Yamaha CR-820 blows fuses

i have a yamaha CR-820 that had a defective driver TR721 and a burned 68 ohm 85ma resistor. I changed both and the sound on the headphone was fine then. However it was distorted on the speakers (one channel). Seems the
problem got worse. When i put in the screws in the TO3 transistors TR723 and TR725 the fuse F803 and or F803 blow and power is out (wil do it evertime). I exchanged all caps in the channel (except 2 small ones near the TO3 which are hard to reach. I checked with an ohm meter the transistors in the channel and they appear ok. I changed the TO3 transistors (power transistors) and checked them and look fine too. Hope that someone can give me some hints what to try as this is a very nice looking unit and it would be a shame if it would stay unused.

did you put the insulators back for the power transistors ?

The mica insulators are of course put back also.

nongrata said:

The mica insulators are of course put back also.

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Inspect the mica and the the transistor bases for burrs that may be compromising the mica's integrety. Or your mounting screws are to long. Or the transistor sockets may not be properly seated/positioned on the heatsink.

Another thought. Are you putting the correct transistor in the correct socket ?

Screw are all the same, all original (or at least were in original) and they do not touch anything.
The transistors are mounted good as fas as I can see. In the socket and of course in the right direction.
TR725 is 2SB557 or MJ21194 and TR723 is 2SD427 or MJ21193. Before the fuse trouble started I exchanged the Transistors form the left to right channels but the distortion did not change channel.
I put in a double mica (just to be sure as test). I had no 1.6 fuse left and put 2A in. One channel distorts without the screws. Screws in the relais does not click or the the 68 ohm 250mw goes up into flames (now a 68 ohm resistor 1/4 Watt) or the fuse blows. If the fuse blows it goes quite fast but the 2 TO3 get very hot. Looks there is a short. The MJ21194 and MJ21193 are quite tough it seems.
The A814 and C1625 drivers also seem still ok. I also checked the CE if they are shorted instead of a broken BE BC for power and driver transistor.

One channel distorts without the screws

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Of course it will. One of the mounting screws on each output connects the outputs collector(the case) to the voltage rail.

TR723 is 2SD427 or MJ21193

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2SDxxx is and NPN. MJ21193 is and PNP. This combination won't work ! You have them installed in the wrong positions. Put the MJ21194G where the 2SD was and the 193G where the 2SB was.

You are right, not very smart. Changed them and no fuses blow when the screws are in. However stil distortion (started like that). Think the power transistors are not working. Drivers still seem fine. ill check more tomorrow, we have no visitors here. Thanks already for you help.

The distortion could be caused by a lot of things. Dirty switches and controls are most common.
Once you get the Onsemi transistors in place. Check and readjust the idle current/bias.

Distortion is gone and the amps sounds great but there is still something wrong. Turned out that the 2 resistors were far to high in spec and caused it.These were the 4,7 ohm ones (near the 1k5k 2w and TR719 and TR721). Sound is great but the bias is not good. The bias is almost 0 when the volume is 0. When I turn op the volume the bias goes up. If rather loud will go to 20 or 30 mv. TR719 and TR721 got hot then of course. Does not look good to me.

Changed the 68 ohm to 270 ohm, TR719 and TR721 do not get hot anymore. No distortion and the receiver has been playing without problems and getting not more then Yamaha hot. Want to thank everyone that here that helped my to repair.