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andrelim

CK2III help

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I recently built a CK2III.

So far the +15V and -15V test pads measure 15.1V and -14.9V.

But nothing else measures correctly.

IPB Image

The green voltages are the voltages I measure, the white/red are the voltages they are supposed to be at.

I cannot seem to get a constant voltage at resistors R23 and R47. They range form 0.5mV to 30mV.

And I cannot hear anything when I hook up some cheap headphones to it.

I get a DC offset of 0.4mV to 10mV on both left and right channels.

Any help is greatly appreciated.

Here is the circuit diagram from the AMB website.

IPB Image

Edited by andrelim

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Hi Andre,

Well it happens to the best of us no matter how experienced we are at diy.

From my guess it's rather hard to fail if you're building from a proven/tested circuit board.

At least you have the correct supply voltage of +/- 15V.

 

If you had followed the silkscreen orientation of the transitors and IC you are half

way there although you could have inserted the wrong type i.e. npn or pnp .So recheck each

location(part number eg. BC 560c) tallys with the schematic.Then come the resistors,I believe they are the 1% metal

film type with 4 colour band ID.If you don't know the clour band code then at least measure them

in circuit although there will be places where they don't measure as coded on their colour band.

Nonetheless it gives a pretty good indication of correct resistor values.If all this tallies then

you have got a working circuit.

 

So check this for now. Good hunting. :yes:

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I have managed to get some sound on both channel after replacing the output transistors and resoldering all the solder joints. However it is still extremely distorted and intermittent. DC offset on both channels is around 0.5mV. However voltages across the board are still not the voltages they are supposed to be.

IPB Image

I am at a loss as to what to do now.

Any DIYer in Singapore looking to do a kind deed/for a challenge? :yes:

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I have managed to get some sound on both channel after replacing the output transistors and resoldering all the solder joints. However it is still extremely distorted and intermittent. DC offset on both channels is around 0.5mV. However voltages across the board are still not the voltages they are supposed to be.

 

I am at a loss as to what to do now.

Any DIYer in Singapore looking to do a kind deed/for a challenge? :yes:

 

 

Hi Andre,

What the heck do you think I'm doing? :)) Actually I've done this kit for a friend

years ago,he said he's not familiar with electronics and it went without a hitch.

 

Can I assume you have taken the advice of my fist post and confirmed that all

components are accounted for in the schematic vs pcb? If so then all should work as designed.

So you have replaced the BD138/139 and got sound but intermitant and distorted,well something

is still not right other than "replacing" all the transistors one by one which is a valid form of

troubleshooting it is tedious and costly.Don't forget the OPA134 opamp too.Although I don't

suspect faulty capacitors,this calls for injecting a signal and looking it in an osciloscope

which I think you don't have by which you would have gone down that path by now.

 

Secondly by resoldering all joints you may have overheated a component although

chances are that if you are careful this will not occur.

 

If I'm not wrong the CK2 designer has put voltage readings in the schematic for checking

and from there you should roughly know where the problem is.The dc offset of 0.5mv is as good as you can get I think.You mean it should be less? (I see it should be in 10uV...a lot less) -_-

 

What I can say is check for shorts between joints and also for breaks of pcb trace.

Use the meter/buzzer for continuity.

 

Here is what I can tell from the schematic:

1. The voltage at R8/9 is almost zero when it should be about -3V.

2. Same for R4 when it shoud be 2.7V

 

This is the small signal section or input please confirm that R1 - R11 are correct in value and R16 is 1megaohm

or 1 million ohms.Check also the copper trace is not broken again with the buzzer or low ohm range @ 200 ohm range.

 

That's for now. Good luck.

Edited by dacboy

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Hi Andre,

What the heck do you think I'm doing? Actually I've done this kit for a friend

years ago,he said he's not familiar with electronics and it went without a hitch.

Sorry no offense meant. I was trying to see if anyone wanted to help me troubleshoot my amp either

1. out of kindness

2. as practise

 

Can I assume you have taken the advice of my fist post and confirmed that all

components are accounted for in the schematic vs pcb?

