C-4 preamp cuts out...Help

I

india42

AK Subscriber
Subscriber
OK, so yesterday, I got a great deal on a C-4 pre with a M-4 amp. Hooked up the amp....ahhhhh, sweeet! Today, I decided to try the C-4, hooked it up, turned on the Pioneer TX-9500, beautiful!
Then suddenly, the sound stops, power is still on (at least the lights are on), no sound. Plugged in some headphones...nothing. When I say nothing, I mean dead silent, no static, nothing.

Anybody have any ideas? I have limited troubleshooting skills, but I can read a schematic, have a DMM, and a soldering iron.
 
I should also mention that the amplifier (m-4) works perfect, I know it's the preamp that isn't working.
 
india42 said:
OK, so yesterday, I got a great deal on a C-4 pre with a M-4 amp. Hooked up the amp....ahhhhh, sweeet! Today, I decided to try the C-4, hooked it up, turned on the Pioneer TX-9500, beautiful!
Then suddenly, the sound stops, power is still on (at least the lights are on), no sound. Plugged in some headphones...nothing. When I say nothing, I mean dead silent, no static, nothing.

Anybody have any ideas? I have limited troubleshooting skills, but I can read a schematic, have a DMM, and a soldering iron.
Click to expand...

First thing. Check your power supply voltages and solder connections within the power supply.( check the solder connections on the two pass transistors that are mounted to the two largest heatsinks.)



Hifiengine has a decent schematic as well as the service manual.
 
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Do you hear any real faint tiny metallic clicks coming from the reed relays shortly after you apply power to the unit ? Approx. 1 or 2 second delay.
 
avionic said:
First thing. Check your power supply voltages and solder connections within the power supply.( check the solder connections on the two pass transistors that are mounted to the two largest heatsinks.)



Hifiengine has a decent schematic as well as the service manual.[/QUOTE

I did download the SM and I checked the power source voltage between TP7 and TP8, it read 30.13V (spec shows '30V +/-.5v) so I think that's OK. I looked at the transistors (they do get pretty hot) and the connections don't appear bad, sometimes it's hard to tell. I also checked the DC offset of the EQ section, and one of the channels (can't remember which one) read 1.6V, so I adjusted that.
I will download the schematic, it's been a long time since I tried to read one, maybe I should find a tech. I would hate to ruin this Pre, it looks so perfect. I got a pretty good deal on it, so maybe it's worth seeking professional help, just thought I could learn something here.

Anyway, thanks for the help, I will try more, but I'm afraid you'll need quite a bit of patience with me.
PK
Click to expand...
 
avionic said:
Do you hear any real faint tiny metallic clicks coming from the reed relays shortly after you apply power to the unit ? Approx. 1 or 2 second delay.
Click to expand...

No nothing like that. Funny thing is, the first time I turned it on, I remember that I heard nothing like that, and it started playing beautifully. It played for about 10 mins. or so, then I hooked up my turntable and I noticed that the phono switch seemed a little dirty (scratchy), so I worked it a little, and then it stopped working, no sound. I turned it off for about 5 mins or so, turned it back on, and it played for about 3 or 4 more minutes and now I can't get a sound out of it...
Thanks again
 
india42 said:
No nothing like that. Funny thing is, the first time I turned it on, I remember that I heard nothing like that, and it started playing beautifully. It played for about 10 mins. or so, then I hooked up my turntable and I noticed that the phono switch seemed a little dirty (scratchy), so I worked it a little, and then it stopped working, no sound. I turned it off for about 5 mins or so, turned it back on, and it played for about 3 or 4 more minutes and now I can't get a sound out of it...
Thanks again
Click to expand...

You almost need a perfectly quiet room or your ear right against the top cover,to hear it.
 
Check the solder connections on the relay driver transistor. It is the third smaller heatsinked transistor
 
The relay(s) I mentioned earlier are small reed relays that are used for muting purposes.
 
I think I've been looking at the for to long, time for a break. I can't for the life of me find a relay, I think I'll eat something, then take another look.

Thanks for all the help, I really appreciate it!

PK
 
Actually there are 3 of those reed relays in there. All three need to work or no sound.
Disreguard the red line in the photo below.
 

Attachments

  • C-4 reed relays.jpg
    C-4 reed relays.jpg
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Ya know, I thought those were some type of relay, boy do I feel stupid. I'm not looking at it right now, but I thought the schematic listed those as metal plate resistors, or something like that, so I disregarded those.
Thanks for the visual aid, I really needed that!!

Paul
 
Just an update, in case anyone is interested. I was in Seattle last week and met up with blhagstrom, long story short, he was able to get this going for me. We had a great visit and some laughs. Many thanks to him, I hope we can meet up again sometime.

As far as the C-4 goes, this is quite an improvement over the Onkyo I was using. Great phono stage, very quiet.

Avionic, you were correct, there were some bad components in the muting circuit so the relays would not function. Now that it's fixed, I can hear a 'tink' after the relays kick in. Much different than the usual 'click' that you can hear with protection relays.

Anyway, I wanted to thank everyone for the help

Paul
 
india42 said:
Just an update, in case anyone is interested. I was in Seattle last week and met up with blhagstrom, long story short, he was able to get this going for me. We had a great visit and some laughs. Many thanks to him, I hope we can meet up again sometime.

As far as the C-4 goes, this is quite an improvement over the Onkyo I was using. Great phono stage, very quiet.

Avionic, you were correct, there were some bad components in the muting circuit so the relays would not function. Now that it's fixed, I can hear a 'tink' after the relays kick in. Much different than the usual 'click' that you can hear with protection relays.

Anyway, I wanted to thank everyone for the help

Paul
Click to expand...
Funny thing about those little relays. I always knew they were there and working, but I never heard them until yesterday. Where I had the unit placed previously I just didn't hear them, but I had it out for a full recap and in the bedroom system where it is running to burn in the caps and run final check it is up at ear level and I heard that incredibly quiet little click. Big difference from most unit I have where the relays make a good "thonk" clicking in.
 
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