Yamaha CR 2020 41Vdc on outputs!

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)

Hi Oilmaster, thanks for that explanation, crystal clear. You gotta wonder sometimes how bad design gets implemented into a system. Cost? Space compromise? Time constraint? (get it to market!!)

Anyway, your LED solution sounds like an excellent one! Assuming the procedure isn't beyond my rookie skill set, and you don't mind, I may have to hit you up for a "how do I..."

Once I get this beast up and running, that is. ;)
 
The broken black wire is an earth, check in rge vicinity, especially the 3 lugs highlighted.
GND2.JPG
 
GND2_LI (2).jpg
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It goes to the lug with the two blue wires.. That is exactly what I wanted to see. If that short black ground wire was connected to the right place..
 
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I'll bet alot of your issues disappear. Once reconnected.
 
CR-2020-lytic-board-02_LI.jpg These are a couple of the Service bulletin resistors I mentioned earlier......:thumbsdown: Totally the wrong size for the job.
 
Measure DC voltage red probe RI pin on power supply board, black probe chassis.
Repeat for pin LI

Thanks, mbz!

It goes to the lug with the two blue wires.. That is exactly what I wanted to see. If that short black ground wire was connected to the right place..

I reconnected that ground wire, and checked the voltage on the outputs.

Dammit. +40.8 vDC for LI, and +41 vDC for RI.

And eventually I need to find that switch that goes in the back here. I put it somewhere safe (it was uninstalled when the unit came to me), but apparently so safe I can't even lay my hands on it. :mad:

coupling-sw-location.jpg
 
Thanks, mbz!



I reconnected that ground wire, and checked the voltage on the outputs.

Dammit. +40.8 vDC for LI, and +41 vDC for RI.

And eventually I need to find that switch that goes in the back here. I put it somewhere safe (it was uninstalled when the unit came to me), but apparently so safe I can't even lay my hands on it. :mad:

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So how in the hell are the pre-amp out and main-in wired without the switch? Another can-o-worms.
 
So how in the hell are the pre-amp out and main-in wired without the switch? Another can-o-worms.
Seems to be yeh....

Well, couple of simple solutions:
- short external RCA cable
- solder direct wires at the back of the RCA terminal
- run the internal pre-out cable directly to the amp board

Despite my CR-2020 was in reasonable state, that missing switch is an open air design, and so it was completely black oxidized...took it completely apart to clean/polish and treat it.
I would prefer no switch at all (i.e. direct wiring) from pre-out to amp board, in case the future owner has no intention to use any part separately.
Having a (cleaned) switch is damned handy to analyze trouble or performance of each amp part individually though...
 
So how in the hell are the pre-amp out and main-in wired without the switch? Another can-o-worms.

Sorry, I should’ve mentioned the missing switch earlier. I hope these are easy to come by, I spent an hour going through my house last night, but came up empty. I’m kicking myself.

I’ll see about pulling the back cover off, at least enough to get a photo of what’s in place of that switch.

That black Dale is suppose to be a fusible resistor ( HW20410 ) 10 Ω @ 220ma = 10Ω @ .484 watts not 5 watts.. Would you replace a 1/2 A fuse with a 5A fuse. I don't think so.. Better order a suitable replacement for that as well.
Here is a fusible replacement by Yageo..
https://www.mouser.com/ProductDetail/Yageo/FRM-50JT-52-10R/?qs=sGAEpiMZZMu61qfTUdNhGztMfEiwFKKTzt9LlPXfiEk=

You will find it much much physically smaller.

Thanks for that info! I appreciate your efforts, and will order up a new one.
 
Seems to be yeh....

