Stuck on troubleshooting sub-amp plate

[Armadillo]

Hi Armadillo,

After removing Q10 I'm getting all kind of weird readings, please see attachments.
All its left now is to order C01, C05, C06 and U01.
I'll post new measurement readings after swapping the parts.

Thanks!

Hi;

Firstly, as a double assurance, with the power off, please measure the ohms of the following resistors to confirm somewhere near to its value ; R02, R03, R04 and R05.
Secondly, as a double assurance, measure ohm [multimeter] across C02 which is 220pf, just to be sure its very high ohms and not short circuited.
Those as silly steps but double assurance before you change the U01 which looks defective. With 50 Hertz input, I would expect output to be 28vpp and not 2.8vpp. [worth to double ensure that the probe attenuation is set correctly  example 1:10? on the probe and on the scope setting.]

Digital oscilloscope - for every measurement, if you cannot see any waves which you expected, then it is worth to press the "AUTO" or "AUTOSET" button on the oscilloscope because sometimes the "trigger" setting is not correct for the signal. I don't know if Rigol scope you are using label it as AUTO?. Do read the user manual about this.

So after you changed the components [C01, C05, C06 and U01], definitely to a re-measurement and expect the output to be ~28vpp if the input is the same as before.
No rush. Take your time   

Edit: Forget to tell you, after you have replaced those components, remember to set signal source from zero volume up slowly before you blow the speaker. Your current input is overkilled. Do note!

[kasumyku]

Q10 is this KTD1304?

https://www.google.gr/search?client=firefox-b&dcr=0&biw=1920&bih=955&tbm=isch&sa=1&ei=4HAAWsOPPMiusAfsg77gDA&q=ktd1304+&oq=ktd1304+&gs_l=psy-ab.3...989.989.0.1125.0.0.0.0.0.0.0.0..0.0....0...1.1.64.psy-ab..0.0.0....0._kYpmf6NK9Q

Hi Pamarakos,

Yes, that’s the Q10 which I removed but it looks there might also be other components faulty, like a few caps and U01 (please see Armadillo’s previous comment and my attachments with measurements)
I’ll be posting updates after parts are replaced. Thanks

[kasumyku]

Hi Armadillo,

After removing Q10 I'm getting all kind of weird readings, please see attachments.
All its left now is to order C01, C05, C06 and U01.
I'll post new measurement readings after swapping the parts.

Thanks!

Hi;

Firstly, as a double assurance, with the power off, please measure the ohms of the following resistors to confirm somewhere near to its value ; R02, R03, R04 and R05.
Secondly, as a double assurance, measure ohm [multimeter] across C02 which is 220pf, just to be sure its very high ohms and not short circuited.
Those as silly steps but double assurance before you change the U01 which looks defective. With 50 Hertz input, I would expect output to be 28vpp and not 2.8vpp. [worth to double ensure that the probe attenuation is set correctly  example 1:10? on the probe and on the scope setting.]

Digital oscilloscope - for every measurement, if you cannot see any waves which you expected, then it is worth to press the "AUTO" or "AUTOSET" button on the oscilloscope because sometimes the "trigger" setting is not correct for the signal. I don't know if Rigol scope you are using label it as AUTO?. Do read the user manual about this.

So after you changed the components [C01, C05, C06 and U01], definitely to a re-measurement and expect the output to be ~28vpp if the input is the same as before.
No rush. Take your time   

Edit: Forget to tell you, after you have replaced those components, remember to set signal source from zero volume up slowly before you blow the speaker. Your current input is overkilled. Do note!

Thank you for the precaution regarding the input level!

Regarding the measurements:
-R02, R03, R04, R05 all read OK.
-C02 measures around 25Kohms
-I know you haven't mentioned for me to check but also C05, C06 measure around 25Kohms and C01 measures around 85kohms.
-for the probe matching the scope attenuation, I think I had them right but just in case I have attached pics
-regarding AUTO function: I try not use it most of the times but, in cases like this (when I don't see anything on the screen) I do use it. I appreciate the fact that you have pointed that out also.

