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Old 14th October 2012, 02:30 PM   #481
AndrewT is offline AndrewT  Scotland
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Are you confirming you have measured 0.26Vdc (between signal Hot and Signal Return) before the DC blocking cap?
Where is that coming from?
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Old 14th October 2012, 03:03 PM   #482
Marra is offline Marra  United Kingdom
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Bob;restor values all seem ok and I've triple cleaned the boards and checked for solder links can't see any.
Some of the resistor values don't give an instant value but ramp up to the correct reading.

Andrew; yes its minus .26v which goes down and then back up again and once the relay clicks which isn't straight away I initially get 3.5v on the output and this then slowly drops in value.I havent left it powered up to see how low it gets as I did'nt want to burn anything out.
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Old 14th October 2012, 03:04 PM   #483
AndrewT is offline AndrewT  Scotland
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so you have 3.5Vdc on the output
where is the -0.26Vdc?
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Old 14th October 2012, 03:07 PM   #484
Marra is offline Marra  United Kingdom
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Across the input connectors before the input cap connects to the circuit.
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Old 14th October 2012, 03:14 PM   #485
AndrewT is offline AndrewT  Scotland
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if the DC blocking cap is not leaking then the input offset voltage cannot appear across the input.

You must have an error here. Somehow voltage is appearing across Sig to Sig G.
You must find how that is getting there.
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Old 14th October 2012, 03:16 PM   #486
Marra is offline Marra  United Kingdom
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Where to look is the question.
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Old 14th October 2012, 03:20 PM   #487
AndrewT is offline AndrewT  Scotland
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study the input with a microscope.
There must be something putting voltage on the RCA side of the DC blocking cap.
Is the input voltage zero when you add a dummy resistor to the RCA socket?
Is the input voltage also zero when you "short" the input socket?

Does the output voltage vary for any of these three conditions?
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Old 14th October 2012, 03:26 PM   #488
Marra is offline Marra  United Kingdom
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I am no doubt showing my ignorance here but what value dummy load would you recommend Andrew?
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Old 14th October 2012, 03:28 PM   #489
AndrewT is offline AndrewT  Scotland
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0r0 and 100r and 1k0 and 10k etc.

Get cheap RCA plugs and insert resistors to create your dummy test loads.

Mine are white plastic and easy to write on with sharpie (indelible pen).
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Old 14th October 2012, 03:44 PM   #490
Marra is offline Marra  United Kingdom
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Thanks Andrew I'll check that out and see what transpires.
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