Amp In Protection Mode

[Rick79]

Excellent !

Have you got a good replacement cap for C613?
If you have, insert it (take care of polarity) and re-measure the output voltage.
What do you get?

yeah, I installed it already and I get 0.04V at R627 leg that use to be lifted

 

[dorke]

O.K
With volume at minimum measure the voltages ( 200mV DC range) on both legs of
R645, R647 and compare wit R646 and R648 of the other channel.
What do we get?

 

[Rick79]

O.K
With volume at minimum measure the voltages ( 200mV DC range) on both legs of
R645, R647 and compare wit R646 and R648 of the other channel.
What do we get?

The voltage readings bounce around when playing music so I can't get a specific reading.
The resistors are the square white boxes with 3 pins.
It's printed the board showing one side of R646 & R645 sharing the same pin and that pin reads 67.1mV with no volume and reaches up to 90.1mV with minimum volume.
The other pin of R645 reads 59.0mV with no volume and reaches up to -26.1mV with minimum volume.
The other pin of R646 reads 70.5mV with no volume and reaches up to 137.1mV with minimum volume.

R647 & R648 share one side of their pins also and it reads 01.2mV with no volume and reaches up to -06.9mV with minimum volume.
The other pin of R647 reads -01.7mV with no volume and reaches up to -104.1mV with minimum volume.
The other pin of R648 reads 00.1mV with no volume and reaches up to 63.1mV with minimum volume.

 

[dorke]

Rick,
Only at minimum volume please !

You have marked the resistors the wrong way !

For the left channel you have a single white resistor ,
Measure with both probes on R645 then both probes on R647 they should be both on that same resistor.

For the right channel you have the other single white resistor ,
Measure with both probes on R646 then both probes on R648 they should be both on that same resistor.

that is a total of 4 readings.

 

[Rick79]

Rick,
Only at minimum volume please !

You have marked the resistors the wrong way !

For the left channel you have a single white resistor ,
Measure with both probes on R645 then both probes on R647 they should be both on that same resistor.

For the right channel you have the other single white resistor ,
Measure with both probes on R646 then both probes on R648 they should be both on that same resistor.

that is a total of 4 readings.

I just realized the right channel resistor is misprinted on the board showing R647 & R648. No wonder why I got them mixed up. It should be R646 & R648.

When I took the readings I was using chassis Ground also.

OK, with both probes on the resistors.
R646 reads -06.1mV
R648 reads 05.5mV

R645 reads 04.6mV
R647 reads -08.9mV

 

[dorke]

Rick ,
I would check again the center pin of the white resistors,
DCV(200mV range) relative to GND for both channels.

The left channel readings above are a bit un-equal.
What do you get?

 

[Rick79]

Rick ,
I would check again the center pin of the white resistors,
DCV(200mV range) relative to GND for both channels.

The left channel readings above are a bit un-equal.
What do you get?

OK, but do I take the reading with minimum volume or no volume at all? If I turn the volume up just a little, i can't get a specific reading, the voltage goes up and down depending on the music and amount of volume used.

 

[dorke]

Minimum volume=zero volume=no volume.

One more thing I forgot to say,
let the amp worm up for about 5 minutes before you take the readings.

 

[Rick79]

Minimum volume=zero volume=no volume.

One more thing I forgot to say,
let the amp worm up for about 5 minutes before you take the readings.

OK. 69.3mV on the left channel resistor center pin & -05.0mV on the right channel resistor center pin.

 

[dorke]

At zero volume.
And after 5 minutes warm up.
Try trimming the left channel down closer to the right channel reading with VR601.
Then remeasure R645,R647 voltages relative to R646,R648 voltages.

 

[Rick79]

At zero volume.
And after 5 minutes warm up.
Try trimming the left channel down closer to the right channel reading with VR601.
Then remeasure the R645,R647 voltage relative to R646,R648 voltages.

OK, I got them both to about 06.5mV

 

[dorke]

Is that the mid point voltage?
What about the "4 resistors" voltages?

Edit:
If these are the resistors voltages,your amp should play well now.
You can try it with music and speakers,at low volume first then crank it up.

 

[Rick79]

Is that the mid point voltage?
What about the "4 resistors" voltages?

Edit:
If these are the resistors voltages,your amp should play well now.
You can try it with music and speakers,at low volume first then crank it up.

Yeah I cranked it up and it sounds good.

 

[dorke]

That is nice to hear.
Our work here is done ...at last.

 

[Rick79]

That is nice to hear.
Our work here is done ...at last.

Yes! Thanks for everything

 

[Rick79]

That is nice to hear.
Our work here is done ...at last.

I had posted in the forum about a TECHNICS Receiver. I was wondering if you know where I can find the service manual or schematics that tells the value of the resistors?