Shorted HOT's in newer TV's

[radiotvnut]

Over the years, I've seen many newer solid state TV's with shorted horizontal output transistors. Knowing that they often have help shorting, I usually check things before installing a new HOT. Things such as proper operation of the power supply, bad caps, bad solder connections, and testing the flyback with a ringer. After doing all this, I'll power up the set with a good HOT. Sometimes, I'll get lucky and the set will work. Other times, the HOT will either blow instantly or it will overheat and short again in a brief time period.

I know some of you have been in the repair business for a long time and I'd like to know is there any other way I can possibly keep the new HOT from shorting if there's still a fault with the chassis? Several years ago, a friend had about $10K worth of Sencore equipment and one of those pieces of equipment would perform a "load test" on the entire horizontal sweep circuit; but, I don't have the luxery of owning such expensive equipment. The only thing I have is a late '70's era Sencore flyback and yoke ringer and, in the newer SS sets, the flyback must be taken out of circuit for an accurate reading. And, this is one area where tubes are more forgiving. If there's a problem in a tube HOT circuit, one generally has a little warning. In a solid state set, the HOT can be destroyed instantly. Right now, I'm working on a 32" 2002 Toshiba that uses an oddball HOT that's $10 plus shipping. I resoldered a bunch of questionable connections, replaced a questionable electrolytic cap in the power supply, checked the 130V B+, and performed a ring test on the flyback. Everything seems to be OK; but, I'd sure hate for the new transistor to go up in smoke as soon as I push the power button. $10+shipping for transistors gets expensive at that rate.

As far as older SS sets from the '70's, I don't recall seeing nearly as many from that era with shorted HOT's. And, it was often easy to find the problem on the ones with shorted HOT's. And, those older '70's era sets didn't seem to run as hot. I have a Zenith CCII and a Sylvania superset from the '70's. Both use a metal cased TO-3 style HOT mounted on a decent heatsink. These sets can run for hours and the heatsink will be only slightly warm. Now, take a later model Chinese made CRT set and the HOT heatsink will be very hot after 30 minutes of operation. In the newer sets, they must be running these parts right up to their maximum design limits. That could explain why they don't last as long.

[Findm-Keepm]

One old trick we always used was a 100W litebulb in series with the collector supply to the HOT. Sometimes you can isolate the flyback pin and connect the lightbulb there, other times, break the trace running to the collector and tie it in there. Bulb bright? Too much current running through the HOT, meaning something else is wrong, usually shorted diodes in the scan-derived supplies (flyback secondary(ies), a shorted cap, a high-ESR cap or two in the scan supplies, or something downriver fed by the scan derived supplies (Vert output, audio output, tuner, etc.) If the bulb is dim, low current being drawn by the sweep circuit, so let it run for a few minutes, power down, and check the HOT and flyback temps. Warm? probably ok to restore the collector supply. HOT? look at the tuning side of the fly - the driver xistor (leakage) /driver transformer (shorted turns, intermittent, etc). ALWAYS check for cracks in the area of the flyback - large mass mounted to a flimsy board=crack potential and cracked runs are not uncommon.

With the lightbulb in circuit, the scan voltages will be lower, so don't be alarmed with a shrunken pic, bad pincushion, or other subtleties.

Hope this helps,

[radiotvnut]

Thanks for the information. I'll give that a try.

[zapro]

Sometimes it's the small booster capacitor right next to the HOT that has changed value. If this is not OK the HOT will usually just blow up again when replaced.

[radiotvnut]

I found the suspected reason for the HOT failure in the Toshiba. There was a 33uf, 160V high temp. electrolytic that connected between one terminal of the primary winding of the horizontal driver transformer and ground. This cap had been very hot and the paper was shrinking and scorched looking. The TV worked fine for several days after replacing the cap, HOT, fuse, and resoldering some questionable connections.

Now, if I can just get the owner to pick it up, which seems to be a problem with everything I take in lately.

