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[N49]

Hi, Got a Toshiba 46HMX85. Bulb failed to light a few days ago. Read everything I could find and took the entire TV apart to check for anything obvious, and because I always wanted to. One thing I'm confused about is the constant mention of a Spark Gap on the ballast. This thing looks pretty solid state to me and cant figure out where the spark would be. There are a pair toroidal coils and a pair of rather small transformers on the board. I had the board in front of me while I powered up the TV but heard no clicking and saw no flash. I can confirm 300vac in and I believe 65 vac out. Bottom line, do all ballasts spark or can the ignition voltage be generated another way. Don't want to play trial and error with a TV that is worth a helluva lot less than the sum of it's parts.

Thanks in advance

[grayfox]

Hello N49,
I think maybe you misread some info on your Toshiba. The output ignition voltage from your ballast should range at about 15kv and it is not safe to test with a multimeter. This is needed for the "arch gap" located in the center filament that contains the mercury vapor inside the Lamp, it looks like a tiny glass bubble. Inside is where the "gap" is located and the mercury helps the "spark" ignite between the electrodes, that is why if you test a UHP lamp for continuity, it fails, because of the gap. Look at the diagram on this link for more info
http://www.discount-merchant.com/how-dl ... a/141.html

[N49]

Pepe, thanks for the URL explaining the anatomy of a Mercury Vapor lamp.

I had a close look at the ignition chamber on my bulb and noticed it had a small crack and the interior was a bit black. My last bulb exploded so this is why I was suspecting the ballast when this lamp failed to light.

I was aware of the high ignition voltages the ballast produces during the start up sequence. My digital meter has a built limiter so I hoped it worked when I hooked it up. Sure enough, the meter indicated it was overloaded for a few moments and the voltage then stabilized around 60 volts before the sequence repeated itself. I connected to jumper cables to the lamp plug and help them roughly 1/8 - 1/16 inch apart while someone fired up the TV, yet there was no spark. I then took a breath and tapped one of the leads with my finger during start up and soon regretted it.

I ordered a new bulb and will receive it in a few days. I will know by then if I will be ordering a new ballast to go with it.

[grayfox]

Wow you tested the ignition charge! yes many times I have to re-calibrate my multimeter after a charge like that. But like you saw it is only for the ignition charge, once lamp is lit the voltage needed to keep it on is lower. Let me know if the lamp worked out!

[N49]

Installed the lamp, held my breath and pushed the power. Luckily it lit as I decided I would cut my losses if something else was wrong with this TV.

Do you know of a site that documents the service menu's for Toshiba's? I can get into it but it really isn't user friendly. Seems to be based on a complex sequence of inputs from the remote and TV controls.

I could always spend the 10 dollars and buy the service manual.

[grayfox]

hhhmmmm I do not know of a site that hosts for all models, but i might find a PDF for your model I will look for one... all I found was the owners manual
http://www.devicemanuals.com/guide/Tele ... E9UWT.html

do you need to reset the lamp timer or what kind of service are you trying to perform?

[JackfUp]

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