hitachi 42hdt79 problem
 

OK first off I am in no way a electronics repairman but I'm trying to learn.. I had a Hitachi 42 inch plasma given to me that the screen cycles on and off about every 10-15 seconds and the blue power light goes on and off with the cycling. From my research on this model and this problem I find that the digital main board is a common problem for this set and was wondering if anyone had experience with this particular set. The set is model number 42hdt79 and the main board is jp50763. Is there a way to check the main board? Any good sites for parts anyone might recommend?

I also noticed on the main power board that one of the caps has a very slight bulge on the top. it is the 3300UF 100V cap, well at least that's what it has printed on it. Would a bad cap cause the cycling on and off problem?

It might. Any bad capacitors in that set (or any other) will cause problems of some sort. I'd replace that bulging cap ASAP, as it is of course defective. Once it is replaced, your set may well work like new again.

I'd also look for any other caps that have bulges (especially on top) or other signs of defects. Any time a capacitor bulges and the bulge is noticeable (even if it isn't), it means the part may eventually explode and cause other problems; in any case, the cap is definitely defective and must be replaced.

I imagine (don't know for sure) that even tiny electrolytic capacitors such as are used in today's electronics (not just televisions) can explode violently if they are overloaded to the point of the casing being distorted, and if the device in which they are used is not shut off promptly. What is probably happening is that the capacitor is getting so hot the electrolyte solution inside is literally boiling and producing steam. The small capacitor cannot take the expansion caused by the steaming (there is no outlet for the steam in these components, so there may be no smoke or other telltale signs of trouble), so it can or could explode -- not unlike standard tubular electrolytics in tube-type radios and TVs when they short or otherwise become defective.

I used to hook up scrounged lytics from equipment as new as the 90's to AC voltage in excess of their VDC rating to see the metal cans BLAST OFF across the the street (this was done outside of course) for entertainment. ANY lytic can blow if it has the right voltage on it's terminals.

On many Hitachi plasma sets, if the two "digi" boards (main and sub digital boards) are not mated properly, you'll get the symptoms you describe. The connector that fails to mate is below the rubber cushion, to the right of the tuner. Pull the two boards apart and reseat the upper board, making sure the connector properly mates.

Many boards have been called bad, only to have the mating problem.

Hitachi has called this out before:

No Picture, Blue LED blinks, some LEDs on the Digi-Main remain lit. (They are supposed to go off after the power cycle).

Cycles On/Off Blue On, No Picture,
Maybe Static Picture
Auto Programming doesn't work correctly. Doesn't lock in normal channels, but does lock in unused channels.

The Digi-Main is not seated correctly into the Sub-Digital PWB.

Simply pressing on the connector won't fix.. The connector must be unplugged and then reseated.

Digi-Main must be "PUSHED" together with the Sub-Digital PWB for the connector PVM to PSM to seat correctly.
Failure to do so will result in the above symptom.
If any of the LEDs on the Digi-Main are lit, suspect a bad digi-main.

The 3300uF cap is in the Vs power supply, and could also cause the cycling problem. You might want to get a replacement - Mouser or Digi-Key should have a replacement. Check the dimensions! Diameter and length are important, and are measured in millimeters. Don't install an 85 degree cap - always (on plasma sets) use 105 degree capacitors.

Cheers,

(The 3300uF cap is in the Vs power supply, and could also cause the cycling problem. You might want to get a replacement). it is not going to heal itself replace the darn thing.

Yup, those 3300 mfd caps are known bulgers and cause all sorts of symptoms, I would look into that, if that doesn't work, if the picture looks funky, lots of maldischarge, look into the ysus board on that model for 2 small SMD mosfets that could cause it too. they are usually located near the buffer board output. These are like 1/4" square and soldered to the board. the type of mosfet I believe are labeled FS10. And yes thare is also a heat detector on the scaler board that might need to be reseated, this chip is behind a lockdown holder.
Many flakey issues on this Hitachi/fujitsu TV.

But hopefully its just the capacitor in the PS.
Good luck