Yamaha CR 2020 41Vdc on outputs!

Check your solder connections on regulator pass transistors TR712 & TR715

I did while I had the board out they are replaced as pictured.

upload_2017-9-13_19-0-29.jpeg

Measure dc voltage between RI(RED probe) and LI(BLACK probe), probably
need mV scale, important to note sign pos or neg mV.

positive xxmV indicates problem on right channel (yellow wire)
Negative xxmV points to left channel.

+230mv R1

Curious if lifting R1 would allow the relay to close and Left channel to play.

And yes confirmed +41 on both channels
 
First step, identify faulty channel by measuring voltages between RI and LI as per
post 9.

Once faulty channel identified you have a choice of a labourous hunt to track down
the source of this voltage via voltage measurement or you can diode test key transistors.
In circuit diode test will probably be ok, looking for a short. In this case I suggest
diode testing starting with TR611, TR612

No idea how to diode test. In or out of circuit. Will scan YT for video
 
Plenty of good posts on how to diode test as per avionic above.
I like this one from markthefixer who updated a graphic from echowars.
Red/black refer to probe orientation.

DiodeTest.JPG
 
+230mv R1
Right In (yellow wire) is higher than LI, problem with right channel. TR611 and maybe TR612 are prime candidates, however certainly check outputs
(TR613,4).

Curious if lifting R1 would allow the relay to close and Left channel to play.
If left channel dc offsec is below threshould then relay should activate. If this is just a solder connection then ok to try, but carefully secure
this floating wire. If this is a wire wrap connection then don't tinker.
 
Hi guys, this fine piece of Yamaha gear is under new ownership. (Thanks Mid-Fi!) Though I've always been fond of Pioneers, I feel Yamaha nailed it with this series. I've never worked on any Yamaha gear, and am a novice, as I've only repaired about a dozen pieces, in a variety of types. (Turntables, receivers, reel-to-reels, equalizer...) But they were all Pioneer. Not familiar (at this point) with Yamaha terminology nor the "Yamaha way" of doing things. That's not a criticism, just an observation from a rookie.

Regardless of the gear, I don't know how to troubleshoot electronics. I can follow instructions, and don't jump all over the place. Can't read a schematic for crap, though.

So where're we at? I've opened up the beast and gotten access to the main Circuit Boards--I think Yamaha refers to both boards as Main Circuit Board 1?

I pulled TR611 and TR612 (1 from each board) and hit them with the diode test, they're all good. I then tested the outputs, TR613, TR614 (again, from both boards) and they all checked out good, too. (Testing done the six-way testing method.)

I've left them out of the boards for now. When they go back in, I'll clean off the the old thermal grease and apply new. (Clean off old flux, etc)

I'm not sure of the next step, and would gladly accept suggestions.

Thanks,

Jeff

PS I have a copy of the Service Manual as well as the three service bulletins
 
What voltage are you seeing on the output transistor cases(collector). Should be around + and - 60vdc.
 
What voltage are you seeing on the output transistor cases(collector). Should be around + and - 60vdc.

Ok, I'll put all the transistors back in. When I power it up and check the voltages, I'm assuming positive to the case collector, and negative to chassis ground?

BTW Here are the correct ( exact) resistors for the service bulletin
You will need two of each..
https://www.mouser.com/ProductDetail/Ohmite/93J22RE/?qs=sGAEpiMZZMtTURnxoZnJAKfV%2by28kSnliksfpOSpVU0=
https://www.mouser.com/ProductDetail/Ohmite/93J33RE/?qs=sGAEpiMZZMtTURnxoZnJAH%2bfrh0DY3Azih2JkIbYPbw=
I can tell by the previous photo's that the ones installed are to large physically and could be a potential for shorting out other components on the electrolytic board.

Thanks for that, avionic! I'll get those ordered.
 
If the negative rail is missing to the amplifiers that will cause the positive rail to be present at the output -- ie DC offset
The pos and neg. rails must be equal. ie +60 and -60vdc (ballpark)
 
Ok, cleaning, new thermal grease, transistors back in. Decided to check my work with dim bulb, it lit bright, then quickly dimmed. Excellent.

Put my DMM to work. I'm getting -59 vDC on both 554 outputs (the ones toward rear of unit) and +59 vDC on the 424 outputs. Does that mean my power supply is doing what it's supposed to?

And I've ordered the resistors.

fyi, one existing symptom, don't know if it plays a part or not, is none of the white lamps illuminate. (I haven't investigated these at all, but thought I should mention it)

I do get a red power light that comes on.
 
Post a photo of the top of the Electrolytic board showing the solder lugs and wires connected.
 
fyi, one existing symptom, don't know if it plays a part or not, is none of the white lamps illuminate. (I haven't investigated these at all, but thought I should mention it)

I do get a red power light that comes on.

The thing with the white light bulbs is that they are hooked up in "parallel-series", meaning that two sets of two lights in parallel are connected on series. A very twisted way to ensure same light intensity (current regulation). The weak point in that design is that if one bulb dies, than the parallel brother gets the full current of the other set in series and burns out quickly.....and then the entire chain is dead..... really shitty design.....

In other words: you need to order 4 new light bulbs, and in theory you should match the bulbs that are in parallel, otherwise a different current runs through them and shortening the lifespan even more. I converted everything with warm white leds, 5 of them in series (which includes the dial pointer light) with a 220 ohm resistor, all fed from the VU-meter lighting terminal (hence no longer using the dedicated lighting supply terminal for the dial pointer)
 
Post a photo of the top of the Electrolytic board showing the solder lugs and wires connected.

Ok, started digging in. The first thing I notice is loose wire. Loose as in not connected on one end. I don't know if a fragile connection gave way as I started to move the board that plugs into the cap board or what, but there it is. One end is connected to Pin E, the other end I have no idea where it's supposed to be.

Moving on.

I took some shots, let me know if I didn't get what you were after.
 

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