Cambridge Audio A1 Mk3 SE Repair
Bought this amplifier, it was advertised as 'faulty' in Cash Convertors here in the UK.
Two faults - one mechanical and one electrical.
1) Mechanical Fault - a loudspeaker output 'post' was missing, so I just replaced this temporarily with a 4mm threaded pan head screw.
2) Electrical Fault - more complicated obviously. Playing back the amplifier through a pair bookshelf Mission speakers, the left channel appeared to be fine, but no sound from the right channel, except for a permanent low level 'hum', which was independent of volume control setting.
I was eagar to find a service manual online, solely for the use of the circuit diagram. Unfortunately, the circuit diagram sourced from www.hifiengine.com was dissimilar from this version of the A1. There appears to have several variations made by Cambridge Audio.
My immediate thoughts about the faulty right channel was that the power amplifier had developed a problem.
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| Power amplifier based on the LM4766T - here desoldered. |
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| New LM4766T power amplifier IC |
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| LM4766T in circuit with new electrolytic capacitors. |
NE5532P OP Amps
There are two NE5532 OP Amps employed to voltage-amplify and add both bass and treble filtering to the LM4766 audio power amplifier.
Earlier I set up the oscilloscope, and traces at the outputs of each OP Amp indicated that these OP Amps were good - so the fault was after the volume control stage.
Re-assembled the Cambridge A1 MKIII and Now Ready to Go!
This amplifier was sold in Sept 2023.
