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Yamaha CA-800 protection relay not working

mikevinci said:
Why is it still maintaining -70V on the negative rail?
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Possibe faulty TR701, TR702

mikevinci said:
Could I try connecting the power stage and verifying its behavior?
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Target voltage is +/-50V, you have +64V and -70V.
Expect a significant DC offset, you may do futher damage, so no please don't connect power amp stages.

Test TR701 and TR702, b/c/e voltages to GND may help, also please give part number (TIP...? or ) for each
 
I've checked TR702 and TR701; now I'm getting +B=64V and -B=-62V with DBT

I have reinstalled the original transistors TR702 2SA673 TR0703 and 2SC1213
If necessary, I can have substitutes for TR702 with 2SC1318 S and for TR703 with 2SA1015 or 2SA673 "C" (I don't have the one that corresponds to the "S" version).

TR701=MJE15033G
TR704=MJE15032G
 
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Zener diodes D703 and D706 replaced with 30V 0.5W diodes.

Current measurements are +B 58V and -B -58V. The unregulated power supply for the power stages provides +43V and -43V. Relay click after 3-4 seconds power On.

Do I think these are more acceptable measurements?
 
mikevinci said:
I've checked TR702 and TR701; now I'm getting +B=64V and -B=-62V with DBT

I have reinstalled the original transistors TR702 2SA673 TR0703 and 2SC1213
If necessary, I can have substitutes for TR702 with 2SC1318 S and for TR703 with 2SA1015 or 2SA673 "C" (I don't have the one that corresponds to the "S" version).

TR701=MJE15033G
TR704=MJE15032G
Click to expand...
Are you sure you have those correct? At first you have TR702 as a 2SA and then as a 2SC
 
I replaced TR701 and TR704 with their original 2SA671 and 2SC1061, respectively. It seems the previous TR701=MJE15033G and TR704=MJE15032G were defective, or at least that's my interpretation. I've now managed to lower the voltage from +56V to -56V without DBT.


I think it might be time to connect the power amp output and test it, right?
 
mikevinci said:
I think it might be time to connect the power amp output and test it, right?
Click to expand...
Yeah, connect one side first then dbt power up, check bias is below 20mV as a safety margin. Do not attempt to set bias to spec (47mV?) while on DBT. Then repeat for other side (dbt bias under 20mV)
 
After performing the polarization as instructed, I'm still having problems. The speaker output emits noise but doesn't play any music, and there's no sound when I connect headphones to the Phone output either.

I'm testing with the AUX2 input and have verified the signal on the source board all the way to its output via the Molex connector that carries the signal to the preamplifier.

It seems I have another problem in the signal path.

Where can I measure or what test can I perform to verify the signal, at least at the headphone output, and rule out other possible faults before assuming the problem lies with the amplified power board?

Thanks again a million times over
 
Did you set bias off DBT, 47mV between TP's.
Have you performed the other adjustments, ie, 15Vdc and 0Vdc offset.
Forget class A for time being.

Set coupler switch to OFF, connect iphone/ipod at minimum volume to main-in RCA's, slowly increase iphone volume. Any audio?

Some easy test points for audio,
L&R power amp boards IN and OUT wires

Volume Board White(L), Pink(R) wires in the Yellow, Brown, Red,,, wrap, Black wires are GND.
Test all white and pink wires on this board, important to note wrap colour, eg, red ok but yellow not ok...
 
Yes, I made the adjustments exactly as you described, but I still had no sound.I traced the signal on the input and output cables of each board until I saw that the signal stopped at the filter board and wasn't outputting.I directly replaced the 2SC1345 TR501, 502, 503, and 504 with 2SC1815s, and ohhhhh, music to my ears!


I adjusted mode normal and the Class A to 0.8v and it also sounds wonderful.

The only issue I've noticed is a popping sound from the speakers when I lower the power switch and the speaker selector is set to A, B, or AB.

To avoid this, I turn the selector to OFF before turning the power off and on, and it doesn't happen.

Is there anything I can check to prevent this noise from the speaker outputs?
 
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To be honest, the Yamaha CA-800 has been a real pain; it drove me crazy and almost made me throw in the towel prematurely. However, I must admit that it was absolutely worth dedicating every last minute of time and effort to repairing this unit because the result has been very satisfying.

I own several systems from various brands, and I hadn't heard these models before. I realize I was missing out.

It sounds magnificent, incredibly pleasant and sweet.

I am incredibly grateful to "mbz" for his vast knowledge, his generosity in sharing it, and his endless patience in helping me. Without his help, I never would have been able to achieve this.

Thank you, thank you so much, and a million times thanks.
 
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mikevinci said:
The only issue I've noticed is a popping sound from the speakers when I lower the power switch and the speaker selector is set to A, B, or AB.
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A pop when turning the amp off.

Try setting rear coupler switch to off then run the test again, power on, any power off pop, expect no.

Is the power on lamp working, it helps run down C714.

Have you replaced the RC snubber across the power switch.

mikevinci said:
It sounds magnificent, incredibly pleasant and sweet.
Click to expand...
Yeah the CA-800 is a nice amp, PITA to work on. The CA-1000 is slightly better. The CA-1010 and CA-2010 have a different sound but also easier to work on, nice amps again. Generally the yamaha seperates are a step up again, eg, C-??/M-??
 
mbz said:
A pop when turning the amp off.

Try setting rear coupler switch to off then run the test again, power on, any power off pop, expect no.

Is the power on lamp working, it helps run down C714.
Click to expand...
If it works well, it's an LED lamp.
mbz said:
Have you replaced the RC snubber across the power switch.
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What is the damper? The switch lever spring?
mbz said:
Yeah the CA-800 is a nice amp, PITA to work on. The CA-1000 is slightly better. The CA-1010 and CA-2010 have a different sound but also easier to work on, nice amps again. Generally the yamaha seperates are a step up again, eg, C-??/M-??
Click to expand...
 
I was wondering if it would be advisable to install film capacitors in parallel with the power supply capacitors for the power stages?

And also at the 220V input?

I saw it in a YouTube video about repairing this amplifier.
 
mikevinci said:
I confirm that it can still be heard even with the switch in the OFF position and the speaker selector activated.
Click to expand...
Pop coming from power amp stage. Might be an issue with relay not opening quick enough.

Have you increased C714, should be 220uf or C714 should be 47uf
Test D709 then R717, should not be failed open

mikevinci said:
What is the damper? The switch lever spring?
Click to expand...
See page 11 of service manual Power Switch Circuit Board and C731 and C732, these are the RC snubber on this board
 

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