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Has the amp developed this fault while you have had it ? or is the amp an acquisition.
Once the amp has done this quarter turn thing, does it then work normally with the volume control responding correctly to the remote control ?
I've no magic answers for this problem, but gathering as much info as possible always helps.
Has the amp developed this fault while you have had it ? or is the amp an acquisition.
Once the amp has done this quarter turn thing, does it then work normally with the volume control responding correctly to the remote control ?
I've no magic answers for this problem, but gathering as much info as possible always helps.
The motor control for the volume pot. is pre-programmed in a PIC microcontroller. This is likely not a fault and many remote controlled amplifiers operate this way, turning on with the last used or a preset moderate volume level. I have a few amplifiers that also do this, including a DIY magazine design, so it wouldn't be an unusual feature for the period.
After all, turning up the volume each time you power up is no simpler. The actual control setting will be determined only by how long the motor spins and there is no hardware adjustment to alter this timing.
Some remote volume controls can be programmed for this default volume setting via the remote control keypad, much as any modern TV and AV gear. If you have the user manual, you will be able to read the operating instructions and see whether it was adjustable via the remote or not, for yourself. However, I can't locate one on-line.
After all, turning up the volume each time you power up is no simpler. The actual control setting will be determined only by how long the motor spins and there is no hardware adjustment to alter this timing.
Some remote volume controls can be programmed for this default volume setting via the remote control keypad, much as any modern TV and AV gear. If you have the user manual, you will be able to read the operating instructions and see whether it was adjustable via the remote or not, for yourself. However, I can't locate one on-line.
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Ian... this is what I was initially wondering, however setting a preset level on a motorised pot either needs a method of feedback for the angular rotation or a cruder 'turn it fully down first and then run for xxx seconds' to put it in the approximate area needed. Each of those needs to mute the audio for the duration.
Is the Cambridge that sophisticated ?
Is the Cambridge that sophisticated ?
Hi Mooly - I don't see any feedback from the motorized pot. on the schematic and my DIY version was almost as basic as you suggest too. I think it just relied on timing to reach full ACW and slip the clutch to mute from any position and at power-off. I honestly can't recall whether other settings are stored in the micro at all but my DIY remote has a fixed un-mute level, same as at power-on. Just power-on and after a delay, it simply winds CW for 2-3 seconds.
I have a recollection that volume settings could be stored by the time it took from motor stating current to the increase of slipping current in the mute cycle but I'm not certain on what that was done. I wonder though; what if someone replaced the pot when it wore out (as the remote types really do!) with a different motor type?
Have a look at the motor control schematic on sheet 6 (discrete motor control) or sheet 9 (IC version) here and see if you can spot anything which I may have missed. Cambridge Audio A500 Manual - Stereo Integrated Amplifier - HiFi Engine
I have a recollection that volume settings could be stored by the time it took from motor stating current to the increase of slipping current in the mute cycle but I'm not certain on what that was done. I wonder though; what if someone replaced the pot when it wore out (as the remote types really do!) with a different motor type?
Have a look at the motor control schematic on sheet 6 (discrete motor control) or sheet 9 (IC version) here and see if you can spot anything which I may have missed. Cambridge Audio A500 Manual - Stereo Integrated Amplifier - HiFi Engine
Ah, there will be the problem - no remote control for setting anything
If you look at the pic linked here: http://www.hifi-pictures.net/amplifiers-home/Cambridge Audio A500/platka.jpgyou'll see that the rear of the volume pot has a DC motor and gearbox attached. The motor will have 2 leads protruding which connect typically to a 12V supply to run the motor in either reverse or forward, so both leads must "float" above earth. If you look at the schematic, you'll see the motor power is connected via CN3 which should be removable.
But - make certain it can't be reconnected in reverse unless you leave some form of label there. The lead should have a keyed plug to prevent this but I can't be sure about it. Tie the lead back with a non-conductive tie or string if it threatens to contact anything on the board and write yourself a memo to stick on the bottom plate as a reminder of what was done.
Voila! No power - no spin and the motor controller should be safe enough with no load.
Ed. You beat me to it , Old n cranky!
If you look at the pic linked here: http://www.hifi-pictures.net/amplifiers-home/Cambridge Audio A500/platka.jpgyou'll see that the rear of the volume pot has a DC motor and gearbox attached. The motor will have 2 leads protruding which connect typically to a 12V supply to run the motor in either reverse or forward, so both leads must "float" above earth. If you look at the schematic, you'll see the motor power is connected via CN3 which should be removable.
But - make certain it can't be reconnected in reverse unless you leave some form of label there. The lead should have a keyed plug to prevent this but I can't be sure about it. Tie the lead back with a non-conductive tie or string if it threatens to contact anything on the board and write yourself a memo to stick on the bottom plate as a reminder of what was done.
Voila! No power - no spin and the motor controller should be safe enough with no load.
Ed. You beat me to it , Old n cranky!
How different? Don't they have inverted labels so you could read the speaker terminal labels from the top as everyone tries to at some time.
http://www.son-video.com/images/static/Rayons/Hifi/ChainesCompos/Cambridge/A500Ar_TG.jpg Copying the manual page and posting could also be helpful here.
http://www.son-video.com/images/static/Rayons/Hifi/ChainesCompos/Cambridge/A500Ar_TG.jpg Copying the manual page and posting could also be helpful here.
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