CA-1010 Unable to adjust Class A bias, Normal OK

[Yamaha5000]

 

[Yamaha5000]

OK so you've replaced almost all transistors in the power amp (wtf?)
Post a hi-res pic of the faulty power amp board both component and solder side.
Do you have a 4-5K VR to replace VR302 (2.2k)?

1. Dropped on my head within moments after birth.
3. Yes a 5K

 

[Yamaha5000]

5K makes no difference VR302 still staying at 21.1mv

 

[mbz]

The pulses of heat (post #36) probably points to intermittent silicon. TR311, TR312 appear to act as switches taking VR302 out of "play" for class AB. Problem is the VR is permanently out of play ie, for class A.

Normal TR311 E= -0.57, C=-1.14, B=-1.17 looks wrong.
Maybe E= -1.17, C=-1.14, B=-0.57 so VR302 is bypassed.

For class A you have TR311 E= -0.68, C=-1.25, B=-1.27
Maybe E= -1.27, C=-1.14, B=-0.68 so VR302 is still bypassed.

TR311 is controlled by TR312, this is possibly failing. Maybe a solder
bridge around TR312, or issue (orientation, short..) with D305 or a
problem with TR315 or that "diode/shorting link"

 

[Yamaha5000]

Normal TR311 E= -0.57, C=-1.14, B=-1.17 looks wrong.
Maybe E= -1.17, C=-1.14, B=-0.57 so VR302 is bypassed. Measured once again: E -1.18 C -1.18 B -.59

For class A you have TR311 E= -0.68, C=-1.25, B=-1.27
Maybe E= -1.27, C=-1.14, B=-0.68 so VR302 is still bypassed.

TR311 is controlled by TR312, this is possibly failing. Maybe a solder
bridge around TR312, or issue (orientation, short..) with D305 or a
problem with TR315 or that "diode/shorting link" Measured once again: E 66.4 C -1.18 B 66.4



D305

 

[Yamaha5000]

For class A you have TR311 E= -0.68, C=-1.25, B=-1.27
Maybe E= -1.27, C=-1.14, B=-0.68 so VR302 is still bypassed. Measured once again: E -1.18 C -1.18 B -.59

 

[Yamaha5000]

that "diode/shorting link" The other Main Board has this same Diode installed

 

[Yamaha5000]

So I thought what the heck just give it a try. Placed a jumper across that Link/Diode. With this in place I now have the ability to set the Class A Bias, but not the Normal Bias. Pull the jumper out and goes back to being able to adjust the Normal, but not Class A.

 

[Yamaha5000]

Also with Class A Bias being set the heat sink begins to heat up.

 

[mbz]

Looking at the schematic for the CA-2010 suggests the diode should be a 21V zener

 

[Yamaha5000]

That does make sense,

Any suggestion for a part number replacement?

 

[Yamaha5000]

That does make sense,

Any suggestion for a part number replacement?

?

 

[Yamaha5000]

Looks like you have addressed this issue before:

https://audiokarma.org/forums/index.php?threads/marantz-2265-power-board-diode-replacement.792908/

 

[Yamaha5000]

Once again this was from the thread https://audiokarma.org/forums/index.php?threads/yamaha-ca-1010-major-restoration.972558/

Before:


After: The diode is not exactly in same position as in the before photo, making me think it has been replaced.
The thread gives a parts list but no diodes have been described.
The thread gives a link to a CA-2010 and it defines a D315 WZ-210 21V, 1/2 Watt Zener NZX20C-133

 

[Yamaha5000]

From the CA-2010 thread

 

[mbz]

Would be good to have the yamaha spec for the diode so can better tailor, candidates are,


Since it's a switch function it probably doesn't need to be super accurate. Since
the NZX20C-133 worked in the CA-2010 then ok for the CA-1010. My initial choice was
Mouser 771-NZX22A,133 21.4V 2% 500mW
EDIT: Zener voltage is not super critical, the zener acts like a switch. In AB the +B rail is at about +55V and the B1 rail at about +65V so the zener doesn't conduct so TR315 remains off with TR312 off. TR311 is on so bypassing VR302. In class A +B rail is about +22V so there is >21V across the zener so current flow from TR315e turns on TR312 which disables TR311 so VR302 is "in play"

 

[mbz]

Looks like you have addressed this issue before:

https://audiokarma.org/forums/index.php?threads/marantz-2265-power-board-diode-replacement.792908/

Hardly consider the Marantz 2265 (psu) issue to be the same as the CA-1010 (bias) issue.
I generally post on a small number of amps so yeah, possibly in the past I've chimed in on CA-1010 bias issues.

 

[Nashou66]

Is this your board? Why is there a diode next to the J , which I assume should be a jumper. Or is the PCB silk screen wrong?

Just wondering.

Nashou

 

[Yamaha5000]

Hardly consider the Marantz 2265 (psu) issue to be the same as the CA-1010 (bias) issue.
I generally post on a small number of amps so yeah, possibly in the past I've chimed in on CA-1010 bias issues.

I was referring to the 21V Zener Diode not the Marantz

 

[Nashou66]

I simply do not know how to answer your question.

Nashou