A5 repair
I have repaired an A5 with blown SAP's in the left channel (and R225 and R226 were also burned out). I used the schematic for the A500 and replaced all the transistors.
I noted that at least 2 resistor values are different on the A5. R226 and R213 appear to be 100R instead of 39R as shown in the A500 schematic.
Are there any other differences between the A5 and the A500?
I have repaired an A5 with blown SAP's in the left channel (and R225 and R226 were also burned out). I used the schematic for the A500 and replaced all the transistors.
I noted that at least 2 resistor values are different on the A5. R226 and R213 appear to be 100R instead of 39R as shown in the A500 schematic.
Are there any other differences between the A5 and the A500?
Im looking at an A5,
On one channel I replaced a damaged SAP15, with a new set of SAP16s. The left channel is fine, running at 13mV at pins S and E as stated before on this thread. On the problem channel I have no bias at all. The trim pot is not faulty.
Could someone please suggest where I need to look next.
Thanks very much
Charlie
On one channel I replaced a damaged SAP15, with a new set of SAP16s. The left channel is fine, running at 13mV at pins S and E as stated before on this thread. On the problem channel I have no bias at all. The trim pot is not faulty.
Could someone please suggest where I need to look next.
Thanks very much
Charlie
I got my cambridge audio A5 amps from ebay UK 3 weeks ago ( my old amps was cambridge P40), I hooked up it with mission 780 speaker and the nakamichi cd-4 cd player/denon dcd 920 cd player. At first the sound not clear as I expected and also low level sound. Then I hooked up bi-wire with the monster speaker cable (over 15 years old), after I cleaned the contacts both speaker cable and the banana plugs, the effect was totally different, it sounds great and I only need to turn the volume to around 8-9 oclock position and get the satisfied sound in volume and quality.
My tragedy happened last weekend, my friend visited me with his favourite speaker cable (he made by himself with some cat 5 power cable), suggested me to try. As I don't know much about, I hooked it with the HF speaker out, and my own with LF speaker out in by-wire mode. As I turned on the A5, the sound so strange in low level sound and the left channel even has noise with out music. no more than 1 min, I smelt the burning smell and smoke, I turn off and unplug the amps at once. I don't know what is going wrong, but I no longer has the left channel back to work, and the right channel even with uncleared sound as I hook up back with my monster cable.
I opened the cover, and the 4 sap 15 still looked normal but I could smelt the burning smell from them, I suspected that both of them need to replace, however I also find the blue colour variable resistor Citec rv201 had blown bubble on it, it should be burnt. I try to find the replacement, but there was no model number on it? where I can get those replacement?
I like the cambridge sounds, unfortunately I am in Canada, don't know whether I can fix it by myself or not?
My tragedy happened last weekend, my friend visited me with his favourite speaker cable (he made by himself with some cat 5 power cable), suggested me to try. As I don't know much about, I hooked it with the HF speaker out, and my own with LF speaker out in by-wire mode. As I turned on the A5, the sound so strange in low level sound and the left channel even has noise with out music. no more than 1 min, I smelt the burning smell and smoke, I turn off and unplug the amps at once. I don't know what is going wrong, but I no longer has the left channel back to work, and the right channel even with uncleared sound as I hook up back with my monster cable.
I opened the cover, and the 4 sap 15 still looked normal but I could smelt the burning smell from them, I suspected that both of them need to replace, however I also find the blue colour variable resistor Citec rv201 had blown bubble on it, it should be burnt. I try to find the replacement, but there was no model number on it? where I can get those replacement?
I like the cambridge sounds, unfortunately I am in Canada, don't know whether I can fix it by myself or not?
It sounds like either there was somehow a short, or perhaps the HF and LF were wired out of phase, causing a short. The distortion will have been the VI protection working hard to save the transistors - in vain as a prolonged short will still cause damage.
