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Discussion Starter · #1 ·
Hey guys, I've been working on this TV for a while and I'm out of ideas. Here's hoping someone can help (but I'm not too optimistic haha)

Symptoms:
- Plug it in, the protection relay clicks 3 times and the TV won't power up. Blinking red power light on the front (steady blink, no error code)

I got this TV from a neighbor, he had to replace the convergence ICs a while back. The TV worked when I got it, but sometimes wouldn't power up and you needed to "bump" it to get a picture. The convergence was still a bit off in places, and it couldn't be fixed with the touch focus feature or the settings in the menu. I didn't try going into the service menu to finetune it.

We brought it back to my apartment in the back of a truck, and it was cold outside (maybe a factor). Plugged it in.....and it didn't work at all. That's when it started blinking. Since then, I've replaced the convergence ICs (they were STK392-110s, I figured maybe they were from the bad batch) with STK394-160s (which were near IMPOSSIBLE to find) and still the same issue. We've pulled both the boards out, taken the front off, looked for anything that might have jarred loose on the ride over here. Everything is connected, nothing is obviously broken, and all the traces look clean. None of the fuses look blown. We've tested several spots on the PCB with a multimeter and current is getting to certain parts of the board. At this point, I'm all out of ideas.

I'm sure we could get a service call on this TV, but I'm trying to avoid the cost of having someone actually come out and diagnose the thing. I'm just not sure if it's worth it on an older TV like this. I've googled everything I could, found a thousand different people with a thousand similar problems, but I've seen everything from the convergence ICs to the flyback to the capacitors dying. I'm not expecting someone here to instantly tell me "here's your problem" without being able to actually see or work on the TV, I just wanted to bounce this info off as many people as possible and see what your ideas/opinions might be.

Thanks
-Geoff
 

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IIRC, these sets have some pico fuses which you cannot tell are bad by looking at them. Are you getting + and - supplies to the convergence ICs.
 

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Needing to smack it SCREAMS cracked solder joint.

The ride home could have easily broken even a marginal joint loose.

I got a 10 dollar 27" Panasonic TV off Craigslist this way.

I love it when they say turns off randomly :).

My 13" test TV on my workbench had the same problem. After my hand hurt from being the Fonz I decided to find the little gremlin in that set too.

The only way to find them is with a magnifying glass and patience.
 

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Discussion Starter · #4 ·
Sorry I've taken so long to reply, I posted the original message right before I left for spring break and I've just now gotten time to dig into my TV again.

RE:lcaillo, I've checked all the pico fuses for continuity, and they all seem to be ok. They could be blown but shorted somewhere else, but I haven't been able to find anything like that. As for power to the convergence ICs, I'm not sure where on the board to check for that, but see below.

RE:Krankshaft, when I picked up the TV from my neighbor, he said that when he replaced the ICs the first time, he had a few cold solder joints and that was the reason for the bumping. I should have said that in the original post, but for some reason I didn't. I've gone through and checked both of the main boards for cracked solder, and resoldered a couple places that looked suspicious, but that didn't help anything. I got pretty excited at first because I saw a joint that was loose and wiggling, with barely any solder on it, until I realized it was only a heatsink. Oh well.

Now on to the new developments. I remembered reading something a while back about disconnecting power to the ICs and seeing what happened, so I did some googling and found the page I was looking at then. Here's the link, but to summarize, disconnect P807 and see if the TV turns on. I couldn't find P807, so I disconnected P803 instead, and the TV actually did turn on, and the protection relay clicked twice instead of three times. The TV could be turned on and off, and the light wasn't blinking anymore, but there was still no picture.

That got me thinking, I read somewhere when I first started trying to fix this TV that when the convergence chips go bad, sometimes some of the resistors go bad at the same time. I didn't try replacing them when I replaced the ICs, mainly because I couldn't tell from the color bands what their resistances were supposed to be. Does this sound like something I should try? I can easily post pictures of the resistors if you think it will help.

-Geoff
 

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A bad convergence IC almost always takes a resistor or two out with it.

On my recent Toshiba 42H82 convergence IC replacement it took out a 1.8 ohm resistor.

It's body had a hairline crack on it and was open circuit. This crack was small however metal film resistors are made by depositing a thin metal film on the outside of a ceramic core. Then a flameproof coating is applied over the metal film. So even a tiny crack can tear this fragile film and render the resistor open.

The resistor heated up so much before it blew that it turned a gold color band black. Luckily the service manual set me straight on the value.

Check the convergence output resistors with a multimeter and they should be within 5% of their printed rating.

They won't be far from the convergence ICs they are located on two big heatsinks on the signal board you can't miss them. They will have STK-xxx-xxx printed on them.

Personally I never memorized the color band values for resistors so I always go here:

http://www.dannyg.com/examples/res2/resistor.htm

Just input the color bands and it tells you the resistance and tolerance.

As for the TV powering up when the connector is removed are the tubes getting filament voltage?

If you look at the glass necks for the 3 tubes they should glow orange.
 

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A bad convergence IC almost always takes a resistor or two out with it.
Maybe, maybe not. I fix several sets a week and the majority do not have any bad resistors. Some sets are more likely than others to damage resistors when the chips go. Philips and Hitachi sets are most likely to need resistors. Mitsubishi and Toshiba sets rarely do.
 

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Thats funny I have two Toshiba 42H82s and BOTH of them fried the same 1.8 ohm resistor when the stock STK-392-110s went.

