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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
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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