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#46
08-24-2008, 06:52 PM
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No TV is designed for the "long haul" anymore. Companies want to keep you coming back for more and this will not happen if their TV's last 30 years. I still like Sanyo TV's and I think they are the best buy for the money, given what else is out there. But, even the newer Sanyo TV's are not as well made as the ones from the early to mid '90's.
I believe that all you need to do is touch the temperature probe to the heatsink and it should register a reading. 
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#47
08-24-2008, 07:15 PM
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Well, the new HOT shorted. Here's the details:
Played the TV for over a half hour. I watched maybe half of America's Funniest Home videos, and about 5 minutes of the Simpsons before it went. I attached my multimeter's temperature probe to the heatsink, about maybe an inch away from the HOT (close as I could safely get it), and it got up to a high reading of 198 degrees Farenheit. This was with the back of the TV off and some mild air movement, not to mention the extra heatsink I put on. Also, I noticed that the TV's picture concaved slightly when the picture had a lot of white in it. PS: Got rid of the channel number staying on screen. Thank you giant universal remote!
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#48
08-24-2008, 07:46 PM
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195 F is MUCH too hot for a transistor. Anything above about 70 C would make me worried. That 150 C rating is probably the junction temperature which will be a lot hotter than the heat sink, or case. It's also probably the absolute maximum rating, not the idea rating.
You either have a problem in the HOT collector circuit, or a problem with the drive to the base. A HOT needs to be turned on and off quickly and fully by the base signal. If it's not, it will over heat and fail quickly. The fact that the sides were pulling in is a definite problem. I'm not familiar with this set, so I can't really give you much advice there.
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#49
08-24-2008, 07:58 PM
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Quote:
Could there be a bad cap causing the HOT to overheat and short?
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#50
08-24-2008, 08:28 PM
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I have seen bad caps in the horizontal drive circuit cause this type of problem.
As a general rule, no transistor or IC should ever get too hot to touch. Certainly nothing in a TV should be able to boil water.
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| Audiokarma |
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#51
08-24-2008, 10:58 PM
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Look for any small electrolytic caps in the horizontal drive circuit. Also, trace that B+ input pin of the flyback back to the power supply and I'm sure you'll find at least a 47 uf, 160V cap in the circuit. Pull that cap and check it. I had a sharp come my way with a shorted HOT. I replaced the HOT and the set still had some picture pulling and shifting. It turned out to be a defective electrolytic cap in the B+ line.
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#52
08-24-2008, 11:04 PM
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Quote:
EDIT: Found a bad 4.7uf @160 volt cap in the power supply. As I have no boards with a suitable replacement, I'll have to suspend the hunt until I can get a new cap.
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#53
08-24-2008, 11:23 PM
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That's probably the culprit. If you've got a local electronics parts house besides ratshack, you should be able to get it locally. Remember, you can go with a higher voltage rating on the new cap if a 160 V is not available.
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#54
08-24-2008, 11:32 PM
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Oh I know just the place!
I just need some money... blew my budget on the HOT's and shipping... Damn I hate being poor. Also, I'd probably go with higher voltage anyway. With caps, I like to go with a voltage well above what is needed, and 105c caps, even if the old cap was an 85c one. Less wear on the new cap.
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#55
08-24-2008, 11:39 PM
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My local electronic store wanted $10 for a 100 uF, 350V cap. I told them no thanks. I can order the same cap for probably $3. This is one of those stores that used to cater to the the radio & TV repairmen. Now, they cater to mostly commercial needs and I don't think they're making too much money at that.
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| Audiokarma |
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#56
08-24-2008, 11:46 PM
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I could probably get the cap for $5 at my local electronics store (NOT Radio shack)
... I just need the $5... Hopefully I'll either get paid what I'm owed by a "friend', or someone will buy a TV off me. Most of my replacement caps come from junked TV boards that I save (I test them beforehand) However, i don't have a single board with a 4.7 that's rated for 160 volts.
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#57
08-25-2008, 12:33 AM
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Do you have any low cost / free means of advertising your TV's? Around here, we have a classified paper that's sold at the convenience stores and we have a call in swap and sell program on a local AM radio station. There's another paper that reaches more people; but, it cost $17 for an ad. I'll sometimes go that route if I have many TV's. In some ways, the DTV transition is hurting the sell of ordinary TV's. People would rather spend their money on a modern set. In other ways, there are people that can't afford a FP set; so, they are happy to give $100 for a nice 27" analog set. I just wish the days of getting $100 for a 19" rotary tuner TV would come back; but, I know that's not going to happen.
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