Convergence Repair Initial Success then Failure - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 10 Old 07-13-08, 11:38 AM Thread Starter
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Convergence Repair Initial Success then Failure

Hello,

I have a Panasonic PT-53TW53 53 in. Rear Projection HDTV. Recently, the TV would not power on and flashed the service code indicating a problem with the convergence circuit. After much research on the net (mainly the great thread here by lcaillo - Thx!) I decided to tackle the repair myself by replacing the two (STK392-110) convergence amps in the set. I also checked the resistors and on first pass and nothing seemed out of whack, one 2.2 ohm 2 watt resistor was slightly discolored but read consistently with the other 2.2s on the board.

Anyway, after I replaced the STKs, I turned on the set an got a beautiful picture. Victory, I thought…but a few minutes later the set powered off and I was back at square one. Upon further review of the board I now see that two resistors are discolored. Both 2.2 ohm 2 watt (+/- 5%). They read 2.7-2.9 ohms, out of spec. There are a total of 6 such resistors in the convergence circuit and they all read the same high level, but only two are discolored. On my first review I dismissed this as a problem as they all read high so I attributed the issue to my meter.

I now plan on replacing all six resistors and the amps (again). I bought the svc manual for the tv but there is no clear schematic for just the convergence circuit. My question is, do you think replacing the six resistors and amps is the way to go? or should I have a Panny tech handle the repair?

I was so proud of my desoldering/soldering work...I'd love to see this to completion by my own hand. At this point, it's not a matter of $$$, more so a return on the investment I've made so far.

Thanks for any and all help.

Jerry
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post #2 of 10 Old 07-13-08, 06:21 PM
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Re: Convergence Repair Initial Success then Failure

A 2.2ohm resistor reading 2.7-2.9 in circuit shouldn't be anything to worry about. It does sound like you have one or both of the convergence amps that has gone bad again. I would also suggest you look through the entire convergence circuit for a cold solder or loose connection. That could be causing the problems.
Have you checked the supply (+Vcc) voltage to the convergence amps? Make sure that voltage is within specs.
post #3 of 10 Old 07-13-08, 06:32 PM
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Re: Convergence Repair Initial Success then Failure

Quote:
da_ezman wrote: View Post
A 2.2ohm resistor reading 2.7-2.9 in circuit shouldn't be anything to worry about. It does sound like you have one or both of the convergence amps that has gone bad again. I would also suggest you look through the entire convergence circuit for a cold solder or loose connection. That could be causing the problems.
Have you checked the supply (+Vcc) voltage to the convergence amps? Make sure that voltage is within specs.
Well, it could be something to worry about. Some meters will have a few tenths of an ohm in the leads that is not compensated for, so it could be that. It could also be that you are reading the yoke resistance and the resistors are actually open. As stated in the convergence thread, the resistors should be checked with the yoke leads unplugged and the chips removed. Sometimes, to be sure, depending on the circuit, you have to lift one side of a resistor to test it. It is best to simply replace any that are discolored. My money is on an open resistor. Certainly could be a bad IC, but if you bought them from a reputable supplier as suggested, not likely, even though you used the inferior STK392-110 again. The problems with these are usually repeat failures months or years down the road. If you used any vendor other than the ones listed you may have received bad parts, which is very common with this IC.




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post #4 of 10 Old 07-13-08, 08:23 PM Thread Starter
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Re: Convergence Repair Initial Success then Failure

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lcaillo wrote: View Post
Well, it could be something to worry about. Some meters will have a few tenths of an ohm in the leads that is not compensated for, so it could be that. It could also be that you are reading the yoke resistance and the resistors are actually open. As stated in the convergence thread, the resistors should be checked with the yoke leads unplugged and the chips removed. Sometimes, to be sure, depending on the circuit, you have to lift one side of a resistor to test it. It is best to simply replace any that are discolored. My money is on an open resistor. Certainly could be a bad IC, but if you bought them from a reputable supplier as suggested, not likely, even though you used the inferior STK392-110 again. The problems with these are usually repeat failures months or years down the road. If you used any vendor other than the ones listed you may have received bad parts, which is very common with this IC.
Thanks for the advice. Just to clarify, I removed both discolored resistors and they still tested at 2.7-2.9 ohms. (same as the others, still on the board) Why wouldn't this be an issue if the spec'd tolerance is +/- 5% which means they should be reading 2.09-2.31 ohms? BTW, I also noticed in the Hitachi kits (that include both ICs and resistors) it is the six low ohm resistors that are included in the repair kit. It looks like the low value resistors more likely to fail.

As for the ICs, i got them on EBAY from a dealer claiming they were made in Japan original Sanyos. The markings on the ICs themselves were not consistent (in terms of production date and size/font of lettering and #'s.) Maybe one or two were bad/fake. - My bad.

