Cambridge Audio A5 repair job

pulseezar · 4th June 2008, 02:33 PM

Hi all,

I have a Cambridge Audio A5 amplifier that has a fried SAP15 transistor. I took it to richer sounds to get repaired but they want £80 to do the job, unfortunately I don't have that money so I'm looking at repairing it myself. I can use a soldering iron fine but I was hoping anyone with experience of this could tell me if any other components are likely to be broken too, and also where I could source the SAP15 transistors from. I checked rapid electronics but they only have SAP16.

Theres a pic for you to take a look at if it helps.

Thanks loads!

Jan Dupont · 4th June 2008, 03:53 PM

Most of the time the driver transistors goes the same way as the output transistors

You may need to change those to....

It will take some skills to measure and identify what has blown up.....

Why did it blow up in the first place ?

bosedtobosed · 4th June 2008, 03:56 PM

cricklewood electronics have them about £6

reddish75 · 4th June 2008, 04:23 PM

ok, first of all you really need check if there is any evidence of burning around any resistors then replace both positive and negative transistors on the blown channel. also i would recomend replacing the driver transistors mje350, and mje340. having done this check if there is any evidence of burning around any resistors, after you have done this and before doing anything else build a dim bulb tester this site gives you the basic idea http://www.antiqueradio.org/dimbulb.htm obviosly ground goes to ground which this site dosent show!
then with your amp pluged into this power it up, if the bulb lights up and stays on you still have a problem, if not you now need to adjust theidle current which is done by monitoring the voltage between pins s and e of the output transistors (see their datasheet) to achieve a voltage of 13mv.
now check your dc offset this should be anywhere between 0-20mv, now normally would connect a dummy load to the amp to test it fully but seems your a beginner at this i doubt you have one so connect back to your speakers at your own risk as they say!

chris

x-pro · 4th June 2008, 05:17 PM

Farnell has in stock both SAP15N and SAP15P for £4-58 each +VAT.

Cheers

Alex

dodo · 5th June 2008, 02:37 PM

little of topic , but can someone advise me the matching procedure of the SAP N and SAP P darlington trnsistors
Is it this same Vbe and Hfe as standard BJT transistors ?

Thank You in advance

tvi · 11th April 2009, 02:17 AM

This is for the A500
Part 1

Regards
James

tvi · 11th April 2009, 02:19 AM

part 2

jaycee · 11th April 2009, 02:32 AM

SAP16 is usable in this amp.
Cambridge dont appear to match them.

If they blew, be sure to check the bias trimpot isn't dead, or your replacements will blow.

thebadproducer · 11th May 2009, 06:42 PM

Hi Pulseezar,

I have just been given the same amp with exactly the same problem, have you had any luck with your repair job?

Also, to Jaycee, I have some SAP16's with which to replace the SAP15's (I was told they were a drop in replacement) should I replace all four of these so there is symmetry?

Thanks,

Charlie

4th June 2008, 02:33 PM	#1
pulseezar diyAudio Member Join Date: May 2008	Cambridge Audio A5 repair job Hi all, I have a Cambridge Audio A5 amplifier that has a fried SAP15 transistor. I took it to richer sounds to get repaired but they want £80 to do the job, unfortunately I don't have that money so I'm looking at repairing it myself. I can use a soldering iron fine but I was hoping anyone with experience of this could tell me if any other components are likely to be broken too, and also where I could source the SAP15 transistors from. I checked rapid electronics but they only have SAP16. Theres a pic for you to take a look at if it helps. Thanks loads!

4th June 2008, 03:53 PM	#2
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Most of the time the driver transistors goes the same way as the output transistors You may need to change those to.... It will take some skills to measure and identify what has blown up..... Why did it blow up in the first place ? __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

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4th June 2008, 03:56 PM	#3
bosedtobosed diyAudio Member Join Date: May 2008	cricklewood electronics have them about £6

4th June 2008, 04:23 PM	#4
reddish75 diyAudio Member Join Date: Aug 2006	ok, first of all you really need check if there is any evidence of burning around any resistors then replace both positive and negative transistors on the blown channel. also i would recomend replacing the driver transistors mje350, and mje340. having done this check if there is any evidence of burning around any resistors, after you have done this and before doing anything else build a dim bulb tester this site gives you the basic idea http://www.antiqueradio.org/dimbulb.htm obviosly ground goes to ground which this site dosent show! then with your amp pluged into this power it up, if the bulb lights up and stays on you still have a problem, if not you now need to adjust theidle current which is done by monitoring the voltage between pins s and e of the output transistors (see their datasheet) to achieve a voltage of 13mv. now check your dc offset this should be anywhere between 0-20mv, now normally would connect a dummy load to the amp to test it fully but seems your a beginner at this i doubt you have one so connect back to your speakers at your own risk as they say! chris

4th June 2008, 05:17 PM	#5
x-pro diyAudio Member Join Date: Apr 2003 Location: London	Farnell has in stock both SAP15N and SAP15P for £4-58 each +VAT. Cheers Alex

5th June 2008, 02:37 PM	#6
dodo diyAudio Member Join Date: Dec 2004 Location: Bydgoszcz , small town in Poland	little of topic , but can someone advise me the matching procedure of the SAP N and SAP P darlington trnsistors Is it this same Vbe and Hfe as standard BJT transistors ? Thank You in advance

11th April 2009, 02:32 AM	#9
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	SAP16 is usable in this amp. Cambridge dont appear to match them. If they blew, be sure to check the bias trimpot isn't dead, or your replacements will blow.

11th May 2009, 06:42 PM	#10
thebadproducer diyAudio Member Join Date: May 2009	Hi Pulseezar, I have just been given the same amp with exactly the same problem, have you had any luck with your repair job? Also, to Jaycee, I have some SAP16's with which to replace the SAP15's (I was told they were a drop in replacement) should I replace all four of these so there is symmetry? Thanks, Charlie

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