I'm working on a Cambridge Audio P60, which puts out a very loud buzz on all outputs, including headphones. Unfortunately it's a massive struggle to get anywhere, as the schematic available does not have a board diagram, and bizarrely my P60 does not have part labels on the board! So none of the components are named and therefore it is very difficult to know what is what according to the schematic.
Has anyone experience with working on one of these who could help me out?
Many thanks,
R.
Has anyone experience with working on one of these who could help me out?
Many thanks,
R.
Hi,
I see there is an older thread on the P60
cambridge p60 is alive
Could you attach a photograph showing the top of the main board.
Does the buzz sound like power hum?
The issue may be the failure of the power supply smoothing capacitors, no longer filtering the AC ripple after rectification.
I see there is an older thread on the P60
cambridge p60 is alive
Could you attach a photograph showing the top of the main board.
Does the buzz sound like power hum?
The issue may be the failure of the power supply smoothing capacitors, no longer filtering the AC ripple after rectification.
There are two main smoothing capacitors , one is attached to the power supply positive output and the other to the negative output of the full wave bridge rectifier .
Hi both,
Really sorry for the long delay in getting back to you - had a family crisis I needed to deal with. I have replaced the main filter capacitors and sure enough the main issue is resolved - the loud hum is gone and i have full functionality in the RIGHT channel. The LEFT channel however barely passes sound, you can just about hear the music on it, but it is very quiet and sounds super bit-crushed. Any idea what would be causing this? Again - without part numbers on my board it is so hard to work with the schematic.
D
Really sorry for the long delay in getting back to you - had a family crisis I needed to deal with. I have replaced the main filter capacitors and sure enough the main issue is resolved - the loud hum is gone and i have full functionality in the RIGHT channel. The LEFT channel however barely passes sound, you can just about hear the music on it, but it is very quiet and sounds super bit-crushed. Any idea what would be causing this? Again - without part numbers on my board it is so hard to work with the schematic.
D
Attachments
I take it you don't have tools ?
Normally you inject a 1KHz sine wave at the input which is the preamp section ,see if it reaches SW6-amplified --if so connect signal generator to the input of the power amp and check for an amplified signal at the output .
If you don't have audio test equipment then test for the correct voltages with a multimeter -
preamp= -18 Volts .
power amp 34Volts +/-.
Normally you inject a 1KHz sine wave at the input which is the preamp section ,see if it reaches SW6-amplified --if so connect signal generator to the input of the power amp and check for an amplified signal at the output .
If you don't have audio test equipment then test for the correct voltages with a multimeter -
preamp= -18 Volts .
power amp 34Volts +/-.
You're right, it does. Though according to the image of a board with text labels on this site (5th image down) it's R91. Is it definitely R2?
Either way, it reads 1.41k, I cannot ascertain from the colour bands if this is correct or not. I'm finding it hard to make out what the second band colour is. The closest matches to my best guess right now is Black, Violet, Green, Gold which comes to 700k, but the last band looks more like orange to me and I really have no idea what colour the second one is.
I do have tools, but I don't know where to check for 18v, where SW6 is or the input of the power amp is due to an unlabelled board. I can say that I'm pretty sure the issue is in the power amp, as the preamp LED which flashes in accordance to the music is flashing with equal gain on both the left and right channels.
EDIT: Have checked voltage on 4 fuses, can confirm that we have +/-34v on both channels.
Last edited:
Well Richard if you have tools then you can recognize electronic parts , then you can take readings of the components .
The -18V rails are near the 2 sets of diodes which have their outputs connected together , the circuit diagram is pretty rough probably hand drawn.
I do notice a fet connected to the input , if I remember correctly JLH had a design with this type of thing in it to mute the input but I cant remember which version it was .
The -18V rails are near the 2 sets of diodes which have their outputs connected together , the circuit diagram is pretty rough probably hand drawn.
I do notice a fet connected to the input , if I remember correctly JLH had a design with this type of thing in it to mute the input but I cant remember which version it was .