Hitachi 50UX58B

[wwiiflyer]

My Hitachi from 1999 just broke. We were all watching TV when a "pop/snap" was heard and then the TV went out - no power led light. Opened the back and say no swollen capacitors etc. Did notice that when first plugged in a few green leds come on and then they all go out and a "protect" LED comes on. This led flashes at a rate of above once per second or once every two seconds. No other LEDs are on at this point. Something in the HV section?

[mark]

yes, I have had many of the ceramic caps in the hv section cause a problem.
if you heard a snap, look at those.
they are blue, and ive seen them short, or start to leak.
they pull the b+ down and trigger an over current condition.

also, look to make sure there is not one of the green leds that does not light up.
if one isnt lit, thats the supply with the fault

[wwiiflyer]

Looked at the blue ceramic caps -- only saw two small ones; but, they look ok. Will need to get under main board to see if shorted. Made note of LEDs and order in which they come on when set is first plugged in:

Instant on is +12V (Green LED)
Instant on is 27V (Green LED)
Instant on is 23V (Green LED)
Instant on is 32V Audio (Green LED)

About one second later -9V (Green LED) followed by -5V (Green LED)

The B+ 120V (green LED) never comes on

The next LED to lite is the red "protect" LED

Where can I get a schematic and do I just start checking all CAPs for shorts? What about a blown fly back? I guess I could call a technician; but, this now has my curiosity and the components don't look that complicated.

[Larry E]

Hi, you need to call a tech, Mark is right about the shorted cap in the
HV circuit, you also need a chemical fuse as yours is open and you
have to order it from an electronics supply house (and no I don`t
mean Radio Crack) so call your local tech, should be a cheap fix, unless
you go in there and make it more difficult, Larry E

[THE GREAT OZ]

HELLO, Both of these gentalmen are right, however don't forget the H.O.T this transistor is a common failure and the snap is somtimes the case blowing out the side. The dead ringer is your B+ not comming up. Also look for a large power mosfet transistor that might be damaged. This device is close to the flyback it may not look damaged but a measurement bettween the gate and drain may show dead short.

[Guest]

I'd like to try and repair on my own if possible. Where can I get schematics on this unit? Didn't find any on this site or several links.

HOT - case ok no visble damage.
Blue CAPs ok no shorting.
Hadn't found the culprit yet (hadn't spent much time on it TV broke at a bad time...but, that's always the case) - will start removing main board for a component by component check.

Over the years this is my third big screen --- they always seem to break about 6 to 7 years old. First was an Advent projection (repaired this one many times), then an RCA (main board had Hitachi written on it) and now an Hitachi. In fact my father's big screen Hitachi went 5-1/2 years and my friends went about 7. What kind of life are you guys seeing out there?

[mark]

I have seen the caps go leaky, basically turn into a resistor. it wont read shorted but when voltage is applied it breaks down and then is shorted.
and, when power is removed it reverts back to being resistive.

when I get one of these, I just replace the caps THEN try it.
its usually about 70% of the time, the cause of the failure.
now, VERY RARELY is the HOT an issue in these sets. they dont run these at as high a voltage as other manufacturers, and so they last a bit longer.
flybacks are another story.

life on hitachi sets? I still see 10+ year old hitachi sets, but most of the time, these sets have _never_ been repaired.
they are just failing after 10 years, and most are convergence issues.
they seem to come in waves

on your set, you need to look at the resistance on that b+ line to groung and make sure its not something really low.
may not be a short, but the leaking cap as I described.

you probably need to take it into a shop, but since you want to give it a crack, DO IT NEATLY ...

take out the HOT (horizontal output transistor), and replace the pico fuse. this is going to be the hard part because this is a special fuse.
I do things a little differently then most people, I use some clip leads and a similarly rated gma fuse and clip lead it in for troubleshotting.
if it nails it with the HOT out of the set, its not the flyback or the HOT
its a cap, more than likely.

try this, but I suggest you make a call. once you have toyed with it, and then call a servicer you may pay a little more, expecially if the set is all taken apart, ect

also, be up front. tell them what you did.
I hate a customer that denies everything, only to confess later.
it makes my life unessesarily hard. if your up front, the servicer will probably appreciate it. believe me, I would.

[wwiiflyer]

I removed the main board tonight. Was able to get a good look at all the components and access the bottom of the board. Found one of those "Blue" ceramic caps with a small hole in it - small black spot below it. The capacitor's number is C707 and it was blown "open" and was not shorted. I'll see if one of the "true" electronic stores in my area can get one. This "pico"/chemical fuse that you are mentioning - can you point me in the right direction. Does it look like a resistor or a capacitor? What does Hitachi commonly label these on the board - CF, RF, etc. ?


P.S. -- What is the "SK01" labeled pushbotton. It states in front of the white PC board mounted button "Service Only"? Is this some type of reset?

[Guest]

Well I replaced C707 (blue cap) and the 2A pico fuse (E994). Set is back in service - still a great picture. It's getting pretty hard to find good electronic supply stores. Even the big internet and mail order companies did not have good assistance with trying to match this capacitor - had to buy a "genuine" Hitachi part.

I'd still like to know what SK01 - the white "service only" switch is.

[Guest]