Yamaha CA-800 protection relay not working

[mbz]

Voltages are better but still not 100%

GND/OUT -> 0.4V

Did you try the "Mid Point Adjustment" as per manual, VR601

Anode D602/GND 0.6V
Cathode D602/GND 1.8V

This looks like measurement error
Expect anode +1.8V, cathode +1.2V

TR608
GND/B -> -0.091V
GND/E -> -0.28V
GND/C -> -44.4V

More measurement error
TR608b = -0.091V same point as D602 anode = +0.6V

 

[mikevinci]

Voltages are better but still not 100%


Did you try the "Mid Point Adjustment" as per manual, VR601

Yes, 0,032V

This looks like measurement error
Expect anode +1.8V, cathode +1.2V


More measurement error
TR608b = -0.091V same point as D602 anode = +0.6V

Correct, these measurements correspond to TR609, not TR608, my mistake

 

[mbz]

Yes, 0,032V

32mV is still a little high, ideal target is 0mV, with less than 10mV being acceptable.

 

[mbz]

I can't adjust the Class B bias to 0.047V; it only allows me to set it to 0.022V with the variable resistor fully extended at one end.

The replacement output transistors probably have different characteristics (hfe, Vbe,,,) to the originals. The work around is to add resistance in the bias circuit. Replace R614(10k) with 12k then dbt power up make sure normal then try to set bias without dbt, you may need to incresase R614 to 15k.

Important, I assume you are not setting bias while on DBT, set bias back to zero if you have done this.

 

[mikevinci]

The replacement output transistors probably have different characteristics (hfe, Vbe,,,) to the originals. The work around is to add or reduce resistance in the bias circuit, give me a moment.

However, in the other power stage, which I haven't had any problems with, I was able to get it working even though it uses the same transistors, 2SC1116 and 2SA747.

I think there's still something wrong with this repaired power stage.

In fact, when I switched to Class A (with the amplifier off before switching), the protection circuit activates and the relay doesn't click. This didn't happen with just one stage before connecting this last one

 

[mikevinci]

Not sure the switch cap is faulty.

Connect amp to a power board then try powering off at the power board or wall switch not amp switch, do you still get a pop?

I tried turning it off using a power strip without the switch, and it doesn't click when I turn it off; it only clicks when I use the power switch. This means it must be the switch itself that's faulty, not capacitors C731 and C732.

 

[mbz]

In the repaired channel have yuou replaced any of TR605, TR608,9 TR610, 611?
If so what with.

 

[mikevinci]

The replacement output transistors probably have different characteristics (hfe, Vbe,,,) to the originals. The work around is to add resistance in the bias circuit. Replace R614(10k) with 12k then dbt power up make sure normal then try to set bias without dbt, you may need to incresase R614 to 15k.

Important, I assume you are not setting bias while on DBT, set bias back to zero if you have done this.

Correct, I do it without DBT

 

[mikevinci]

In the repaired channel have yuou replaced any of TR605, TR608,9 TR610, 611?
If so what with.

TR605 = 2SC485 replacedTR608 = 2SC1124 not replacedTR610 = 2SA747 replacedTR611 = 2SC1116 replacedTR609 = 2SA706 not replaced

 

[mikevinci]

Overall, there was progress, but I need to keep working on it; I still have things to work out.

 

[mbz]

TR605 = 2SC485 replacedTR608 = 2SC1124 not replacedTR610 = 2SA747 replacedTR611 = 2SC1116 replacedTR609 = 2SA706 not replaced

Where did you purchase the replacements? Are they fake or reliable.

I need to keep working on it; I still have things to work out.

Yeah, seem to be jumping about a little. Pick the biggest problem then work on it. Forget about class A until you sort out normal.

Are power supply voltages ok (looks reasonable)
Does the relay click 4-6seconds after power on
Do you have audio out of the repaired channel.

The 22mV(or whatever) bias is not a big issue so put that on hold, focus on the above 3 items first

 

[mikevinci]

¿Dónde compraste los repuestos? ¿Son falsos o auténticos?

