Hello , I got an old SONY TA-11 amplifier and it has 3 missing resistors . I have already found them in the schematic online . The problem is that schematic says , for example that R136 is 390 Ohm or R234 is 1kOhm . Tolerance isn't shown anywhere in the manual/schematic online... so is there any way to find it ?
I uploaded an image (manual) that says some specifications .

 

Are you sure they are supposed to be fitted? It is not uncommon for the schematic, and even the circuit board to be lagging on changes to the actual circuit.

 

Are you sure they are supposed to be fitted? It is not uncommon for the schematic, and even the circuit board to be lagging on changes to the actual circuit.

pretty sure , actually I found him wasted close to trashes . Someone has removed the resistors for some reason . I guess they were damaged because it has black dust under every missing resistor .

 

OK. If the resistors were burnt then it is likely that some other fault caused the burning.
Usually in the parts list it will say something like "All resistors 1/4W 5% unless otherwise specified". Does yours have something like that?

 

OK. If the resistors were burnt then it is likely that some other fault caused the burning.
Usually in the parts list it will say something like "All resistors 1/4W 5% unless otherwise specified". Does yours have something like that?

Yes , It says "all resistors are in ohms 1/8w unless otherwise noted."

 

If it is not specified then the tolerance is unlikely to be critical. You could have a look at the other resistors and see what tolerance they are but I wouldn't worry about it too much.

However, I do expect that when you power it up with new resistors they will burn again.
Can you post the schematic here then we can speculate what other components should be tested.

 

If it is not specified then the tolerance is unlikely to be critical. You could have a look at the other resistors and see what tolerance they are but I wouldn't worry about it too much.

However, I do expect that when you power it up with new resistors they will burn again.
Can you post the schematic here then we can speculate what other components should be tested.

Of course thanks for your time sir ! I will try to upload the manual , because I don't know how clear the image will be .

 

Readable, just about!
Are you sure the resistor numbers are correct?
The numbers you give are one in each channel, but different parts of the circuit.

 

Readable, just about!
Are you sure the resistor numbers are correct?
The numbers you give are one in each channel, but different parts of the circuit.

The resistors R133 R136 and R235 are missing , totally correct just check them . Thank you for helping me out sir

 

If R235 was burnt that strongly suggests that Q210 is damaged (open circuit base emitter?).
Can you test it?

 

If R235 was burnt that strongly suggests that Q210 is damaged (open circuit base emitter?).
Can you test it?

You mean to check if there is any short circuit that affects the transistor ? I can clearly see that there is kind of burn under Q209 .

 

You mean to check if there is any short circuit that affects the transistor ? I can clearly see that there is kind of burn under Q209 .

Yes, you can check both Q209 and Q210 junctions for open or short circuit.

 

Do you know how to test a transistor? Do you have a digital multimeter with an diode range? You are going to need to remove from the circuit and test a number of the transistor to find the fault.

 

Do you know how to test a transistor? Do you have a digital multimeter with an diode range? You are going to need to remove from the circuit and test a number of the transistor to find the fault.

Actually I am going to buy a multimeter , the problem is where should I place the probes ?

 

Yes, you can check both Q209 and Q210 junctions for open or short circuit.

I checked them , and they don't seem like damaged from short circuit or open . I guess I will have to test them with a multimeter

 

I guess I will have to test them with a multimeter

Yes, I'm afraid so.

 

If we are going to try to walk you through a repair, I got to ask... How about soldering? Do you have soldering equipment and skills? To start, you will need to remove the transistors from the circuit to make meaningful measurements on them. When you buy that DMM, be sure it has a 'diode' range.

 

In regards to tolerance, there's never any harm in getting better parts. So in a case like this where you're just buying a few parts and the price difference will be so minimal, get the best you can find and they are sure to be suitable. 1% are most likely fine.

This probably doesn't apply to your stereo so ignore this, but I did work on a differential audio circuit the other day and the parts manufacturer recommended 0.1% parts for better noise rejection. Here's an excerpt from the data sheet:

"In differential mode the tolerance of the source and feedback resistors which set the gain of an amplifier is important. 1% resistors give a 40dB CMRR whereas 0.1% resistors give a 60dB CMRR. Use 0.1% resistor arrays for even better performance."