Yamaha CR-620 Problem

Donkey!

AK member
I've got a CR-620 with a relay failing to close on power up.

The unit powers up, but won't go out of protection.

I'm reading -39.54 volts on one side of the relay and 1.3 mv on the other.

Obviously something is not right. If I were to wire the relay closed, I would be getting close to 40 volts on the speakers terminals.

Could this be the drivers. the finals all tested good.

And ideas on what to look at
 
If your output transistors test good it is quite possible that the drivers (2SB and 2SD large TO-92 types) can be bad. Also you need to look at the two 68 ohm fusistors (white ceramic body) and the 4.7 ohm 1/4 watt resistors that are enclosed in fireproof fabric near the outputs. If your drivers blew and did not take out the outputs you are lucky. BTW the drivers are still available, I just ordered some from B&D Enterprises (www.bdent.com).
 
Would they be 2sd438s and 2sb560s by chance?

Also, doesn't reading rail voltage on only one side of the relay imply that only one channel has issues.

Also Merry, there are more then two white ceramic resistors at the base of the of heat sink. oh never mind. I get it.
 
Ok i'm an idiot. It is the finals. I pulled two and they checked out and must have forgotten to check the other two. :scratch2:

Anyways. Pulled the two rotten tranies. And it comes out of protection.

Now I just wonder and hope that the pre-drivers and drivers are all good.

Actually, most times when finals are bad in the amps I repair. the drivers were all fine. Here's to hoping. :beerchug:

Does anyone know of a good replacement for 2sb531s and 2sd371s?

All I need is two npn and two pnp with similar specs and I'm good to go.

I have a local shop that stocks parts but not a great assortment.
 
Try the OnSemi site, I believe they suggest the MJ15015 and MJ15016. If it comes out of protection you were lucky as most times they take the drivers with them. If you have more than two 68 ohm fusistors ther it is a strange CR-620, and yes 2SD438 and 2SB560 sounds right.
 
Try the OnSemi site, I believe they suggest the MJ15015 and MJ15016. If it comes out of protection you were lucky as most times they take the drivers with them. If you have more than two 68 ohm fusistors ther it is a strange CR-620, and yes 2SD438 and 2SB560 sounds right.

There are only two 68 ohms resistors and another set of 4 ceramic resistors for each channel. Didn't measure them.
 
You can check those flat emitter risistors for spec at 0.22 ohms as sometimes a dying output will take one out, I check them just as a matter of routine. The fusistors are the cylindrical ones and if open or off value a 1/4 watt 68 ohm resistor will happily give up its life if there are any problems with the drivers.
 
You can check those flat emitter risistors for spec at 0.22 ohms as sometimes a dying output will take one out, I check them just as a matter of routine. The fusistors are the cylindrical ones and if open or off value a 1/4 watt 68 ohm resistor will happily give up its life if there are any problems with the drivers.

Ahh ok, the cylinder one. I measure the square ones and they read .2 give or take.

Are the 68 ohm ones the ones with fabric on them?

I'm pretty sure everything is ok, before I pop new finals in, I'm going to put the two good old ones I have in the left channel and see what happens.

Maybe the lazy way, but what the hell, right.
 
What are the odds that all of the lights are out in this puppy. The L.E.D. lights work, for stereo and FM and AM and so on, but they should LEDs last forever.

I haven't yet measured the voltage on the source to the panel lights. But I think it's strange that all the lights don't work.
 
Pardon my ignorance but I don't see the 68 Ohms fusistors on the schematic from the link I posted. Is there a modification I should know?
 
The 68 ohm fusistors run between the two drivers and parallel the 1500 ohm 1 watt resistors. The ones enclosed in fabric are the 4.7 ohm resistors that connect the drivers to the outputs.
 
Thank you Merrylander,

If I understand, the 68 Ohms fusistor (only one per channel) is connected directly between the emitters of the two drivers (TR719/21). Thus, the driver stage operates in class A. There is also a resistor (1.5K/1W) between each driver's emitter and the feedback point, between C731/733. Same for the other channel.

In a way very similar to the CR-820. I found the schematic for the CR-820 on Hifiengine.com, but this schematic in unreadable.

The schematic for the CR-620 on the link I posted is incomplete, or is there two version of the CR-620? What do you know about this?

Thanks!
 
The power and driver board of the 620 and 820 is the same PC board, just some differences in the driver transistors and the 2SB in the idle current adjustment chain. Ther is one error in both schematics; in the power supply they tap off AC ito a violtage doubler setup quite seperate from the main B+. On the schematic they show the output of tis double as some 45 V going into a 2200 ohm dropping resistor and coming out the other side as 72 V - damn good trick if you can pull it off. Someone simply reversed these voltages and they should be swapped left to right.

Somewher out there on the 'net is a Yamaha 620.rar file that has a clean schematic in it, hifiengine? CRS kicked in and I can't remember where I found it. I have the usual 11 x 17 in the SM but I wanted something to throw at the DesignJet so these tired old eyes can read it.
 
The power and driver board of the 620 and 820 is the same PC board, just some differences in the driver transistors and the 2SB in the idle current adjustment chain. Ther is one error in both schematics; in the power supply they tap off AC ito a violtage doubler setup quite seperate from the main B+. On the schematic they show the output of tis double as some 45 V going into a 2200 ohm dropping resistor and coming out the other side as 72 V - damn good trick if you can pull it off. Someone simply reversed these voltages and they should be swapped left to right.

Somewher out there on the 'net is a Yamaha 620.rar file that has a clean schematic in it, hifiengine? CRS kicked in and I can't remember where I found it. I have the usual 11 x 17 in the SM but I wanted something to throw at the DesignJet so these tired old eyes can read it.

So then a 620 could be made into a 820, in terms of the power amp.

What are the parts differences, I may try it.
 
So then a 620 could be made into a 820, in terms of the power amp.

What are the parts differences, I may try it.

Hmm, new power transformer, higher voltage filter caps, new output transistors, new driver transistors new TO-220 transistor in the idle current chain, oh and probably a new voltage regulator transistor, the one with the little heat sink.
 
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