Oddly enough the same STK channel failed on both the one that handles the red channel's horizontal movement.

I guess certain models have their quirks.
 

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Discussion Starter · #8 ·
The tubes aren't glowing orange, as far as voltage goes I'm a little wary of poking around the picture tubes when the set is on because of those lovely thick red high voltage cables.

I've tried checking the resistors with a multimeter, but the multimeter I have right now isn't working right. I'm going to steal my dad's digital one sometime this week or next weekend to test them again. I tested both the 1.8 and 220 ohm resistors, and they all seemed to be good. The x1 scale isn't working, but on x10 the 1.8 ohm resistors tested somewhere between 0 and 5 ohms, and the 220 ohm resistors tested around 210. I'll be able to tell exactly what they are when I get the digital multimeter, mine is......old.

-Geoff
 

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Discussion Starter · #9 ·
Ok using a digital multimeter, all of the 1.8 ohm resistors tested around 1.9-2.1, except for one that was around 2.5. The 220 ohm resistors tested around 219-223. I know that sometimes resistors on a PCB will test a slightly different resistance than if they weren't on a board, but are they ok? I know they're slightly outside the 5% range, and resistors are cheap, so should I just replace all of them to eliminate that factor?

Thanks again for all the help, I really don't want this TV to turn into a 200lb doorstop.

-Geoff
 

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Did you test the resistors with the yokes disconnected? If not, disconnect them and try again.
 

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On my Toshiba I tested both the 1.8s and 220s in circuit however I removed the signal board from the set so that I could work on my workbench.

One of them had a hairline fracture on it.

I had to remove my hyper module during the summer and I decided to remove it while the board was still on the plastic chassis it was more of a pain then it was worth.

So now I always remove the board to save myself the aggrivation.

The yoke connections on my set were on the far left of the signal board they are at the front of the board from the back of the set.

There should be colored marker marks on each of the connectors the red connector should have a red mark and the blue connector should have a blue one. The green wasn't marked on my set.

From left to right they are connected this way Red, Green, Blue.

It could be that the vertical output IC failed.

Unlike classic CRTs when vertical sweep fails a protection circuit kicks in to prevent the horizontal line from burning into the screen.

I don't know if this protection system just cuts off the color signals to the tubes or just shuts down the tubes completely though.

I'm sure lcaillo knows what this circuit does in these sets.

If thats not the issue I would search on the power board the filament voltage is derived from the flyback transformer.

Check the Horizontal Output Transistor first.
 

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There are lots of reasons for shutdown. I would have to do some research and troubleshoot it to figure it out. I cannot do that online. I would refer to the service and training manuals (if any) and examine the set to determine anything. It is simply not practical to do troubleshooting via messaging. I provide symptom-repair information and information that is general knowledge, but there is not much more I can do for you on this one.
 
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Sorry to jump in this thread with my own problem, but I can't seem to find where to start my own! I have a Toshiba 55H70 that began bowing just green, mostly in the lower left of the picture. I took out the board with the STK392-110's and would like confirmation that the STK394-160's are the most desirable replacement. What's the best source for these? There are pairs of this chip on ebay for $43, and I am just about ready to get them....
Leanard: Thank you for all your well written information!
 

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Yes the STK 394s are better then the 110s.

I performed this upgrade on my Toshiba.

I wouldn't go through E-Bay the best source is from Tritronics you can get both of them for 37 bucks.

At this link:

http://www.tritronicsinc.com/storefrontB2CWEB/itemdetail.do?action=prepare_detail&itm_id=567178

Tritronics is an authorized reseller for Hitachi the company that these ICs were originally made for.

I can't say the same for any E-Bay seller.

Also be sure to check the resistors around the STK ICs since in some circumstances they can go open as well.
 

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Please start a new thread for each problem.

Look at the Hitachi kits in the Convergence Repair sticky in the parts post. You can get these from Tritronics, Andrews, Vance Baldwin or other Hitachi parts distributors. Check the prices on the various kits and get the cheapest one. They all have the STK394-160 and resistors for particular Hitachi models. It is the best way to buy them even if you don't use the resistors.
 
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Sorry... I'm new to this. I did order a kit and I do appreciate the help. We are about to remove the heatsinks and the old chips. I'll follow up when the new parts come in. I hope UED is a reputable vendor...

Thanks!
 

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I assume you mean Union Electronics Distributors when you mention UED. If so, yes, they are a reputable supplier and you should have no surprises.
 

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Don't forget to clean off and apply new thermal compound to both the heatsinks and the ICs.

The kits don't include this (although they should) if you forget this step the new ICs won't live very long.

You can get it at Radioshack or any computer store.

Wipe off the majority of the old stuff with a paper towel.

Then remove the residual with rubbing alcohol.

I put a little bead down then spread it with a straight razor knife (like a butter knife on bread) to ensure a flat even coat.

Once both surfaces are coated apply the IC to the heatsink lining up the screw holes then wiggle it while applying pressure downward to seat it into the compound.

Then fasten both screws don't over tighten them or you will either strip the aluminum threads or crack the IC package.

Be very careful that all of the pins line up when installing the IC / Heatsink.

One of my ICs had a slightly bent pin from the factory and I was fighting with it to get it into the hole for the longest time.
 
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Complete success! Thank you very much! The job was a bit easier than I thought it was going to be. The next task will be to clean and fine tune it. I sure hope these newer and better ic's last as long or longer than the last ones.
 
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