The output transistors will be damaged, likely the bias trimpots too.. Any 100 ohm linear trim pot that has the same pin out should work. It is likely the VI circuit is also damaged, and possibly the next stage back. Quite a mess. It depends how much experience you have here, as to whether this is repairable by yourself.
The output transistors will be damaged, likely the bias trimpots too.. Any 100 ohm linear trim pot that has the same pin out should work. It is likely the VI circuit is also damaged, and possibly the next stage back. Quite a mess. It depends how much experience you have here, as to whether this is repairable by yourself.
IF you want to try, then I would do the following:
* Replace the output transistors, and the bias trim pot. Also replace the capacitor across it (C220 on the schematic posted earlier)
* Pull and check the VI limiting transistors (Q215/216) - if either one is damaged, check the associated parts (D212, D215, R241, R254, R238-240, R258-260)
* If there was damage in the VI circuit, test/replace the VAS stage transistors, Q214, Q218, Q219 and surrounding resistors.
The schematic posted by tvi earlier on in the thread is for the right hand channel. the left channel has different part numbers but is otherwise identical. You should be able to find a copy of the Cambridge Audio A500 schematic online - it is the same amp internally.
* Replace the output transistors, and the bias trim pot. Also replace the capacitor across it (C220 on the schematic posted earlier)
* Pull and check the VI limiting transistors (Q215/216) - if either one is damaged, check the associated parts (D212, D215, R241, R254, R238-240, R258-260)
* If there was damage in the VI circuit, test/replace the VAS stage transistors, Q214, Q218, Q219 and surrounding resistors.
The schematic posted by tvi earlier on in the thread is for the right hand channel. the left channel has different part numbers but is otherwise identical. You should be able to find a copy of the Cambridge Audio A500 schematic online - it is the same amp internally.
thanks Jaycee for your brief explanations, I have just download the A500 schematic, need to check the readin of the parts as you mention first.
Unfortunately it is hard to get the sap 15 in Vancouver of bc. I find some ebay sellers from, but don't know they are selling the fake one or not? don't know will affect the sound quality or not?
However will
Unfortunately it is hard to get the sap 15 in Vancouver of bc. I find some ebay sellers from, but don't know they are selling the fake one or not? don't know will affect the sound quality or not?
However will
Hi guys
I now is an old thread but I have something strange on my CA A5.
The amp is working (it powers up), leds on the board light up and I'm about to connect my cheap speakers but...
In place os the normal SAP15/16N/P I have Kenwood TRAITR N/P transistor on it...
Setting the bias to 13mV right now
Will update tomorrow and let you guys know how it sound
I now is an old thread but I have something strange on my CA A5.
The amp is working (it powers up), leds on the board light up and I'm about to connect my cheap speakers but...
In place os the normal SAP15/16N/P I have Kenwood TRAITR N/P transistor on it...
Setting the bias to 13mV right now
Will update tomorrow and let you guys know how it sound
OK, back again
The victim now is a A500RC but since the amp board is the same as in the A5 I decided to use this thread.
Amp is working (replaced 2 SAP transistors, trimpot, cap and 1 zener diode (3.3V 600mv D206)) but something is still amiss...
Amp is working fine but one channel has a 3mvDC offset and the other one 100mvDC.
Bias is set to 13mV on both channels and is stable after 1 hour.
Can someone give me some pointers were to look ?
Regards
Ric
The victim now is a A500RC but since the amp board is the same as in the A5 I decided to use this thread.
Amp is working (replaced 2 SAP transistors, trimpot, cap and 1 zener diode (3.3V 600mv D206)) but something is still amiss...
Amp is working fine but one channel has a 3mvDC offset and the other one 100mvDC.
Bias is set to 13mV on both channels and is stable after 1 hour.
Can someone give me some pointers were to look ?
Regards
Ric
Any history on the A500?
When you say working, I assume you mean normal audio output power and clarity.
If the offset is your only concern, it may have been so from manufacture, unless the specification says otherwise.
