recapping yamaha c2 preamplifier

krell

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good morning friends,
long ago i visited one of hifi guy , he is running a exotic set up with krell amp, all the items in the set up is very impressive. i was speech less when i heard his set up for a moment.i started to observe the components in the system. the amp is krell ksa 200s,speakers were jbl l4333/L300,,, player is pioneer reference player.
then come to pre---i saw a yamaha c2quitely sitting on one side. the first look it is solid metal chunk.
i asked him about the pre, he told he tried krell krs2/3 and some of the finest names in the business but none was likes his intrest.
it really amazing, its a no nonsence pre with full with very high quality components.
i saw one ad in ebay, the seller describes it is not working.
i paid usd250including shipping to my place.
its around 10kg.
after receiving the power is not switching on .
i opened the amp and primary diagnostics inform that power is not extending from the switch.
the micro switch is the culprit,its a alps switch , the reason is that the contacts get oxidized and they are not contacting properly.
i disconned the micro swith , its a sealed one, hence drilled the revits and opened. found contacts are bad, cleaned with crc but no use, finally took very fine ememry paper and done little sanding.
switch on the amp:clapping:
now the amp is in power,happyness was not last long, found a slight hum on both the speakers increasing with volume.
googled net and found that aged caps are one of the reason, before doing some other tests i decided to go for recap.
the total electrolytic caps in the pre is 33 .
selected caps are "NICHICON MUSE FINE GOLD SERIES" and bypolar caps are nichicon muse caps.
ordered the caps from Korea(original re seller-no fakes),received caps from EMS in 5 days(cost of shipping with all caps is $60)
started recapping,
first i made drawing and took plenty of images which shows the direction/polarity of the caps.
the bipolar caps doesn't have direction, you can place them in any direction.
desoldering done by heating the joint then use the desoldering pump to remove most of the lead from the joint.its a must otherwise you damage the traces.
cleaned with plenty of wipes.
done one at a time.
first power section then switch on, then tone control board...etc l,its easy to trace if some thing goes wrong.
the result....
listening one the best preamp in my life, dead quite,amazing dynamics,very very musical.
very very good.













Yamaha C-2 on thevintageknob.org
 
Hi krell - thanks for posting this. I was given a Yamaha C-2 from my father which looks immaculate inside, and I'm having the same issue. Fuses are all fine but no power. Can you let me know how you found out that the issue was with the power switch? I'm wondering if mine is having the same issue and I'm very curious about your troubleshooting process with this one!

Thanks!

EDIT: Link to pics:
 
Last edited:
Hi krell - thanks for posting this. I was given a Yamaha C-2 from my father which looks immaculate inside, and I'm having the same issue. Fuses are all fine but no power. Can you let me know how you found out that the issue was with the power switch? I'm wondering if mine is having the same issue and I'm very curious about your troubleshooting process with this one!

Thanks!

EDIT: Link to pics:
Hi mate,

I am the second proud owner of Krell's fine Yamaha C2 preamp. In all probability, your C2's power caps are dead. I would recommend you to check on forums that can recommend choice of reputed technician/s from whom you can get this jewel repaired.
The one awesome bit of the Yamaha C2 is that its easily repairable and most of the parts are available even today after more than 35 years of its release.
 
Hi, krell and aarmath,
I am a proud owner of C-2, too. Bought it in 1977, and still own.
Long time ago, I had exactly same problem of the power micro-switch, and repaired as the same way. Grad to know somebody did the same thing.

I made several other repair as follows, which may help you:
1. Missing output signal: This was because of a solder crack between output relay and RCA jack.
2. Muting SW malfunction: Again, this is due to the slide switch contact failure. We have spare contacts on the switch which can be used in parallel.
3. Tone control switches: This was a nightmare. Contact failures everywhere. I pulled out those two rotary switches and took it apart to pieces. Carefully wiped contacts on board and sliders, repeated for all eight gangs. applied very little amount of lube.
4. Same for volume control: Contact btwn sliders and carbon resisters were unstable. Took it to pieces, cleaned the surface of resisters and cleaned the slider. applied clean lube. Note that the innermost finger of sliders were too close to the shaft, and the track missed the carbon surface. Moved it to outside a little.
5. Replaced all chemical caps: With higher temperature rating (105'C) ones (except bi-polar), and higher voltage ones. Recent caps are much smaller. For the smoothing cap on power board, I used 100V 470uF x4.

Tak
 
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