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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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Video output transistors for Sylvania Superset
Hello all,
I've got this 20 year old Sylvania Superset TV (model # RNE980) and I'm trying to track down some replacement video output transistors for it. They are in a TO-202 package, made by Motorola, and have the following markings: 513 K 250-3 Anybody know anything about these? Barring any suggestions, I'm probably going to try either NTE228A or NTE171, since they're the only video output transistors with the same pin configuration that I've found. But I hate to stick random parts in to the TV. Thanks -- Elliott |
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The outputs are 250-3. The NTE equivlent is NTE171. What is the problem with the set. Voltages on the outputs are about 100volts at the collector, 4.0volts on the base, and 3.5volts on the emitter. Check the dc voltages first then you can scope the base to see if the correct video waveform is present. If you are missing a color, check the outputs from the color decoder ic (ic50). Be sure to check the CRT for shorts as well. Also check for bad solder joints. Good luck, Bill Christian Technology "E P" wrote in message om... Hello all, I've got this 20 year old Sylvania Superset TV (model # RNE980) and I'm trying to track down some replacement video output transistors for it. They are in a TO-202 package, made by Motorola, and have the following markings: 513 K 250-3 Anybody know anything about these? Barring any suggestions, I'm probably going to try either NTE228A or NTE171, since they're the only video output transistors with the same pin configuration that I've found. But I hate to stick random parts in to the TV. Thanks -- Elliott |
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#3
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"E P" wrote in message om... Hello all, I've got this 20 year old Sylvania Superset TV (model # RNE980) and I'm trying to track down some replacement video output transistors for it. They are in a TO-202 package, made by Motorola, and have the following markings: 513 K 250-3 Transistors are pretty easy to sub, I'd just find some from a scrap TV or monitor and try them, if the pinout is different just twist the leads around to make it fit. |
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For a while there were big red shadows appearing on the right side of
objects on the screen; they were intermittent at first but now they seem to always be there, and they're growing. I don't have the proper tools to diagnose the TV, but I figure I can't do any worse than the TV repair place I took it to did (they charged a big pile of money and didn't actually do anything). There's another (presumably unrelated) problem: when I turn on the TV, it's very fuzzy for about 30 seconds. I figured I'd start with the color thing, and then tackle the focus thing with a can of air and see if anything reacts badly to cold. Then the third thing that bugs me is that the screen overscans about 1 inch too far all the way around. But one thing at a time... While cleaning dust and grime off of stuff, I've noticed two bad solder joints on the main chassis board, both on what appear to be power resistors (R400 and R401). I'd replace them both if I knew for sure what they are because R400 has a big crack along one of the flat sides, and R401 has weird bubbles all over it. But they're both connected to what appears to be high voltage, and I don't want to put the wrong thing in there (maybe they're bleedoff resistors?). Anyway, I'm looking at the output transistor for two reasons: first, the two 12k resistors that are connected to the collector of what appears to be red's output transistor (Q11) are both severely cooked; second, if I unplug J18, the screen has this sort of red/brown color (I assume it should be dark if there's no input signal). My plan at this point is to replace all three output transistors, and for good measure I'm thinking I'll also replace the resistors that are directly in the signal path (for each color, that appears to be four 12k resistors, a 330ohm, a 3.3kohm, a 390ohm, a 150ohm, and a 1.5kohm; I'm debating the pair of potentiometers). Am I going about it right? I feel like I should do the same thing to all three channels; even if balance isn't an issue, if one is dead then maybe the others are on their way out. And although I'm sure that most of the resistors aren't bad, resistors are cheap so I don't see any problem with putting new ones in. Anyway, thanks for the help. -- Elliott "Bill Renfro" wrote in message ... The outputs are 250-3. The NTE equivlent is NTE171. What is the problem with the set. Voltages on the outputs are about 100volts at the collector, 4.0volts on the base, and 3.5volts on the emitter. Check the dc voltages first then you can scope the base to see if the correct video waveform is present. If you are missing a color, check the outputs from the color decoder ic (ic50). Be sure to check the CRT for shorts as well. Also check for bad solder joints. Good luck, Bill Christian Technology "E P" wrote in message om... Hello all, I've got this 20 year old Sylvania Superset TV (model # RNE980) and I'm trying to track down some replacement video output transistors for it. They are in a TO-202 package, made by Motorola, and have the following markings: 513 K 250-3 Anybody know anything about these? Barring any suggestions, I'm probably going to try either NTE228A or NTE171, since they're the only video output transistors with the same pin configuration that I've found. But I hate to stick random parts in to the TV. Thanks -- Elliott |
