OK Just to let everybody know in advance that electronics isn't my strong point.
I seem to have a oroblem with intermittent fading and then return of volume, it gets soft and then louder again.
The local Yamaha certified repair techie has had a look at the unit and says he cannot find anything wrong with the unit.
It isn't any of the power amps as they work fine with other controllers, so I am sure the problem is in this Yamaha.
Any ideas?? I am not sure at this stage whether to sell it off or repair, up until now I have been very happy with it.
I have read the threads relating to C-80's and this problem did not come up.If I keep it I will follow the other advice and do some serious ventilation of the case.
regards
Ted
I seem to have a oroblem with intermittent fading and then return of volume, it gets soft and then louder again.
The local Yamaha certified repair techie has had a look at the unit and says he cannot find anything wrong with the unit.
It isn't any of the power amps as they work fine with other controllers, so I am sure the problem is in this Yamaha.
Any ideas?? I am not sure at this stage whether to sell it off or repair, up until now I have been very happy with it.
I have read the threads relating to C-80's and this problem did not come up.If I keep it I will follow the other advice and do some serious ventilation of the case.
regards
Ted
HELP please
BUMP!!!
Problem is getting worse,have to do something soon; OK do I try and fix problem or just buy a new pre-amp?? I know it's not exactly a DIY query but my thing is speakers not the stuff further up the line.
Given the state of the worlds economy maybe I should just buy new and keep a factory in China busy, what a shame!!
BUMP!!!
Problem is getting worse,have to do something soon; OK do I try and fix problem or just buy a new pre-amp?? I know it's not exactly a DIY query but my thing is speakers not the stuff further up the line.
Given the state of the worlds economy maybe I should just buy new and keep a factory in China busy, what a shame!!
you might just set this pre-amp aside, and fix it later.
these are simple to build -
http://www.diyaudio.com/forums/showthread.php?postid=1226446#post1226446
these are simple to build -
http://www.diyaudio.com/forums/showthread.php?postid=1226446#post1226446
Yamaha C-80
Do both channel's fade in and out???? How about the phono input???? I have a C-80 and had power supply problems which caused noise and loss in phono input. The 6800uf caps and a few diodes were bad. Seperate power supply for phono. I will see if I can find my service manual for C-80.
Do both channel's fade in and out???? How about the phono input???? I have a C-80 and had power supply problems which caused noise and loss in phono input. The 6800uf caps and a few diodes were bad. Seperate power supply for phono. I will see if I can find my service manual for C-80.
Hi moondawg, I had a similar problem caused by overheating ...bias offset, Is there any distortion or erratic sound output?
Sounds like you might have a leaky or dry psu cap? if they arent working properly you get power dips on the supply side! cheap enough and easy to replace!
Never trust repair mens diagnoisis they mostly do the bare minimum ie, if you have a blown o/p transistor they will only replace the failed one not all of them...PLZ Dont fuel the Chinese economy, these things are built with a self destruct button, There are some decent valve amps now tho!
Best advice is to take off the cover and get stuck in armed with your digital multimeter..Unplug it first obviously!
Start looking for obvious stuff like dry solder joints etc bulging caps, discoloured resistors etc...
if it all goes horribly wrong..think of it as a learning curve!
we all have to start somewhere!
Sounds like you might have a leaky or dry psu cap? if they arent working properly you get power dips on the supply side! cheap enough and easy to replace!
Never trust repair mens diagnoisis they mostly do the bare minimum ie, if you have a blown o/p transistor they will only replace the failed one not all of them...PLZ Dont fuel the Chinese economy, these things are built with a self destruct button, There are some decent valve amps now tho!
Best advice is to take off the cover and get stuck in armed with your digital multimeter..Unplug it first obviously!
Start looking for obvious stuff like dry solder joints etc bulging caps, discoloured resistors etc...if it all goes horribly wrong..think of it as a learning curve!
we all have to start somewhere!