Well, couple of simple solutions:
- short external RCA cable
- solder direct wires at the back of the RCA terminal
- run the internal pre-out cable directly to the amp board

Despite my CR-2020 was in reasonable state, that missing switch is an open air design, and so it was completely black oxidized...took it completely apart to clean/polish and treat it.
I would prefer no switch at all (i.e. direct wiring) from pre-out to amp board, in case the future owner has no intention to use any part separately.
Having a (cleaned) switch is damned handy to analyze trouble or performance of each amp part individually though...
Thanks, Oilmaster, I like the RCA cabling idea. Simple, and can be unplugged if need be for troubleshooting. Pioneer uses uninsulated metal jumpers, perhaps that’s another option?

Of course, I still need to determine how it’s currently being bypassed.
 
Well those jumpers leave the signal path unshielded.... perhaps I am too sensitive but I prefer shielded signals :)

Question is if the PCB behind the switch is also gone, because in that case there is no signal at all....
 
For better or worse, here are the sockets. I pulled the back cover off, and then removed the mounting screws holding in Pre Out and Main In. The Pre Out connections were fine (meaning, still soldered), but a paired connection of wires (clear insulation, but are red in the protective tubing?) either broke off as I lifted the piece up, or were already broken loose. The white wire, also fragile, did break loose as I was carefully examining it.

Let me know if anyone wants to see different angle or whatever.

pre-out-main-in-01.jpg

pre-out-main-in-02.jpg

pre-out-main-in-03.jpg
 
Well that wouldn't work anymore..... the cable screens really must be connected to outer bushings of the RCA connector (central pin at the back). Otherwise the signal 'loop' is disconnected.

Somebody on eBay is parting out a CR-2020; in case you wish to reinstall a PCB then check out what he has left.

The transparent sleeve is meant as a thermal protection of the signal cables where they near/touching the heatsink
 
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

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).

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.

OK, agree grounding issues can/does cloud any voltage measurements but maybe if RI was disconnected/unsoldered then that
might confirm the theory.

Under no circumstances should speakers or headphones be connected.
 
When you get the new power resistors in, hereby some hints.
As Yamaha suggests, they should be kept off the board.
Well...... right..... then this would happen..... the PSU control board would clash with one or more resistors o_O

AK-1.jpg

MUCH MUCH better would be to mount those resistors on the back side of the PCB, as they get plenty of free air and the heat is kept away from that confined space on the component side, avoiding all kinds of long term issues. The longer the legs the better to reduce the stress on the PCB tracks; those resistors get hot and expand. The large number of power on-off operations cause as many thermal cycles. Also less heat is dissipated to the PCB.

AK-2.jpg

Not the nicest piece of work regarding the tracks, but my board was really fried....loosing various pieces of copper tracks in the process. I had to insert special rivets (and to get the $300 PCB riveting tool for that). I did bent the legs of the power resistors towards each other for more mechanical hook-up strength and in some case replacing the lost tracks.

AK-3.jpg

Here a view after final re-installation; it shows the space and air the power resistors have; it really works out well: the components on the other side stay nicely cool, as does the PCB. Nice warm air flowing out of the top; they really do get hot.

AK-4.jpg

Now that I am on it; I have to warn you for an important **** up by Yamaha: one of the + marks for the left 50V/1000uF capacitor is on the wrong side.
And so did I wrongly install that cap:

AK-5.jpg

So what happened.... due to power resistor in front of it, it did not explode in my face (current limiter, for once....). I had one spare, replaced it, and all starting to work fine.....ooooffff :oops: ESR value had tripled, though capacitance was still near 1000uF. When I opened up that cap 4 weeks later (for fun), it had a huge pressure inside ! Like it was boiling. No joke thus.

However, these caps are part of the power rails to the PSU control board which didn't work correctly at all (no surprise). It did afterwards, but only after the following happened as well:

Another BIG WARNING: do NOT power up the unit without the PSU control board inserted to the PSU capacitor board !!!! Because those 1000uF/50V will see ~65V in that case. In order to have the voltage below 50V, there must be a current flowing through those power resistors (i.e. the rails need to be loaded). In case the control board is not inserted, those power rails are not loaded and thus raise to the voltage upstream of the power resistors !!
 
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