Technics su x 101

MrChips

Joined Oct 2, 2009
30,714
Ok. Thanks for this.
Two points to note.

1) Next time you have to do this, write down the pin number and voltage in columns. We don't know what is your left and right.
For example:
1 = 48mV
2 = 39V
3 = -39.2V

2) Pay attention to the sign of the voltage shown on your DMM. Sign is very important!


Ok. On with the diagnosis. Do not connect a loudspeaker to the outputs. 39V on pin-4 is enough to blow the speaker.

Measure the voltage at each leg of R511 and R533 with respect to GND.
Report this as
R511-A =
R511-B =
where A is closest to IC501 and B is away from IC501.

Do the same for R512 and R534.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
Hi
Thanks.
I got
R511. A. 12.9v. B. 12.38v
R512. A. 2.4mv. B . 2.3mv
R533. A. 12.16v. B. 12.56v
R534. A. 2.2mv. B. 2.1. mv.
Thanks for that.
 

MrChips

Joined Oct 2, 2009
30,714
Ok. Please do the same for

R505
R506
R507
R508

Please report the sign on the DMM, while making sure that the BLACK (-) lead of the DMM is on GND.
Repeat the measurement at IC501 pin 10.
Repeat the measurement at the Left and Right speak outputs.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
Ok. Please do the same for

R505
R506
R507
R508
Ok. Please do the same for

R505
R506
R507
R508

Please report the sign on the DMM, while making sure that the BLACK (-) lead of the DMM is on GND.
Repeat the measurement at IC501 pin 10.
Repeat the measurement at the Left and Right speak outputs.

Please report the sign on the DMM, while making sure that the BLACK (-) lead of the DMM is on GND.
Repeat the measurement at IC501 pin 10.
Repeat the measurement at the Left and Right speak outputs.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
Hi

Thank you.
I have measured.
R 505. A=0.74v. B=6.85v
R 506. A=0.1mv. B=0.1mv
R 507. A=12.2v. B=12v
R 508. A=0.1mv. B=6.5mv.

IC 501 pin 10 =14.28v
Terminal l =39.8v
Terminal R=4.8mv
Thanks.
Have a nice weekend.
Jeff
 

MrChips

Joined Oct 2, 2009
30,714
We may eventually have to replace IC501, SVI 3102B.

Before we go that route, replace C523.
3.3μ 50V electrolytic capacitor.
Watch the polarity of the capacitor on removal and replacement.
 

bassbindevil

Joined Jan 23, 2014
824
Why not use the ohms (or continuity range) to check for a short circuit between the speaker output terminal and the positive supply rail? If there's a dead short, the IC is kaput.
 

LesJones

Joined Jan 8, 2017
4,174
That is a very good point as transistors normally fail with collector emitter short circuit. It might also be worth the TS checking for a short between the speaker output and the negative supply rail as there is still some doubt about the polarity of the voltage on the speaker as he did not at first give the polarity of voltage readings.

Les.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
That is a very good point as transistors normally fail with collector emitter short circuit. It might also be worth the TS checking for a short between the speaker output and the negative supply rail as there is still some doubt about the polarity of the voltage on the speaker as he did not at first give the polarity of voltage readings.

Les.
Hi
Thanks. Mr Chips, Mr Les Jones and Mr bassbindevil.
I have read some tread for that.
www.psaudio.com/pauls-posts/serve-you/
But as a newbie I still searching for what negative supply rail is.
I bought IC 501from China (only available at the moment) .
Will take a month to arrive.
I will be learning from forum.
 

LesJones

Joined Jan 8, 2017
4,174
The negative rail is just a voltage that is negative with respect to ground. Just as the positive rail goes to pin 2 of the amplifier package the negative rail goes to pin 3. This is required as the negative part of the output wave form has to go negative with respect to earth.

Les.
 

MrChips

Joined Oct 2, 2009
30,714
If you are willing to learn some more,
Go over your voltage readings again on IC501 from pins 1 to 14.
Record your results in a column format as I said.
Pay attention to the sign as shown on the DMM. The sign is very important too.
Keep the BLACK lead on the DMM on GND.

Be very careful not to short the test lead on adjacent pins.

When you have done this we will discuss about the negative rail.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
Hi
Thanks you Sir,
I have swapped C 523.
I have measurement of IC 501.

