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Yamaha CR-600: up & running again

The picture really clarified it for me thanks.
TR719 is originally a 2SA572 which I cannot find the pin out for line. Do you have that information?
The replacement is a KSA-992FTA which is ECB. I can follow the circuit board trace diagram to orient it but I would like to know the 2SA572 pin out as a reality check.
 
Let me try to help. Earlier in the thread I mentioned that from a date code in my receiver (date code: April 1976), that my receiver was apparently a "late manufacturing run" unit (CR-600 was produced from ~1973-76). One of the assembly changes through those years apparently involved TR719. As found, in the TR719 position, 2SA763 was substituted in my unit for the documentation indicated 2SA572. My TR719 appeared to be original (did not appear to have been previously serviced), therefore I'm assuming it was an assembly run change.

The 2SA763 pin-out was ECB as is the sub KSA992F; therefore a straight "drop-in" solution. In my limited experience, assembly run component changes do not typically involve altering copper traces on circuit boards so I would imagine 2SA572 & 2SA763 have the same pin-outs.

BUT...>>>

The best approach would be to remove your 2SA572 and check pin-out & transistor orientation (which is the "front"). Again, "6-Way Check" or other test device you might have should give you the answer. This way you can be sure of your KSA992F installation.
 
This transistor is really stumping me...
Sorry but I was not clear on one thing: My board does not have 2SA572s on it. It has some other numbered part I can not find anything on either.
The text on the transistor reads 45 A763 WL 4B. Clearly this must be the 2SA763 you mentioned was in your unit and yes it must have the same pin out as the 2SA572: ECB.

I have read about the 6-way test and have been using it when I pull the transistors. However it does not help with the problem I am having: differentiating between the Emitter and the Collector. All the online guides say to look up the pin out lineup on the data sheet, which I cannot find.
Anyway, identifying the Base is straight forward using the diode testing function of my meter.
Unfortunately my meter (Fluke 87 V) does not have a transistor testing ability.
The transistor measures identically BE and BC (0.7ish).
Pardon the EE101 question but how can you tell which is the Emitter and which is the Collector?
As far as my meter is concerned, this is just two diodes back to back in series...

I am looking at three sources of information at once here: the actual connections on the circuit board and the way the actual transistor was orientated, the parts map as shown on the circuit board trace, and the schematic, both from the service manual.
If the actual old part, which worked by the way, was ECB, then the collector was attached to ER.
The circuit board from the manual shows the part oriented with the emitter attached to ER.
The schematic shows the part oriented with the emitter attached to ER.

Should I follow the documents or reproduce what was there?
 
Please disregard the second part of my question. I did not realize that PNP transistors are different in the schematic labelling. All three sources agree and the problem is cleared up. I still wonder though how to tell the emitter from the collector?
 
No problem, glad you solved it; perseverance….

Apologies, if I made (6-Way check) more difficult than it needs to be; my thought was to get you the pertinent information without having to buy any tools. The key is in the “ish” you mentioned above. For PNP transistors, Veb will normally be slightly higher than Vcb; with this info you can identify Collector/Emitter by comparing the voltages.

For example, this is the check of TR719 (2SA763) which was removed from my unit.
1766249537914.png
Good luck.
 
Yes, but the junctions in the NPN would be polarized the reverse direction.
So, for NPN transistors, Vbe will normally be slightly higher than Vbc.

Example, the TR707 and TR708 transistors that we discussed earlier.
1766262457758.png

This is not foolproof, if the junctions have broken down the readings will be off but it can give an indication of pin-out.

Keep going.
 
Ok I finally got the nerve up to apply power. After 10 seconds the relay did not close and I powered off. The resistors R745 and R747 had reached 90C but I don't think the magic smoke got out. A bit of a smell though... I had set the new pots to roughly the same resistance setting as the originals.

I think the left channel is working properly. TP 2-4 read 0.085V(target 0.023V) and TP 4-6 read 0.4V(target 0.01V). So while out of adjustment, they are not bad as a starting point.

The right channel is not. TP 1-3 is 1.95V and TP 3-5 is 1.3V. Yicks!! Both R745 and R747 are equally dropping 1.95V so I think both output transistors are fully on.

