Yamaha C-4 preamp failure

[Amplifierz]

Hi AK'ers.
I have a C-4 preamp providing my M-4 with juice. But it doesn't do the job like it is supposed to. When i turn it on 1 channel fails, i have to turn it off and turn it on again a few times for it to work.
I have recapped the thing and redid all of the solder work. I think the problem is in one of the relays, but i don't know what types i need and how many. I also heard of the fact that the VD1212 diodes need replacing as well as the 2SA458 transistors. Can somebody point me in the right direction? How many i need of each replacement to make it sing again?

 

[Blue Shadow]

This thread: http://www.audiokarma.org/forums/index.php?threads/explosive-c-4-fun.454346/ identifies 9 VD diodes and 8 458 transistors. Maybe someone knows the relay part numbers.

 

[avionic]

I also heard of the fact that the VD1212 diodes need replacing as well as the 2SA458 transistors

Most likely not going to fix your issue.. Out of maybe 20 or so C-4's that I have reworked. I have found one VD1212 that was actually a problem. It was causing and intermittent popping noise in both channels.

The 2SC458 transistors are use in the amplifier circuit " current mirrors " and have never been and issue in any of the C-4's I've worked on. These are not the outhouse TO-92's and are still a pretty reliable transistor in that part of the circuit.

 

[avionic]

I think the problem is in one of the relays,

Well there are 3 each.Reed relays ---- RL-6442-H132 / 12VDC.. Source for exact replacement --- parts unit or maybe ebay ????

 

[Amplifierz]

@Blue Shadow Thx for the thread!

@avionic Most likely replacing them is not fixing my issue, but when i am in there i might as well do it right... Those relays are a pain in the ass. Can't find anything about em.. Would be a shame to scrap my newly recapped C4 just because of a few damn relays..

 

[avionic]

There are dozens of options for the relay ( If it is actually your issue )

Search ( reed relay) at mouser or digikey..

Point to point wiring may be required

 

[Amplifierz]

Alright Dave, thanks. But i am not really skilled as you may already know
So exactly pinpointing where the problem is might be a challenge.

And sending my problem to you again is going to be $$$

 

[avionic]

With the C-4 upside down. While your issue is present.Find the function switch wafers. and gently wiggle them back and forth. While listening for it to cut in and out.

 

[avionic]

And sending my problem to you again is going to be $$$

So true.. I'll try to help you pinpoint the issue.

 

[avionic]

Here are two of the three. The 3rd one is right next to the rear of the volume control. Very very lightly tapping on these may also help to identify a fouled set of contacts.

 

[Amplifierz]

My English isn't that great eather..function switch wafers? I know what the function switch is, but wafers? Care to explain? Before i wiggle the wrong thing back and forth

 

[Amplifierz]

View attachment 1146517
Here are two of the three. The 3rd one is right next to the rear of the volume control. Very very lightly tapping on these may also help to identify a fouled set of contacts.

You sir, are a Legend! Thanks now i know what to look for.

 

[avionic]

This wafer switch has two phenolic wafers. The wafers have contacts riveted to it.

To clean.. Spritz deoxit onto the riveted (fixed) contacts and rotating contact.Then rotated back and forth a couple dozen times.

 

[Amplifierz]

Ahhh those! You think it's a contact issue? I have Deoxited the living shit out of those 'wafers' when i got the unit.

 

[avionic]

View attachment 1146540 This wafer switch has two phenolic wafers. The wafers have contacts riveted to it.

To clean.. Spritz deoxit onto the riveted (fixed) contacts and rotating contact.Then rotated back and forth a couple dozen times.

Some times..It is necessary to disassemble . To get the rotating contacts clean.

 

[avionic]

Ahhh those! You think it's a contact issue? I have Deoxited the living shit out of those 'wafers' when i got the unit.

Your english isn't that bad...LOL.. Try wiggling them . They still may be and issue.

 

[Amplifierz]

Copy that. It's 22:38 in the evening here so i am calling it a night. Will try those things you mentioned asap.

 

[avionic]

View attachment 1146517
Here are two of the three. The 3rd one is right next to the rear of the volume control. Very very lightly tapping on these may also help to identify a fouled set of contacts.

If a relay is the problem. It will be the one by the volume control. RY301.

 

[Amplifierz]

Thanks for your assistance Dave. I would be really lost without your knowledge, and probably spending to much cash at the local repairguy.

 

[avionic]

Another thing to try. Try using both the pre-out 1 then the 2 .. See if there is any noteable difference in performance. Those switches could also cause your issue.