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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Sony KV27S15 weak CRT
This set has a weak CRT and blinks on and off. I jumped the two
parallel resistors on the CRT board which are in series with the heater and the pix came on. The same thing happens if I tweek the screen up slightly. I decided to do both and the picture seems to be holding. I realize this is a "deadman walking" however I would like to give the customer some rough idea as to life expectancy. Does anyone have any information, after returning a set like this, (with an explanation of course), perhaps feedback from customers on this? Also, it occurred to me that jumping the series heater resistor will increase the heater current through the flyback. Should I be overly concerned about this on a set whos' days are numbered anyway? Thanks, Lenny Stein, Barlen Electronics |
#2
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Jumping the resistors will certainly raise the heater current. This will
hasten the life in the CRT that is left. But, considering that it is almost gone anyways, there is not much difference here. As the CRT is going weak, the auto controlled bias circuits keep biasing the CRT more and more to maintain its performance as best as possible. Eventually they run out of range, and cannot maintain the proper current. This also means less anode current, and thus the set is designed to go in to protection when the anode current is below a certain amount. Raising the heater current allows for a greater amount of emission. I have seen tubes last anywhere from a few days to a few months like this. There is no accurate way to predict anything with this type of affair. The greater heater current may also cause the flyback to run a bit warmer, and it may also put a bit more of a load on the horizontal output transistor. This area is a bit robust, and should normally be able to take the added load. After running the set for about an hour with some type of a cover over it, if you can, take a temperature reading of the horizontal output transistor. It should not exceed about 60 to 70 degrees Celsius. At about 80 to 90 degrees Celsius, the transistor would be working at near its maximum temperature range for long duration operation. -- Jerry G. ====== wrote in message oups.com... This set has a weak CRT and blinks on and off. I jumped the two parallel resistors on the CRT board which are in series with the heater and the pix came on. The same thing happens if I tweek the screen up slightly. I decided to do both and the picture seems to be holding. I realize this is a "deadman walking" however I would like to give the customer some rough idea as to life expectancy. Does anyone have any information, after returning a set like this, (with an explanation of course), perhaps feedback from customers on this? Also, it occurred to me that jumping the series heater resistor will increase the heater current through the flyback. Should I be overly concerned about this on a set whos' days are numbered anyway? Thanks, Lenny Stein, Barlen Electronics |
#3
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I did the same but jumped with a .5 ohm to limit the inrush somewhat
(KV2786R) Been 2 years, no effect on the flyback but I was still unsatisfied with the picture. The back of the tube was still clear with no signs of "silvering" I took a chance with an old BW Rejuvenator. I wired it to a color CRT socket and gave the guns a "shot" one at a time. It paid off, I was lucky. -Joe wrote in message oups.com... This set has a weak CRT and blinks on and off. I jumped the two parallel resistors on the CRT board which are in series with the heater and the pix came on. The same thing happens if I tweek the screen up slightly. I decided to do both and the picture seems to be holding. I realize this is a "deadman walking" however I would like to give the customer some rough idea as to life expectancy. Does anyone have any information, after returning a set like this, (with an explanation of course), perhaps feedback from customers on this? Also, it occurred to me that jumping the series heater resistor will increase the heater current through the flyback. Should I be overly concerned about this on a set whos' days are numbered anyway? Thanks, Lenny Stein, Barlen Electronics |
#4
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Jumping the heater resistor on that set can cause immediate failure of the
heater on startup due to the excessive inrush of current. Perhaps simply taking its value down by 1/2 would not be so bad as the resistor will still limit the inrush current somewhat. The G2 increase is usually the best bet. If you know exactly what you are doing and have the schematic on hand, you can 'fiddle' with the akb feedback resistors on a weak gun to make the akb levels closer. What them on start up on the oscope. Less than 1 year is typical. I usually tell people to start looking and shop around for the lowest price on the best tv set they are willing to buy. With the impending transition to digital, might not be a bad time to start shopping. David |
#5
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"dkuhajda" bravely wrote to "All" (09 Dec 04 19:20:11)
--- on the heady topic of " Sony KV27S15 weak CRT" dk Subject: Sony KV27S15 weak CRT dk From: dkuhajda dk Jumping the heater resistor on that set can cause immediate failure of dk the heater on startup due to the excessive inrush of current. The heater filaments are rather tough. In fact the CRT is evacuated by running the filament white hot and igniting the "getter" which removes any remaining gas the vacuum pump didn't. For example a 6 volt crt filament is designed to be run at well over 10 volts for that purpose. The resistors are there to protect the flyback output from the surge not the filament. dk Perhaps simply taking its value down by 1/2 would not be so bad as the dk resistor will still limit the inrush current somewhat. Okay, it is wise but as explained it may not be needed. dk The G2 increase is usually the best bet. If you know exactly what you Increasing G2 won't help if the emission is too low. The picture will be brighter but it will "posterize" due to the video limiting. It's okay if all you watch are cartoons, though. ;-) A*s*i*m*o*v .... I ran Doublespace on my monitor & get 2 more TV channels. |
#6
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"Joe" bravely wrote to "All" (10 Dec 04 01:53:02)
--- on the heady topic of " Sony KV27S15 weak CRT" Jo From: "Joe" Jo I did the same but jumped with a .5 ohm to limit the inrush somewhat Jo (KV2786R) Jo Been 2 years, no effect on the flyback but I was still unsatisfied Jo with the picture. Jo The back of the tube was still clear with no signs of "silvering" Jo I took a chance with an old BW Rejuvenator. I wired it to a color CRT Jo socket and gave the guns a "shot" one at a time. It paid off, I was Jo lucky. Jo -Joe Sometimes the cathode gets dusty and this hinders the emission. The rejuv clears away the film and restores emission. Sometimes all the grids get dirty and no amount of rejuv will clear that. A*s*i*m*o*v .... I know flyback, ultor, and 47 other dangerous words. |
#7
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"Ultor" now thats one I haven't heard in awhile....
Lenny. |
#8
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Oh BTW, thanks for everyones opinions and advice. It is very much
appreciated. Lenny. |
#9
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"Ultor" now thats one I haven't heard in awhile....
Lenny. Heheheh. "The ultor zapped me!" "What? I think you've been watching too much 'Flash Gordon.'" "No. I forgot to arc it to the DAG first!" - Reinhart |
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