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Linear power 2502iq offset problems
Linear power 2502iq offset problems
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Old 14th September 2019, 11:56 PM   #1
maurosubito is offline maurosubito
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Default Linear power 2502iq offset problems

Hello, I'm working on a linear power 2502iq.
It had audio section burned, transistor, emitter resistor, drivers, muting transistor.
Now all is new, amp works but one side has 40mv DC offset, other side has 500mv DC offset.
I tried to reverse all the small transistor but result is the same, 500mv offset in the same side.
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Old 15th September 2019, 02:07 AM   #2
Perry Babin is offline Perry Babin  United States
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Are there any op-amps in the preamp section?

In most feedback circuits, there is an electrolytic capacitor that is in the voltage divider, in the branch that goes to the audio ground. This prevents the amplifier from amplifying DC (which would increase offset). If that capacitor is leaking electrically, the offset could be higher than normal.
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Old 15th September 2019, 07:37 AM   #3
maurosubito is offline maurosubito
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There is 1 opamp but opamp is ok, capacitors are all new, I changed all the electrolitic caps and checked poliester caps when I see this problem.
Can i use mpsa56 to replace all the mps8599?
I see that 1 mps8599 is leaking, when I reverse its the good channel has 120mv DC offset than 40 with other mps8599.
The damaged channel has 500mv every time.

Last edited by maurosubito; 15th September 2019 at 08:02 AM.
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Old 15th September 2019, 08:03 AM   #4
Perry Babin is offline Perry Babin  United States
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In some of the Linear amps, the op-amp is used for DC offset.
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Old 15th September 2019, 08:26 AM   #5
maurosubito is offline maurosubito
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OP amp replaced with new op275, but now has new problem, rail voltage is 6volts, power supply don't produce rail voltage.
I had +-48 volts up to 5 minuts ago

Last edited by maurosubito; 15th September 2019 at 08:33 AM.
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Old 15th September 2019, 08:35 AM   #6
maurosubito is offline maurosubito
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I don't know the problem but amp hands rail voltage now, this is a ??????.

But now sounds but with new opamp (op275) has the same offset in the same channel.
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Old 15th September 2019, 08:38 AM   #7
Perry Babin is offline Perry Babin  United States
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Is the offset voltage the same for both channels?

Are you measuring the offset directly across the speaker terminals with a speaker connected (with no capacitor in series, like you may have for test speakers)?
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Old 15th September 2019, 08:43 AM   #8
maurosubito is offline maurosubito
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Yes, I measured offset across speakers cable with speakers, without speakers, when it sound.
1 channel has about 40mv, other channel has about 500mv
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Old 15th September 2019, 08:56 AM   #9
Perry Babin is offline Perry Babin  United States
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Are you measuring the offset with or without signal.
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Old 15th September 2019, 09:03 AM   #10
maurosubito is offline maurosubito
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With and without don't change
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