CurtPalme.com Home Theater Forum

brandonnys · Joined: 12 Feb 2010 Posts: 12

I'm sorry I don't have a more descriptive term for what I'm seeing on my projection TV, but it really is going crazy.

I turn on the TV for about 20 minutes, and the picture is great. No corruption, perfect alignment. Then...

1. It usually starts with the image shifting either left or right. All colors are in sync and correct, but the image is about 2 inches off to one side, and usually about 2 inches higher, leaving black 2 inch bars on the bottom and side.
2. Then, there will be black diagonal bars on the screen, and the colors will go dark (like the contrast got kicked way down).
3. Then, it just goes nuts, zooming in and out, flashing different colors, etc.

If I leave the TV off, it will eventually run right again, but like I said, only for about 20 minutes. I thought it was the 2 chips toward the back of the TV getting too hot, so I affixed a mount and put two fans back there to cool them off, but that doesn't seem to be it. Any suggestions?

For a visual representation, check out my YouTube video of it: http://www.youtube.com/watch?v=f-v0_vIzYMw

Thanks!

-Brandon

brandonnys · Joined: 12 Feb 2010 Posts: 12

Another Note:

I have the TV hooked up to a 1080i HD Cable box source, but this TV will do the same thing when hooked up to my XBox360 running 480p and 720p. I have a Nintendo Wii hooked up Composite, but I haven't tested to see if this will also do this. I did switch between sources (1-5) and it seemed to still do it to the sources that didn't have anything connected.

Also Note:

Audio is perfect.

**Curt Palme** · Posted: Sat Feb 13, 2010 12:19 am Post subject:

THe problem is the content. It's a McDonald's commercial. Smile

Looks like a sync problem to me, something internal in the set. MacGuyver might chime in here, he's the RP expert, but my guess would be something called a low level component failure, in other words, not a big chip or transistor, or something very obvious.

With the loss of sync comes color flashing, brightness level changes, etc.

Sorry, I've never worked on an RP set, so I can't assist any further.

brandonnys · Joined: 12 Feb 2010 Posts: 12

Hi Curt,

Thanks for getting back to me about this issue. I'm not sure if I'm the first guy in the wolrd to have this issue, but I've searched high and low on the internet trying to find a fix for this issue and nobody has been nice enough to share it with me.

I'm pretty electro-savvy, so if it's just popping out a pot or a cap or something and soldering a new one in, I'll just head down to NorVac and get some new parts.

Thanks a million!

-Brandon

brandonnys · Joined: 12 Feb 2010 Posts: 12

I haven't found solution to my problem on my own yet. I opened up the TV and inspected the mainboard all over... nothing looks fried, bulging, leaking, or visibly arching. I don't smell anything (other than a large amount of dust). I haven't tested any components though, since there's about 60,000 of them on there and testing them individually would take for ever. Is there an area I should focus on?

-Brandon

brandonnys · Joined: 12 Feb 2010 Posts: 12

I really hope Mac comes back... it's killing me that I can't watch Family Guy on my TV anymore... Very Happy

brandonnys · Joined: 12 Feb 2010 Posts: 12

So,

I decided to bite the bullet and just buy a service manual for my TV. I have it here in front of me... Man, there are a lot of block diagrams! This guide even has full circuit diagrams and printed circuit board images... dang!

Anyway, does anyone have an idea of where I should take a look first? Curt, you suggested a sync issue. Where do you think I could look for sync issues on the board? I'm not a TV expert, by any means, but I am familiar with electronics.

Thanks!

brandonnys · Joined: 12 Feb 2010 Posts: 12

So, I let the thing sit for a couple days, and tried turning it on today. All the LEDs inside were green, and the image stayed good for over an hour. Then, the image crapped out again. I was in a composite input instead of a component, so I guess the issue is independent of the source.

I'm going to make some guesses, hoping that someone might know where I can start... I've looked over the diagrams and found a sync separation circuit. Should I test the components on that circuit, or is that just a waste of time? My manual has waveforms and voltage readings, so I'm assuming I can just check out a bunch of the components to see if there's a short or something... I'm really just fishing for a suggestion. I'm about ready to Craig's List this beast... Nobody knows what is wrong... Well, not for under $200 to look at it, and another $400 to fix (as quoted by my local TV repair guy).

PLEASE HELP IF YOU CAN! I don't want to have to sell it because it's a pretty nice TV when it's working.

HD-DAVE · Joined: 16 Feb 2007 Posts: 223 Location: Delta, BC

I would first look for obvious things like loose connectors, burned components (which it sounds like you've already done). I will often let a set sit a awhile to discharge the HV / flyback (if its a CRT), then one by one disconnect and re-connect all the interconnecting cables/harnesses to see if its just a simple case of oxidation. While you are doing that if it isn't too difficult to inspect the bottom of the PC boards (Power Supply, Deflection, Input/Control/etc) for cold solder joints (google it for a picture of what one looks like)... a poor solder joint could definitely cause temperature related intermittants like your seeing...metal expansion/contraction.