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Hi Elliott
What did the repair shop tell you? What you are describing sounds like the CRT is dying. The red gun has low emission. That will cause the red bleed on the right side of objects. A weak CRT will also cause the focus problem. Focus gets better after the CRT warms up. When the set is on and warmed up, if you turn the brightness down the red trails should go away, or be noticably reduced. The picture will be dim, but will likely be sharp, and the color will be ok. When you turn the brightness up the red trails will reappear. The 12K resistors on Q11 collector connect to the 193volt source and are likely overheating because of the low red gun emission of the CRT. The other resistors are probably ok. If the picture colors are ok except for the red trail the transistor is probably ok. The only resistors in the signal path are the 330 and the 1.5K. The red drive pot is also in the signal path, but these are likely ok. The overscan could be slight blooming because of load on the high voltage supply. R400 and R401 are thermistors in the power supply. If the set is working they are ok. Remember the set is quite old, and CRTs don't last forever. I think you may only be seeing the symptoms of the real problem. To repair the set you would have to replace the CRT, and the 12K resistors that were overheating. Of course I haven't seen the set and neither of us has done any voltage checks or looked at any waveforms or checked the CRT, so I may be totally wrong. Just my thoughts based on your observations. That's why I wondered what the repair man told you. Good luck, Bill Christian Technology "E P" wrote in message om... For a while there were big red shadows appearing on the right side of objects on the screen; they were intermittent at first but now they seem to always be there, and they're growing. I don't have the proper tools to diagnose the TV, but I figure I can't do any worse than the TV repair place I took it to did (they charged a big pile of money and didn't actually do anything). There's another (presumably unrelated) problem: when I turn on the TV, it's very fuzzy for about 30 seconds. I figured I'd start with the color thing, and then tackle the focus thing with a can of air and see if anything reacts badly to cold. Then the third thing that bugs me is that the screen overscans about 1 inch too far all the way around. But one thing at a time... While cleaning dust and grime off of stuff, I've noticed two bad solder joints on the main chassis board, both on what appear to be power resistors (R400 and R401). I'd replace them both if I knew for sure what they are because R400 has a big crack along one of the flat sides, and R401 has weird bubbles all over it. But they're both connected to what appears to be high voltage, and I don't want to put the wrong thing in there (maybe they're bleedoff resistors?). Anyway, I'm looking at the output transistor for two reasons: first, the two 12k resistors that are connected to the collector of what appears to be red's output transistor (Q11) are both severely cooked; second, if I unplug J18, the screen has this sort of red/brown color (I assume it should be dark if there's no input signal). My plan at this point is to replace all three output transistors, and for good measure I'm thinking I'll also replace the resistors that are directly in the signal path (for each color, that appears to be four 12k resistors, a 330ohm, a 3.3kohm, a 390ohm, a 150ohm, and a 1.5kohm; I'm debating the pair of potentiometers). Am I going about it right? I feel like I should do the same thing to all three channels; even if balance isn't an issue, if one is dead then maybe the others are on their way out. And although I'm sure that most of the resistors aren't bad, resistors are cheap so I don't see any problem with putting new ones in. Anyway, thanks for the help. -- Elliott "Bill Renfro" wrote in message ... The outputs are 250-3. The NTE equivlent is NTE171. What is the problem with the set. Voltages on the outputs are about 100volts at the collector, 4.0volts on the base, and 3.5volts on the emitter. Check the dc voltages first then you can scope the base to see if the correct video waveform is present. If you are missing a color, check the outputs from the color decoder ic (ic50). Be sure to check the CRT for shorts as well. Also check for bad solder joints. Good luck, Bill Christian Technology "E P" wrote in message om... Hello all, I've got this 20 year old Sylvania Superset TV (model # RNE980) and I'm trying to track down some replacement video output transistors for it. They are in a TO-202 package, made by Motorola, and have the following markings: 513 K 250-3 Anybody know anything about these? Barring any suggestions, I'm probably going to try either NTE228A or NTE171, since they're the only video output transistors with the same pin configuration that I've found. But I hate to stick random parts in to the TV. Thanks -- Elliott |
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#7
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The repair shop told me they were replacing the safety cap, which they
