returned it to the customer. A few weeks later the customer brought it back,
this time with a different symptom; the set tries to power but makes a
buzzing sound, and shuts off.
With the front cover removed, I soon saw the source of the buzzing sound.
A small round white component off the HV transformer (looks something like a
large diode) lights up bright blue appearing to arc internally. The lamp
does not power up at all. I checked the lamp and it is fine, so at this
point I'm suspecting a bad ballast...... but with replacements costing up to
$200, I sure hope it isn't.
Thanks for any advice.


That sounds like the starter but I could be wrong there.

That part shouldn't be expensive. The Ballast electronics in those
DLP's are very basic.
If you have a service print, I think you'll find it to be a
thermo switch that opens after it gets hot. The idea is to energize the
bulb with more voltage so that it arcs in the lamp to get it started.
The heat expands the electrodes thus allowing the lower voltage to then
maintain it.

They are are no different than metal H type lamps used for high output
lighting. Our electricians are always replacing the ballast kits..
Most of the time the starter switch is burnt out from excessive
restart attempts due to a bad bulb.
Ours use a three wire. Some use 2.
--
http://webpages.charter.net/jamie_5"

Bad DLP Ballast?
 

I have not worked on your model of set, but from past expeience I
found that a defective lamp can damage the ballast, and or the
starter. A defecive ballast can also cause a lamp failure.

In many systems the starter is part of the ballast supply.



Jerry G.

--

You may end up having to change the two together to fis this problem.


Jerry G.


__

Chris F. wrote:
Me again with this miserable Zenith DLP TV. I made a post about this about
a month ago regarding lamp replacement, I was able to do it successfully and
returned it to the customer. A few weeks later the customer brought it back,
this time with a different symptom; the set tries to power but makes a
buzzing sound, and shuts off.
With the front cover removed, I soon saw the source of the buzzing sound.
A small round white component off the HV transformer (looks something like a
large diode) lights up bright blue appearing to arc internally. The lamp
does not power up at all. I checked the lamp and it is fine, so at this
point I'm suspecting a bad ballast...... but with replacements costing up to
$200, I sure hope it isn't.
Thanks for any advice.

Bad DLP Ballast?
 

And I suppose replacement is the only option? The customer won't want to put
another $200 into this set, and in all fairness they shouldn't have to.

"Jerry G." wrote in message
...
I have not worked on your model of set, but from past expeience I
found that a defective lamp can damage the ballast, and or the
starter. A defecive ballast can also cause a lamp failure.

In many systems the starter is part of the ballast supply.



Jerry G.

--

You may end up having to change the two together to fis this problem.


Jerry G.


__

Chris F. wrote:
Me again with this miserable Zenith DLP TV. I made a post about this
about
a month ago regarding lamp replacement, I was able to do it successfully
and
returned it to the customer. A few weeks later the customer brought it
back,
this time with a different symptom; the set tries to power but makes a
buzzing sound, and shuts off.
With the front cover removed, I soon saw the source of the buzzing
sound.
A small round white component off the HV transformer (looks something
like a
large diode) lights up bright blue appearing to arc internally. The lamp
does not power up at all. I checked the lamp and it is fine, so at this
point I'm suspecting a bad ballast...... but with replacements costing up
to
$200, I sure hope it isn't.
Thanks for any advice.

Bad DLP Ballast?
 

On Sat, 6 Sep 2008 08:26:52 -0700, "Chris F."
put finger to keyboard and composed:

Me again with this miserable Zenith DLP TV. I made a post about this about
a month ago regarding lamp replacement, I was able to do it successfully and
returned it to the customer. A few weeks later the customer brought it back,
this time with a different symptom; the set tries to power but makes a
buzzing sound, and shuts off.
With the front cover removed, I soon saw the source of the buzzing sound.
A small round white component off the HV transformer (looks something like a
large diode) lights up bright blue appearing to arc internally. The lamp
does not power up at all. I checked the lamp and it is fine, so at this
point I'm suspecting a bad ballast...... but with replacements costing up to
$200, I sure hope it isn't.
Thanks for any advice.

It probably won't help, but anyway I've uploaded this LG Powerpoint
presentation entitled "Service info for replacing ballast/lamp in LG
projection TVs":

http://www.eserviceinfo.com/download.php?fileid=37366
http://www.eserviceinfo.com/download.php?fileid=37367

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Bad DLP Ballast?
 

On Sat, 6 Sep 2008 08:26:52 -0700, "Chris F."
put finger to keyboard and composed:

Me again with this miserable Zenith DLP TV. I made a post about this about
a month ago regarding lamp replacement, I was able to do it successfully and
returned it to the customer. A few weeks later the customer brought it back,
this time with a different symptom; the set tries to power but makes a
buzzing sound, and shuts off.
With the front cover removed, I soon saw the source of the buzzing sound.
A small round white component off the HV transformer (looks something like a
large diode) lights up bright blue appearing to arc internally. The lamp
does not power up at all. I checked the lamp and it is fine, so at this
point I'm suspecting a bad ballast...... but with replacements costing up to
$200, I sure hope it isn't.

This forum suggests that LG had a bad run with 5kV lamps:
http://www.avforums.com/forums/archi.../t-415699.html

Problems with starting ...

Thanks for any advice.

This patent has an explanation of how a typical 2-pin ballast works:
http://www.freepatentsonline.com/6781328.html

It includes basic circuit diagrams.

AFAICT, a capacitor is charged to about 370VDC at which time the
starter (discharge gap) breaks over, and the capacitor's energy is
then dumped into a HV transformer. I would check those particular
components first, although the inverter section could also be at fault
(the inverter and HV output winding are in series). I believe the
output of the transformer should be 5kV.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.