Cambridge Audio Azur 551P MM Preamp - No output

[mediaman083]

Hello everyone!

Recently my Cambridge Azur 551P stopped putting out sound after years of great music. After testing with my Fluke meter, there is no voltage present from the AC adapter at all. I had another AC 12V 300ma adapter to test with (the original AC adapter is 12V 500ma) and so I did.

Unit powers up, but there is no buzzing at all when touching the line input cable from the turntable. I am somewhat new to circuitry, but I do know enough to look for blown/bulging caps. I only saw one that was looked ever so slightly puffy in the power supply section, but after testing with an ESR meter and the Fluke meter, none of them seem to be terribly out of range. All of the diodes seem good upon first check.

I am at a loss on where to look next, or what I should be looking for. Any help would be greatly appreciated, as I would love to get this unit back into service soon.

[bowerbird980]

Re: Cambridge Audio Azur 551P MM Preamp - No output

In your second picture; the diodes and 'lytics (capacitors) are a bridge rectifier and power supply. First thing I would do is make sure you are getting +/- Voltage Rails. Measured form GND you should see something in the neighborhood of +8VDC on R42 and -8VDC on R43.

[bowerbird980]

Re: Cambridge Audio Azur 551P MM Preamp - No output

Next step:
If the voltage is sagging feel around for something getting warm.

If it looks okay check the voltage at the supply pins of the op-amps (IC's). I can't read the part# on your pic so just google them. Probably dual op-amps, so the supply pins are 4 and 8. (count from the dot counter-clockwise)

[mediaman083]

Re: Cambridge Audio Azur 551P MM Preamp - No output

Hello again!

Thank you for the previous response bowerbird

So I checked the voltage on R42 and R43. They are as follows:

R42: +3.6v
R43: +0.5v

I also checked the op amp's which are Texas Instruments NE5532's.

Both are identical with pins 4(VCC-) at +0.9v and pins 8(VCC+) are both at +2.1v

Nothing is getting warm as far as I can tell, but I did notice when I plug in the adapter that after unplugging and powered on.. the led will just slowly fade out. It would never do that before, just would shut down immediately.

I also found out there were some cold solder joints for the switch itself, so I went ahead and fixed that first but it didnt seem to be of any help.