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Trouble shooting Cambridge Audio 651C
Trouble shooting Cambridge Audio 651C
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Old 30th November 2019, 07:30 PM   #11
Mooly is offline Mooly  United Kingdom
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Trouble shooting Cambridge Audio 651C
Good question

Yes, the scope will always trigger on the same point of the waveform irrespective of absolute phase compared to another point. You need to use a dual beam or dual trace scope (which most are tbh) and then you will see the phase difference between the traces as both are displayed at the same time.

I'm trying to think whether a single beam would show any phase difference if you used the external trigger option and triggered it from one phase while viewing the other. I'd have to think about that.
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Old 1st December 2019, 03:12 PM   #12
bma is offline bma  Netherlands
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Trouble shooting Cambridge Audio 651C
I'm doing my best to read, learn and understand to reach enlightenment. One day...

I've purchased the Hantek 2D72 a 2-channel digital oscilloscope. I guess that should work, at least once I receive the 2nd probe?

That aside; given the measurements above wouldn't it be logical to assume the failure is to be found in the circuit behind R44/R45? Also, couldn't I just measure AC V between R44 and R45 to determine whether the signals are in and out of phase?

Once again, thanks for your help.
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Old 1st December 2019, 05:10 PM   #13
Mooly is offline Mooly  United Kingdom
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Trouble shooting Cambridge Audio 651C
The fault may very well be after R44/45... and something I've thought of that I should have mentioned at the start is to check that the grounds of the RCA output sockets are OK. If the print is cracked and the ground floating then you would get these symptoms.

Assuming the grounds are OK then we do need to look with the scope at the phase relationship of a mono signal. Given that audio is (in the scheme of things) very low frequency you should be able to use ordinary wire to connect the scope to the circuit.

You could certainly look at the outputs that way and then work forward. For a mono signal each trace should match the other, and if the scope has an 'invert' function for the second channel (which inverts phase) and also an 'add' function (which adds channel 1 and 2) then you should see nothing but a straight line as the two signals (one inverted by the scope) add together.
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