I also have an older 31" Toshiba that had vertical problems. They won't pick that one up. Then, some woman brought me a severely beat up low end RCA CTC177 console that she just had to have fixed. I've been trying to contact her for estimate approval for 2 months. Every time I call, a man answers the phone, claims she's not home, and will have her call me. Of course, she hasn't called. The next time I call, I'm going to tell whoever answers the phone that she has until Friday to tell me something. After that, it goes to the trash. Then, another guy brought me a Chinese made Yamaha front surround sound system that i couldn't do anything with. He was supposed to have picked it up 2 weeks ago; but, it's still in my way.

While all this is going on, I have tons of MY OWN stuff that I'd like to fix; but, can't do so because everyone else's crap is in my way. I'm just going to have to learn to say "NO" when someone wants me to fix something.

[Findm-Keepm]

Not sure how Mississippi law reads, but mechanics lien laws apply here. After 30 days from the first notice (verbal or written), we would send a certified letter (return receipt requested) giving the customer 7 business days to pick up the set, or it would be disposed of for repair costs. We couldn't charge anything more than what we had in the set, else the difference went to the original owner. Dad sold a lot of sets for 25 bucks or so.

If the customer refused the letter, once it was back in our hands, the 7 days started. Only about half of the folks would come pick them up, and usually with a lame excuse about "why didn't you just call?"" or "I moved recently."
Yeah sure, just gimme my 30 bucks.

On the Toshiba, do you have a VA48 or VA62? Often we would substitute the horizontal drive to see if the problem was in the driver or in the output. Stuff like your cap would be easier to diagnose that way. With the VA62 and an SC61, you could monitor the collector waveform and "see" any irregularities that the driver/output were producing.

The trouble shooting matrix for a HOT running warm or hot was: check the regulator for proper voltage => check the scan derived supplies for proper voltages => install the light bulb => check for temps => check ESR on all driver/scan derived supply caps => sub H drive => ring flyback => break out the magnifying glass to check for cracks. If you got this far, look at the yoke (shorted turn or two), the the return/tuning mylar caps, and even the Xray shutdown circuits (some sets will load the regulator, others disconnect the drive - a leaky transistor will load the drive in some cases).

I recently got an HR Diemen flyback tester, and have modified my matrix to include testing the fly earlier. I haven't found a bad one this way recently, but man does it show the problem when the flyback is bad. I've also got the expanded freq HR Diemen tester (for monittor flybacks) off eBay but haven't even used it. The gold disc with that is full of priceless transformer info though.

Cheers,

[timmy]

i see it this way all these modern sets are only to last just so long and then just throw it in the trash so that we go and buy another and keep the economy up. society is nothing but a throw away society and besides china, mexico,taiwan, hong kong, all have to keep busy building and selling these throw away items, to us. so if we were engineers of electronics we could possibly take these sets and modify them to fix the design flaws that those countrys incorporated into them in the first place we would be able to still use them 20+ years.although the crts did get much better and last longer so i guess they coudnt scimp on eveything,lol. well evey year things just get cheaper and cheaper and well i guess we are forced to live with progress.

[radiotvnut]

Originally Posted by timmy

i see it this way all these modern sets are only to last just so long and then just throw it in the trash so that we go and buy another and keep the economy up. society is nothing but a throw away society and besides china, mexico,taiwan, hong kong, all have to keep busy building and selling these throw away items, to us. so if we were engineers of electronics we could possibly take these sets and modify them to fix the design flaws that those countrys incorporated into them in the first place we would be able to still use them 20+ years.although the crts did get much better and last longer so i guess they coudnt scimp on eveything,lol. well evey year things just get cheaper and cheaper and well i guess we are forced to live with progress.

Yep, that's the way it is now. Right now, one of the local electronics stores is advertising a 42" LCD TV for $399. With a price that low for what most people consider to be the "must have" TV, it makes it difficult to get any decent amount out of a certain good used RCA 35" CRT set that I have. And, in the future, I look for LCD TV prices to come down even more. I can certainly see them selling new 32" TV's for under $200.