Few amps, have an adjustment so the place to adjust is the matching of Q212,Q222 etc by Vbe
('not sure which channel you refer to but there will be same parts, perhaps Q202 etc. in the
other channel. A schematic for one chanel is on the first page. It may require anything from a
swap over of existing transistors to buying a few and testing Vbe on your multimeter and swapping
them in the circuit to improve the match and thus lower offset. That's why manufacturers don't bother.
Practically, it doesn't matter but if DC imbalance worries you, go ahead.
When you say working, I assume you mean normal audio output power and clarity.
If the offset is your only concern, it may have been so from manufacture, unless the specification says otherwise.
Few amps, have an adjustment so the place to adjust is the matching of Q212,Q222 etc by Vbe
('not sure which channel you refer to but there will be same parts, perhaps Q202 etc. in the
other channel. A schematic for one chanel is on the first page. It may require anything from a
swap over of existing transistors to buying a few and testing Vbe on your multimeter and swapping
them in the circuit to improve the match and thus lower offset. That's why manufacturers don't bother.
Practically, it doesn't matter but if DC imbalance worries you, go ahead.
Last edited:
Hi Ian
Got this amp of *bay as non working...
The previous owner blown one of the outputs (left) and he had the briliant idea of putting some copper wire on the fuses to power it up again.
I replaced all the damaged parts and got it working (is not the first one I fix) but the strange thing is the channel I fixed as a offset is 3mv and the one that was not damaged is 100mv.
Since this never happend before I was asking for some help were to look.
Ric
Got this amp of *bay as non working...
The previous owner blown one of the outputs (left) and he had the briliant idea of putting some copper wire on the fuses to power it up again.
I replaced all the damaged parts and got it working (is not the first one I fix) but the strange thing is the channel I fixed as a offset is 3mv and the one that was not damaged is 100mv.
Since this never happend before I was asking for some help were to look.
Ric
Hi Ric
Since posting, I noticed usual objections to offhanded claims about large
offset being OK on other anmps. The offset is up to 35mA even on a brand
new Marantz Pearl-lite amp here. Check the "advice on changing transistors
in Rotel amplifier" thread) for interest
It seems that there may be issues with caps and you can assume in 10+ year
old amps, some caps are drying a bit and by 20 it definitely needs new PS
main caps, bypass rail caps and feedback cap renewed as a matter of course.
Some say this causes the high offset. 'Not sure as I don't work on those
models but read and think about it. If you have doubts about what next,
come back and we'll see what help is available.
You won't damage anything in your speakers at 100mV or wreck the sound
but if the drift continues, it must be fixed. I'd start with input transistors as
above and look for electrolytics to replace while you are in there.
Most cap. changes won't do anything for DC balance in the amp but you might look at the VI limiter circuit parts and all diodes in the front end for suspects, just as you found D206. If the sound is as clear and the stereo image as you would expect, I wouldn't get too concerned about serious stuff
yet.
Since posting, I noticed usual objections to offhanded claims about large
offset being OK on other anmps. The offset is up to 35mA even on a brand
new Marantz Pearl-lite amp here. Check the "advice on changing transistors
in Rotel amplifier" thread) for interest
It seems that there may be issues with caps and you can assume in 10+ year
old amps, some caps are drying a bit and by 20 it definitely needs new PS
main caps, bypass rail caps and feedback cap renewed as a matter of course.
Some say this causes the high offset. 'Not sure as I don't work on those
models but read and think about it. If you have doubts about what next,
come back and we'll see what help is available.
You won't damage anything in your speakers at 100mV or wreck the sound
but if the drift continues, it must be fixed. I'd start with input transistors as
above and look for electrolytics to replace while you are in there.
Most cap. changes won't do anything for DC balance in the amp but you might look at the VI limiter circuit parts and all diodes in the front end for suspects, just as you found D206. If the sound is as clear and the stereo image as you would expect, I wouldn't get too concerned about serious stuff
yet.
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