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Discussion Starter #1
Hi Guys,

I just recently Picked up an AV-56WP74 with a convergence problem. I was able to successfully repair it so I thought I would share my experience with the forum in the hopes it will help others get their set repaired.

I took some pics, but unfortunately I’m a terrible photographer so bare with me! I also don’t have any photo editing software beyond Paint so I can’t really give arrows, notes, etc. on the pics themselves.

I will spread this out through a series of replies as I can't figure out if I can embed pictures in line with test while posting so I'll just do the text followed by the pic and then do a reply for the next text and pic.
 

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Discussion Starter #2
Well ! Our camera was set to high resolution so the picture file sizes are too big to be posted here!

OK, I'll try to get to my desktop machine tomorrow where I have more software and hopefully I can squeeze the pictures down to a more reasonable size.

Sorry for the delay, I'll be back tomorrow!

Steve
 

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Discussion Starter #3
First, here’s what the tv looks like.

The board that has the convergence amplifiers on it is behind the front panel on the right hand side, to get to it you need to remove the front panel. It’s one large piece of plastic! It’s held on by six screws. Four are on the outside edges and come from the back into the front, the other two are small ones behind the flip down plate for the front a/v inputs.
 

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Discussion Starter #4
Here’s a pic of the screws on the outside edge (excuse the looks of the case, it was just dusty – it’s cleaned up spic and span now!). I forgot to take pics of the ones on the front a/v inputs (though they are visible in later pics), just flip the a/v cover down and you’ll see ‘em.
 

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Discussion Starter #6
That black panel in the center comes off next. It’s just held on with four screws. Here’s what it looks like with it removed, the black heat sinks on the right are for the convergence chips (they are mounted on the other side of the heatsinks)
 

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Discussion Starter #8
There are six cables connected to the board, I’ve labeled their sockets in the preceding pic. Cable 3 can’t be removed from the board so you have to unhook the other end of it. It breaks into three connectors. Two go back to a silver module that’s accessed from the back and one goes up to a CRT tube board right above the convergence board. The wiring runs through some plastic wire holders that twist around to latch. Carefully untwist them and remove the wiring.
 

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Discussion Starter #9
Two of the connectors connect here to this silver board on the back i/o panel (you have to remove the back access panel – I didn’t take pics of that. Makes sure the power is unplugged before you do this. Beyond the shock hazard you could also disable your digital input – see the sticky note at the top of the forum about this), just label them and unplug them.
 

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Discussion Starter #11
Now Cable three should be unhooked and you should be able to fish it out and hang it out the front of the case.

Cables 4, 5, and 6 are next, just label and unhook them.
 

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Discussion Starter #12 (Edited)
Once all the cables are disconnected then you can remove the board. There are no screws holding the board down, it’s just held down by four plastic tabs in the front. Gently pull up on the STK heat sinks while releasing them and the board should come out.
 

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Discussion Starter #13
The back edge of the board just slides under some tabs. So, to remove pull up and press the clips back. The board will come up, then pull forward a tad and it’ll come right out. To reinstall just make sure the board is under the back tabs and then press down and it’ll snap right into place.
 

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Discussion Starter #14
My camera batteries went dead now so there’s a few steps without pics . . .

OK, now the board is out. Removal and reinstallation of the convergence ICs is straight forward. Just use your Radio Shack de-soldering iron and de-solder all the connections on the STK chips then remove the mounting screws and gently pry. The STK is stuck to the heat sink with some old dried out grease but it’ll let go with a gentle pry. Now gently pull on the chip and see if it will come out. If not then keep gently pulling on the STK chip while you warm up the solder pads on the bottom – it’ll soon let go and come right out.

Clean the old grease off the heat sinks. I used a utility knife blade to scrape most of it off and then finished up with a paper towel and some alcohol.

Apply a thin layer of heat sink grease to the back of the replacement STK chip. I imagine any heat sink grease would work but I use Arctic Silver as I work on PCs all the time so I have it on hand.

