Cambridge A3i Amplifier Repair скачать в хорошем качестве

Cambridge A3i Amplifier Repair

Fault Amplifier powering on, but speaker protection relay not changing over. Amplifier in protection mode. Initial inspection identified two burnt out resistors as shown in the video. R104 & R105 100 Ohm 1/4 Watt resistors replaced. Further checks made and Q102 BC550 was found to be short circuit collector to emitter. The A3i develops a number of issues over time, many are well documented for example dry solder joints on the Amplifier board, and intermittent failure of the 4 green LEDS. What is not documented is the failure of the signal transistors due to physical breakdown. Often a smell that can only be described as rotting fish is evident, also what appears to be a semi dry liquid can be seen on the circuit board and around the pins of the transistors. The above was the case with this Amplifier, all the right and left channel signal transistors were removed and the circuit board thoroughly cleaned and then dried to remove all traces of the liquid. Failure to remove all the liquid can result in erratic operation with the protection circuit triggering due to high floating DC offset. The liquid is slightly conductive. All the left and right channel signal transistors were replaced also the FETs. Q1,Q2 BC550 Q3,Q4 BC546 Q5,Q6 BC556 Q7 FET ZVP3306 Q8 BC640 Q10 BC639 Q11 BD139 Q12 BD140 Also LED 1, 2 Green 5mm As above for the right channel add 100 to the reference number for example Q101, Q102 etc When the FETs fail often they read diode junction on the transistor tester. Due tot he age of the Amplifier the speaker protection relay was also replaced 24 V DC Coil DP/CO. C8 / C108 100uF 63V also had to be replaced due to high ESR and very low value. All user controls and switches cleaned with De-Oxit to ensure reliable noise free operation. Bias for each channel set to 12 millivolts. Amplifier fully tested working correctly.