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Author Topic: Peavey CS400  (Read 243 times)

gbono

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Peavey CS400
« on: March 09, 2020, 09:27:41 PM »
http://schems.com/bmampscom/peavey/Peavey_CS-400%20(C-Series,%207-79)%20Schematic.pdf

CS400 with damaged (but functional) R16/17 - part of a zobel network? The amp is causing the light bulb limiter to glow brightly but the amp did not blow fuse. Is this an issue with high frequency oscillations on the output?

phatt

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Re: Peavey CS400
« Reply #1 on: March 10, 2020, 12:53:58 AM »
First check the DC Voltage at the speaker output?
If not very close to Zero then the circuit is faulty.
Yes could be HF problems.
If the amp is working (No DCV on output) then I'd replace the burnt components and see if they run hot. Better minds here will know more. :tu:
Phil

Enzo

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Re: Peavey CS400
« Reply #2 on: March 10, 2020, 01:21:16 AM »
R17 is zobel network.  But look on your schematic.  R16 is parallel to the output choke L2.   L2 is heavy wire.  It carries the main current to the speaker.  The only reason for R16 to burn is if that coil is open.  More likely the solder fails at one end, or the coil wire breaks at one end.  In which case unwind a turn and fix it.

R16 is 50 ohms, but in circuit the coil is parallel so it measures "shorted".  If R16 measures 50 ohms, then the coil is open.  Open coil means all the output has to flow through that resistor.

gbono

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Re: Peavey CS400
« Reply #3 on: March 11, 2020, 06:55:19 PM »
So the inductor looks good. The leads are soldered to the pcb without issue. I noticed that the connector that ties the inductor, ground and +- 59V is also blackened (got hot). Could the issue be that C4 is shorted?

Enzo

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Re: Peavey CS400
« Reply #4 on: March 11, 2020, 07:49:17 PM »
Is R16 still missing?  Measure resistance across its solder pads.  Should show a dead short if the coil is intact.  If it reads open, your coil is open.   A favorite place for coil to break is inside those little molex pin "posts".  Tug on the coil, does it want to pull out?

C4 shorted?  Why waste time asking us, get out your meter and find out.

gbono

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Re: Peavey CS400
« Reply #5 on: March 20, 2020, 02:22:14 AM »
Back on this since it's solitary confinement here...

The inductor/coil is not open and all solder joints are good. No shorted capacitors and the diode across the output good too. DC on the output terminals is .9V channel A and 5V on channel B.