I didn't go with the STK394-160 as recommended for fear of these not working with my particular TV. Can anyone confirm as to whether they would work in this particular application?

At this point I am thinking these six resistors and going to the 394-160s. (although these seem hard to find at the reputable distributors)

Thanks again,
Jerry


Update: I can't find the 394-160s at any rep dealer. Is there another alternative? (e.g. STK392-150)

Last edited by xmonger; 07-13-08 at 10:29 PM. Reason: update
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post #5 of 10 Old 07-14-08, 06:22 AM
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Re: Convergence Repair Initial Success then Failure

I wish that I could get through to people BEFORE they buy these ICs. I have heard of so many people getting burned by bad replacements for these chips that I cannot count them. Use ONLY the suppliers that I have listed. If you use the STK394-160 buy them ONLY in the Hitachi kits, not as individual parts, even though you will not need the resistors. This assures that you get OEM parts and usually the lowest price.

As I said above, your meter may not zero out the lead resistance and you may be adding that to your measurement. Regardless, when in doubt, replace the parts. They are too cheap to waste time and effor guessing. Also, triple check your solder work and make sure that you have the supply voltages at the ICs for BOTH positive and negative supplies.




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post #6 of 10 Old 07-14-08, 09:47 AM Thread Starter
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Re: Convergence Repair Initial Success then Failure

Quote:
lcaillo wrote: View Post
I wish that I could get through to people BEFORE they buy these ICs. I have heard of so many people getting burned by bad replacements for these chips that I cannot count them. Use ONLY the suppliers that I have listed. If you use the STK394-160 buy them ONLY in the Hitachi kits, not as individual parts, even though you will not need the resistors. This assures that you get OEM parts and usually the lowest price.

As I said above, your meter may not zero out the lead resistance and you may be adding that to your measurement. Regardless, when in doubt, replace the parts. They are too cheap to waste time and effor guessing. Also, triple check your solder work and make sure that you have the supply voltages at the ICs for BOTH positive and negative supplies.
Lcaillo, thanks again. I hope others can learn from my mistake. Even when vendors claim original Sanyo parts, you don't always get them.

I can't find the 394-160s, even in kits, from any reputable dealer. I just ordered the STK392-150s from Acme along with the resistors. The 150s should be better than the 110s, I hope.

Finally, I will triple check all solder work, however, I am a little unclear as to how to check the supply voltages.

Currently, I have removed the bad ICs. Should I replace the resistors and put the board back in the TV (without new ICs) and check the voltages? Also, I'm not how to exactly take the readings. I'll have to hit the svc manual I guess.

Thanks,
Jerry

Last edited by xmonger; 07-14-08 at 11:10 AM. Reason: re-phrase question
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post #7 of 10 Old 07-14-08, 09:31 PM
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Re: Convergence Repair Initial Success then Failure

Any Hitachi parts distributor, of which I have several listed in the vendors, will have the kits.

I don't understand what is difficult about measuring the voltages. Black lead on ground like the tube bulkhead and red lead to each pin. If you see the +/- voltages in the 24-30 volt range on some of the pins the supply is getting to the IC. Really, if this is not a concept that you understand, you should probably be leaving the repair to a professional.

There is no problem running the set with the ICs off of the board. This allows you to verify the supplies and to check for offsets on the inputs to the chips. It is NOT ok to run the set with the chips installed and bad or missing resistors, nor with the convergence yokes disconnected.




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post #8 of 10 Old 07-16-08, 11:32 PM Thread Starter
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Re: Convergence Repair Initial Success then Failure

Update

I ordered the STK392-150s and six 2.2ohm resistors from Acme on Monday afternoon and received the parts today. The ICs from Acme definitely had a different "feel" and look than the Ebay STK392-110s. I am confident that the ICs from Ebay were not original Sanyos.

Anyway, I replaced everything this evening, and the TV works great. I had the set on several hours with no problems. I'm keeping my fingers crossed that it stays this way.

I don't know if it was bad parts or missing a resistor the first time around, but lesson learned. Buy parts from reputable vendors only.

Lcaillo, many thanks again, your posts were invaluable to me.

Jerry
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post #9 of 10 Old 03-17-10, 05:44 PM
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Re: Convergence Repair Initial Success then Failure

Hey Leonard (Icaillo) I have the same TV and need the parts list referenced in this thread to fix my PT56TW53G. I tried to IM you via AIM but you are logged out. My AIM name is rasdamaan01. Gimme a shout please.

-ras
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post #10 of 10 Old 03-17-10, 08:29 PM
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Re: Convergence Repair Initial Success then Failure

Please start a new thread for a new problem and discuss it publicly, not in PMs or IMs. Parts lists are available in the service manual which we recommend you have before attempting any repair. Please read the first ten posts in the convergence repair thread very carefully:

http://www.hometheatershack.com/foru...e-repairs.html




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