[titomica]

Hi
I'm new to this forum and I'd like to say hello to everyone.

I'm writing as I'm an owner of a Cornet2 kit (finished and tested yesterday evening)

here my problem:
when I connected the unit it sounded flawlessly for about 30 minutes. there was low level of hum except a very high sensitivity when touching the RCA cabling coming from the turntable (I could hear clearly all the noises through the speakers)

then I switched off the unit as I placed it in a temporary position and replaced it on the right shelf, I had to unplug et replug the RCAs
I switched on again the unit and I touched the stereo/mono switch and suddenly I heard a bad noise though the speakers (I already have tested this switch in the first 30 minutes without any audible issue).
My Integrated then put itself in safety mode by deconnecting from the source.
I switched on again the integrated and launched the turntable and realized that only the left speaker was working.

I've tested the integrated and it is ok, the right channel works with other sources.
the problem comes clearly from the phono module.

any hints about how to troubleshoot?
I'm not very experienced and this kit has been my first serious soldering project.
I think I can solder quite ok but my problem is that I do not reaally understand what I'm doing... 

thanks a lot in advance

[hagtech]

Try swapping cables.  It sounds like a bad interconnect.

jh

[titomica]

Unfortunately it is not a bad interconnect...
Already tested swapping and still there is only left channel working.

There's some.hum disappearing when touching the body of the stereo/mono switch.

[poty]

Well, there are 2 interconnects: from the input and the output sides. Have you tried to swap both?
If the Mono switch put in "ON" - do you still hear the sound from only the left channel?
Do you have a multimeter and could you measure some points on the PCB?
Can you look into the case - maybe there is something that catch your eyes? (disconnected wires, blackened parts or something unusual)

[titomica]

of course I tried both, input and output channels 
the left channel works in stereo and mono modes and the right one does never work

I've a multimeter and I'd like to get some suggestion about where to check....   

I put some pics of the board so that you can get an idea of my kit

[poty]

Looks neat and marvelous. 
Before some measurements could you do something else? With greatest cautions with the Cornet 2 powered on, connected to your integrated amplifier with low volume set and the other hand in your pocket try to touch by a screwdriver or tweezers the following points:
- the center pin of RCA right output;
- V202's (the small tube near the big tube ) pin 8 (the pin second from the gap counterclockwise);
- the same tube pin 7 (the next pin counterclockwise);
- V201's (the middle small tube) pin 6;
- V201's pin 7;
- V200's (the tube next to Mono switch) pin 6;
- V200's pin 7.
You should hear loud hum from the right channel with each touch. If at some point you won't hear the hum you may stop and not go further. Please report at what point you will first loose the hum signal.

[hagtech]

I have to say first off - twisting wires randomly does NOT help.  You must twist the correct pairs.  Twisting with the wrong wire makes the situation even WORSE.  For example, the two green wires on the secondary of the power transformers is a good choice.  Red and yellow wires is bad.  Same thing with the input and output signals.  There is NO point twisting the left and right signals together!  Theoretically they should be twisted with their own ground - but I realize this is difficult with the given PCB, which was designed for a particular RCA connector.  In short, you are actually injecting more noise than you are eliminating.  On the plus side, most of what you have done is relatively benign and won't really make an audible difference. 

Back to the subject at hand - I do not see anything obviously wrong with the build - it looks fine.  I still think it is a connection issue.

jh

[titomica]

Looks neat and marvelous. 

thanks 

ok, I tried to follow your suggestions and I've been touching the center pin of the RCA right output (the one in the picture with the red cable welded in it)
no hum coming out

the problem is that I tried to check if my test was done properly so I "touched" with a screwdriver the center pin of the LEFT RCA and.....  no audible hum came out 

[titomica]

I have to say first off - twisting wires randomly does NOT help. 
jh

thanks for the suggestions....  I used some teflon tape believing to shield "more" ......   

[poty]

...I've been touching the center pin of the RCA right output (the one in the picture with the red cable welded in it) no hum coming out
the problem is that I tried to check if my test was done properly so I "touched" with a screwdriver the center pin of the LEFT RCA and.....  no audible hum came out 

Are you sure the integrated amplifier was switched on and the volume is not turned to mute?

[titomica]

Absolutely YES

[poty]

Hm... Could you touch the places while you are holding metal part of the the screwdriver (one finger is enough)?
Even without that there should be some noise... Can you pull out the interconnect going to your intergated amplifier from the Cornet 2 side and touch the central pins of the RCA from the interconnect just by finger?

[titomica]

testing the interconnect to the integrated it becomes clear now why I heard no hum before
I had to put the volume knob almost at the max to hear something.... 

before I kept the volume knob only at 1/4 and at 1/2 max.. 

have to stop my researchs this evening but I'll keep updating next steps 

a huge thanks poty !


ps:
this is where the Cornet2 will end up when it will work (I hope.....)

[titomica]

so, after the first step (center pin of right RCA)  there was no hum coming from the right channel
I checked anyhow the second step (V202 pin8) and hum came out from left channel.

weirdly once again when I connected the cornet to the integrated and then switched it on I heard a buzz from the speaker and the integrated put itself in safe mode.

[poty]

Please excuse me to force you to repeat: I don't understand clearly what you have done and what are the results. Touching pin 8 of V202 starts hum in the left channel? Or what?
In my opinion, the protection of your integrated amplifier triggers because of some problems in the output circuit (R119, C208, R222, output RCA). For example, a cold joint of R222 could lead to big pulse of voltage (around 150V) at the output.
Please check the voltage at the output RCAs (between center pins and the shells) preferable during powering on. Also at the R119 (one of the probe to either of the leads, the other - to the ground socket at the inputs).

[titomica]

I checked the center pin right RCA output by touching it with a screwdriver and there was no audible hum
I didn't stop as you said but went to the second step you suggested; touching pin 8. this step gave me audible hum from left speaker


voltage at output RCA is 0 at left channel and quite variable at right channel, going from 0.6 to 3 mV (measuring DC or do I have to measure AC?)

[poty]

Switch off the Cornet disconnect output interconnects and measure resistance on the output RCAs (left and right) (between center and shell).
I must explain what I want. Sorry, but yesterday I saw the answer very late and cannot make enough attention to it.

I checked the center pin right RCA output by touching it with a screwdriver and there was no audible hum

Between the point and the interconnect there is only RCA. If you insist that the interconnect is OK (by the way - touching the center pin of the right channel of the interconnect from the Cornet side should produce the hum!), then there are only two possibilities:
1. Bad RCA connector.
2. Something shorted the central pin to the ground.
I think the first possibility is unlikely, so asking you to measure resistance I'm trying to reveal that it is the second that is the source of the problem.

I didn't stop as you said but went to the second step you suggested; touching pin 8. this step gave me audible hum from left speaker

I hope (to prevent my brain from bursting) that you just chose the wrong side of "pin 8". Try to touch all the 9 pins one by one - at least 2 of them should hum on the right channel output.

voltage at output RCA is 0 at left channel and quite variable at right channel, going from 0.6 to 3 mV (measuring DC or do I have to measure AC?)

Yes, it should be DC. I asked you to measure the voltage at R119 to ground too - have you done than?

[titomica]

thanks for the great support poty,

I'm not having enough time these days to "work" 100% on the problem.
tomorrow evening cornet MUST work