I have checked what I can but I used vishay dale CMF resistors which are brown and have no color bands. That was not really a smart move now that I think about it.

 

If so then all should work as designed.

So you have replaced the BD138/139 and got sound but intermitant and distorted,well something

is still not right other than "replacing" all the transistors one by one which is a valid form of

troubleshooting it is tedious and costly.

 

Don't forget the OPA134 opamp too.

The opamp is used to remove DC offset right? Since my DC offset is 0.5mV can I assume that it is working fine?

 

Although I don't suspect faulty capacitors,this calls for injecting a signal and looking it in an osciloscope

which I think you don't have by which you would have gone down that path by now.

I just downloaded trueRTA and I'm going to use the oscilloscope to check the signal. ALthough its not as good as a real oscilloscope I'm hoping its better than nothing.

IPB Image

This is what I got in TrueRTA when playing a 1K hz sine wave, though my sound card isn't calibrated so I cant measure voltage properly.

 

Secondly by resoldering all joints you may have overheated a component although chances are that if you are careful this will not occur.

I was careful to heat each component for less than a second, so I'm hoping nothing is damaged.

 

 

If I'm not wrong the CK2 designer has put voltage readings in the schematic for checking and from there you should roughly know where the problem is.

Yeah the image I uploaded is the schematic found on the AMB website, with the voltages I measured (in green) above the correct voltages.

 

The dc offset of 0.5mv is as good as you can get I think.You mean it should be less? (I see it should be in 10uV...a lot less) -_-

What I meant was that I removed the DC offset of 110mV I had previously, not that 0.5mV is bad.

 

What I can say is check for shorts between joints and also for breaks of pcb trace.

Use the meter/buzzer for continuity.

I checked it once, but I will go through it more carefully again.

 

Here is what I can tell from the schematic:

1. The voltage at R8/9 is almost zero when it should be about -3V.

2. Same for R4 when it shoud be 2.7V

 

This is the small signal section or input please confirm that R1 - R11 are correct in value and R16 is 1megaohm

or 1 million ohms.Check also the copper trace is not broken again with the buzzer or low ohm range @ 200 ohm range.

 

That's for now. Good luck.

R2, R7 and R11 are correct. When I measure R16 in circuit it is 900K ohms.

If I measure the resistors in circuit it wont be accurate will it?

Thanks for your help

Edited by andrelim

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Hi Andre,

You are pretty smart with electronics ... what with that software scope...I myself have

not been successful finding one on the net... mostly trial or crippled ones.But I have a 60 Mhz.

scope on hand if I have tough dog problems like this. :yes:

 

Now if I assume your soundcard is or has low noise performance,I'm looking at purely

the 1 Khz. signal then the little wiggles at the top and bottom peaks of the sine wave is evidently

the intermitant noise you hear and it varies from half cycle to cycle.Noise like this may be hard to trace

but from what I mention about the input section of you measuring almost zero volts should tell you

that that part is very suspicous.If I assume the resistors are all correct then my logic will have to

assume Q5/6 may be faulty.Small transistors like that can easily damaged by insert them forcefully

into the pcb,that is making them sit close to the pcb thereby stressing the leads to break from

the silicon chip,the gold wire or maybe copper is very thin.so essentially you have a break but

it may still be in contact with the pad so partial contact is made.

 

Use your scope to probe Q5/6 one of them may give more distortion and the other one may

see a perfect sinewave.I don't have to tell which one is bad right? :yes:

 

Probe also the jfets 2SK74/SJ70 ...by the way these have stopped production but still availabe

at Sim Lim tower.

 

I normally assume the opamp is good which most times and seldom give problem.Yes it looks

like it balance out the dc offset.

 

R16 if you measure 900k ohm in circuit then it's close to the 1 meg value, yes you got it right.

 

You can use dale resistors which are prefered by audiophiles but double check or measure them before

stuffing into pcb.

You can do it Andre. :prettyprincess:

Edited by dacboy

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Check the values of R2 through R6. Make sure they match up nicely. It appears that your front end is the problem. If all lines up then you probably have an issue with either the input fets or C1 through C4 (check that they are not damaged).

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