Cambridge Audio A3i repairs and mods - Page 20

homemodder · 22nd January 2013, 01:41 PM

Fairchild bds are using the same die as the bcs, onsemi have changed though.

RS232 · 22nd January 2013, 02:03 PM

By old I mean very old, I have brand new BD135/6 and BD139/40 with around 15 years.
I can always put in the MJE243/253 that X-PRO recommended.
I'm preparing an parts order for Farnell and a couple more transistors is not going to brake the my bank account (50xIRFP240 and a few other bits).

Ric

RS232 · 05:54 PM

New problem
Replaced the BC639/640 with BD139/140 (original Philips one from the 90s) but they still get very hot and after a few tracks on the cd player it just shuts of (no sound )
I'm I missing something ?
Some small heatsinks on the BDs ?
The bias is set to 15mv

RS232 · 9th February 2013, 09:54 PM

Ok, got this one working with the BD139/140 replacing the BC639/640 with a bias of 10mV.
On the the second one (DOA) I found a missing zener diode (ZD1) and a faulty ZVP3306...
After replacing the missing/faulty parts the amp worked fine (+/-2 hours), set up the bias to 10mV closed the amp power it up and nothing.
After looking for obvious faults I found out that the ZVP3306 was dead again...
Any ideas what can be causing the Fet to fail ?

Ric

comancho · 15th March 2013, 06:32 AM

Hi everybody

Sorry for my english.

Very interesting thread.
I just look for serivice manual of A3i, my unit is faulty and i have only a partial schematic,
after some time it get very very hot.
I found my A3i in the trash, some jerk threw it away.

Gianni

Ian Finch · 15th March 2013, 05:03 PM

In case you didn't see the OP schematic and comments or search the web yet:
cambridge audio a3i Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

BELLENud · 9th June 2013, 06:46 PM

Hello all,

Thanks a lot for all the useful informations on this forum and for the schematics.

I also got mine in a bin, in a dirty state (traces of burn inside, fuses blown, short circuit inside).

I replaced the 4 leds (burned) and several cap and resitor around them (mainly for security reasons).
I cleaned everything and also replaced one 2SA1216 in short circuit, setted the biases to 12mv then the A3I was back to life and givign me a very nice sound.

Since then, I still have a strange problem: the 2 F4A250V fuses are occasionally blowing, the 2 at the exact samle time. The amp can work for 3 months without loosing its fuses or for only a couple of hours.

The mesured DC voltage is higher than it should (+38,8V, -38,8V), when it should be +34V -34V according to schematics.
AC voltage mesured is 29V/29V, but I cannot find the value it should be.

-What is your ideas for the reason of this over range voltage ?
-What should I check/do to fix this ?

Thanks a lot in advance,

Nicolas (from france)

27th January 2013, 05:51 PM	#193
RS232 diyAudio Member Join Date: Jan 2006 Location: Swindon	New problem Replaced the BC639/640 with BD139/140 (original Philips one from the 90s) but they still get very hot and after a few tracks on the cd player it just shuts of (no sound ) I'm I missing something ? Some small heatsinks on the BDs ? The bias is set to 15mv Last edited by RS232; 27th January 2013 at 05:54 PM.

15th March 2013, 05:03 PM	#196
Ian Finch diyAudio Member Join Date: Apr 2010 Location: Coffs Harbour, on the east coast	In case you didn't see the OP schematic and comments or search the web yet: cambridge audio a3i Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics __________________ regards

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22nd January 2013, 01:41 PM	#191
homemodder Account disabled at member's request Join Date: May 2006	Fairchild bds are using the same die as the bcs, onsemi have changed though.

22nd January 2013, 02:03 PM	#192
RS232 diyAudio Member Join Date: Jan 2006 Location: Swindon	By old I mean very old, I have brand new BD135/6 and BD139/40 with around 15 years. I can always put in the MJE243/253 that X-PRO recommended. I'm preparing an parts order for Farnell and a couple more transistors is not going to brake the my bank account (50xIRFP240 and a few other bits). Ric

9th February 2013, 09:54 PM	#194
RS232 diyAudio Member Join Date: Jan 2006 Location: Swindon	Ok, got this one working with the BD139/140 replacing the BC639/640 with a bias of 10mV. On the the second one (DOA) I found a missing zener diode (ZD1) and a faulty ZVP3306... After replacing the missing/faulty parts the amp worked fine (+/-2 hours), set up the bias to 10mV closed the amp power it up and nothing. After looking for obvious faults I found out that the ZVP3306 was dead again... Any ideas what can be causing the Fet to fail ? Ric

15th March 2013, 06:32 AM	#195
comancho diyAudio Member Join Date: Mar 2013	Hi everybody Sorry for my english. Very interesting thread. I just look for serivice manual of A3i, my unit is faulty and i have only a partial schematic, after some time it get very very hot. I found my A3i in the trash, some jerk threw it away. Gianni

9th June 2013, 06:46 PM	#197
BELLENud diyAudio Member Join Date: Nov 2012	Hello all, Thanks a lot for all the useful informations on this forum and for the schematics. I also got mine in a bin, in a dirty state (traces of burn inside, fuses blown, short circuit inside). I replaced the 4 leds (burned) and several cap and resitor around them (mainly for security reasons). I cleaned everything and also replaced one 2SA1216 in short circuit, setted the biases to 12mv then the A3I was back to life and givign me a very nice sound. Since then, I still have a strange problem: the 2 F4A250V fuses are occasionally blowing, the 2 at the exact samle time. The amp can work for 3 months without loosing its fuses or for only a couple of hours. The mesured DC voltage is higher than it should (+38,8V, -38,8V), when it should be +34V -34V according to schematics. AC voltage mesured is 29V/29V, but I cannot find the value it should be. -What is your ideas for the reason of this over range voltage ? -What should I check/do to fix this ? Thanks a lot in advance, Nicolas (from france)