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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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CTC169 and sub flyback 232191 incompatability notes
I ran into this myself a few times. Without the Sencore somehow you need to
excite the fly. With nothing connected to the anode output, shorting the black wire to the normal ABL pin (not sure of the number right now, but it's the one with the spark gap) will distort the waveform on a direct view fly, but not on a PTV fly. Doing this on a Sencore, you should get a "bad" indication with the short in place. I don't know if it will show up on a normal flyback ring tester. It would probably have to be excited to the point where it's putting out at least 600-700 volts to show up for sure. With lower voltages you might get false negatives on some because of normal tolerances. Let's put it this way, however you excite it, if there is any + voltage on the black wire it is probaly the wrong part. You should have a negative voltage there if anything. Of course now a few of us have some flys in stock, now to figure out what they're for. Of course they will probably work in many CTC169s but they might put out a bit too much HV for a 27". I know this much, if you reroute the ABL line as in a direct view and insulate the black wire a PTV set will run, but you should disconnect the power to the HV booster board or it will be going full blast trying to regulate. I actually had to ship one like that in the past, the customer was getting to be quite the hothead, but he was told about it. It was safe, but we told him about, like when something blows up the image will bloom. As far as we could tell, before we had this thing figured out, the focus voltage going into the secondary of the HV boost transformer had caused it to fail. We are pretty sure of this because in the end the only thing it took to fix that set was the flyback. Of course we went through the lytics in the power supply and we usually have a look at the 15V line on these, none of these other things were the cause of failure. JURB |
#3
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CTC169 and sub flyback 232191 incompatability notes
BTW, I forgot to mention, even though I knew about this, we do appreciate the
heads up on it. Speaking of heads ups, maybe it's time for another one. A few of us have been bandying around the idea of certain subject lines in here. I think "Heads Up:_____" wouldn't be a bad idea. From time to time we could post some unusual stuff like this, like the STK4274s with lot# 7027 will not work in Hitachis, the subwoofer on XBRs and so forth. I'll let you go now, I'm going to write one. Wouldn't be a bad idea to encourage others to do likewise. JURB |
#4
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CTC169 and sub flyback 232191 incompatability notes
"JURB6006" wrote in message ... Of course now a few of us have some flys in stock, now to figure out what they're for. Of course they will probably work in many CTC169s but they might put out a bit too much HV for a 27". I know this much, if you reroute the ABL line as in a direct view and insulate the black wire a PTV set will run, but you should disconnect the power to the HV booster board or it will be going full blast trying to regulate. I actually had to ship one like that in the past, the customer was getting to be quite the hothead, but he was told about it. It was safe, but we told him about, like when something blows up the image will bloom. As far as we could tell, before we had this thing figured out, the focus voltage going into the secondary of the HV boost transformer had caused it to fail. We are pretty sure of this because in the end the only thing it took to fix that set was the flyback. Of course we went through the lytics in the power supply and we usually have a look at the 15V line on these, none of these other things were the cause of failure. JURB In my case, I used a "direct view" flyback in a PTV and routed the ABL pin to the HV regulator and simply insulated and didn't use the black wire ( focus pin) After a day or two the flyback crapped out. As for why, not sure, mighta been the fact that it was salvaged from a 36" set that had been struck by lightning. Or it mighta been because I later discovered that a little 820pf cap was shorted out on the HV splitter and was impeding the negative feedback to the regulator circuit, which I will have to guess probably caused the HV regulator circuit to try to boost the HV as much as it could, thinking that the HV was low. However, before I had hooked the HV lead back up to the HV splitter, I has measured it at 28KV so I assumed all was ok with the regulator. I suppose it's entirely possible that the 820pf cap died at the same time the flyback did,, chicken,,, egg? Anyway, if I hadn't already fixed over 12 different things wrong with this TV,, I guess I'd be adventurous enough to experiment some more with this. That's right,, this was the TV from HELL. Now, only thing left to do is to add up how much money I lost by fixing it :-) Thanks for the tips -- DM-- |
#5
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CTC169 and sub flyback 232191 incompatability notes
"JURB6006" wrote in message ... I ran into this myself a few times. Without the Sencore somehow you need to excite the fly. With nothing connected to the anode output, shorting the black wire to the normal ABL pin (not sure of the number right now, but it's the one with the spark gap) will distort the waveform on a direct view fly, but not on a PTV fly. Doing this on a Sencore, you should get a "bad" indication with the short in place. I don't know if it will show up on a normal flyback ring tester. It would probably have to be excited to the point where it's putting out at least 600-700 volts to show up for sure. With lower voltages you might get false negatives on some because of normal tolerances. Let's put it this way, however you excite it, if there is any + voltage on the black wire it is probaly the wrong part. You should have a negative voltage there if anything. Oh, I forgot to mention,, not having a fly ringer, I simply used my trusty old ancient (relic from the past) vacuum tube 350V bench supply. Reasoning that, with a certain amount of voltage, the diodes in the HV secondary should forward conduct in one direction. The simple test here is that the flyback for the PTV should not have any forward conduction to any one of the pins on the bottom of the flyback, whereas the flyback for the "direct tv" would. Anyway, I was able to verify that my new flyback was indeed as intended for a PTV, as I had no forward or reverse conduction to any pins on the bottom of the fly,, only conduction to the black wire (as it should be for a PTV fly) Interestingly enough, I didn't get any forward conduction until close to 100 volts. So, if anyone wants to try this then, be advised that you may need a voltage source of 120 volts or more. Also be advised to use a current limiting resistor as you don't want to fry the diodes in the flyback HV winding. I played it safe and used 47K I imagine that one could fabricate a 160 volt source by simply rectifying the AC line with a diode and capacitor. ( Bearing in mind to be careful with this unless you also use an isolation transformer) In fact, I suppose that if one wanted to, they could simply rectify the line with the diodes in the HV winding itself to feed a 47K load resistor and simply look at the the polarity of the rectified pulses on the scope Only, I guess here, again you would need an isolation transformer to use the scope, unless you used both vertical channels set to invert and add. ah! here's an idea for a simple tester, use the aforementioned setup with an LED in series with it. The LED would have to be set up to conduct in the same direction as the diodes in the HV winding of course. Ok, lets see how this would be, one wire from the wall AC would go to the cathode of the LED, then the anode of the LED would hook up to red HV wire from the flyback, then the other wire from the wall would go to a 6K-10K resistor and from there to a test probe that you could use to probe the pins under the fly or the black wire. However, AKAIK, the black wire would conduct on either flyback, so the real test would be whether or not there's conduction to the pins under the flyback. ( actually the only two pins in question would be the two that are completely opposite the side where there are no pins) Like you, I can't recall which one of these is the one in question, no biggie to check both though. A refresher,, conduction ( lighting of the LED) to either of these two pins would indicate that the flyback is for what you termed a "direct tv". If the LED doesn't light up when probing the pins under the fly, then its a fly for a PTV Though the black lead would conduct on either flyback, (PTV or direct tv), perhaps there might be a slightly noticeable brightnesss difference in the LED that would indicate whether this lead is being used as a focus lead ("direct tv") or whether it is the low side of the HV winding ( PTV). Dunno,, maybe someday I'll build this complicated circuit and see :-) =^^= DM |
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