As one channel is working and one is not, I can compare to try and track down the problem.
No voltage drop across R733 and R735 so no current through TR709 and TR711.
I am suspecting something around TR707 as I was trying to be a smarty pants and flip the transistor around so the flat side would touch the heatsink.
Pardon me for trying to compare this to a tube amp, but is TR707 doing the phase splitting?

I am afraid to turn the amp on for more then a few seconds. Would it be safe to remove the output transistors and continue testing with less worry? Until I have current through TR709 and TR711, the output transistors could sit it out maybe...

Maybe related or not to the above problem, I notice when I turn the amp off the positive rail drops to zero instantly but the negative rail drops extremely slowly.
Thanks for any thoughts.
 
Ok, let’s establish a starting point. I don’t recall but had you powered-up the unit before the work began or is this the first power-up? If you powered-up previously, do you know if the protection relay energized? We’re trying to determine if a problem was created during repairs; double-check the work done so far, and if you are suspicious of the TR707 installation, inspect it carefully.
Tell me, are you using a “dim-bulb tester” on the power line?
And your last question; yes, you can remove the final output transistors (TR713, 714, 715 & 716) and continue testing. While you have them out, check them for damage.
 
The unit was operating before the work began. The relay operated and sound came out. There was some leaking capacitors on the power amp board and evidence of overheating on the power distribution board which prompted the repairs. The unit was actually exceptionally clean inside and not covered in tobacco resin.
I removed the output transistors from the right channel and the relay works properly. The output transistors test OK.
I did not use a dim-bulb tester but I suppose I should have. I think if I continue with these types of restorations I will invest in a variac.
I can continue now comparing left to right and try to track down the problem. I will let you know what I find. Thanks again.
 
Ah the pain continues...
I put the output transformers back in and changing the resistance of the pot did not have any effect on the high current.
Removing them and studying what I have done again, I noticed some possible issues with differences between the circuit board stuffing diagram and the schematic.

Firstly, on the stuffing diagram, the labels of the right channel resistors R725 and R729 are reversed. I checked the actual resistance values and this seems to be the case. The corresponding resistors on the left channel are not even shown on the diagram at all. The manual PDF I am working with has two versions of this diagram. The first diagram on page 37 is missing these labels, the second diagram on page 85 does show them. Irritating but I don't think this is related to the main problem.

One problem I am having is the orientation of TR705. The stuffing diagram has this orientated with the collector at the top, close to the edge of the board. But that pad connects to R717, which connects with the emitter on the schematic! The diagram shows the emitter on the lowest pad, but that pad connects to R723 which connects to the collector on the schematic! So to get the actual part to correspond to the schematic, I took the transistor out and flipped it around. It now electrically matches the schematic I think...

As a reality check:
You earlier posted a photograph which showed the orientation of TR706 and I did mine the same way. As well, I bent the leads on these transistors to turn them 90 degrees as you did. Do you recall if TR705 is oriented the same way, as in the front of the transistors facing the short side of the board?

I seem to now also have no negative rail at the power amp module. When in the process this has failed I cannot say. Probably early as you might recall I mentioned that I noticed the positive filter cap dropping to zero quickly after powering off but the negative cap drained very slowly.
There is negative voltage at the main smoothing caps and I discovered that the 3A fuse in the negative rail on the power distribution board is blown. I am going to track down some replacement fuses now. Would it be worthwhile for me to build a light bulb load to put in line with the AC power before trying to apply power again?
 
I tracked down the solder bridge that caused the short. It was on the last place I testing after removing many components to isolate the short. Figures...
But this TR705 orientation issue is still holding me up. I noticed that the photograph you posted of the power amp board with the components labelled
shows the original Sony 25C1124 TR705 in 'backwards' according to the schematic. I forgot that I had actually taken a picture of the amp board prior to disassembly and both my
25C1124 are pointed the same way, facing left. So I can't explain why they were like that on your board, but I think the schematic is lining up with the reality of the way my board was built.
 
DS,
There were a few subjects, let me try to help a bit, if I can.

