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-   -   In circuit resistor testing? (http://www.videokarma.org/showthread.php?t=132999)

kbmuri 11-08-2007 04:55 PM

The best way to check resistors in-circuit is to take all the tubes out of the set, get a Sams sheet for the set, and do the entire resistance chart from top to bottom. If every check in the chart checks out, you've probably checked all of your resistors. If a chart entry does not check out, trace the schematic's resistors between point A and point B (of the current chart check) and make sure your set has the same ones. Sometimes the chart is wrong, when the unit they took original readings from is a slight production-run revision from your set (I learned the hard way). If the resistors in your set are different, but the resistors in your set between point A and point B add up to what you're reading, in the same way that the resistors in the schematic add up to what's in the chart, then you're still ok. If you get a reading that can't be explained, then lift the leads of the resistors in that path. If they check out, then probably you have a short or shorted capacitor nearby. If they don't check out, then of course replace them. You can pass 95% of your resistors this way, leaving them in-circuit.

Also if you have the Sams sheet, then you don't have to guess if 1/4-watt is ok or not. The parts list will tell you what wattage you need. Doesn't hurt to go one step higher (e.g. a 1/2 watt where 1/4 is called for), in case your 50-year-old TV isn't as up-to-spec as it was when it was born. But that's just me being cautious. I imagine the parts list knows best and you're fine meeting what's called for. Never go under, of course.

freakaftr8 11-08-2007 05:25 PM

Does anyone have a sams for the ctc-16 chassis?
Thanks for that great information kbmuri! I have a sheet, it's not sams, it's an actual RCA schematic that came with the set when it was new. But the sheet doesn't explain wattage in restsiors unless there is a 1 watt or higher. I did not know standard resistors in these sets were 1/2 watt. Oops

old_tv_nut 11-08-2007 06:51 PM

look at
http://www.mikroe.com/en/books/keu/01.htm
for some info on size vs. watts

Bill R 11-09-2007 12:31 AM

Most of the resistors in a 16 are 1/2 watt or higher. 1/4 watt resistors are to small, and will fail. I didn't see any 1/4 watt on the schematic. There are some 1, 3, 5, and 7 watt resistors as well. Use 1/2 watt resistors for the small ones. The glossy film resistors will be ok, jsut be sure they are the right size.

Bill R

freakaftr8 11-09-2007 12:18 PM

Thanks guys, im in the process of replacing the 8 or so out of tolerance ones with the right size.


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