I always prefer to keep the original components when making replacements, except in cases where a component is known to malfunction due to design flaws or is simply problematic. In those cases, if I can find them, I usually buy them from a local, generally trustworthy shop that stocks older components. However, I'm aware that you can never be entirely sure of their condition, even if they're new and unused, due to their age.

On the other hand, since these components aren't so specific, I buy from Mouser.

In this case, with the exception of the KSC1815 installed to replace the 2SC485, the rest of the replacement parts are old stock: the 2SC485, 2SA747, and 2SC1116.

Sí, parece que andas un poco disperso. Elige el problema más grande y luego trabaja en él. Olvídate de la clase A hasta que resuelvas lo normal.

¿Los voltajes de la fuente de alimentación son correctos? (Parecen razonables)

OK. It's a great achievement it's given me quite a headache to figure it out.

¿El relé hace clic entre 4 y 6 segundos después de encenderlo?

Yes

¿Tienes audio en el canal reparado?

Pending testing.

I still need to figure out why one of the channels (white cable) has no audio. Something is wrong with one of the sound cards, specifically with the volume, balance, tone, and filter settings

I tried connecting the preamp output of the unit to the main input, but I still don't get audio from that channel.

La polarización de 22 mV (o la que sea) no es un gran problema, así que dejémoslo de lado y centrémonos primero en los tres puntos anteriores.

 

[mbz]

I still need to figure out why one of the channels (white cable) has no audio.

White cable = left channel

I tried connecting the preamp output of the unit to the main input, but I still don't get audio from that channel.

Try the following...
Get some wire 250mm-500mm, tack/solder one end to IN solder pad on left channel power amp, use the other end as a probe, great if you could connect to probe or minnigrabbers or similiar, don't want the probe end to fray and short.

Set volume to 9oclock position

On the volume board test the white(L) wires in the Brown wrap, repeat for the Red then Yellow wrap. Do not test the Orange wrap, these will be at full volume.

 

[mikevinci]

Thanks for the instructions, they're very welcome.

This morning, while checking the wiring, I noticed that the brown cable that goes from the audio output of the tone control board back to the balance board (I think that's what it's called) wasn't making good contact. The sound would cut in and out just by turning the tone control board slightly, so that solves another problem. two channels working.

 

[mbz]

So what's the next problem?

 

[mikevinci]

So what's the next problem?

Wait, let me tell you about my latest blunder, or at least that's how I interpret it, since I don't know any better.

for not waiting for your instructions and next steps

In my country, there's a saying, "stick to what you know," and how true it is!

 

[mikevinci]

In my excitement, seeing that both channels were working fine, I turned it off and switched to Class A.

Oh my God!

It instantly exploded, and the 330-ohm resistors (R623) on both channels started smoking.

The foolishness of switching has claimed four victims so far: all four power transistors. We'll see what else is damaged.

Another setback. I have to start all over again and diagnose the resulting problems.

I admit I'm a disaster. You don't need to tell me, I'll say it myself I'm sorry for being so stupid

It's likely claimed more victims; I didn't want to continue for today.

When this happened to me in the morning, I had to leave the repair room and go for a walk to clear my head; I couldn't keep looking at the mess I had made.

A real disappointment.

Tomorrow I'll assess the collateral damage and look for replacement parts

 

[mikevinci]

The thing is, when only one power stage (the one that had always worked) was connected during the repair about 8-10 days ago, I tested it in Class A mode after adjusting the bias to 0.8V, and it worked perfectly, with excellent audio quality.

This happened after connecting the second, "repaired" power stage

 

[mikevinci]

Reemplazar NPN y PNP. Los MJ21193G y MJ21194G funcionarán. Quizás otros tengan mejores sugerencias.

I will include these power output transistors in my next order from Mouser

Es dudoso que esto sea suficiente para activar el circuito de protección.
Consulte la sección de ajustes "Ajuste del potencial del punto medio" del manual de servicio, utilizando el ajustador VR601.


Sí, el relé debería hacer clic. Intenta ajustar VR601 a menos de 20 mV.

Por favor, publiquen aquí todos sus comentarios/preguntas; hay mucha gente dispuesta a ayudar.

 

[mbz]

Replace failed transistors/resistors...
Set both VR603 and VR604 for minimum bias
Power up with DBT get both channels working in Normal/AB, DBT dim