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Old 11th January 2012, 11:21 PM   #1
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Default Cambridge Audio A500 - Worth Repairing ?

I picked up a Cambridge Audio A500 amplifier the other day, mainly because I liked the look of it.

It didn't cost me anything but both 4A fuses on the main board are blown, suggesting the SAP15s are probably deceased.

I haven't tried replacing the fuses and just firing it up yet (nowhere round here to stock them) but assuming the power amps are blown is this amp worth spending the money on to replace them?

I'm competent with a soldering iron so it'd just be the component costs.
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Old 13th January 2012, 04:09 PM   #2
system7 is offline system7  United Kingdom
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Always worth fixing good ol' equipment if its cheap! I don't suppose basic audio amp technology has changed in 40 years, so if it's an OK design and the 10-y-o A500 is, go for it.

Schematic: http://x0546.orbbox.com/files/storag...A500intsch.pdf

Seems the output transistor's built-in emitter resistances mostly tends to blow.
Cambridge audio A500 amp with broken right channel

But I'd first replace the fuses, which will be 20mm 4A T (Time-delay T, not Fast F) types on anything around the power supply. You might get lucky and find they just popped at a loud party or something.
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Old 14th January 2012, 02:55 AM   #3
jaycee is offline jaycee  United Kingdom
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Can guarantee the SAP15's have expired due to the lousy heatsink in this unit. If someone had it on loud for a party, they're toast. A good bit of kit let down by Cambridge skimping on the heatsink!

Unfortunately both the SAP15 and SAP16's are obsolete. The nearest is STD03 with external 0.22R emitter resistors, if you can get them.
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Old 14th January 2012, 07:31 AM   #4
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Rapid electrinics still sell the sap 16's
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Old 14th January 2012, 11:16 AM   #5
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Get them from here, no problem. Better to upgrade to STD03 though.

Profusion plc, Audio Semiconductors and Components
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Old 7th February 2012, 09:41 PM   #6
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Sorry it's been a while since I replied to this thread but I've only just gotten round to looking at it.

Before doing anything else I popped a couple of new fuses in and connected it up to my iPod and a couple of speakers I had laying about.

Result? Sound, from both channels, and quite reasonable sound too.

Next step is to try it with some better speakers and a turntable. Fingers crossed it's just as System7 suggested and that someone was driving it really loud at a party sometime.
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Old 7th February 2012, 11:07 PM   #7
jaycee is offline jaycee  United Kingdom
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Very lucky - usually the SAPs fail, short circuit which then blows the fuses!
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Old 25th April 2013, 10:38 AM   #8
OXAUDIO is offline OXAUDIO  United Kingdom
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I've recently been asked if I can repair an A500 in which the mains transformer primary is open circuit, but all 3 internal fuses are intact, and the SAP15s check out O.K. 'cold'
I haven't checked other components, but is it worth(a) replacing the SAP15s with STD03s
and (b) spending 45.00 for a new mains transformer. BTW, does the transformer have a built-in thermal fuse?
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Old 25th April 2013, 11:08 AM   #9
Mooly is offline Mooly  United Kingdom
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If its open then it probably does have a thermal fuse, but whether it does or does not, if it is OC within the tranny then its not user repairable.

Any replacement should be powered up with a bulb tester first to check all is OK. I don't know what sort of tranny is used but if its just a standard split winding (eg 20-0-20) then an off the shelf replacement is probably possible at far lower cost. Worth checking that the bridge rectifier is OK. If nothing obvious is found then you just have to power it up carefully and be prepared (possibly) to do further work. Or it could just be the tranny.
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Old 25th April 2013, 11:17 AM   #10
OXAUDIO is offline OXAUDIO  United Kingdom
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Quote:
Originally Posted by Mooly View Post
If its open then it probably does have a thermal fuse, but whether it does or does not, if it is OC within the tranny then its not user repairable.

Any replacement should be powered up with a bulb tester first to check all is OK. I don't know what sort of tranny is used but if its just a standard split winding (eg 20-0-20) then an off the shelf replacement is probably possible at far lower cost. Worth checking that the bridge rectifier is OK. If nothing obvious is found then you just have to power it up carefully and be prepared (possibly) to do further work. Or it could just be the tranny.
The transformer is toroidal, with a 30-0-30v secondary, and the bridge rectifier(4 diodes similar to 1N5407s) checks out O.K., so(fingers crossed!) it's only! a faulty tranny.
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