didn't do (it took them three weeks to not do it). Oddly enough, the safety cap is the only thing that's ever gone wrong with the TV until now; it burned a 1/4" hole through the circuit board a few months after we bought the TV. They didn't say that anything else was wrong, though I wonder if they even turned it on. The red trails behave exactly as you say when I turn down the brightness, I guess that's a bad sign. It seems weird that low red emission creates more red on the screen, but I don't pretend to understand how the tube works. I'll not worry about R400 and R401 except to fix the solder joints. The set is in fact very old (I remember the phone conversation with the TV repair people ... none of them had ever seen a TV in a wooden cabinet before), but it's been rock solid until now so I hate to get rid of it, especially because I wanted my next TV to hang on the wall, and I can't afford that yet. I'll fix the bad solder joints and replace those couple of resistors, and see what happens. There is a small amount of documentation glued to the inside of the set that has a bit of diagnostic information; I'll try to read that a bit more closely and see what kind of voltages happen on the CRT neck board. Replacing the tube seems a bit excessive given the age of the set, so I guess I just nurse it along for a bit longer. On a side note, I read on the Internet (so I know it's true?) that you can do things like fiddle with the heater voltage to help the tube along for a bit longer. Is this really safe? It doesn't strike me as a good idea, but I like to explore all of the options (at least the good ones). Thanks -- Elliott Bill Renfro wrote: Hi Elliott What did the repair shop tell you? What you are describing sounds like the CRT is dying. The red gun has low emission. That will cause the red bleed on the right side of objects. A weak CRT will also cause the focus problem. Focus gets better after the CRT warms up. When the set is on and warmed up, if you turn the brightness down the red trails should go away, or be noticably reduced. The picture will be dim, but will likely be sharp, and the color will be ok. When you turn the brightness up the red trails will reappear. The 12K resistors on Q11 collector connect to the 193volt source and are likely overheating because of the low red gun emission of the CRT. The other resistors are probably ok. If the picture colors are ok except for the red trail the transistor is probably ok. The only resistors in the signal path are the 330 and the 1.5K. The red drive pot is also in the signal path, but these are likely ok. The overscan could be slight blooming because of load on the high voltage supply. R400 and R401 are thermistors in the power supply. If the set is working they are ok. Remember the set is quite old, and CRTs don't last forever. I think you may only be seeing the symptoms of the real problem. To repair the set you would have to replace the CRT, and the 12K resistors that were overheating. Of course I haven't seen the set and neither of us has done any voltage checks or looked at any waveforms or checked the CRT, so I may be totally wrong. Just my thoughts based on your observations. That's why I wondered what the repair man told you. Good luck, Bill Christian Technology "E P" wrote in message om... For a while there were big red shadows appearing on the right side of objects on the screen; they were intermittent at first but now they seem to always be there, and they're growing. I don't have the proper tools to diagnose the TV, but I figure I can't do any worse than the TV repair place I took it to did (they charged a big pile of money and didn't actually do anything). There's another (presumably unrelated) problem: when I turn on the TV, it's very fuzzy for about 30 seconds. I figured I'd start with the color thing, and then tackle the focus thing with a can of air and see if anything reacts badly to cold. Then the third thing that bugs me is that the screen overscans about 1 inch too far all the way around. But one thing at a time... While cleaning dust and grime off of stuff, I've noticed two bad solder joints on the main chassis board, both on what appear to be power resistors (R400 and R401). I'd replace them both if I knew for sure what they are because R400 has a big crack along one of the flat sides, and R401 has weird bubbles all over it. But they're both connected to what appears to be high voltage, and I don't want to put the wrong thing in there (maybe they're bleedoff resistors?). Anyway, I'm looking at the output transistor for two reasons: first, the two 12k resistors that are connected to the collector of what appears to be red's output transistor (Q11) are both severely cooked; second, if I unplug J18, the screen has this sort of red/brown color (I assume it should be dark if there's no input signal). [...] |
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The red trails behave exactly as you say when I turn down the brightness, I guess that's a bad sign. It seems weird that low red emission creates more red on the screen, but I don't pretend to understand how the tube works. To make it simple, it is not that there is more red. The problem is that the red that is there can no longer be cut off or focused properly at normal brightness levels.. I'll fix the bad solder joints and replace those couple of resistors, and see what happens. Replacing the resistors might help, but the new ones will likely overheat as well. The 12K resistors are a series parallel circuit so you would need to replace all 4 of them. Interesting the total of all 4 is only 12K. I suppose it was cheaper to use 4 smaller resistors than one higher wattage resistor. May have also been a heat concern. There is a small amount of documentation glued to the inside of the set that has a bit of diagnostic information; I'll try to read that a bit more