Cambridge Audio A3i problem (have searched)

[Richiekuk]

Hey all.

I have pulled my old A3i out of the loft for a resurrection. It was put up there due to a fault with one of the channels.
I've read loads about LED 2 and q8 transistor, but I still have sound coming from the dodgy channel, it's just really quiet!

Could this be due to the usual suspects, or something else, as I still have "quiet sound"?

Any help greatly appreciated.

Thanks

Richie K

 

[wakibaki]

Have you got any test gear?

You can try a few things. Make sure there are no dry joints in the faulty channel by resoldering them (all). If you have a HIGH IMPEDANCE earphone (old crystal type in ear) you may be able to put on some source and run through the left and right channels and find a point where the volume drops off, obviously an oscilloscope is the preferred tool.

Otherwise look for different DC conditions on the good channel and the bad one with a DMM.

Be very careful when working on the amp when it is powered up, not so much from the chance of hurting yourself (just stay away from the mains transformer) but if you inadvertently short across the wrong 2 terminals with the DMM probe you can easily destroy an active device.

w

 

[tiefbassuebertr]

ask diyaudio member "X-Pro".
Check out also this threads:
http://www.diyaudio.com/forums/solid-state/128424-cambridge-audio-a3i-integrated-amplifier.html
http://www.diyaudio.com/forums/solid-state/122378-cambridge-audio-a3i-repairs-mods.html
http://www.diyaudio.com/forums/solid-state/133547-cambridge-a3i-fixed.html
http://www.diyaudio.com/forums/solid-state/121654-schematic-cambridgeaudio-a3i.html
http://www.diyaudio.com/forums/solid-state/137377-cambridge-a3i-will-not-work.html
http://www.diyaudio.com/forums/solid-state/162751-help-cambridge-a3i.html

 

[jaycee]

Are all of the LEDs lit inside? if not, then thats the fault.

 

[Richiekuk]

Right I've had a look. All the LEDs lit (I'd tested them all anyway before power on).
I've tested Q8 aswell, and that works.
I'm stumped now, as everything I've read leads to these 2 components.

By the way the problem is Right channel really quiet!

Richie K

 

[Richiekuk]

I've just realised I was testing the transistor whilst it is still in the pcb, so not really a conclusive test (derr).

I'm not that up with components. Really need help to be honest!

Thanks

Richie K

 

[jaycee]

Yes, pull it and test. Check Q10 as well. If in doubt, replace.

The a3i power amp board is connected by a signal cable. It may be worth checking if the fault is in the preamp stage by disconnecting this cable, and sending an audio signal from a controlled source (such as an mp3 player) into the power amp directly.

Also, try tapping on the relay near the speaker terminals while it's on. The contacts could be bad.

 

[Richiekuk]

Cheers Jaycee, will try the latter 2 first (not too keen on de soldering a PCB, with my pigs tits).
How would I connect the Mp3 player to the power amp board (I assume you mean the white connector)?

Thanks

Richie K

 

[jaycee]

Without having a full service manual (ive only seen the power amp schematic) or one to look at closely, I can only guess, but the connector will probably have screened cable on it. You should be able to see white and red wires, and the shield parts of the cable connected. The white and red would be left and right input respectively, and the shield would be ground.

X-pro would be the guy to ask as he designed the thing 🙂