cambridge a3i LED fail

[danjos]

hi all
first post, sorry to be asking questions straightaway!

ive read a fewhi all
first post, sorry to be asking questions straightaway!

ive read a few threads regarding various problems with the A3i... i understood some of it, but i could do with some clarification:

After 10-15mins use from cold my a3i outputs a thump to the speakers and goes silent.

Using this diagram as a basis, http://www.diyaudio.com/forums/showthread.php?s=&threadid=88461&highlight=

LED1 is the one that goes off.

After a cooldown period, again 10-15mins, the amp will work again for a short time.

I assume theres a heat problem somewhere, but im not sure what LED1 fail indicates?

any advice on how to progress toward a fix would be welcome


thanks
dan

 

[x-pro]

After 10-15mins use from cold my a3i outputs a thump to the speakers and goes silent.

Using this diagram as a basis, http://www.diyaudio.com/forums/showthread.php?s=&threadid=88461&highlight=

LED1 is the one that goes off.

After a cooldown period, again 10-15mins, the amp will work again for a short time.

I assume theres a heat problem somewhere, but im not sure what LED1 fail indicates?

any advice on how to progress toward a fix would be welcome

Hi Dan,

it is just the LED itself that dies from heat. Unfortunately that is a known problem. LED should be lifted at least 10 mm from the PCB. You'll need to replace the LED with another green 5mm one (careful with it's polarity!). If the rest of LED's are not lifted from the PCB you may want to replace them all.

Cheers

Alex

P.S. - if you want the schematics of A3i, please email me. I've designed it.

 

[danjos]

wow, straight from the horses mouth !
cheers alex.

the LED still works, so can i just lift it clear of the board? i guess i'll have to re-solder it if the connection is lost?

just out of interest, how does the overheated LED stop the amp producing sound? does it just simlply trip the protection circuit/relay stuff ?

 

[x-pro]

the LED still works, so can i just lift it clear of the board? i guess i'll have to re-solder it if the connection is lost?

just out of interest, how does the overheated LED stop the amp producing sound? does it just simlply trip the protection circuit/relay stuff ?

Hi Dan,

LED loses contact internally when hot - I suspect it was just a batch of bad quality chinese LED at the time. When it happens the VAS gets a huge offset and the protection circuit cuts the output off - just as well because otherwise your speakers would not be happy.

Cheers

Alex

 

[danjos]

thats great, thanks for the help alex.