1. 152mv. Very much moving
2. 39v
3. 39v
4 39v
5. 13v
6. 12v
7. 0.256mv
8. 13v
9. 52.4mv
10. 12.8v
11. 12v
12. 0 v
13 0.4mv
14. 145mv. Moving.
Also got
C 523
1. 138 mv. Close to c501
2. 97mv.
Speakers terminal measurements are same as Last time Left terminal 39v.

I am waiting for c501.
Thank you very much.
Jeff
 

MrChips

Joined Oct 2, 2009
30,714
Please confirm that you confident that your data is correct.
If you are absolutely certain then something is wrong.
I expected to see some negative voltages in your data.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
Hi
Thank you Sir,
I measured it again.
1. 0.25v
2. 37v
3. 38.8v
4. 38.7v
5. 12.5v
6. 49.6mv
7. .251v
8. 13.5v
9. 0
10. 15.5 v
11. 14.7v
12. 0.1mv
13. 0.4mv
14. 0.2v

Thank you.
 

LesJones

Joined Jan 8, 2017
4,174
If you do not have about -38 volts on pin 3 of the amplifier IC then during your fault finding you must have done something that has destroyed the negative part of the power supply. You have previously had a negative voltage on pin 3 so you have caused another fault.

Les.
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
If you do not have about -38 volts on pin 3 of the amplifier IC then during your fault finding you must have done something that has destroyed the negative part of the power supply. You have previously had a negative voltage on pin 3 so you have caused another fault.

Les.
 

MisterBill2

Joined Jan 23, 2018
18,176
It would make the list of measured voltages a lot more useful if we knew the common reference point. That may have been stated before, but one-point voltage listings provide not much value.
 

MrChips

Joined Oct 2, 2009
30,714
In all of your reported measurements you have never indicated a negative voltage.
Let us analyse this situation and look at all possibilities:

1) There is no negative voltage in your circuit.
2) Your test meter is broken, either the negative sign is non-functional or the internals are damaged.
3) The test meter is set to the wrong measurement range.
4) The test leads of the meter are placed at the wrong test points.
5) There is something else going on in the test procedure that we have not been told.

You need to go through this analysis and try to locate the reason for no negative readings.
For staters, take an ordinary battery such as a 1.5V or 9V battery and try to measure its voltage.
Reverse the connections to the meter and see if you can get a negative reading.

Edit: I have reviewed your posts and looked at the photos on post #10. You have a DIGITECH QM1524 DMM and it shows a negative sign.
I suspect you are ignoring this information and you are failing to report the negative sign. Repeat your measurements and pay attention to the sign and report accordingly.

DIGITECH QM1524 DMM.jpg
 

Thread Starter

jeffOO

Joined Mar 8, 2020
25
In all of your reported measurements you have never indicated a negative voltage.
Let us analyse this situation and look at all possibilities:

1) There is no negative voltage in your circuit.
2) Your test meter is broken, either the negative sign is non-functional or the internals are damaged.
3) The test meter is set to the wrong measurement range.
4) The test leads of the meter are placed at the wrong test points.
5) There is something else going on in the test procedure that we have not been told.

You need to go through this analysis and try to locate the reason for no negative readings.
For staters, take an ordinary battery such as a 1.5V or 9V battery and try to measure its voltage.
Reverse the connections to the meter and see if you can get a negative reading.

Edit: I have reviewed your posts and looked at the photos on post #10. You have a DIGITECH QM1524 DMM and it shows a negative sign.
I suspect you are ignoring this information and you are failing to report the negative sign. Repeat your measurements and pay attention to the sign and report accordingly.

View attachment 201895
Hi
Thanks for replying.
I am sorry for my reading.
I didn't know this symbol have to be read.
Yes It have few.

My reading this morning is.

1. 0.196v
2. 39.3v
3. _39.4v
4. 39.4v
5. _12.3v
6. _49.8mv
7. _0.248v
8. 13.4v
9. 0
10. 15.79v
11. 14.6v
12. 0
13. 0.4mv
14. 196mv
I have to admit . I did short pin 3 and 4.
When I measured it this morning.
This reading is after short reading.

Thanks for your kindly help Mr Chips and Mr Les Jones, Mister bill2.

Jeff
 
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