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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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Magnavox RH8524AK08 Confusion...
Ok,
Now I'm really confused... I got a parts list and schematic for the set however the board revision is not in my set. The Deflection board is B10326. C44 is burned and marked as follows: MDC 680K N3300 2KV The schematics I have show .001 or 470pf for this cap. C43 has the following markings: 2n6 J 2000V Phillips 376 KP/MMKP HQ 90 12 The schematics I have show .0086 or .0091 for this cap. Does anyone have the correct value for C44? The electronics place I went to indicated 680pf while all info I can find indicate it would be marked 681K for 680pf and 680K would be 68pf. Thanks! Kirk S. |
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"Bill" wrote in message
... In article , says... snip C43 has the following markings: 2n6 J 2000V Phillips 376 KP/MMKP HQ 90 12 Are you sure that isn't 8n2? Look real close. Crud, I've got Tylenol medicine head! 6n2 for sure! It is a blue rectangular box about 1" long by .25" wide by .75" high. Got out a magnifying glass and checked it again. The schematics I have show .0086 or .0091 for this cap. Does anyone have the correct value for C44? The electronics place I went to indicated 680pf while all info I can find indicate it would be marked 681K for 680pf and 680K would be 68pf. Some makers don't use the third digit as a multiplier until they need it. The 470pF caps on some of these boards are marked 470K Yeah, I guess I'd need to find some older literature and manufacturer data to determine what the markings mean. These boards went through several revisions. As near as I can tell, the earliest green boards with square feed-through pegs used C43 8600pF and C44 1000pF. Then they did away with the feed-throughs and used C43 9100pF and C44 470pF. Then they updated to a different sweep transformer and used C43 8200pF and C44 680pF. I have examples of all three varieties on the scrap shelves. Some of the late updates may not have made it into the service manual supplements. The board has a sticker indicating that it is a replacement from 1990. Jumper B30 has been cut. My literature indicates panel is A10320 instead of B10326. The short answer is to use whatever the board came with, which in your case apparently was 680pF. Ok, got some 680pf 2kv caps. Much smaller than the originals. I suppose a 68pf cap would be absolutely tiny, eh? The markings are just confusing to me. What is the purpose of these caps? Filtering? What would the effect be if I use the wrong (larger value) cap? Confusing for a hobbyist that can't read to figure out much less a trained tech! Thanks! Kirk S. |
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"Bill" wrote in message
... In article , says... The board has a sticker indicating that it is a replacement from 1990. Jumper B30 has been cut. My literature indicates panel is A10320 instead of B10326. That tracks. Replacement modules usually have most of the latest updates. And sometimes extra parts that you don't need, depending on what it is replacing. A couple extra connectors aren't present on my set either... What is the purpose of these caps? Filtering? What would the effect be if I use the wrong (larger value) cap? These capacitors "tune" the sweep circuit, for want of a better word. It's not a resonant circuit, but you do need to control the slew rate when the output transistor turns off (retrace). Ok... That is pretty much greek to me! You may have noticed that the two capacitors are connected in parallel. The larger value capacitor is a rolled film, and does the bulk of the "tuning", but the circuit apparently also needs high frequency suppression, which rolled films are not good at, so they also put in a smaller ceramic. Most boards also have a ferrite bead on the output transistor. Yes, it did. I put it back when I took the transistor out to test it. You probably would not notice much difference if you put in a 1000pF or 470pF instead of 680pF, since this capacitor is only about a tenth of the total. Maybe a tiny change in sweep width. But you have to assume the maker knew what they were doing unless circumstances compel you to do otherwise. Yes, the 470pF cap seems to be working ok. The picture was as good as it has ever been. Since my training is in computer programming, I wouldn't assume to know more than the maker. Just confused as to the markings on that cap. Thanks for the help, my free TV lives on. Kirk |
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