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.
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.
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/storage/CambridgeA500intsch.pdf
Seems the output transistor's built-in emitter resistances mostly tends to blow.
http://www.diyaudio.com/forums/solid-state/143009-cambridge-audio-a500-amp-broken-right-channel.html
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.
Schematic: http://x0546.orbbox.com/files/storage/CambridgeA500intsch.pdf
Seems the output transistor's built-in emitter resistances mostly tends to blow.
http://www.diyaudio.com/forums/solid-state/143009-cambridge-audio-a500-amp-broken-right-channel.html
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.
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.
Unfortunately both the SAP15 and SAP16's are obsolete. The nearest is STD03 with external 0.22R emitter resistors, if you can get them.
Get them from here, no problem. Better to upgrade to STD03 though.
Profusion plc, Audio Semiconductors and Components
Profusion plc, Audio Semiconductors and Components
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.
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.
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?
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?
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.
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.
The transformer is toroidal, with a 30-0-30v secondary, and the bridge rectifier(4 diodes similar to 1N4507s) checks out O.K., so(fingers crossed!) it's only! a faulty tranny.
Measure the physical size of it and see what's available,
Your Search Results | CPC | Results
Free delivery here at the moment if you follow the instructions.
Your Search Results | CPC | Results
Free delivery here at the moment if you follow the instructions.
Having measured the original TX and compared it with those on offer from CPC, none of theirs will fit. The original (180VA, 230VAC* primary) is 100mm. diameter x 55mm high, and there is barely 5mm clearance either side of the TX, so it looks as if I'm going to have to get one from Richer Sounds, unless I can source an identical one from one of the other suppliers, such as CHS, Cricklewood, etc.
* A thought occurred to me whilst typing this, which is that the transformer may have failed if the local mains voltage was 240v or higher.
* A thought occurred to me whilst typing this, which is that the transformer may have failed if the local mains voltage was 240v or higher.
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The manufacturer must design and guarantee their product to work anywhere on the harmonised supply voltage.
The limits are 216Vac to 254Vac.
That rule does not affect the user.
It is the responsibility of the retailer to ensure that every mains powered product they sell meets the requirements for the voltage range of the harmonised supply.
The limits are 216Vac to 254Vac.
That rule does not affect the user.
It is the responsibility of the retailer to ensure that every mains powered product they sell meets the requirements for the voltage range of the harmonised supply.
So, in round figures, Andrew, the transformer should be O.K. between -6 and +10% of the nominal mains voltage?
The 160va one should fit. The difference between 160 and 180 va is of no practical significance unless you are running the transformer at 100% of its rating. In normal use in the amp its a fraction of that, perhaps as little as 5% at idle and nothing even approaching 180 va until the amp is well and truly toasted.
MCTA160/30 - MULTICOMP - 160VA TOROIDAL 2X30V | CPC From This Range
Transformers are very conservatively rated. No worries on any mains variations.
MCTA160/30 - MULTICOMP - 160VA TOROIDAL 2X30V | CPC From This Range
Transformers are very conservatively rated. No worries on any mains variations.
Yes,
it's the old British standard supply tolerance of +-6% with an extension downwards to include Europe's standard range for their 220Vac.
In the UK it has become +6% & -10% but we never use the extra 4% between 216Vac and 226Vac.
Our supply still has a tolerance of +-6%.
But the manufacturer must design for the whole range of the harmonised supply.
The retailer must buy in universal standard transformer that are designed for that full range of voltage when the transformer is described as a universal transformer. Usually it will show as 220/240Vac
If the retailer shows it as 230Vac, you should ask them if it is a universal transformer for use on the UK's 240Vac supply. That question implies that the retailer knows the UK is upto 254Vac and that the retailer has ensured the design meets that voltage range requirement.
There would be nothing wrong with describing the transformer as 220/240Vac and 230Vac:30+30Vac @ 330VA. But few retailers do such. They generally miss either the 220/240 or miss the 230:
it's the old British standard supply tolerance of +-6% with an extension downwards to include Europe's standard range for their 220Vac.
In the UK it has become +6% & -10% but we never use the extra 4% between 216Vac and 226Vac.
Our supply still has a tolerance of +-6%.
But the manufacturer must design for the whole range of the harmonised supply.
The retailer must buy in universal standard transformer that are designed for that full range of voltage when the transformer is described as a universal transformer. Usually it will show as 220/240Vac
If the retailer shows it as 230Vac, you should ask them if it is a universal transformer for use on the UK's 240Vac supply. That question implies that the retailer knows the UK is upto 254Vac and that the retailer has ensured the design meets that voltage range requirement.
There would be nothing wrong with describing the transformer as 220/240Vac and 230Vac:30+30Vac @ 330VA. But few retailers do such. They generally miss either the 220/240 or miss the 230:
Just to clarify things, the transformer manufacturer has labelled the one used in the A500 as being 230VAC 180VA. Obviously Richer Sounds, as Cambridge Audio's Authorized UK spares distributors would insist that only the approved type be fitted, but, as the Multicomp 160VA one is almost £10 less than the 'proper' one, it may well suffice. Up to the amplifier's owner, I guess!
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