That new 42" LCD is composed of many surface mounted parts and service information is probably not readily available. Those two factors limit what the technician can do to such a set. Unless the technician gets lucky and finds that the bad part to be something simple, like a power supply cap, his only option will be to replace the defective board. That is, if the board is even available. Even if the board is available, the TV will probably fail again within a year or two. By that time, the set will have reached the five year old mark, something "better" will have come along, and the set owner will not worry about trying to fix the old one.

As far as CRT sets, I can fix many of those without a schematic. I've seen 20 year old models, that had zillions of hours on them, still working fine or were easily fixable with cheap generic parts. But, those are considered "obsolete" now and people don't seem to mind paying out the butt for a new TV that will be dead in 3-5 years. Here lately, people have been giving me perfectly working CRT sets because they upgraded to a flatscreen. And, it's about gotten to the point where a used CRT TV has no value. Right now, I have a 19" for $25 and a 13" for $15 listed on CL and on another local online classified site. You wanna guess how many replies I've had? NONE! When I first started fooling with TV's a 12" B&W was a quick sale at $25. Now, it's hard to get that much for a good working 19" color set WITH a remote! And, if a good working color TV isn't worth $25 to them; then, they don't need a TV. Let them go buy the latest Chinese off brand flatscreen and it's not going to do them any good to come crying to me when it breaks.

In the past, I've sold used TV's to people and I would see some of these people, often years later, and they would go on about how well the TV was still working. Part of me wouldn't mind picking up some broken flatscreen TV's that I could possibly fix and sell; but, the thought scares me. Knowing how unreliable they can be, all I need is to fix up one of these sets, sell it to someone, and have them back on my butt when it dies in two weeks. And, telling people upfront that there is "no warranty" is like talking to a wall. I can promise you that if the TV you just sold them goes out within a month or two, they will be back with it and they will either be expecting a free repair or a refund, I don't care what they were told prior to the sale. And, if the price of new flatscreen TV's keeps coming down, there will be little resell value on used ones. It will be just like it was when wal-mart started selling new 19" color TV's for under $100. Who's going to pay $50-$75 for a used 19" set when they can get a new one with a warranty for under $100?

[timmy]

its all unbelievable these days well people should not complain about not having money.i went to the dump the other day to ask when spring clean up is to watch for roundies and picked up a 27 inch akai flat screen in the bin came home plugged in, it was dead and it was only 5 years old but this unit was spotless but after 2 hrs and 3 caps and a zener later it works great. still theres nothing like the old sets. this flat screen tv is still selling refurbished between 300-500 bucks so i guess ill hold on to it or ebay it.

[radiotvnut]

One other thing that holds me back on buying broken flatscreen TV's is the price that's often wanted. Back in the day, I never paid over $10 for a broken TV. Now, everyone seems to want big bucks for even the broken flatscreen's. Frankly, I'm not willing to gamble that much money on something that I may or may not be able to do anything with.

As far as everyone thinking they must have the latest thing, I guess that way of thinking has been around since the early days of television. In the late '40's, everyone thought the little 7" and 10" round CRT sets were the greatest. By the early '50's, 17" and 21" sets became common. It was at that point that these small screen sets that were so great just a few years earlier started being replaced by sets with a larger screen. I'd say that by the mid-to-late '50's, the little small screen sets of just 10 years earlier were virtually un-sellable and the only people still using them were the poor and those who used the small screen set for a bedroom TV. Then, color took off in the '60's and that's what everyone had to have. Then, solid state became the norm by the mid '70's and it wasn't too long before people started dumping their tube sets. Then, remote controlled cable ready sets came along in the '80's, etc, etc, etc.

