MOTM

If you are sure all 4 filter caps are OK AND recall there is no
self-resonance below ~ 200Hz (see Theory section), that's all I can think
of. 

Did you check that the voltage is changing on the emitter of Q11. And Q11 is
a PNP not NPN.

Paul S.


-----Original Message-----
From: motm@yahoogroups.com [mailto:motm@yahoogroups.com] On Behalf Of
peng3002
Sent: Friday, April 06, 2012 7:05 PM
To: motm@yahoogroups.com
Subject: [motm] MOTM-490 pcb build resonance doesn't work

I just finished a 490 last night. Fired it up today to do the trimming and
found the resonance pot has no detectable effect.
It passes audio and the Freq controls all function. I pulled one end of the
iABC resistor (R29) and measured current - approx 0.2mA with a 68K resistor.
Replaced with a 39K resistor and I got around 0.3mA.
Double and triple checked all parts, IC, diode and cap orientations, etc.
Everything checks out. I also traced nearly the whole circuit with the DMM
and that checked out OK, too. 
This leads me to believe I have a bunk 5517 (this was sent to me with the
pcb so I don't know its source. ON semi chip).

I'm hoping this is a problem that has come up before and the mystery can be
solved.
Any suggestions, areas to re-probe, etc would be greatly appreciated.
Just wanted to throw this out there for suggestions before I pull and
replace the 5517.

Thanks,
Phil




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