Does the headphone output also fade?
The headphone amp bypasses the "invert amp" so if the headphone out is good then the problem is most likely with the "invert amp"
I'd first suspect the mute transistors, I have shadowed them in the attached pic.
If you need it I have the service manual, its 13meg though.
hope this helps
Regards
James
The headphone amp bypasses the "invert amp" so if the headphone out is good then the problem is most likely with the "invert amp"
I'd first suspect the mute transistors, I have shadowed them in the attached pic.
If you need it I have the service manual, its 13meg though.
hope this helps
Regards
James
Attachments
C-80
I would suspect the power supply because you said both sides do the same thing. Both invert amps are both bad. Could be but not as likely. The 6db flat amps are ahead of the invert amps any way. If you are pluged into the reg outs the inverts are out of the picture. The original unit had 4 leg 4700uf 35v cans. The power supply is pushing them very close to 35v. I could not find that size in a 4 leg that would fit the pc board holes. I had to get 6800uf 63v 4 leg caps. Takes 4 of them. C367, C368, C211 & C212. The only ones I could find were on EBay and they are taller than orig caps and you can not put cover back on. I also replaced the diodes in the supply's while working on it. The extra uf and voltage give a cleaner and less to the max on caps working voltage. I have not had any problems since then. Sounds great. There are + & - test bus points near supply. Check with scope for level & ripple noise.
I would suspect the power supply because you said both sides do the same thing. Both invert amps are both bad. Could be but not as likely. The 6db flat amps are ahead of the invert amps any way. If you are pluged into the reg outs the inverts are out of the picture. The original unit had 4 leg 4700uf 35v cans. The power supply is pushing them very close to 35v. I could not find that size in a 4 leg that would fit the pc board holes. I had to get 6800uf 63v 4 leg caps. Takes 4 of them. C367, C368, C211 & C212. The only ones I could find were on EBay and they are taller than orig caps and you can not put cover back on. I also replaced the diodes in the supply's while working on it. The extra uf and voltage give a cleaner and less to the max on caps working voltage. I have not had any problems since then. Sounds great. There are + & - test bus points near supply. Check with scope for level & ripple noise.
C-80
Sorry I did not get back with you last night as I was watching the UF / LSU football game. I am a big UF fan. This preamp uses a lot of discrete parts not like newer units with dual opamps where 1 bad opamp could affect both channels. To have 2 bad transistors in the same place in both channels is very unlikely. If you had some test equipment you could insert a sine wave to both channels thru tuner input and check the output along the signal path. There is a known problem with this unit with the power supply and breakdown of the filter caps over time. I hope this helps.
Sorry I did not get back with you last night as I was watching the UF / LSU football game. I am a big UF fan. This preamp uses a lot of discrete parts not like newer units with dual opamps where 1 bad opamp could affect both channels. To have 2 bad transistors in the same place in both channels is very unlikely. If you had some test equipment you could insert a sine wave to both channels thru tuner input and check the output along the signal path. There is a known problem with this unit with the power supply and breakdown of the filter caps over time. I hope this helps.
Wow!! Rocco I'm impressed, buying them is no problem ( shame about the exchange rate ) are they a direct drop-in replacement??
I'd better start on the case mods __MMmmm these are too tall for the case as is aren't they??
The Chinese do deserve the same standard of living that we aim for but if they were bound by the same environmental and human rights standards we work to they could not compete, I'll try and keep my money circulating in the country here if possible
I'd better start on the case mods __MMmmm these are too tall for the case as is aren't they??
The Chinese do deserve the same standard of living that we aim for but if they were bound by the same environmental and human rights standards we work to they could not compete, I'll try and keep my money circulating in the country here if possible
Moondog,
I remember working on a Yamaha C-something. could have been an 80, but I recall it had some rather large copper bus bars for DC and gnd running across the circuit board. Check all of the solder joints with a magnifying glass, I'm sure you'll find a few broken ones, that's all it took for the one I serviced.
