Discussion in 'Yamaha' started by Demiglaz, Oct 23, 2018.
Correct two different transistors .Ones a PNP and the other and NPN.
The whole metal case is the collector on the TO-3 style transistor.
UPDATE: Okay, please refer to the photo below. In the photo, the back of the unit is on the left, and the front (faceplate) is on the right. Counting the transistors from left to right, Nos. 1 and 2 are good, No. 3 is bad, and No. 4 is good. No. 3 is a 2SD371. Should I just go ahead and replace all four of these transistors? That is, replace two 2SD371 transistors and two 2SB531 transistors? If so, can you please suggest replacement parts/equivalents?
I'd just replace 3 & 4
MJ21193G and MJ21194G Onsemi's from Mouser or Digikey
Are the mica insulators still in good shape?
I assume by mica insulators you mean the very thin, plastic-looking "gaskets" between the transistors and the frame. If so, yes. They seem to be in great shape -- gunked up with white heat sink compound, but perfectly intact.
Okay, I will order those parts from Mouser and report back. As you know, those transistors are plug-ins, so no soldering! Thanks again for your help. Very much appreciated. Hopefully these new parts will get my friend up and running again. Silly to get so attached to a stereo component, I know, but I am attached nonetheless. Will report back.
Might want to pick up a packet of new thermal compound.
Good call on the thermal compound. Order placed. Will report back next week after parts arrive and I install them. Hope this is my fix. Fingers crossed. Thanks again for all of the help.
UPDATE - November 2, 2018 * * * Parts arrived yesterday, and I installed them. Against your advice, Avionic, I went ahead and replaced all 4 output transistors (seemed most economical to order all four because shipping cost was the same). And then, the moment of truth. I powered up the unit, and guess what? Relay clicked on with a slight delay like normal. Phew! I think that was my problem. I played the receiver for about three hours last night -- varying the volume, but usually about middle range -- and no sign of any problem, My sweet CR-620 sound is back.
Avionic, thanks so much for your help. Very much appreciated. Your patience and generosity are admirable. I couldn't have figured this out on my own.
The CR-620 is a wonderful receiver, but the couple I've worked on both suffered from seriously degraded capacitors. I'm not one to suggest total recaps most of the time, but these things are the exception, at least for the power board. Almost every cap in the thing tested low in value. It worked, but the sound quality really suffered. I've got a page on my site that was aimed at tuner alignment, but I added a whole section on the cap issue.
Did you go throught the idle/bias adjustments ? With the new outputs installed.
Conrad, thanks for the advice on recapping. Any idea where I can find radial replacements for the two 6800uF 45V filter caps?
Avionic, I did not go through the idle/bias adjustments after installing the new output transistors. Could you please tell me how to find the TP1, TP2, TP3 and TP4 test points on my board?
Look at the service manual and the silkscreening on the printed circuit board.
Found them. TP1-TP2 came in at 14.1mV. TP3-TP4 came in at 12.2mV. With a little patience, I was able to get them both to hold at 8.0mV. I'm on a roll here! Thanks again for all of your help.
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