No phono on C-2101 pre-amp, usual suspects wanted.

[jd-audio]

Solved! No phono on C-2101 pre-amp, usual suspects wanted.

Hello all,

Can you help to determine what is wrong:

New-to-me C-2101 pre amp works fine, except for the phono inputs (1+2):
There is no sound at all on both inputs (no difference selecting MC/MC-high/MM). Both CH no sound.

I have the SM and have measured DC-adjustment 0V on the Equaliser Amp Circuit: Right CH is OK (ca. 0 mV, and adjustable), but Left CH is ca. 65 mV (adjustable between ca. 50-75 mV).

Flat Amp DC-adjustment is OK for both CH (but has nothing to do with the phono inputs I assume).

There are absolutely no optical signs of defects (no burns, leaks, corrosion, etc).

What can be wrong?
Are there usual suspects?

Some (tech) help would be much appreciated.
It is a bit frustrated as I just made lots of effords to get together a set of B/C-2101 to use as my main set to listen to vinyl (already sounds great with CD input after solving some minor issues on the power amp).

John.

 

[Pepa]

What can be wrong?
Are there usual suspects?

John.

John,I don't have SM,but dirty relays are a common problem in that preamp :yes:

 

[jd-audio]

Hello Pepa,

Yes, lots of relais (13!) in this pre-amp. They all seem to work fine (including the 2 for phono input, they click and I have "tapped" on them, no difference).

As each of the two phono inputs has it's own relais (who both seem to work fine) and the DC measurement of one CH is way off spec, I do not suspect a relais problem.

The SM is available on HifiEngine
http://www.hifiengine.com/manuals/sansui/c-2101.shtml

Thank you for your input, it is highly appreciated.

John

 

[avionic]

Check for correct power supply voltages feeding the F-4606 EQ board.

 

[Pepa]

OK,I download SM...thank you :thmbsp:

If you can hear click of relays,that's good sign,but signal contacts can be dirty also.

According to your written text (above),you have DMM and know how to use it.
Can you read shematic?
If so,you have marked points in SM with the expected voltage.Measure them,and post differences.

Start from power supply...like avionic sad :thmbsp:

 

[jd-audio]

Hello Avionic and Pepe,

You have found me out: I am no Tech.

I can check/adjust DC and Bias as I do understand the DMM basics, I also have some basic soldering skills and (sometimes with some help ) can identify resistors and capacitors, but unfortunately I can't read scematics.


I do understand that checking the voltages on the board can locate the problem. I also see the voltage indications on the scematic, but can not match the measuring point in the scematic with the real board (I have the pre-amp open in front of me and the scematic beside it, as I was hoping to figure out where to measure, but no, I simply can't figure it out).

Most of my Sansui vintage gear problems I have solved with common sense and some basic skills, but this seems to be out of my league.

So maybe I have to take some scholing or just bring the pre-amp to a technician?

*UPDATE*

I have started to do some measurements and getting some results:
Part of my readings give the Voltages as expected (+/- 0,5V) but part give 0 V.
How can I best post results (how to identify each measuring point)??
I do not understand (yet?) where the start (power supply) and end of the circuit is.

John

 

[jd-audio]

:scratch2: I think I understand the procedure and did the measurements on the EQ board:

Expected --> Measurement:

14V --> 13,5V
28V --> 29,7V
+/-28,5V --> 28,5V / -27,8V
+/-29V --> 29,2V / -28,4V
+/-30V --> 29,7V / -28,9
-17V --> - 15,7V

Now for the bigger differences:

+/-0,3V --> 0,0V / -0,0V (actually ca. +/-0,07V) location is Q7 and Q8 !!

Can we do something with this?

John

 

[jd-audio]

power update

In the mean time I have put the C-2101 pre amp aside (for a short time) and hooked up the B-2101 to my main system for the first time to see if it beats the AU-517 (why wait for the C-2101 to come "online" - Carpe Diem).

Wow, woow,
Sister Sledge - Lost in Music 12" on pristine vinyl.
Driving my Gale GS-401 speakers (owned from new, refurbished some years ago) for the first time with Sansui B-2101 RMS/200W/8Ohm/ch power amp (AU-517 as pre, nice combination btw) full throttle... fluorisent meters all the way up... heating up the power amp..no top cover.. feeling the warm black aluminium heat sinks "hands on"... my ears are popping... this is great.

Hope you know what I mean.

Just cooked dinner for the family, got to go to work tomorrow, but for now, life is good..with Sansui (and Gale).

John.

 

[jd-audio]

Problem solved, lessons learned.

John,I don't have SM,but dirty relays are a common problem in that preamp :yes:

In the end you were right: It was a "dirty" mechanical problem.

I realised that the measured Volts ware fairly close to expected, so I re-measured DC setting and discovered that I made a mistake before (measuring wrong side of the resistor): DC is OK for both CH.

So back to the relays. Cleaned them but still no effect.
Only other mechanical thing in the signal path was the MC/MC-high/MM selector switch. BINGO! After 2 cleaning rounds some sound was back, but it took 4 cleaning rounds to completely solve the problem.

Unbelievable: No sound at all due to a very dirty selector (not even after working the selector several times).
Looking at the input cinch plugs (only signs of use on CD/tuner) I suspect that the selector switch and phono were never engaged on this (extremely nicotine contaminated) pre.
Anyway, I am happy now as the pre works fine on all inputs and I have now a complete working B/C-2101 combo to listen to vinyl.

This shows again the importance of a good cleaning.

Thank you Pepe and Avionic for your input and effords :thmbsp:

John

 

[Pepa]

In the end you were right: It was a "dirty" mechanical problem.

I realised that the measured Volts ware fairly close to expected, so I re-measured DC setting and discovered that I made a mistake before (measuring wrong side of the resistor): DC is OK for both CH.

So back to the relays. Cleaned them but still no effect.
Only other mechanical thing in the signal path was the MC/MC-high/MM selector switch. BINGO! After 2 cleaning rounds some sound was back, but it took 4 cleaning rounds to completely solve the problem.

Unbelievable: No sound at all due to a very dirty selector (not even after working the selector several times).
Looking at the input cinch plugs (only signs of use on CD/tuner) I suspect that the selector switch and phono were never engaged on this (extremely nicotine contaminated) pre.
Anyway, I am happy now as the pre works fine on all inputs and I have now a complete working B/C-2101 combo to listen to vinyl.

This shows again the importance of a good cleaning.

Thank you Pepe and Avionic for your input and effords :thmbsp:

John

John,that's excellent :thmbsp:

To tell you one thing, first time I saw the restoration job of G8000 (I think) by AK member Kale,I thought this guy is crazy and has a lot of free time to do job like that.
After several years spent on AK a lot of things become much clearer.

For example...at the moment I'm working on one TOTL receiver,Sony STR-V7.
I decided to do an experiment with switches.After several chemical (DeOxide) treatments,and treatment in an ultrasonic bath,one would have thought that the switches in excellent condition now.
Well,that is not true at all.

Just look at these pictures:

Here we expect zero resistance

difference between the chemically treated and hand polished switch

So,my thoughts are that the Deoxide is just first aid and nothing more

To be precise,I do not use Deoxide,but Kontakt 60,Kontakt 61 and Kontakt WL

 

[jd-audio]

Yes Pepe, same kind of switch.

I know (thanks to AK and experience) that most problems on "partly" working (Sansui) gear is solved by a good cleaning. But only now discover the possible extend of the contamination. Your pictures are speaking for themselves about this.

I also drool over the beautifull pictures and posts of Kale.

John