Which STK chip to use is a question. The board comes with STK392-110 chips in it. It’s hard to argue with using them as replacements since they ran for several years originally and it eliminates any compatibility questions. There are a couple newer chips that are considered upgrades though as they run cooler. The STK392-150 and the STK 394-160. The STK394-160 is not sold through normal distribution channels, they are only sold through Hitachi parts dealers. It’s most economical to purchase them in a Hitachi convergence repair kit which comes with the chips and some resistors.. See Leonard’s convergence repair threads for more info on this.

So far I have repaired two of these sets – one I used the STK392-150 and on mine I used the STK394-160 and both sets have been running fine so far. I believe the STK394-160 is considered to be the superior chip.

Install the STKs to the board – make sure all the legs are straight and into pcb board holes. Press the STK up against the heat sink and move it around just a little to smear the grease around a bit, then install the STK to heat sink mounting screws. This works great as it holds the STK chips for you while you solder them – now solder the STK legs to their solder pads being very careful to not create any solder bridges.

Many times when the convergence amps go out they also take out a resistor or two. Not always, but sometimes. The only real way to test the resistors is to lift one leg out of the circuit and take an ohm reading of it. You’ll need a very accurate meter though. Personally I figure if I’m going to pull one leg up I might as well pull both and just replace the resistor so I usually replace them all with new ones.

In the case of this particular set there are thirteen convergence resistors and they are all located right in front of the STK chips. From left to right the first eleven are orientated vertically. They are:

(all are 5% tolerance metal film resistors)

R854 - 1.5 ohm 1 watt
R855 - 150 ohm 2 watt
R851 - 220 ohm 2 watt
R850 - 2.2 ohm 1 watt
R858 - 3.3ohm 1 watt
R859 - 220 ohm 2 watt
R862 - 1.8 ohm 1 watt
R873 - 220 ohm 2 watt
R863 - 150 ohm 2 watt
R847 - 150 ohm 2 watt
R846 - 1.5 ohm 1 watt

The last two are orientated horizontally, they are:
R842 - 2.2 ohm 1 watt
R843 - 220 ohm 2 watt

Again, I’m a fan of just replacing them all. Case in point, in the set I just repaired all the resistors looked good but they all had their values printed on them and on one the value was no longer visible. If you looked closer the body of the resistor was slightly discolored and the legs were discolored, as was the board where the leg went through to the solder pad. I tested the resistor after I removed it and it still tested OK, but there’s no way I’d trust it. We’re already saving so much money repairing our set ourselves that in my opinion there’s just no sense in trying to cut corners – especially with cheap things like resistors!

Some other notes on the resistors – resistors come in all shapes and sizes, the ones I bought were a little larger than the originals. That’s just fine, as long as they are the right value, wattage, and material they’ll work fine. You’ll note they have long legs and are mounted above the pcb, that’s because they are of a higher wattage and need some room to dissipate the heat so when you mount the new ones make sure you mount them like the originals and not down on the board. I also try to evenly space them apart so they aren’t tight up against each other even if I have to bend around on them a bit.

Here’s a couple before and after pics of my board.
 

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Discussion Starter #15
Once the board is fitted with it’s new STKs and resistors then you can place the board back into the set. I found it was easier to plug cables 4, 5, and 6 in before I remounted the pcb. To remount the pcb just slide the board under the tabs in the board holder, then press down and it should snap right into place. Then I carefully routed the #3 cable back to the silver board at the rear i/o panel and plugged the connectors back in. I did the same for the #3 CRT connector. Then I made sure to route the cable through the wiring holders and re-secured them. Then just reattach the numbers 1 & 2 cables – the round cylinder thing on the #1 cable is held by the wiring holder just to the left of the board.

Remember, these units have the booby trap that disables the digital input if you apply power to it with the rear panel off (this was mentioned earlier, Leonard has a sticky in the JVC repair forum concerning it) so it’s best to completely reassemble the unit before powering it up.

Once mine powered up I did an auto-convergence, then I let it warm up for half an hour and did the auto-convergence again, then I checked the manual convergence but my set was spot on so I didn’t have to perform any manual convergence.

There you have it . . . if anyone has any questions or if I need to make something clearer just post a note and I’ll try to help if I can!