Craig
I remember working on a Yamaha C-something. could have been an 80, but I recall it had some rather large copper bus bars for DC and gnd running across the circuit board. Check all of the solder joints with a magnifying glass, I'm sure you'll find a few broken ones, that's all it took for the one I serviced.
Craig
Hi all; I've paid for the caps, my partner wil bring the back from the USA in about a month.
I've just started to cut holes in the case to allow extra height and for airflow.
I have checked the solder joints but haven't found anything obvious, I think I need a bigger magnifier, mine is only 3X, a bigger brighter lamp may help too.
I need some new toys
regards
Ted
I've just started to cut holes in the case to allow extra height and for airflow.
I have checked the solder joints but haven't found anything obvious, I think I need a bigger magnifier, mine is only 3X, a bigger brighter lamp may help too.
I need some new toys
regards
Ted
Just completed some quick angle grinder surgery on the case.
added vent in the bottom ( 3 X 5 inches of punched mesh ) and added a big hole in the top; 6inches by 9 inches where the pairs of smoothing caps are, used the opportunity to give another 1/2 inch of clearance.
http://farm4.static.flickr.com/3039/3028465851_87e8dc2a2e.jpg?v=0
http://farm4.static.flickr.com/3146/3029301652_e3c1a12cca_m.jpg\
Even with no other modifications this is a big improvement in SQ, it's been playing now for a hour or so and top of the case is only just warm.
How could Yamaha have got it so wrong when these units were first designed?? As I now have an extra 12 /15 millimetres to play with is it worthwhile using bigger heatsinks internally?? or is the nventilation on its own going to keep the heat down//
regards
Ted
PS Sounds better when cooler!!
added vent in the bottom ( 3 X 5 inches of punched mesh ) and added a big hole in the top; 6inches by 9 inches where the pairs of smoothing caps are, used the opportunity to give another 1/2 inch of clearance.
http://farm4.static.flickr.com/3039/3028465851_87e8dc2a2e.jpg?v=0
http://farm4.static.flickr.com/3146/3029301652_e3c1a12cca_m.jpg\
Even with no other modifications this is a big improvement in SQ, it's been playing now for a hour or so and top of the case is only just warm.
How could Yamaha have got it so wrong when these units were first designed?? As I now have an extra 12 /15 millimetres to play with is it worthwhile using bigger heatsinks internally?? or is the nventilation on its own going to keep the heat down//
regards
Ted
PS Sounds better when cooler!!
I have been monitoring the tenperature inside the case since I did the cut and shut with the angle grinder, picture shows temperature after being turned on all night and then playing music for an hour or three.
I'm not unhappy with this result, ambient temperature inside the house is 18C
http://farm4.static.flickr.com/3052/3033962402_334ce7b8dc.jpg?v=0
Do I need to change the internal heatsinks??
I'm not unhappy with this result, ambient temperature inside the house is 18C
http://farm4.static.flickr.com/3052/3033962402_334ce7b8dc.jpg?v=0
Do I need to change the internal heatsinks??
Help with soldering needed
Hi fellas;
The replacement caps have arrived, very well packaged and cheap compared to local prices.
I have my doubts about my ability to do this repair on my own and don't want to use a paid technician if I can help from forum members.
Is there any-one in the Reservoir Preston Coburg area whi could help out for a couple of hours, helper will be fed and I am willing to pay in speakers bits.
The extra cooling seems to have helped but when we turn the volume right up the fading problem returns.
Regards
Ted
Hi fellas;
The replacement caps have arrived, very well packaged and cheap compared to local prices.
I have my doubts about my ability to do this repair on my own and don't want to use a paid technician if I can help from forum members.
Is there any-one in the Reservoir Preston Coburg area whi could help out for a couple of hours, helper will be fed and I am willing to pay in speakers bits.
The extra cooling seems to have helped but when we turn the volume right up the fading problem returns.
Regards
Ted
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