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Thread: Rhodes Satellite amp confusion

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    Supporting Member Randall's Avatar
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    Rhodes Satellite amp confusion

    1970s Fender Rhodes 2x12 powered cabinet that doesn't pass signal, only some hum. I have both rails +/-43v. outputs test good. As I trace my signal, I find that if I apply it to the neg side of the 5uF/50v cap after the input trim pot, I get nothing, ut if I apply it to the positive side of that same cap it comes out loud and clear. So I figure bad cap, right? Popped in a new one and same issue. Then I clip in different values and here is where it gets weird. FOR A TIME, the original cap WORKED SOMEWHAT, but any new ones, not at all. Old cap tests OK. Now, after much noodling around no cap works. HOWEVER, I can see signal getting to Q1 base and at it's emitter to a little lesser extent.

    So, why does essentially shorting this cap make it work? Was the old cap intermittantly shorting or leaky to the extent it acted like a piece of wire? So Here I am at clip in a cap of similar value, nothing. Short the clip leads together and, loud.

    Q1 - 3 test good, but here is something that has me wondering, I have 32v on the base of Q1, is that turning it off? Here are what I see for voltages in the section:

    Q1 b = 32.6v
    c = 33.8
    e = 32.5

    Q2 b = 25.3
    c = 26.8
    e = 32.5

    Q3 b= 26.6
    c = 27.0
    e = 26.0

    Sure wish they had bothered to include voltages on this print:
    http://www.fenderrhodes.com/org/ch11/fig11-12.jpg

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    Last edited by Randall; 05-05-2018 at 12:04 AM.
    It's weird, because it WAS working fine.....

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    Supporting Member The Dude's Avatar
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    Neither Q1 or Q2 is biased properly. Is Q1 shorted B-E? I'm assuming that in your post, Q2 base is supposed to be positive (misprint)? Either way, an NPN transistor should have the base approximately .6 V more positive than the emitter. So, Q2 isn't right either. Is the B-E junction open? Use diode check function on your meter and check the transistors.

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    don't forget the joker g1's Avatar
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    Agree with above, also, I think when you originally injected your signal at the + end of C13, you were somehow biasing Q1 with your test gear.

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    Supporting Member Randall's Avatar
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    You are correct sir! I doubled checked those two NPNs and Q1 was indeed shorted B-E. I checked it before on a B&K transistor tester so I think I may have used the wrong setting. Anyway, it is passing signal now. Now I have to address the caps situation to relieve it of it's hum

    Thank you!

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    It's weird, because it WAS working fine.....

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