Now, regarding the parts:

It seems that I cant find anyone selling this Q10 KTD1304 but Ebay and shipping from China is so slooooow.
Would you know by any chance a CrossRef/alternative for Q10 or some other online sellers( I've tried Digikey, Mouser and Newark and no luck) ?
Here are the rest of the parts that I'm about to order:

For U01
https://ca.mouser.com/ProductDetail/NJR/NJM4558M-TE1/?qs=sGAEpiMZZMtCHixnSjNA6NG6IBDWSupwerxZzjC5lQk=

For C05 and C06
https://ca.mouser.com/ProductDetail/Panasonic/EEE-FK1C220R/?qs=%2fha2pyFadugyxpIbZVcwfvp4YAOdsJG%2fwGkS7w0%2f1WHn2b1efBuOcA==

For C01
https://ca.mouser.com/ProductDetail/Panasonic/EEE-FK1C100R/?qs=qE6bgDGEOCvwL%2FHBRL1emg%3D%3D

[Armadillo]

It seems that I cant find anyone selling this Q10 KTD1304 but Ebay and shipping from China is so slooooow.
Would you know by any chance a CrossRef/alternative for Q10 or some other online sellers( I've tried Digikey, Mouser and Newark and no luck) ?
Here are the rest of the parts that I'm about to order:

There is a direct replacement from ebay for KTD1304. This is not a critical part to operate your amplifier, so you should be able to wait a bit longer for it through the mail while you enjoy the boom.

Since your circuit is using rectified mute signal from the preamplifier, you can try BC817, BC818, KSC326.

Alternatively, confirm that the dismantled KTD1304 is not faulty by measuring it with a transistor tester or multimeter [watch youtube how this can be done].

  

[Armadillo]

Regarding your previous measurement that the base of the KT1304 read -ve voltage, I was thinking of visiting it later after your amplifier is repaired but since you are going to buy the transistor, so you should also verify the Diode D200 [see attached] using multimeter on Diode Mode to check it, one side conduct and one side don't.
1N4148 let's hope it didn't turn into a resistor [both side conduct at some ohms].

[kasumyku]

Hi Armadillo,

Transistor Q10 has been damaged in the process of removing it from the board so no chance of testing it
Regarding diode D200, it tested OK.
I'll be posting updates after getting the parts in.

Thank you again for your time, patience and support!!!

 

[kasumyku]

Armadillo, it works!!!!!!!

A million of thanks wouldn’t be enough to show you my appreciation !!!
I think it works better than when it was new, because it hits such low frequencies now that I haven’t heard before.

As I mentioned, I have a ton of questions for you but I’ll limit to just a few:

1. Why is not a gradual increase of signal when tracing it through the preamp board, from the low level input up to the last opamp’s output. I mean why the signal amplitude is up and down at outputs of the op amps(or even no readings at the input of the first couple of opamps). Shouldn’t the signal increase after each op amp?
2. How did you know or what made you think that the caps were bad( BTW, all were indeed bad)
3. What are some good books regarding audio amplifiers on how every stage works or how it should behave and also the most important thing how to troubleshoot in the same way you have guided/shown me.

I hope you understood my questions as you can see that english is not my 1st language

Thank you!!!

[Armadillo]

Congratulation! 
I am happy for you. Well done!

1. Why is not a gradual increase of signal when tracing it through the preamp board, from the low level input up to the last opamp’s output. I mean why the signal amplitude is up and down at outputs of the op amps(or even no readings at the input of the first couple of opamps). Shouldn’t the signal increase after each op amp?

Because some of the sections/stages are actually frequency bandpass filters, in this case specifically low frequency filter and they do loss/attenuate the power through it, some are buffers or amplifiers to cater for the designed losses through the sections.

2. How did you know or what made you think that the caps were bad( BTW, all were indeed bad)

In electronics, there are the small signal and the large signal to deal with. Electrolytic/MLCC capacitors age through time especially with larger signal it handles at that section. Further more, this amplifier is for low frequency amplification, hence it needs larger capacitor to pass the low frequency signal across in fidelity. Hence it is appropriate to change it especially since the symptom is loss of amplification.

3. What are some good books regarding audio amplifiers on how every stage works or how it should behave and also the most important thing how to troubleshoot in the same way you have guided/shown me.

As you continue your journey in electronics, the troubleshooting skill will come with it, and gained through time and your exposures. Judging by your interest in electronics, I am sure one day you can be the better expert in it.  Let me flip through the notes and will drop you a note on the book on amplifiers.  Cheers;

Regards;

Armadillo

[pamarakos]

Armadillo, it works!!!!!!!

A million of thanks wouldn’t be enough to show you my appreciation !!!
I think it works better than when it was new, because it hits such low frequencies now that I haven’t heard before.

