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Phillips 7871 , in protection mode

H

hungsolow

New Member
hello and thank you for reading and helping, I am a bit green on this stuff but interested in learning. Have needed tools and a bit of exp. so I have this Phillips 7871 that will not come out of protection mode any and all hell appreciated
 

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Start by testing the output transistors and emitter resistors. Also, looks like a thermal sensor there on the heat sink. Check that too.


Rob
 
hungsolow said:
Ok ok I found one bad output, and can't find a part number for replacement! Original is toshiba 161-6
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That's 99.9% likely a Philips part number, and the actual Toshibas are probably long out of production, anyway.

I've used the Vetco search function to begin finding equivalents, as one way to start - they will often be able to give you a suggested NTE equivalent for that Philips number, and you can take it from there. It's also possible to find an equivalent by adding "ECG" to the Philips number, to get - in this case - ECG161, and again, you can begin tracking down equivalents based on the datasheet, case type, and all that good stuff. There are other great NTE equivalent sites if you opt to use other equivalents or know of better replacements.Here's the vetco catalog: http://www.vetco.net/catalog/

Finally, you can get lucky and someone else has posted the best current-production equivalent from OnSemi or whoever, somewhere online. I can tell you that based on the 4 Philips I've done or am doing (2x 7871, 5781, and a 5721), they were fond of using what are now equivalent to 2n3904, 2n3906, NTE232, and NTE234. I've had good luck with the NTE parts from Vetco (also MCM or Allied) and I like the Fairchild versions of the others from Mouser or Digi-Key, but I know many around here don't have that same experience with NTE.

For what it's worth, I also can recommend going to a modern op-amp in the tuner and pres sections - I used an OPA2134 with great results. I also went overboard with Muse and Silmic II caps in the preamp and amp sections in one of the 7871s I did, and I like to think it sounds better than the one where I just used good-quality Panasonic or Nichicon electrolytics. In the amp section, it's also worth replacing the film caps with good modern film caps.
 
Robisme said:
Good eye. So driver transistors were probably bad too.

How about a pic of the output transistor.

Rob
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Sorry guys, had surgery so I haven't touched this in a while but here is pic of bad transitor only schematic and parts list are for a 7851 will parts be the same difference in output between the two different models? Thanks
 

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161-6, shows as 161N6 in Manual which shows as NTE87 on NTE site. Should be able to cross to an onsemi from that info.
 
hamrules said:
161-6, shows as 161N6 in Manual which shows as NTE87 on NTE site. Should be able to cross to an onsemi from that info.
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It does? My manual has nothing other than a BS Philips number that doesn't cross to anything. The actual parts are stamped 179-2 (under a Motorola logo.) I was considering 2N3055 as a substitution. Your thoughts?
 
The Manual I referred to was for the other one listed in the post. Sorry , I should have specified.
 
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