Yamaha C-4 pre

Take a look at how the power regs are installed. Mine had only glue attaching the heat sinks to the PCB and it had all decayed and come loose. Because, you know, HEAT. The HS is drilled for a screw and there's a hole in the PCB for it but none was installed. that's just lazy.
A lot of Yamaha gear is known for cracked PCB traces and cracked solder joints. These can be a bear to find and fix.

I just did this with a C-80. Had to clean up all the dried glue, remove the trans and HS', pair of resistors (replaced) and polypropylene caps (replaced) and rework everything. Found some perfect fit screws in my junk piles and added the insulated shoulder washers for a clean install and no more glue. Funny they all have holes and sinks set up for screws but they're never in there. Some bean counter must have decided it was more cost effective. It was also another one that I had to remove and grind/burnish/polish a corroded ground busbar on. I hit them with a coat of clear lacquer so they won't tarnish before re-installing.
 
Some bean counter must have decided it was more cost effective.
Sometimes I wonder it this isn't true with the solder or soldering technique they use.To much tin not enough lead or something like that.:scratch2:
 
C-4 Power on switch?

I have a C-4 and it has been GREAT for 25 years !!!

I have a problem now though. When I power it up it will shut down after a few seconds. The Power switch light will light up and then go out. It looks like the power switch is bad or is there a relay that holds the power on until power is turned off.

Either way its either the switch or a relay.
Any one no where to get these parts?

Does anyone have a Service manual?

Guy
 
Probably missing one of your power supply voltages..Got one here doing the same thing.Needs the regulated power supply rebuilt.Also a unit that old will probably need a few if not all the electrolytic capacitors replaced to bring it back to spec.
 
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I have a C-4 and it has been GREAT for 25 years !!!

I have a problem now though. When I power it up it will shut down after a few seconds. The Power switch light will light up and then go out. It looks like the power switch is bad or is there a relay that holds the power on until power is turned off.

Either way its either the switch or a relay.
Any one no where to get these parts?

Does anyone have a Service manual?

Guy

They're pretty complex and not easy to work on. A few simple issues took me 3+ hours to find and fix. The manual is available online if you Google for it but this is somewhat advanced stuff, mechanically and electrically.
 
Either way its either the switch or a relay.
Any one no where to get these parts?
Actually it has three little reed switch relays ( metal can - sealed)... I really doubt that they are the root cause.
 
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Well I know I could work on it ! The only trouble would be getting schmatics and then after troubleshooting or shotgunning would be the getting parts.

The main problem I have is time and test equpment.
 
The schem is in the SM, and can be found in the AK yamaha database with a little searching around here. A high res schem is also available at hifiengine as I recall. Parts abound at digikey, mouser, bdent, etc. you can do 95% of the repair with a meter, good soldering gear and skills. What are you waiting for? Get cracking and get her running! :D
 
Actually it has three little reed switch relays ( metal can - sealed)... I really doubt that they are the root cause.

Remember, I have a C-4 here for parts, some pieces already gone, but let me know if you ever need one of those relay cans.
 
Yamaha C-4 Preamp (Finally)

Yes, I finally got the C-4 Service Manual and Schematics !
I also have the C-4 disassembled and turned it on to take some measurements.
Guess what? It turned on and it will not fail.
Boy an intermittent problem. Fun, fun, fun !!!

The problem is probably on the Power C-Board or would it be on the Flat Amp C-Board(1) since that's where the lamps are connected too.

I guess I can get a heat gun or cold spray to try and make it fail.

Any ideas?
 
This is an old post.... and mine at that!

Well, I had an intermittent problem(s) on mine too! One was a ground connection on the PCB that needed "restored". The other problem was a cracked trace from a slightly bowed PCB. Once these were repaired, I have not had a bit of trouble.

After I fixed the cracked trace, and I was bench testing, it would still cut out as I probed the PCB with a non metalic probe. Once I got in the area of that screw and held the PCB down, all was good!

On p5 from my SM, internal appearance (upper side), there is a screw located abt 1/2 way back from the volume control and 1 inch in from the side that holds the PCB to the chassis. I re flowed solder there, replaced the screw and have not had a problem since.

Check that area out while you're in there.
 
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My C4 is running fine months after a variety of repairs. It's been mentioned before but bears repeating that Yamahas of that era are prone to intermittent solder joints. I bang on and push the boards with a (plastic) pen while it's running to try to find the problem. This usually works.

Very nice units with a characteristic problem.

I have a C2 I have to open up again. It works fine but the owner is a chronic cable-swapper and all of the RCA jacks are intermittent now. This is a pain to fix.
 
My C4 is running fine months after a variety of repairs. It's been mentioned before but bears repeating that Yamahas of that era are prone to intermittent solder joints. I bang on and push the boards with a (plastic) pen while it's running to try to find the problem. This usually works.

Very nice units with a characteristic problem.

I have a C2 I have to open up again. It works fine but the owner is a chronic cable-swapper and all of the RCA jacks are intermittent now. This is a pain to fix.

As an(ex)owner of a C2x,the problems with connection caused me a lot of grief. :tears:
 
Hmm, sounds like it would be a good idea to make a whole whack of 6" male/female RCA cable pairs, so as to save the connector plane some stress..... says the guy with a C-2 and a "missing" Aux-right..
 
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