Yamaha CR-820 Issue - Loud Buzz Only After Relay Click

[AHart]

After powering on, the relay clicks then a very loud buzz comes through, no music. The buzz is on both channels.

It happens on all inputs. It happens on speakers and headphones.

Here is a video of what it sounds like coming through the headphones:

DC offset measures 8 mv on right channel and -11 mv on left.

Checked all fuses and they are fine.

Not sure where to start. I'm guessing a transistor is bad on the main amp board but not sure where to start.

Any ideas?

 

[avionic]

The buzz is on both channels.

Both channels points to the power supply.

 

[avionic]

Possible solder connection or leaky capacitor.

 

[AHart]

Thanks - I will start checking caps and connections today! Most all of the caps have a red dot on the top of them as if someone went through already. Interesting.

 

[AHart]

C814 & C815, both 100uf/50v caps have tested bad.
C804 33uf/16v is also bad.

That's all I've found so far.

I'll replace and report back!

 

[ludoviko]

C814 & C815, both 100uf/50v caps have tested bad.
C804 33uf/16v is also bad.

That's all I've found so far.

I'll replace and report back!

any update on this problem, i seem to have the same problem currently with a yamaha cr 820.

 

[mbz]

any update on this problem, i seem to have the same problem currently with a yamaha cr 820.

Start with the power supply since both channels affected. Depending on your skill level you could either do
a health check of the power supply voltages or take a punt and recap/replace the power supply caps. The
health check would be quicker, will try and get some test points.

 

[avionic]

Welcome aboard Ludo

 

[mbz]

Service manual is not real good, check dc voltage at jumper marked in blue, on main amp board, expect
about +30Vdc


EDIT: Carefully measure the dc voltage of the metal case of the output transistors.
These are large metal transistors mounted to the heat sink, take care to probe the transistor
only, don't short to the heat sink. expect one at about +40Vdc the other at -40Vdc. (expect
ok otherwise dc offset...)

 

[ludoviko]

Ok so to elaborate on my particular issue. I purchased this unit knowing it had this issue, i figured since the unit sat for 15 years in garage of the original owner that maybe the pots were dirty and just needed cleaning with deoxit. I opened the unit and yes it was dusty but besides that its looks pretty good. The unit powers on and the relay clicks 3-4 seconds after and immediately there is a loud buzz/hum that eventually dies down after 5/10 minutes but the hum although considerably less is still there. The hum persists on all inputs radio/aux/phono/tape. Moving the bass control knob and the loudness control knob will affect the audible level of the hum. Also there is a sweet spot on the am/fm selector that when pressed in so that neither the am of fm is active the hum disapears on all inputs (aux/phono/tape) and operates as it should, perfect. But there is no way to actually keep that am/fm selector in that sweetspot.

I am not a skilled electrician, i have in the past troubleshooted certain issues with other vintage audio equipment mostly mechanical problems with turntables and tape decks and once recapped a small vintage receiver with success. I own a decent multimeter and an esr meter that can supposedly check the esr on capacitors in circuit. I hope this insight on the problem im having with this Yamaha CR-820 helps and i hope theres someone out there with far more experience can guide me in the right direction. Thanks.

 

[ludoviko]

Welcome aboard Ludo

Thank you

 

[Subtraction]

that sounds very much like the noise my formerly owned 620 was making except my noise was not constant. after powering up it would start then make one heck of an ear splitting crescendo maxing out to a panic inducing level...then nothing followed by a weak output with a low annoying constant hum.

so it sounded like a B36 with no exhaust making a low level pass then disappearing

 

[avionic]

Is the noise in both channels. ?

 

[ludoviko]

Is the noise in both channels. ?

Yes on both channels.
Can a bad component in the radio tuner section cause such a problem? The reason I ask is because of what I mentioned in my earlier post. Pressing the the am/fm selector in midway will basically get rid of the hum on all other inputs but will eliminate the use of the radio. I know it sounds strange. And by the way I don’t know if it matters but the hum is more like crackly static(very loud) when I first turn it on which eventually settles down to a noticeable hum. Volume control does not affect hum.

 

[avionic]

Both channels points to the power supply or a common ground issue.

 

[ludoviko]

Thanks for responding. I have little understanding of common ground issues and I’ll have to do some googling and YouTubing for that. But when you say power supply that means any component related to that area like bad capacitors, resistors or transistors?

 

[avionic]

Thanks for responding. I have little understanding of common ground issues and I’ll have to do some googling and YouTubing for that. But when you say power supply that means any component related to that area like bad capacitors, resistors or transistors?

Left and right channels share the power supply circuits. Be it regulated or unregulated power supplies. Left and right channels also share the same ground. ie common ground.

 

[mbz]

Did you check the voltage at the jumper shown in post #10?

 

[ludoviko]

Did you check the voltage at the jumper shown in post #10?

Sorry I hadn’t had time but I just did and on that jumper it’s showing 28.05 after a few minutes of warming up. The pair of output transistors are consistent
at -42.7, 42.7 and -42.7, 42.7.

 

[mbz]

Voltages at power transistors look good, manual has +42.3, -42.1. Regulated supply (28.05) is a little
low, manual has 30.1 or 29V. Measure fusible resistor FR801 (22ohms) in circuit ok, amp powered off.
They do drift high, don't see it as the cause of your problem.