After that, it is really important to check that all power supply voltages are present/stable - which can be done pretty well with a DVM, but takes an oscilloscope ( plus possibly an isolation transformer for safety) to see ripple or dropouts with accuracy.

If your service manual has pictures of oscilloscope waveforms from the test points in the set, and you are skilled and equipped to try and check these you can watch test points in the sync section to see what screws up...

However, your chances are pretty good that you might find a bad capacitor that is causing the symptoms - it doesn't cost much to get a decent ESR (equivalent series resistance) tester you can use to check all the electrolytic capacitors in the sync section - 9 times out of 10 these days I find a bad cap or two has caused a failure. After leaving the set turned off for at least 30 minutes (unplugged), you can use an ESR testor without removing the caps from the board - then if you see one that looks out of spec, you can desolder it for final testing.

Good luck,

Dave

**Curt Palme** · Posted: Mon Feb 22, 2010 9:38 pm Post subject:

A couple of points:

-first, I'm still amazed about the amount of people that email or post 'I don't see any burnt parts'.

Burnt parts were common back in vacuum tube days, due to the voltages and currents involved. With solid state, I'd say that well under 5% of all repairs I've done have involved a smokeshow (not including those that I've caused myself!) on the PC board. Of the boards that did smoke and showed visible damage, I'd say a good 40% of those involved user error, or some external cause like spilled liquid or glycol on a PC board, or someone connecting something incorrectly, or a power/ surge/lightning strike.

Modern TVs (and a bunch of amplifiers and other electronics) have switch mode power supplies that automatically shut down when they sense an overload, which then prevents a smokeshow and further damage to the item involved.

So, while you can look at a PC board, it usually takes a pretty trained eye to find something like a fusible resistor that has blown open, and usually even those show no external signs of damage.

Second, when I was repairing Hitachi and Zenith TVs back in the 80s, the rule of thumb was that Hitachi failed less than Zenith, but when they did, they were a PITA to find. Now, I know we're 30 years later, but I'm guessing the rule of thumb does hold true.

Finding something that's intermittent makes things even harder. Dave above gives good advice, but if you're not a board level tech, it will be near impossible to find a fault like this one. Given that the unit sometimes works indicates that you probably don't have an outright component failure, but more likely a part that's on the verge of failing, like a cap that's out of tolerance, or maybe a solder joint that's iffy somewhere. That's also why you're being quoted the numbers you are for repairing the unit.

Good luck, but this is one where I personally can't give more advice than what's already been given.

brandonnys · Joined: 12 Feb 2010 Posts: 12

Well, since I don't have an oscilloscope just lying around, I guess it's time to call the local TV repair guy up and have him take a look at it. I was hoping I could avoid that, but I guess not... At least now I have a service manual that I can look at if I have, say, a convergence issue, or something more simple later on down the road.

Anyone have a good idea on how much per hour it might cost for a tech to take a look at my board? Ballpark figure is fine.

**Curt Palme** · Posted: Tue Feb 23, 2010 2:01 am Post subject:

I'd say $80-100 an hour. Most places will charge a flat rate the same way car dealers do to do a board swap or whatever. You could always buy a spare board on eBay if you can find one, but of course you take the chance that you're spending money on the wrong board if you guess wrong. Punch in the model of the set on eBay, you never know what you might find.

brandonnys · Joined: 12 Feb 2010 Posts: 12

Did a search on eBay for my board, my tv, everything, and no dice. Apparently I have the only one left. I feel like Eli right now (If you didn't catch the reference, go see "The Book of Eli", it's a good flick).

Anyone have another resource for finding a board for a Hitachi 57TWX20B DP27D chassis?

timbo · Joined: 22 Jul 2007 Posts: 82 Location: Brampton, Ontario

I noticed that you used a composite input and a component input while investigating.

By any chance was there a dvi/hdmi connection hooked up to the television during the problem and during your troubleshooting?

Some Hitachi rptv have had the "scrambled mess" issue while connected to an hdmi source.
It may be that simple.

brandonnys · Joined: 12 Feb 2010 Posts: 12

Nope, no DVI input. There's no HDMI on my set.

Just an update: Left the B**** off for about a week, and turned it on again to see what would happen. It's been on for I think 3 days straight with no issue. WHAT IN THE WORLD WAS GOING ON? And will it come back?

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Test voltage at pin 31 of i401 for 4.7 volts. If incorrect voltage, replace C443.

brandonnys · Joined: 12 Feb 2010 Posts: 12

Well, just as an update, I moved, and the TV moved with me. I plugged it in at the new place, and it started doing this again. I'm not sure what's doing it, but I'm going to follow Mac's expert advice and see what's going on with the voltage. If it's off, I'll know what to do.

-Brandon