However, the above events are not what ticks me off the most. Up through the '80's, new TV's were, for the most part, quality made and they were not selling for bargain basement prices. Even in my lifetime, I can remember when a 19" B&W cost over $150, a 19" knob tuned color portable was around $350, and a 25" color console cost between $500-$1000 (depending on how nice it was). If you wanted a TV for under $100; then, a 9" or 12" B&W were your only options. Other electronics, such as VCR's and stereo's, were also in the several hundred dollar+ range. Heck, a '78 Sylvania 22" B&W console that was recently resuced from a TV dealer still had the $399.95 prce tag on it. Repair parts usually didn't cost out the butt and repair shops, who stayed busy repairing these sets, were common. And, companies were easier to deal with and they didn't discontinue repair parts 90 days after the set was built.

Starting in the '90's, we started seeing ultra cheap bargain basement priced TV's. TV's such as 27" sets with remote and stereo sound for under $200, 19" TV's with remote for less than $100, 13" color TV's with remote for WELL under $100, VCR's for $39, cheap stereo's for $59, etc. It goes without saying that this junk was built as cheaply as possible and was not meant to last very long or to be fixed. It was also at this point that companies became harder to deal with and repair parts were often too expensive or NLA. It was these actions that put the "mom & pop" TV dealers out of business, as well as many TV shops that USED to make good money at fixing TV's and selling used TV's, not to mention all the AMERICAN jobs that were lost as a result of all the domestic TV manufacturers either going out of business or moving offshore. It all boils down to "big foreign business", who doesn't mind stepping on the "little guy", just as long as they can make the most profit. And, yes, I resent the hell out of it and I refuse to spend money on some modern Chinese TV that is garbage when I can pick up a '70's era TV that is designed to be fixed and will last me for several more years. And, if people think I'm weird; then, so be it.

[timmy]

yes its all true what your saying and its a shame how things have gotten these days, fast paced, throw away,toys people have to have society. no i dont think your weird i think the same way but again we are forced to live in this world of progress and alot of things really suck the way things have gotten.

[Jeffhs]

TVs and everything else nowadays are designed to be thrown out for the trash when they fail, a trend that shows no signs of reversing itself any time soon.

Technology evolves and changes so quickly these days that equipment which was top of the line last year is obsolete this year or even sooner. I don't like that one bit, but unfortunately, as Walter Cronkite used to end the old CBS Evening News, that's the way it is. I found an example of this planned obsolescence business just this morning as I was looking for DVDs to rent from Netflix. I found a few of my favorite classic TV shows still on physical discs, but more and more, Netflix is streaming video to Roku boxes, Nintendo Wii gaming consoles, etc. -- and I can't use the streaming option yet because I don't have such equipment; all I have at the moment is a 19" analog color TV, VCR and a DVD player, and a stereo system with a 3-CD changer (but I haven't used the changer more than a handful of times, since I've ripped most of my audio CDs onto my computer's hard drive).

Thank goodness I still have my DVD and VHS collection, as from what I have read on the Web (on websites such as ZDNet.com, et al.) physical DVDs are on the way to becoming obsolete, as VHS did when DVDs came in, and as vinyl phonograph records did when CDs arrived (although I have read and even have seen on a recent TV program on PBS that vinyl is making a comeback).

How much longer will physical DVDs be around? Since streaming video and audio is the wave of the future, I don't hold out much hope for these discs, either DVDs or audio CDs. Even computer software is moving away from boxed physical discs to downloads directly from websites such as ZDNet.com, PCWorld.com, et al. I do not think audio CDs aren't long for this world either, as many if not most listeners are downloading songs and even entire albums from sites such as Napster, et al. I give audio CDs another five years before they are declared obsolete -- and they probably have one foot in the grave already, given the speed at which technology is evolving. Sony, for example, has shuttered at least one of its CD manufacturing plants, leaving only about two still actively producing these discs. How much longer these remaining plants will continue to make these is anyone's guess, although personally I don't think they will be around very long anymore -- I give them perhaps five years at most, although most such plants will probably be gone long before then if streaming video and audio continue to change the media landscape.

[timmy]

all the good and great is gone and all this throw away progress will be forgotten.....