Yamaha Amp CA610 going on protection mode

[Chickendbrave]

Hi Everyone,
I need help with my Yamaha Amp CA 610 which I stupidly connected in parallel with my Vincent Amp SP 31 to a pair of speakers. I know. . . Luckily, I did not switch both on simultaneously. Since then, the CA 610 is going on protection mode when the speakers are connected. Otherwise I can use the headphones with turned off speakers without any problem. What do you think I should look into to solve the problem? I checked the capacitors and they all seem to be in good shape as far as their ESRs are concerned.
greetings from Austria,
Oli

 

[WHONOES]

Sounds like it could have developed a d.c. voltage offset at its output.

Do you have any schematics.

 

[Chickendbrave]

Hello Whonoes,
thanks for replying. The schematic can be viewed better by downloading the Owner's Manual or the Service Manual. Here's the link to the Service Manual
Yamaha-CA-610-Service-Manual - Vintage Hifihttps://www.vintageshifi.com › pdf › telecharge

 

[73's de Edd]

You bravechicken you !

I looked at both the audio output stage design and the manner of headphone connection, and then the protection stage.
I see that if the protection relay engages, it disconnects the power audio from the speakers. (expected . . .duhhhhh . . .)
BUT now here is the IMPORTANT aspect, in that the headphones are getting their drive thru a power limiting 220 ohm resistor from the
power audio output line.
This means that if you are having working headphones and working power meter display, all is being well audio output wise. . . . and with the protection relay NOT being engaged.
Soooooooooooooooooo, why not look at the possibility of either the speakers not being connected to the correct / your expected 2 speaker terminals options or . . . . . alternatively . . . . . the speaker selection switch, is merely just being flipped to the wrong speaker set position.


73's de Edd . . . . .

 

[WHONOES]

Using a DMM (if you have one) check the voltages on TP1 and TP3 with respect to 0V. They should both be less than 100mV. These are the power amp outputs.

 

[Chickendbrave]

Hi Dr. 73's de Edd,

thanks for your warmth and wit. You're not suggesting either a) the polarity of the speaker terminals have been switched in the process of my ingenious faux pas of connecting 2 amps to a pair of speakers, or b) the speaker switch is playing hide and seek with me, are you? I can try to keep playing with hunch b); I suppose it would be a hit and miss case, but I will brave it for to paraphrase Tennyson, better to have hit and missed than not to have hit at all. . But your first hunch a) probably would need less courage and more prudence; Tennyson would be better left for another day, for it could be not only a hit and miss, but also a hit and kablam!

chickendbrave

 

[Chickendbrave]

Using a DMM (if you have one) check the voltages on TP1 and TP3 with respect to 0V. They should both be less than 100mV. These are the power amp outputs.

I remember adjusting these a month ago. Nevertheless, here are the readings, I've just had:
between TP1 & TP2: -10mV
TP3 & TP4: 10.1mV
GND & LO: -14.6mV
GND & RO: 15.9mV

 

[Chickendbrave]

I just tested the speaker outputs today and found out that the Right Channel is short circuited. Could this be a symptom of transistor/s failure?

 

[73's de Edd]

Test again, more carefully, and you should find the left channel shorted also.

 

[Chickendbrave]

Only the RCh is shorted. I guess I would need to test all the components of the R Ch, right? Any suggestions?

 

[WHONOES]

I remember adjusting these a month ago. Nevertheless, here are the readings, I've just had:
between TP1 & TP2: -10mV
TP3 & TP4: 10.1mV
GND & LO: -14.6mV
GND & RO: 15.9mV

Have just come back to this. The tests I asked you to carry are not those that you have performed.
I asked you to check the voltage between TP1 and 0V then TP3 and 0V. These check for any large d.c. offset at the output of your amplifiers.
The first two tests that you performed are for setting quiescent current in the output stages.

 

[Chickendbrave]

Have just come back to this. The tests I asked you to carry are not those that you have performed.
I asked you to check the voltage between TP1 and 0V then TP3 and 0V. These check for any large d.c. offset at the output of your amplifiers.
The first two tests that you performed are for setting quiescent current in the output stages.

Silly me! I knew my wife's right, I'm Olivertwistedhead. So here are the readings:
T1 - Gnd: - 14.3 mV
T3 - Gnd: 15.2 mV; I measured the continuity of this line and found out that it's shorted.

 

[WHONOES]

Before you go any further, you need to determine the cause of the short. It is unlikely though not impossible that the output stage of that channel has been wrecked as it has short circuit protection built in.