Two big problems with my Yamaha CR-2040
- Thread starter Lelle
- Start date
You do realize that there are two different supplys feeding the power amps.
1. +/- 55vdc unregulated rail voltage which are connected directly from the big filter caps to the output transistors collectors.
2 +/-60vdc Regulated which supply the amplifier front end B+/- voltage.
part of the regulator circuit utilizes TR904 and TR905 pass transistors.
Are you sure your not confusing these two different power supplies ?
1. +/- 55vdc unregulated rail voltage which are connected directly from the big filter caps to the output transistors collectors.
2 +/-60vdc Regulated which supply the amplifier front end B+/- voltage.
part of the regulator circuit utilizes TR904 and TR905 pass transistors.
Are you sure your not confusing these two different power supplies ?
Baron K Rool
Well-Known Member
Why is only one of the three transistors mounted with an insulator sheet? Is that the original setup? If not, that might be very bad.
clinic-audio
all on YAMAHA untill 1990
Lelle
Active Member
I've looked in the service manual, and it seems that I have the North European Model of the receiver. Sadly, the North European Model doesn't have a voltage selector, this model is made for 230 volts. Only the general model has a voltage selector. Maybe I should replace the diodes from D902 to D907 and D912 and D913 aswell. I've used a multimeter to measure the 60 and 55 volts. The black lead connected to the chassis (ground), and the red lead to measure the plus and minus voltages.
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What does the back panel ID plate state as to operating voltage ? 220/50hz or 230/50hz ? What does your mains AC actually measure ? According to my service manual the Northern Europian model is 220/50hz. If your actual voltage is higher than 220 then your secondary voltages are going to run higher than stated in the service manual. Replacing the diodes will not lower the voltages.
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clinic-audio
all on YAMAHA untill 1990
Replacing the diodes will not lower the voltages
YES ! for sure !
YES ! for sure !
That explains your slight voltage deviation. Measure the AC voltage off the mains transformers two red wires to chassis ground . Is it more than 45vac ?
Lelle
Active Member
I think it is no way to lower the -55 and +55 volts. They both read 64 volts. The receiver works fine otherwise. I'm going to replace TR903, TR902 and TR901, I haven't done that yet. I suspect that TR915, TR904 and TR905 gets too much voltage or current, because they get very hot. Almost burned my fingers.
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clinic-audio
all on YAMAHA untill 1990
Hello Lelle
Yes, there is a way to decrease - 55V and + 55 V : using a variac will bring you safe working area with your amp . You just have to adjust the output voltage of the variac and the unit will work under the right main power supply voltage and see if the temp is decreasing on TR 901,902, and 915 .
As Avionic said , the unit is under overvoltage at main power supply and that's why those transistors are very very hot .
Put the variac in another room because some are noisy and making vibrations !
Something like this..
http://uk.farnell.com/staco-energy-products/3pn1520b/variable-transformer/dp/4354667
Probably be able to find a used one a lot cheaper on ebay .
clinic-audio
all on YAMAHA untill 1990
this one is cheaper (located in FRANCE)
http://www.selectronic.fr/variac-autotransformateur-3000va.html
http://www.selectronic.fr/variac-autotransformateur-3000va.html
That should get it done..3KVA..:yes:
Lelle
Active Member
Thanks everyone for the answer. A variac sounds like a good idea, but right now I can't afford it.
A 240 volts to 220 volts transformer could have work, but they seem to be rare. In that case it will be 230 to 210 volts, that may be a bit low. As the receiver is rated at 220 volts.
And replacing the transformer in the receiver, I think it will be expensive and hard to find a replacement. So that's out of the question.
But if I use a variac, wouldn't the the +-60 volts get too low? It is 58.5 right now. And the +-55 volts are at almost 65 volts. Can that damage the unit overtime? Amazingly the power amp section works fine with almost 10 volts over spec.
A 240 volts to 220 volts transformer could have work, but they seem to be rare. In that case it will be 230 to 210 volts, that may be a bit low. As the receiver is rated at 220 volts.
And replacing the transformer in the receiver, I think it will be expensive and hard to find a replacement. So that's out of the question.
But if I use a variac, wouldn't the the +-60 volts get too low? It is 58.5 right now. And the +-55 volts are at almost 65 volts. Can that damage the unit overtime? Amazingly the power amp section works fine with almost 10 volts over spec.