closely and see what kind of voltages happen on the CRT neck board. The neck board voltages run from under 5.0 volts to over 5 thousand volts. The voltages on the collectors of the video output transistors are around 100volts. One side of those 12K resistors goes to the 193volt source. The heavy (usually black or red) wire going to the board is focus voltage between 5 and 6 thousand volts. On a side note, I read on the Internet (so I know it's true?) that you can do things like fiddle with the heater voltage to help the tube along for a bit longer. Is this really safe? It doesn't strike me as a good idea, but I like to explore all of the options (at least the good ones). Yes you could raise the heater voltage and that might help for a while. But, the heater voltage on your set comes from an internal winding on the flyback transformer (high voltage). You would have to disconnect it and replace it with the correct number of windings around the transformer core. To many turns the voltage would be to high and tube would be instant toast. I have seen tube brightners for this. They install between the flyback winding and the tube heaters. If you had one you could use a CRT rejuvinator on the tube. Neither solution is going to provide long term reliability. Both could instantly kill the tube and may require a grey scale setup (adjustment of all the controls on the neck board and one on the main board) afterwards. You might want to save your money and put it on a cheap 25" set to last until you can get that flat screen high def LCD monitor for the wall. Bill Christian Technology |
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"Bill Renfro" wrote in message ... .... | I have seen tube brightners for this. They install between the flyback | winding and the tube heaters. Or install a separate 60 Hz transformer with taps. | If you had one you could use a CRT rejuvinator on the tube. .... From $5 up on eBay, but you need to be able to judge how to configure it to this tube. NM |
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The red trails behave exactly as you say when I turn down the
brightness, I guess that's a bad sign. It seems weird that low red emission creates more red on the screen, but I don't pretend to understand how the tube works. The output transistor for the red colour is driven into saturation because of low feedback, thereby causing the bleeding effect. This problem is most likely caused by a low +200V to the CRT board, or by a weak CRT. Replacing the electrolytics on the +200V line is normally the first thing to try, turning up the screen voltage (G2) is a good measure if the CRT turns out to be a bit weak. --- Met vriendelijke groet, Maarten Bakker. |
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Bill Renfro wrote:
The red trails behave exactly as you say when I turn down the brightness, I guess that's a bad sign. It seems weird that low red emission creates more red on the screen, but I don't pretend to understand how the tube works. To make it simple, it is not that there is more red. The problem is that the red that is there can no longer be cut off or focused properly at normal brightness levels.. I'll fix the bad solder joints and replace those couple of resistors, and see what happens. Replacing the resistors might help, but the new ones will likely overheat as well. The 12K resistors are a series parallel circuit so you would need to replace all 4 of them. Interesting the total of all 4 is only 12K. I suppose it was cheaper to use 4 smaller resistors than one higher wattage resistor. May have also been a heat concern. There is a small amount of documentation glued to the inside of the set that has a bit of diagnostic information; I'll try to read that a bit more closely and see what kind of voltages happen on the CRT neck board. The neck board voltages run from under 5.0 volts to over 5 thousand volts. The voltages on the collectors of the video output transistors are around 100volts. One side of those 12K resistors goes to the 193volt source. The heavy (usually black or red) wire going to the board is focus voltage between 5 and 6 thousand volts. On a side note, I read on the Internet (so I know it's true?) that you can do things like fiddle with the heater voltage to help the tube along for a bit longer. Is this really safe? It doesn't strike me as a good idea, but I like to explore all of the options (at least the good ones). Yes you could raise the heater voltage and that might help for a while. But, the heater voltage on your set comes from an internal winding on the flyback transformer (high voltage). You would have to disconnect it and replace it with the correct number of windings around the transformer core. To many turns the voltage would be to high and tube would be instant toast. Disconnect heater pins at tube. Connect a small bulb (VCR sensor lamp works fine). Observe brightness. Now disconnect the mainboard end of the feed from the LOPT (make sure its NOT the return which is often grounded) thread it once through the core and reconnect it (extending it if required). Observe the brightness, if its dimmer, remove the wire and thread it the other way. Remove bulb and reconnect heater. Soak test it and set up Screen and Focus. Perform grey scale adjustments if not self adjusting. box it up and rReturn to customer with a 3 mopnth money back warrenty and a warning to start saving up for a new TV. -- Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* SPAM TRAP set in header, Use email address in sig. if you must. |
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