Steve
 

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Steve, I hope you will be able to help me out. I seem to be having similar issues like yours. But before I start ripping things apart I need to ask you something.
Why would the TV shut off when I plug the convergence box wire into the main board? Bad board, resistor, fuse??? Can you help? And while you at it, I need to know where I can get those parts. Do you sell'em or can you at least point me into the right direction??

Thanks a bunch.........
 

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Discussion Starter #17
Hi Lenoxhawk,

I will do my best to help you but the extent of my knowledge on this set is pretty much summed up in this thread!

I'm not following your question . . . exactly which wire are you plugging in to cause the shut down? I hope you're not working on this thing while it's plugged in and plugging/unplugging things willy nilly!

Grab a digital camera and take us a pic . . .

Leonard, the moderator for this forum, has spent a good deal of time putting together some very helpful threads on the common repairs - one deals specifically with convergence so I would suggest you give it a read.

http://http://www.hometheatershack.com/forums/diy-repair-maintenance/5600-crt-based-rptv-convergence-repairs.html

He also has given a list of trusted parts suppliers. I personally have dealt with Acme and Encompass and both have been excellent - great service and no dud parts yet. DO NOT buy convergence ICs off of eBay or such sources!

http://www.hometheatershack.com/forums/diy-repair-maintenance/4396-repair-parts-distributors.html

These JVCs are a breeze to put convergence chips in so you have a very good chance of recovering the set if convergence is the problem!

Take Care,

Steve
 

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Thanks for your quick reply Steve.

Don't worry, I make sure the unit is unplugged and I press the power button to release any possible stored energy from the system-old trick I was told about a few moons back :eek:lddude:
The wire/plug I'm talking about is the one you have to disconnect from the left main motherboard -looking from the front of the TV set. Which is what is making me think the the whole IC board itself might be bad. However, I'll contact the links you gave me and will try to replace all the resistors the way you did.

One more thing, are the ones you replaced were all different values or did you get all the same value resistors? I counted only 11 resistors on mine where you replaced 13 on yours. Any idea?

he model# on mine is AV-48WP30

Thanks, Aziz.
 

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Get the schematic and find out what the values are. Do not rely on what you hear from others.

A shorted convergence IC can easily cause shutdown.
 

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Discussion Starter #20
Hi Aziz,

I'm not so sure your method drains all the energy out of the system so please be careful! If i recall, the CRTs are right above where you're working.

If you didn't buy your chips from a reliable vendor then they may be bad and they can cause the unit to shut down.

If you didn't check and replace the resistors, and had a bad one, that can damage the new convergence amps and cause this sort of problem too. Always buy from a reliable vendor and always check the resistors. I personally normally just replace all the resistors as to accurately check them you have to pull one leg up out of the pcb anyway - if I'm going to half unsolder them I'm just going to go the bit more and fully unsolder and then just replace them.

I have no experience with this set so I speak with no real knowledge of the subject, but it appears this set is very similar to the WP74 sets and the cooler running Hitachi STK394-160 chips work fine in them so I would seriously consider using them if you haven't already purchased the chips. Hopefully Leonard will chime in here and let you know if this sub has worked for him in the past or not.

I have also used the STK392-150 chips in a WP74 set and they worked fine also.

Acme would have the 150 chips, Encompass I believe is where I got my last Hitachis. Both I think would have your resistors, if not then DigiKey would surely have them and they don't charge a premium for small orders.

I just grabbed the service manual and took a quick look at the schematics, it appears there should be twelve convergence resistors to me. They are as follows:

(3) 220 ohm 2 watt metal film resistors R843, R859, R851

(3) 150 ohm 2 watt metal film resistors R847, R863, R855

(2) 1.5 ohm 1 watt metal resistors R846, R854

(2) 2.2 ohm 1 watt metal film resistors R842, R850

(1) 1.8 ohm 1 watt metal film resistor R862

(1) 3.3 ohm 1 watt metal film resistor R858

I hope that helps Aziz, please post back and keep us updated on how your repair progresses.

Take care,

Steve
 
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