Hitachi 55VG825 Ballast testing

[uberplasma]

Hi everyone

I have an Hitachi 55VG825 55`rear projector that blew a bulb, it was the OEM bulb from 2005, so it was not that unexpected that it would go, got 3200 hours of it so not too shabby. I ordered a replacement bulb and installed it and within 30 seconds it blew, and since I had the rear cover off I noticed that the gas discharge tube was lighting up every few seconds. Ballast`s are somewhat out of my normal line of repairs and was wondering if there anyone knew how to troubleshoot the power without a scope or high voltage adapter for my meter.

Tv is in great shape, from father in law so I know that there was no previous service performed and the Tv was well looked after , he got rid of it only because of the bulb blowing.

Here are some pics, dust has all been blown out, very clean, no visible damage to any component or any odd smells from the boards.

Any help or direction would be greatly appreciated.
Cheers
(couldn't edit first post so reposted)

[ben7]

Re: Hitachi 55VG825 Ballast testing

I don't see how a ballast like this could blow the bulb, but I can see how the ballast might be giving a lower output voltage than what is needed. Your original bulb might still be good...

Ever seen the streetlights go on and off at night? That is because (in this case!) the bulbs are going bad. They require a higher voltage than the ballast can supply when the lamp is hot, and so they flash on and off repeatedly.
~~~
However, if the ballast is bad (not supplying enough voltage when lamp is hot) then it will do the same thing.

Before replacing the ballast, I suggest you try cleaning off the lamp holder contacts very well.

[selldoor]

Re: Hitachi 55VG825 Ballast testing

I think the question is did the bulb blow or is it just not lit?
Did you reset the lamp hours
I also recall reading (years ago so may not remember correctly) some
lamps are in a compartment with a door and if the door is not shut correctly
a switch stops it lighting.

[ben7]

Re: Hitachi 55VG825 Ballast testing

Did you reset the lamp hours
I also recall reading (years ago so may not remember correctly) some
lamps are in a compartment with a door and if the door is not shut correctly
a switch stops it lighting.

Good points, I agree, check those things too!

[R_J]

Re: Hitachi 55VG825 Ballast testing

If the gas discharge is lighting you have highvoltage from the ballast, but there is no load check connections to the lamp, if the lamp is broken or open in any way the discharge tube will activate to protect the ballast.

[uberplasma]

Re: Hitachi 55VG825 Ballast testing

Hi
thanks for all the responses:
Yes the original bulb blew the filament, shattered inside the bulb. The replacement bulb went in fine, good connection and powered up fine and then did the same thing: filament shattered in the bulb within 30 seconds, then i noticed the gas discharge tube glowing, i was looking to see if the foperating, thinking over heating, but they were working. The door switch was rigged closed as I had the back cover off for cleaning(and I am curious)
I will try to find out how to reset the hours
thx

[ben7]

Re: Hitachi 55VG825 Ballast testing

Hi
thanks for all the responses:
Yes the original bulb blew the filament, shattered inside the bulb. The replacement bulb went in fine, good connection and powered up fine and then did the same thing: filament shattered in the bulb within 30 seconds, then i noticed the gas discharge tube glowing, i was looking to see if the foperating, thinking over heating, but they were working. The door switch was rigged closed as I had the back cover off for cleaning(and I am curious)
I will try to find out how to reset the hours
thx

I think you will need a new ballast, this one is simply putting waaay too much power through the filament!

[R_J]

Re: Hitachi 55VG825 Ballast testing

These Lamps don't use a filament. its possible the replacement lamp was bad ie cracked during shipping or instalation

[uberplasma]

Re: Hitachi 55VG825 Ballast testing

Hi
I was thinking too much power too. here are some pics of the bulb, this is the OEM and the replacement looked the same.
I quess I will have to start checking voltage regulators in the ballast to see if one is letting too much voltage through
the replacement came from the distributor with the void if removed sticker already damaged so I am kind of stuck if it is damaged from transport.

[ben7]

Re: Hitachi 55VG825 Ballast testing

Reading up online, it seems that if the ballast isn't giving the lamp enough power, then it could blow the lamp too!

In this case, either:

1. The HV transformer has some internal arc-over, and hence some shorted windings (lower output voltage).
2. One or more of the film capacitors has decreased in capacitance, causing a lower power output.
3. The filter capacitor is bad, although highly unlikely b/c this one is a quality Japanese capacitor made by Nichicon, which looks to have a flat top (not bulged out).
4. One of the switching transistors has degraded.
5. The little electrolytic capacitor has gone high ESR, and is causing instability in the ballast circuit. (Very common for them to go high ESR, even good brand ones do that in hot places!)
6. May be more things to look at, can't think of them right now...

[uberplasma]

Re: Hitachi 55VG825 Ballast testing

Hi
swapped out the ballast and TV runs perfectly. Hard to say if it was the ballast all along or light damaged in shipping, but have lots of ballast hanging around,so it works thanks for all the input!!
Cheers

[ben7]

Re: Hitachi 55VG825 Ballast testing

Hi
swapped out the ballast and TV runs perfectly. Hard to say if it was the ballast all along or light damaged in shipping, but have lots of ballast hanging around,so it works thanks for all the input!!
Cheers

Good job!