AngelAT
Well-Known Member
Hello Yamaha fans,
Today I finished the repair of my Yamaha CR-820.
The guy I bought her from said that she is not working - someone tried to repair her but could not. One transistor was missing and a resistor was unsoldered from one end. The guy also gave me the spare lights that he had bought.
Now I can say that this Yamaha had all typical problems for the model:
The missing trans was TR721. I replaced it using the modern equivalent MJE 15031. Also replaced the complementary TR719 which was also gone. Here I used MJE15030.
The fuse resistor FR701 was also blown. Replaced both channels with Vishay 68 Ohm fuse resistors.
After these I powered her under a DBT. There were no shorts!
But then the relay was not engaging. So first thing I started checking were the end transistors (2SD427 and 2SB557). As you can wisely guess the easily accessible ones were ok. The problem was in the other channel. Still, managed to take them out without having to remove the power transformer. Replaced both channels with MJ15015 and MJ15016 (I know this is a bit of an overkill, but this is what I had available). Managed to put the new trans while blocking the socket with a screwdriver, so that the pins can get well into the sockets. Of course, put some new thermo paste.
Now the relay was already engaging and I could hear sound!
It was time for biasing. And guess what, TP3 and TP4 ok and easily biased, but TP1 and TP2 0,00mV... Another typical problem for the model - R763 and R765 (47 Ohm) defect, so had to replace them also and then the biasing was not a problem (8mV).
At the same time I recapped the power supply.
So finally the time has come for the lights. Here two things made me scratch my head - someone had used the dial point lamp for the middle of the three indicator scale lamps... And the original lamp was nowhere to be seen. Replaced the two blown Indicator scale lamps. The dial point lamp was ok. And then started looking for the third indicator lamp. Fount it stuck between faceplate and tone control board...
Had to unmount the board so that I can access the lamp. Used this opportunity to clean the pots. All lamps installed at their proper placed. Cleaned all switches and the volume pot. Oiled the dial string bearing wheels. Put some grease on the dial pointer bed. Cleaned the faceplate. Be careful when you remove the knob for the station selection - so that the pilar used to do the connection between the knob and the counterweight does not get out. If this happens, most probably you will have to restring.
So now she looks and sounds great!
BTW a question: The input for Phono1 was blocked. Does anyone has an idea why is this done? I still have not tested the phono because I do not feel like removing my main TT just for the test. Or can you guys suggest a way to test phono stage without having to connect a TT?
Happy holidays and stay safe!
Today I finished the repair of my Yamaha CR-820.
The guy I bought her from said that she is not working - someone tried to repair her but could not. One transistor was missing and a resistor was unsoldered from one end. The guy also gave me the spare lights that he had bought.
Now I can say that this Yamaha had all typical problems for the model:
The missing trans was TR721. I replaced it using the modern equivalent MJE 15031. Also replaced the complementary TR719 which was also gone. Here I used MJE15030.
The fuse resistor FR701 was also blown. Replaced both channels with Vishay 68 Ohm fuse resistors.
After these I powered her under a DBT. There were no shorts!
But then the relay was not engaging. So first thing I started checking were the end transistors (2SD427 and 2SB557). As you can wisely guess the easily accessible ones were ok. The problem was in the other channel. Still, managed to take them out without having to remove the power transformer. Replaced both channels with MJ15015 and MJ15016 (I know this is a bit of an overkill, but this is what I had available). Managed to put the new trans while blocking the socket with a screwdriver, so that the pins can get well into the sockets. Of course, put some new thermo paste.
Now the relay was already engaging and I could hear sound!
It was time for biasing. And guess what, TP3 and TP4 ok and easily biased, but TP1 and TP2 0,00mV... Another typical problem for the model - R763 and R765 (47 Ohm) defect, so had to replace them also and then the biasing was not a problem (8mV).
At the same time I recapped the power supply.
So finally the time has come for the lights. Here two things made me scratch my head - someone had used the dial point lamp for the middle of the three indicator scale lamps... And the original lamp was nowhere to be seen. Replaced the two blown Indicator scale lamps. The dial point lamp was ok. And then started looking for the third indicator lamp. Fount it stuck between faceplate and tone control board...
Had to unmount the board so that I can access the lamp. Used this opportunity to clean the pots. All lamps installed at their proper placed. Cleaned all switches and the volume pot. Oiled the dial string bearing wheels. Put some grease on the dial pointer bed. Cleaned the faceplate. Be careful when you remove the knob for the station selection - so that the pilar used to do the connection between the knob and the counterweight does not get out. If this happens, most probably you will have to restring.
So now she looks and sounds great!
BTW a question: The input for Phono1 was blocked. Does anyone has an idea why is this done? I still have not tested the phono because I do not feel like removing my main TT just for the test. Or can you guys suggest a way to test phono stage without having to connect a TT?
Happy holidays and stay safe!
