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Thread: Schematic for RCA RS2640

  1. #36
    Supporting Member The Dude's Avatar
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    I would first check the resistance from emitter to ground to rule out a near short on that 6.8V supply line. Something could be shorted loading down that supply.
    g1 likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  2. #37
    Supporting Member shortcircuit's Avatar
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    Quote Originally Posted by The Dude View Post
    I would first check the resistance from emitter to ground to rule out a near short on that 6.8V supply line. Something could be shorted loading down that supply.
    powered up 11.98 M ohms ,powered off starts around 3k and climbs I quit around 10k and climbing.
    Last edited by shortcircuit; 04-05-2018 at 11:00 PM.

  3. #38
    Supporting Member The Dude's Avatar
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    Ok, firstly, don't ever measure resistance with power applied. You could cause more damage. If you measured a short it would be zero ohms or something near. Infinite is no resistance or open. Since you measure above 10k or in the M ohms, I don't think we have a short, so go ahead and replace the transistor.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  4. #39
    Supporting Member shortcircuit's Avatar
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    Quote Originally Posted by The Dude View Post
    Ok, firstly, don't ever measure resistance with power applied. You could cause more damage. If you measured a short it would be zero ohms or something near. Infinite is no resistance or open. Since you measure above 10k or in the M ohms, I don't think we have a short, so go ahead and replace the transistor.
    Thank you ftkita, lesson learned , I don't have a suitable replacement on hand , only npn I have are 2n3904's

  5. #40
    Supporting Member The Dude's Avatar
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    The 2N3904 is rated for only about a quarter of the current as the original part. I doubt it would last. FYI, here's a datasheet for the original part.

    http://pdf.datasheet.live/datasheets-1/kec/KTC3203Y.pdf
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  6. #41
    Supporting Member shortcircuit's Avatar
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    Quote Originally Posted by The Dude View Post
    The 2N3904 is rated for only about a quarter of the current as the original part. I doubt it would last. FYI, here's a datasheet for the original part.

    http://pdf.datasheet.live/datasheets-1/kec/KTC3203Y.pdf
    believe it or not I actually figured that out 200ma instead of 800,( wondered on a formula for emitter current usage with voltage info I have)but doubted it was going to be that low , have to order transistor , so it will be a few days before we get any results , again can't thank all supporters enough....on to a 70's vibro champ
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  7. #42
    Supporting Member The Dude's Avatar
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    I don't usually recommend NTE parts because they're often a poor cross and cost more than original parts most of the time. That said, since this transistor has to match nothing, you might think about using an NTE or ECG 382. It's rated higher and has a bigger body to dissipate more heat. You might even have a dealer nearby saving you shipping cost making it cheaper than ordering. The basing diagram is also the same.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  8. #43
    Supporting Member shortcircuit's Avatar
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    Quote Originally Posted by The Dude View Post
    I don't usually recommend NTE parts because they're often a poor cross and cost more than original parts most of the time. That said, since this transistor has to match nothing, you might think about using an NTE or ECG 382. It's rated higher and has a bigger body to dissipate more heat. You might even have a dealer nearby saving you shipping cost making it cheaper than ordering. The basing diagram is also the same.
    thanks for the info, dealer near me, I WISH, one horse town, two weeks from everywhere

  9. #44
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    shortcircuit likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  10. #45
    Supporting Member shortcircuit's Avatar
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    Quote Originally Posted by The Dude View Post
    I don't usually recommend NTE parts because they're often a poor cross and cost more than original parts most of the time. That said, since this transistor has to match nothing, you might think about using an NTE or ECG 382. It's rated higher and has a bigger body to dissipate more heat. You might even have a dealer nearby saving you shipping cost making it cheaper than ordering. The basing diagram is also the same.
    Finally received NTE382 to replace Q401 , Success !!! we have audio. Thanks to all the support members for your patience and knowledge , I learned a lot on this one.
    g1, The Dude and eschertron like this.

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