As I mentioned, I have a ton of questions for you but I’ll limit to just a few:

1. Why is not a gradual increase of signal when tracing it through the preamp board, from the low level input up to the last opamp’s output. I mean why the signal amplitude is up and down at outputs of the op amps(or even no readings at the input of the first couple of opamps). Shouldn’t the signal increase after each op amp?
2. How did you know or what made you think that the caps were bad( BTW, all were indeed bad)
3. What are some good books regarding audio amplifiers on how every stage works or how it should behave and also the most important thing how to troubleshoot in the same way you have guided/shown me.

I hope you understood my questions as you can see that english is not my 1st language

Thank you!!!

Sorry for getting into the party:) So I ve read all of it from the beginning but to be perfectly sure, problem was all the capacitors on the amp board? This is what you ve changed and now it works?
Can you please tell me their "codes" on the diagram like for example c01 etc?
Sorry for losing some more time of yours...
Thanks a lot

[pamarakos]

Congratulation! 
I am happy for you. Well done!

1. Why is not a gradual increase of signal when tracing it through the preamp board, from the low level input up to the last opamp’s output. I mean why the signal amplitude is up and down at outputs of the op amps(or even no readings at the input of the first couple of opamps). Shouldn’t the signal increase after each op amp?

Because some of the sections/stages are actually frequency bandpass filters, in this case specifically low frequency filter and they do loss/attenuate the power through it, some are buffers or amplifiers to cater for the designed losses through the sections.

2. How did you know or what made you think that the caps were bad( BTW, all were indeed bad)

In electronics, there are the small signal and the large signal to deal with. Electrolytic/MLCC capacitors age through time especially with larger signal it handles at that section. Further more, this amplifier is for low frequency amplification, hence it needs larger capacitor to pass the low frequency signal across in fidelity. Hence it is appropriate to change it especially since the symptom is loss of amplification.

3. What are some good books regarding audio amplifiers on how every stage works or how it should behave and also the most important thing how to troubleshoot in the same way you have guided/shown me.

As you continue your journey in electronics, the troubleshooting skill will come with it, and gained through time and your exposures. Judging by your interest in electronics, I am sure one day you can be the better expert in it.  Let me flip through the notes and will drop you a note on the book on amplifiers.  Cheers;

Regards;

Armadillo

So it was all the caps after all?
Just in case kasumyku doesn't respond today, can you please confirm?
Sorry for bothering:)

Thanks again for all your knowledge shared.

[kasumyku]

Hi Pamarakos,

No worries, here are the components I have replaced:

U01 (njm4558m)
C01, C05 and C06
Q10 ( diagram asking for ktd1304 but I have used ksc2365)

Also check Q21 and Q22( part of power supply)

Thanks.

[pamarakos]

 Hi Armadillo

I ve got mine returned repaired, he said that he replaced two transistors, didn't say which, everything is working ok as it seems now, except I can't remember if crossover was working when used lfe input or only on l/r input. Because now it works like this.
Have you got any idea? Already asked kasumyku too, if you've got any idea please let me know the soonest so as to return it if it's not supposed to work this way.

Thabks a lot

[Armadillo]

Hi, nice to hear that you got your unit resolved.
For your question, is best for kasumyku to reply you. But I try;
As far as I can tell, lfe input is for low frequency input if your device has already a crossover unit that separates the signal and provides the lfe [low frequency] signal to this sub-amplifier.
if you don't have any device that provide lfe output;
then you can connect the audio signal to the l/r input, because internally it contained low frequency filters to only filters low frequency for the amplifier to amplify.
All this connection details can be found in the user manual.
If you are already using the l/r input and is satisfied with it, then you should be safe.

I trust kasumyku can provide you with better explanation.

By the way, 2 transistors should be cheap for you to send it out for repair? How much it cost you? I think you friend should be reasonable.

[pamarakos]

I ve used lfe always before as my amp shows lfe sign at his preout sub output. Also when lfe is connected sub plays louder than r/l channel.
Let s see what kasumyku will say. Thanks for your response.

[kasumyku]

I don't know if i'm right but looking at the schematic it does look like the cross over pot is only wired for the L/R input and doesn't make any sense because mine does work regardless of the input , but as you can see I'm still at the very very beginning of my troubleshooting journey and to be honest, I'd probably would had very slim chances or none of fixing it on my own if Armadillo wouldn't guide me thru..

[pamarakos]

Funny thing is that I do remember very well that I used this crossover knob to adjust the bass every time together with the volume. I can't remember it wrong. I don't know what to say, I ll filter it from my main amp and never take it back to the repair guy:)