I got a CAMBRIDGE A3i from the car booty last week for £10. [I also got 2x 6metres of LINN K20 cable with LINN banana plugs for £3!!!]
…I didn’t really expect the amp to work but it was worth the gamble. As soon as I switched it on with nothing connected, it started clicking. I hooked up some mission 731’s & a cd player and it just kept cutting on & off from the outset, I got about 3 second bursts of music which sounded fine.
I put this down to the relay behind the big pots, I feel the pots may be the culprits, has anybody else had this problem? Any input would be gratefully accepted.
Eric
…I didn’t really expect the amp to work but it was worth the gamble. As soon as I switched it on with nothing connected, it started clicking. I hooked up some mission 731’s & a cd player and it just kept cutting on & off from the outset, I got about 3 second bursts of music which sounded fine.
I put this down to the relay behind the big pots, I feel the pots may be the culprits, has anybody else had this problem? Any input would be gratefully accepted.
Eric
Attachments
It's not a relay problem. The protection circuits are finding a fault. Don't bypass until you've found why the protection circuit's cutting!
Does the relay click in and out with the speakers disconnected? If so, remove the speakers and start measuring voltages with a VOM. First suspect is DC offset. Trace to the amplifier outputs BEFORE the relay and see if there's any DC voltage above 0.5V on any channel.
Cheers!
edit: check R201 and R202 if any are open or off-spec. It would cause the relay to chatter on and off, as the protection circuit would 'think' that the amplifiers are taking in too much power...
Does the relay click in and out with the speakers disconnected? If so, remove the speakers and start measuring voltages with a VOM. First suspect is DC offset. Trace to the amplifier outputs BEFORE the relay and see if there's any DC voltage above 0.5V on any channel.
Cheers!
edit: check R201 and R202 if any are open or off-spec. It would cause the relay to chatter on and off, as the protection circuit would 'think' that the amplifiers are taking in too much power...
Re: Dc Offset?
Can you check if one or more green LED's on the main amp PCB are blinking or going out when the relay clicks?
Cheers
x-pro
Eggzy said:thanks for that guys,
yes it occurs when the speakers are disconnected too.
i read somewhere that replacing all the caps is a good idea anyway.
thats the only schematic i could find online.
now i'll try to do some swatting to understand dc offset
Can you check if one or more green LED's on the main amp PCB are blinking or going out when the relay clicks?
Cheers
x-pro
eggzy and Chris,
Come to think of it, if the relay stays on long enough, it may be possible to read any DC offset by simply sticking the VOM probes into the speaker output lines - do this for each channel...
Cheers
Clem
ps: x-pro, what do the green LEDs indicate? - if you don't mind...
Cheers
Come to think of it, if the relay stays on long enough, it may be possible to read any DC offset by simply sticking the VOM probes into the speaker output lines - do this for each channel...
Cheers
Clem
ps: x-pro, what do the green LEDs indicate? - if you don't mind...
Cheers
Hi Clem,
The green LED's are the references for current sources. LED2 seems to be variable, so I could see it going out depending on the polarity of DC offset. Q7 will vary the voltage drop in R12 and thus the current through Q8.
I'm lazy and don't like to watch the meter. Stick a pair of meters to the junctions of the R22 resistors on each channel, ref to ground. When the relay clicks, have a look at the meters. Lazier still or for extreme intermittents. Solder a 10R 1/4W resistor to each junction as above to ground and let it sit. When DC offset occurs the resistor will burn out identifying the faulty channel. You could use two each with diodes in series opposite ways, thus giving you the polarity as well. I have done this from time to time on very intermittent units. It allows you to focus more in the area you need to look in. One burned both "polarity" resistors. Int. RF oscillation.
-Chris
The green LED's are the references for current sources. LED2 seems to be variable, so I could see it going out depending on the polarity of DC offset. Q7 will vary the voltage drop in R12 and thus the current through Q8.
I'm lazy and don't like to watch the meter. Stick a pair of meters to the junctions of the R22 resistors on each channel, ref to ground. When the relay clicks, have a look at the meters. Lazier still or for extreme intermittents. Solder a 10R 1/4W resistor to each junction as above to ground and let it sit. When DC offset occurs the resistor will burn out identifying the faulty channel. You could use two each with diodes in series opposite ways, thus giving you the polarity as well. I have done this from time to time on very intermittent units. It allows you to focus more in the area you need to look in. One burned both "polarity" resistors. Int. RF oscillation.
-Chris
Best to keep such things a little distance from the PCB though...
Sometimes an intermittent contact in one of the LED's results in a DC offset on the output, usually the LED goes off as well. It was a common problem on some early A3i's because LED's were soldered too close to the PCB. On the photo here these are on the right distance from the board thought.
2 Eggzy:
First thing would be to understand what part of the protection circuit switches off the relay. It could be a real fault or it could be that the protection circuit is in itself broken...
Cheers
x-pro
i am not worthy
Why would you do that?
The designer is willing to help you repair it! Now if the designer of the Belles amp were here for me to talk to ..... But I'm still going to fix my repair!
It's not ingratitude or anything, I just don't have the advanced electrical skills.
It was a last resort thought...a plan B
but i may have a final go
Why would you do that?
The designer is willing to help you repair it! Now if the designer of the Belles amp were here for me to talk to ..... But I'm still going to fix my repair!
It's not ingratitude or anything, I just don't have the advanced electrical skills.
It was a last resort thought...a plan B
but i may have a final go
Cambridge A3i - has it died?
Have a cambridge A3i that stopped working the other evening, I turned it on an heard a few strage hi pitched sounds, over 2-3 seconds, then nothing. Maybe lasted 2-3 seconds. Didn't sound good. Immediately turned off amp, and tried it again. Nothing - no sound.
What I now notice is the 'click' you normally hear when turning it on doesn't occur - the power LED lights up, and some of the LED's internally (took off the cover and checked which LED's were working when it was powered on - not all of them light up, one is partially lit). The only thing that I did was to leave it on for maybe 2 - 3 days or so - would this have over heated the amp? It's never been abused / played at high volumes.
Just wondering if there's a quick fix - I was going to donate this to my brother-in-law, as I have invested in a new rotel amp. It'd be a shame to bin such a good amp that's given me hours of pleasure over the past 10 years. Sorry, but I have no electronic knowledge at all - very basic.
Have a cambridge A3i that stopped working the other evening, I turned it on an heard a few strage hi pitched sounds, over 2-3 seconds, then nothing. Maybe lasted 2-3 seconds. Didn't sound good. Immediately turned off amp, and tried it again. Nothing - no sound.
What I now notice is the 'click' you normally hear when turning it on doesn't occur - the power LED lights up, and some of the LED's internally (took off the cover and checked which LED's were working when it was powered on - not all of them light up, one is partially lit). The only thing that I did was to leave it on for maybe 2 - 3 days or so - would this have over heated the amp? It's never been abused / played at high volumes.
Just wondering if there's a quick fix - I was going to donate this to my brother-in-law, as I have invested in a new rotel amp. It'd be a shame to bin such a good amp that's given me hours of pleasure over the past 10 years. Sorry, but I have no electronic knowledge at all - very basic.
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