hifiaf
pfm Member
Hi everyone,
I recently took possession of some CB NAP 135s. They needed a service, but they came to me with a recap kit. I plugged them in on receipt, and there was some crackling in one channel, so I proceeded straight to the service.
The recap kit is all standard Naim-approved components. Everything was a like-for-like substitution. I only serviced the regs and amp boards.
I completed the service yesterday, and have spent this afternoon checking the bias (fine), the power rails (fine) -- and the DC offset: not fine!
I've got 190mV in one amp and 130mV in the other.
Any ideas on what might be up? I've checked I've got the right values of tants and caps everywhere and that the orientation is all correct.
I'm hoping it's some obvious thing I've done wrong but naturally I'm a bit worried it's the transistors. But it seems strange that both amps would be affected. Unfortunately I didn't measure DC offset before servicing.
From other threads I see some recommend getting the amp in its case and warmed up to see if it stabilizes.
I recently took possession of some CB NAP 135s. They needed a service, but they came to me with a recap kit. I plugged them in on receipt, and there was some crackling in one channel, so I proceeded straight to the service.
The recap kit is all standard Naim-approved components. Everything was a like-for-like substitution. I only serviced the regs and amp boards.
I completed the service yesterday, and have spent this afternoon checking the bias (fine), the power rails (fine) -- and the DC offset: not fine!
I've got 190mV in one amp and 130mV in the other.
Any ideas on what might be up? I've checked I've got the right values of tants and caps everywhere and that the orientation is all correct.
I'm hoping it's some obvious thing I've done wrong but naturally I'm a bit worried it's the transistors. But it seems strange that both amps would be affected. Unfortunately I didn't measure DC offset before servicing.
From other threads I see some recommend getting the amp in its case and warmed up to see if it stabilizes.