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Yamaha CA-800 protection relay not working

M

mikevinci

Member
I need help with my Yamaha CA-800; the protection relay isn't activating.

The output voltages of the power stages are measuring approximately 80V when they should be approximately 50V. The measurements were taken in mode B. If I measure across TR708, the voltage is 23V instead of 12V.

What should I check?
 
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Set meter to 20Vdc scale

Connect black meter probe to any black speaker connector/ground.
Connect red probe to green out wire (Left channel) expect less than 50mV
Repeat with red probe on yellow OUT wire on right channel
 

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Good morning,

Thank you for your help. The measurement results show that the left channel is shorted due to a PNP transistor, 2SA663, as verified with a multimeter (I need to find a replacement transistor). Its complementary NPN transistor, 2SC793, appears to be working correctly when measured with a multimeter.

The measurements for the right channel, yellow wire and speaker ground, show 130mV.

I disconnected both stages to check the relay click, but it still doesn't activate. I don't know if this is normal or if it should activate even without the power stages connected.

Any ideas?
 
mikevinci said:
I need to find a replacement transistor
Click to expand...
Replace NPN and PNP. MJ21193G and MJ21194G will work. Maybe others will have better suggestions

mikevinci said:
The measurements for the right channel, yellow wire and speaker ground, show 130mV.
Click to expand...
Doubtful that this is sufficient to drive the protection circuit.
Refer to the adjustments section "Mid Point Potential Adjustment" of the service manual, using adjuster VR601

mikevinci said:
I disconnected both stages to check the relay click, but it still doesn't activate. I don't know if this is normal or if it should activate even without the power stages connected.
Click to expand...
Yes the relay should click. Try adjusting VR601 to below 20mV

Please post all comments/questions here, plenty of people to help out
 
mbz said:
Reemplace NPN y PNP. Los modelos MJ21193G y MJ21194G funcionarán. Quizás otros tengan mejores sugerencias.
Click to expand...

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

mbz said:
Sí, el relé debería hacer clic. Intenta ajustar el VR601 por debajo de 20 mV.

Por favor publique todos los comentarios/preguntas aquí, hay mucha gente que puede ayudar.
Click to expand...

mbz said:
Reemplace NPN y PNP. Los modelos MJ21193G y MJ21194G funcionarán. Quizás otros tengan mejores sugerencias.
Click to expand...
Me los cambiaron; fue una de las primeras cosas que hice. Los que tenía en ese momento eran TR704 -> MJE15032G y TR702 -> MJE15033G. Leí que eran buenos reemplazos para este trabajo.
mbz said:
Es dudoso que esto sea suficiente para activar el circuito de protección
Consulte la sección de ajustes "Ajuste del potencial de punto medio" del manual de servicio, utilizando el ajustador VR601
Click to expand...
Todas las resistencias variables VR601, VR602, VR603 y VR604 en las etapas fueron reemplazadas por resistencias Bourns de 4,7 KΩ.
mbz said:
Sí, el relé debería hacer clic. Intenta ajustar el VR601 por debajo de 20 mV.

Por favor publique todos los comentarios/preguntas aquí, hay mucha gente que puede ayudar.
Click to expand...
Revisaré la configuración del VR601 y les cuento. Gracias.
 
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mikevinci said:
Me los cambiaron; fue una de las primeras cosas que hice. Los que tenía en ese momento eran TR704 -> MJE15032G y TR702 -> MJE15033G. Leí que eran buenos reemplazos para este trabajo.
Click to expand...
I'm not so interested in TR702 TR704 yet.
For TR610 TR611 output transistors use MJ21193G MJ21194G
For TR602 TR604 if needed use KSA992 (hfe matched)
 
Please measure dc voltage at R715/R716 marked by red cross, black meter probe connected to chassis/ground.
Expect 0-6 to 1.0Vdc On relay/power supply board underneath amp
 

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mbz said:
Mida el voltaje de CC en R715/R716 marcado con una cruz roja, la sonda del medidor negra está conectada al chasis/tierra.
Espere de 0 a 6 a 1,0 V CC en la placa de relé/fuente de alimentación debajo del amplificador
Click to expand...
Las mediciones en los puntos de resistencia son 0,004 V en ambas resistencias R715, R716 and R717
 
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mikevinci said:
Las mediciones en los puntos de resistencia son 0,004 V en ambas resistencias R715, R716 and R717
Click to expand...
Not sure why you mentioned R717.

0,004V is very low. You needed to have the black probe connected to any black speaker connector. The red probe connected to R716 which is the same as R715 and TR709base. Use 2Vdc scale.

Also can you measure dc voltage at R709 as marked, repeat for R710, again black probe to any black speaker connector/GND. Expect less than 50mV
 

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Finally, the protection relay clicked. With both power stages disconnected, I spent two days tracing the missing signal. I finally found a solder joint at the base of TR709 that, although I had checked and measured it, I hadn't noticed was making poor contact. After that, I resoldered other points to repair the circuit. These are very complicated faults. My sincerest thanks to everyone who helps or offers support; you make it possible for me, like myself, to solve these problems.

Now I'll adjust the right channel stage and test it. On the other hand, I'll replace the left channel output stages because one of them is shorted.

For the final transistors, would it be a good idea to replace the current ones with these two new sets: 2SC793->2SC1116 and 2SA663->2SA747?
 
mikevinci said:
Finally, the protection relay clicked. With both power stages disconnected, I spent two days tracing the missing signal. I finally found a solder joint at the base of TR709 that, although I had checked and measured it, I hadn't noticed was making poor contact. After that, I resoldered other points to repair the circuit. These are very complicated faults. My sincerest thanks to everyone who helps or offers support; you make it possible for me, like myself, to solve these problems.

Now I'll adjust the right channel stage and test it. On the other hand, I'll replace the left channel output stages because one of them is shorted.

For the final transistors, would it be a good idea to replace the current ones with these two new sets: 2SC793->2SC1116 and 2SA663->2SA747?
Click to expand...
I get calluses on my tongue from repeating this but you should always reflow all the solder joints on these old units before starting any work, even if they look good.

The transistor substitutes above should work fine. Pay attention to bias conditions, different transistors have different bias points for optimal operation. You’re going to need a distortion meter to set the bias for minimum distortion but if you don’t have one, don’t worry, your ears will probably never be able to tell. Just follow the SM for starters.
 
A rather unpleasant surprise after making the adjustments according to the manual, and even though they were correct, the result was that the stage with the final outputs is still not producing any audio signal (absolutely zero). At this point, another part begins, which will be to check the board of the preamp and amplifier stage. I will continue reading the forums of this great channel to see if I can identify the problem.
 
I've tried the Aux and Tuner inputs, but neither outputs a signal. The rear switch could also be the problem, so I tested it by directly bridging the preamp and main outputs to rule it out. I'll also check the signal path from the RCA connectors on the board to the input switch to verify continuity.
 
I have a questions:

The normal/Class A switch might be affecting things?. I'm doing all the tests in Normal mode. When I've switched to Class A, I've always done it with the equipment off; I learned that from these forums.
About the relay; if anyone knows the answer, how long does it take to click after being turned on? In my case, it's almost immediate. I only have one amplifier board connected; the other is in the infirmary.

However, "Class A" is another issue I'm still working on. When I turn it on, something's not right; the series lamp is too bright, but in normal mode, it's dim. I suppose changing the switches on the toggle switches would be the best solution.
 
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