Yamaha C4 help needed

At this point. I can tell you what is not causing the problem.
Its not electrolytic capacitors. Its not the power supply or muting circuit transistors or diodes.Its not the MC preamplifier on the function board.
Of course its not any of the smaller circuit boards.
Its something on that function board..

The unit I have here is doing the same thing-only it might act up once a month,week ,day, hour or minute..Therefore its one major PITA to troubleshoot. I've tried heat soaking,freezemisting,boardflexing,component wiggling to try and make it act up.All efforts a big NO-GO.Right now it hasn't acted up for several weeks. I know its not fixed.. I'll probably end up swapping out all 12 of those transistors that I had you remove and check as well as the two VD-1212 diodes and the two zeners..And cross my fingers.




Usually most of the heat is generated by the two pass transistors on the power supply board( the 2 transistors on large heatsinks).Thats why there on heatsinks.

Don't we always replace those just like we always replace SC458 shithouses? :D


Looks like you guys are having fun, I just don't get to stop in here much lately so when I do, I have to give Dave a lot of shit. :D
 
I'm by no means an expert. (Thats why we keep Dave around :D) And Dave would know this better than me. And I might have missed something in this post. But have you ruled out bad solder joints? Not sure if that would cause the problem your having. I know from my C4's that they all had a lot of bad solder joints. Im just thinking out loud. :scratch2:
 
bad solder joints, yes, possibly, should I reflow the whole board? that seems like a lot of work.

today I've reopened the unit and it's been playing all morning. so far so good. It shut down when I was holding my hand above the boards trying to feel the heat from different areas. I touched the one end of D310. I thought maybe it was a bad solder so I resoldered, but it's probably my finger shorting the circuit. Now it i touch it while it's on it shuts down, but if i touch and leaves my finger on it again the power comes back on.
 
The one that I have didn't power on because the light bulb from the power switch was burned.
Yes, mine's running HOT as well.
 
The one that I have didn't power on because the light bulb from the power switch was burned.
Yes, mine's running HOT as well.

The one you have didn't work because of a something other than the light..These units will run forever with out the lamps. Possibly the -12 volt power supply that powers the lamps and muting circuit.
 
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I've reflowed some joints on the function board, most of the joints of the transistors. I'm thinking of doing the whole board, but worried I could damage some components with the heat. Or can I just go for it?

also I'd like to do the vd1212 replacement. two 1n4148 in series right? does it mean I solder a 4148 to another 4148 and put them in place?

I'm starting to enjoy this.

If I get that thing stable, I'm probably going to recap. Should I be careful which brand of capacitor I get, or model, temperature etc?
 
I'd like to do the vd1212 replacement. two 1n4148 in series right? does it mean I solder a 4148 to another 4148 and put them in place?
Yes..As far as reflowing solder.Just be quick when reflowing polystyrene caps and transistors.
Caps --I use Nichicon ES (MUSE)for the non-polar/bi-polar caps . Nichicon PW in the rest.
 
The C-4 protection shuts down when it detects DC. Also check the wave form with a scope, maybe you have oscillation from a bad transistor. Saw this problem before with an A-1.
 
The C-4 protection shuts down when it detects DC. Also check the wave form with a scope, maybe you have oscillation from a bad transistor. Saw this problem before with an A-1.

Explain how this works on a C-4 control amp. I know how it works on a M-4 power amp.
 
Right now I am also in progress of recapping and resoldering my C-4. If you need photos, just tell me.

Actually it is looking like that :) :)

img_74765crjy.jpg



Have fun

Philipp
 
Thanks for the offer Phillip.I have three or four of these units here and at least two parts units.
 
looking through the parts list: c313 is listed as a Z capacitor +-10%, is this just a normal electrolytic with a 10% tolerance?
 

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Hej dirtyblues,

Are you talking of the capacitor on the the Flat Amp Board, next to TR622?

c4xarkd.jpg


I only have the schematic and there it is also written Z 33uF/16V. Nevertheless, when I was replacing it, I found a 22uf/35V instead of the cap mentioned in the schematic. The parts list also says 33uf/16V. This is the value I have replaced it.

May you send me the parts list, when it is possible for you?

thanks a lot

Philipp
 
ok,

I've replaced the electrolytics, a few vd1212, 4 transistors on the headphone board, reflowed the solder points on the function board, deoxited the pots and replaced the bulbs. It's been stable for a few weeks, it sounds good, it looks good, I'm happy.

Thanks a lot avionic, if you ever come to London let me buy you a beer or two.
 

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