R725/729; Good work identifying this documentation error. This unit’s documentation has a few. Documentation errors do crop up from time to time. Sounds like you are on top of this one. Since the unit was originally working I would always default to the actual “as found” component placement on the PCBs as the correct “version” when discrepancies occur.
Good approach taking lots of pictures as you progress, I do the same.

TR705/TR706 orientation; I’ve looked back and can confirm that in this unit, both of these two transistors are installed EBC, with the Emitter leg “closest to the top edge” of the circuit board. (see photos)

1768497240542.png 1768497261785.png

Power supply issues (blown 3A fuse); Yes, you’ll need to resolve this issue(s) before you can reliably work/troubleshoot other sections of the receiver. One thing to note; the design of this receiver incorporated what were called “fusible resistors”. You can search fusible resistors if you need more background. They are denoted with the prefix “FR” in the Yamaha documentation and used throughout the unit but, the power supply board has 4 of them as examples (FR801, 802, 803, 804). I would have them fairly high on the list to check-out.

Dim bulb tester; This is up to you but it gives a couple of very useful advantages, and doesn’t cost a lot. In cases of very high input current the bulb (incandescent) acts like a fuse and interrupts power. Perhaps more importantly, in cases of high, but not overload current levels, the bulb will stay bright after the initial inrush current should have subsided. This gives you a sort of “visible display” of line current going to the unit. There’s lots of info on dim-bulb testers which can be searched.
 
Thanks for confirming my thinking about TR705.
I built the dim bulb tester and with a 75W bulb, it limits the power supply rail voltages to +/-10V.
This allows me to keep the unit on and take voltage readings without worrying about overheating or stressing components. Looking at the correctly working right channel, I was surprised to see the circuit 'works' even at the low voltages. Balance and idle current seem to be unaffected by rail voltages. The engineers who designed this circuit really knew what they were doing!
The left channel though is still not working correctly but I determined to get this solved. I keep coming back to something to do with TR707 as the bias of the following driver transistors is set by it. Wish me luck.
 
Keep going, perseverance.
And by the way, if the external cosmetics on your receiver are as clean as the internal chassis photo you posted earlier, you’ve got a gem of a unit there !
 
It had nothing to do with TR705 or TR707.
In case of someone else in the future rebuilding one of these sweet receivers, I will honestly disclose the mistake I made so that they might not waste as much time as I did.
The Main Amp Circuit Board diagram and stuffing guide has many mistakes including mislabelling the L output transistors TR713 and TR715. Their labels are switched...
Get where this is going? (smile) Yes I followed this diagram and switched the position of the NPN and PNP devices in the L channel. Didn't work of course. The R channel transistors are labelled correctly, so of course it worked fine. So both channels are now operating properly and I will continue testing. Hope to put some music through it tomorrow.
I regret not taking more pictures before disassembly, as I would have caught the problem much more quickly with at picture of back of the heat-sink, showing the original transistors numbers.
PS: Yes my unit is clean and luckily was not owned any time in its life by a smoker. I smoked for 35 years, but this receiver did not live with me then. I will post a picture of it when I get it all back together again. Thanks and Regards, D
 
Congrats, well done… from the Hamamatsu assembly line in 1974’ish to lookin’ sharp in your listening area in 2026... pretty amazing !!
Enjoy.
 
A few issues remained related to switches and pots. I will pass on my experiences as a FYI to those interested.
One volume pot was cutting in and out. I removed the whole assembly of four pots as getting into the assembly while it was on the board seemed impossible.
This stack of four pots in NOT designed to be disassembled or repaired. I used contract cleaner and then contact enhancer on it. Best I can do with it.
So far it seems to be working much better.
The source selector switch was also intermittent. This I removed from the board and it can be disassembled if one is careful.
This selector mechanism is essentially a six gang switch of six positions. It uses a gear set to turn rotary movement into linear movement.
Cheaper then a straight forward rotary switch I suppose? The contact material is quite cheap metal and was severely corroded in my piece.
I polished all the contacts and reset the tension on the sliding spring contact thingies. Works fine now.
Picture is of it before cleaning it up.
CR-600 selector switch.jpg
 
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