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Old 22nd January 2013, 01:41 PM   #191
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Fairchild bds are using the same die as the bcs, onsemi have changed though.
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Old 22nd January 2013, 02:03 PM   #192
RS232 is offline RS232  United Kingdom
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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).

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Old 27th January 2013, 05:51 PM   #193
RS232 is offline RS232  United Kingdom
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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.
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Old 9th February 2013, 09:54 PM   #194
RS232 is offline RS232  United Kingdom
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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 ?

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Old 15th March 2013, 06:32 AM   #195
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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.

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Old 15th March 2013, 05:03 PM   #196
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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
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Old 9th June 2013, 06:46 PM   #197
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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)
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Old 15th March 2014, 10:59 AM   #198
Melhior is offline Melhior  Georgia
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Hi everybody! Smb will be able to put here PCB?

Last edited by Melhior; 15th March 2014 at 11:09 AM.
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Old 15th March 2014, 11:08 AM   #199
Melhior is offline Melhior  Georgia
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Exclamation need PCB Cambridge Audio A3i

Hi everybody! Smb can upload PCB here?
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Old 23rd March 2014, 12:48 AM   #200
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I appreciate that this thread is six years old but I was interested in connecting with anyone who can advise on this amp.
I have had one for some years and today it has decided to retire.
The fault it has developed is that after a few minutes it cuts off and no sound is delivered to the speakers although the cd or cassette player is still functioning and can be heard via headphones direct from device.
I have never had an amp that has developed a fault and so am at a little bit of a loss. If such is an obvious problem for you experts I would be grateful to learn how to repair if such is possible.

If repair is not possible then I need to find an amp that likes classical music and would like to pair with Rogers speakers LS4a 150w 8ohm.

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