Hi guys,
I'm new to the forum, so first I'd like to say hello to everyone. I'm new to the topic, so please pardon my ignorance.
I recently bought a 'fully functional' Fisher CA-350 amp off e-bay. When it arrived, some of the control lamps did not work and one potentiometer knob was loose, but it seemed to work fine. It powered up, the stand by mode lamp turned on for ~3s and it could play music. After about 15 minutes of use I turned it off, came back to it 30 minutes later. It turned on, the meter lights went all the way up, the speakers emitted a loud pop, and the amp switched to stand by. Now I cannot get it out of standby - with speakers connected to it and input signal playing, all I get is the stand by mode lamp lighting up.
Forums seem to suggest that a cap might have been blown, but I opened it up and none of the elements seem to be visibly damaged. I suspect the speaker selector knob might be the culprit, but this is just a wild guess.
Is the amp dead, or am I missing something obvious? Since it cost me 30 pounds I don't think it will be worth taking to a repair shop. I could do a simple fix myself, but I just need to know what needs to be done. Any ideas?
Thanks in advance and sorry for the long post.
I'm new to the forum, so first I'd like to say hello to everyone. I'm new to the topic, so please pardon my ignorance.
I recently bought a 'fully functional' Fisher CA-350 amp off e-bay. When it arrived, some of the control lamps did not work and one potentiometer knob was loose, but it seemed to work fine. It powered up, the stand by mode lamp turned on for ~3s and it could play music. After about 15 minutes of use I turned it off, came back to it 30 minutes later. It turned on, the meter lights went all the way up, the speakers emitted a loud pop, and the amp switched to stand by. Now I cannot get it out of standby - with speakers connected to it and input signal playing, all I get is the stand by mode lamp lighting up.
Forums seem to suggest that a cap might have been blown, but I opened it up and none of the elements seem to be visibly damaged. I suspect the speaker selector knob might be the culprit, but this is just a wild guess.
Is the amp dead, or am I missing something obvious? Since it cost me 30 pounds I don't think it will be worth taking to a repair shop. I could do a simple fix myself, but I just need to know what needs to be done. Any ideas?
Thanks in advance and sorry for the long post.
A wild guess would be about right. It seems Ebay is a dumping ground for dying and dead audio electronics and you may have gotten your ₤30 worth but no more.
These receivers date from 1981 I believe, when Fisher were selling re-badged Sanyo products from Japan but there are no free download service manuals to give detailed repair advice on.
FWIW, my outline of the problem goes like this:
The protection circuit and speaker relay, usually, are there to disconnect the speakers when a fault like DC is detected at the output to the speakers and also when the volume level is set too high for safe operation. Ignore or bypass the protection circuit at the risk of a total meltdown and speaker burn-out when such a fault takes full effect. Obviously, the plan is to prevent damage so you are unlikely to see any damage inside the receiver just yet.
It is expected in old equipment that electrolytic capacitors will eventually dry out and fail, and while it becomes obvious that the largest caps affect the sound the most, some small caps are critical to the operation of the protection circuit too. They can prevent operation even when the amplifier is ok, other than any dying caps as mentioned.
Whatever happens, the amplifier is in need of service work and it may be beyond your skills, equipment or budget for all the parts needed or the work required. Still, you may think you can fix this by replacing just the electrolytic capacitors. Maybe that's possible and you may have nothing to lose now, apart from the cost of tools and parts. Not having a service manual can make it hard for some but you could still succeed with some personal help as you proceed with buying parts, tools, building safe test equipment like a bulb limiter and checking your work.
These receivers date from 1981 I believe, when Fisher were selling re-badged Sanyo products from Japan but there are no free download service manuals to give detailed repair advice on.
FWIW, my outline of the problem goes like this:
The protection circuit and speaker relay, usually, are there to disconnect the speakers when a fault like DC is detected at the output to the speakers and also when the volume level is set too high for safe operation. Ignore or bypass the protection circuit at the risk of a total meltdown and speaker burn-out when such a fault takes full effect. Obviously, the plan is to prevent damage so you are unlikely to see any damage inside the receiver just yet.
It is expected in old equipment that electrolytic capacitors will eventually dry out and fail, and while it becomes obvious that the largest caps affect the sound the most, some small caps are critical to the operation of the protection circuit too. They can prevent operation even when the amplifier is ok, other than any dying caps as mentioned.
Whatever happens, the amplifier is in need of service work and it may be beyond your skills, equipment or budget for all the parts needed or the work required. Still, you may think you can fix this by replacing just the electrolytic capacitors. Maybe that's possible and you may have nothing to lose now, apart from the cost of tools and parts. Not having a service manual can make it hard for some but you could still succeed with some personal help as you proceed with buying parts, tools, building safe test equipment like a bulb limiter and checking your work.
Thanks for the reply Ian, even though it's not too positive. I managed to find a service manual for Fisher CA-250 which, at a glance, seems to have almost the same circuits.
But, since the seller gave me a full refund on the amp, I guess I will just try looking for another one, and put this one up on ebay with a correct description in case someone will want to fix it/need some parts. As you say, I don't think it's worth putting too much money or effort in. If I had more time, I could do it as a project just for the sake of it, but unfortunately not at the moment.
I guess the case's closed.
But, since the seller gave me a full refund on the amp, I guess I will just try looking for another one, and put this one up on ebay with a correct description in case someone will want to fix it/need some parts. As you say, I don't think it's worth putting too much money or effort in. If I had more time, I could do it as a project just for the sake of it, but unfortunately not at the moment.
I guess the case's closed.
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