stk replacement issue

**ssgmccoy** · **09-04-09, 12:14 PM**

I have an issue with a JVC AV-65WP74. I'm not a TV repair specialist. I do know my way around electronics fairly well however and I work on analog/digital medical systems among other things. Several years ago I replaced convergence amps in a Toshiba TV I had and didn't have any issues. My sister gave my mom the above JVC TV. She doesn't have a lot of money, so I'm trying to fix it for her.

When I first tested the TV it wouldn't converge. However, it powered up and was fine otherwise. I had some STK392-110 chips from the Toshiba repair because I had ordered extra. Originally the JVC TV came with STK392-110 amps, but my sister had them replaced and the tech used STK392-150 amps a couple years ago. I replaced the 150 amps with the 110 amps I had. The TV ran for an hour or so while I was adjusting the convergence. Then, it powered off and started a low thumping noise, which I hear is an overcurrent condition detected. I thought these old 110 amps may have been the problem (I didn't get them from a reputable source). I ordered 180 amps to replace them both. I soldered in the 180 amps and then verified all the resistance values of the resistors on the board. I bought replacement resistors, but these all read fine so I decided not to replace them. After installing the board, within about 15 mins the TV powered off and started the low overcurrent thump again. The 180 amps were purchased from MCM. Just for good measure, I replaced all the resistors on the board...but I believe one of the 180 amps have already blown. I noticed that one of the heatsinks was really hot and the other was fairly cool right after it powered down.

The only parts that were touched since the beginning until the power down were the convergence amps. Because the TV powered on and stayed on just fine until the replacements, it leads me to believe it has to be with these amps. I have replaced all the resistors now and checked the diodes on the convergence board (although I'd be suprised if the resistors were the issue since they tested ok). I can buy more amps and replace them. But, before I throw more money down the drain, I'd like some other input here. Do you think the resistors could have read fine, but still had issues at operating current/temp? What can cause the amps to go up in smoke? I just don't want to throw new amps in here and then have the same issue 15-60 minutes later with more smoked amps. Thank you.

**ssgmccoy** · **09-04-09, 01:53 PM**

Just one thing to add to my question. The TV seemed to run fine the first time for quite a while (over an hour). I was attempting to adjust the convergence when it eventually went out. Is it possible to overdrive the ICs? It was almost like I hit some value in memory it didn't like and poof...amp was toast. Second set of amps didn't last nearly as long...like a setting in memory overdrove the new ones and toasted them as well. Only way I see to reset memory is in the menu options...but if these burn up prior to me being able to reset the memory...then I'm in a pickle. I guess I could by a new memory IC and replace it. I would think if my soldering wasn't good or there were other problems the amps wouldn't have lasted as long as they did. But, like I said...I'm not a TV repair tech. I appreciate any insight you all could give me.

**lcaillo** · **09-04-09, 07:46 PM**

Your thread has been moved to the JVC forum to maintain forum organization.

Did you read the first ten posts of the convergence repair thread very carefully. If you did, you would know to check the power supplies to the ICs, which is likely your problem.

My guess is that you either had a weakened fuse that gave out after running the new chips a while or did something to blow one. With one of the +/- supplies open, you can easily blow an IC, or if you are lucky the set will just shut down. Check the supply voltages or check the fuses. IIRC, they are small black semiconductor circuit protectors that look like small transistors with two legs.

Be sure to buy replacement parts from the recommended vendors only.

**ssgmccoy** · **09-09-09, 02:00 PM**

Are the small transistor-looking fuses you are talking about on the convergence board with the convergence amps or on another board? One thing I noticed...looking around inside...there was some gray silicone-like chunks on the bottom of the cabinet. I noticed the three tubes had been glued in place with a lot of this substance. The glue is cracked on all three and the glue has all broken and fallen off of the tube on the right side of the TV (left as you face it). My sister said the convergence problem happened after she moved the TV to clean behind it. We transported the TV on a trailer to my house and it may have bounced around quite a bit. I'm not sure how important this glue is or what happens if these connections fail. Thank you for your help.

**lcaillo** · **09-09-09, 08:46 PM**

They are usually in the power supply.

The glue itself is simply there to keep things from coming loose in transit. It is irrelevant if the connections are solid.

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