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Just getting started on AK

Dswankey said:
Welcome aboard!

You might find the DIY sub forum helpful with regards to "build-from scratch"

https://www.audiokarma.org/forums/index.php?forums/diy.15/

Re; CR-640

Schematic here, I know it's not the service manual but might help if not try here

http://akdatabase.com/AKview/thumbnails.php?album=3&page=7

https://www.hifiengine.com/manual_library/yamaha/cr-640.shtml

Re; Lowrey organ

Hold on to those tube and tranny they might come in handy some day down the road
Click to expand...



Greetings again and thanks for the warm welcome!

Since I could find no information on the web regarding the Schumacher P6414 transformer I had to ring it out myself. The attached is what I came up with. The 12.6V circuit would have minimal value, but since it has a center tap it could provide a lot of filament power (and that's apparently what it used to do since the 12V circuit was divided and powered a boat load of filaments. Additionally, there's a separate 6.3V circuit (E2E, but also has a 3.15V center tap), so even more filament power. The 5V circuit was powering a 5U4G rectifier, so it has to be rated at at least 3A. The primary circuit was tied to a 3A fuse, so an overall 3A rating seems to be about right. Even better, the high power circuit was putting out 710V (E2E) with circuits tied to the center tap at 355V each. This could be a very useful (if large) transformer!

My apologies for not knowing which specific forums to use, but I also have an update on my Yamaha CR-640 project. The massive power shorting has been resolved. Filter capacitors and the STK0050-II output modules have been replaced. I also replaced two transistors and a diode in the protection circuit that were visibly burned. The result is that I can now power the unit on. My previous re-lamping work is still intact. The unit now powers on safely, but no audio output. I noticed a definite lack of a protection relay "click," so the focus remains with the protection circuit. And at this point, I am over my head and was hoping that someone might have some knowledge or recommendations regarding the best approach to troubleshoot in this area. I realize that a Yamaha CR-640 is not a super-value product, but it sounded very good in the past and it is cosmetically in outstanding condition. It's worth some effort to bring it back.

Again, sorry for not posting in the right places, but any guidance on where to best post these two topics is appreciated.

Many thanks!
Jack
 

Attachments

avionic said:
TEWS Intermediate Test Equipment it was replaced by TISS TEWS Intermediate Support Suite .. My initial AFSC was F-15 EW/ECM . Early 90's was certified on both Manuals and Automatic test stations as well as TISS..
Click to expand...

What an incredible coincidence! I was a 326X1A (automatics, later the AFSC was changed to 326X4B, but it combined operations and maintenance on the automatic stations). I had 1,000 hours of technical training before being sent to a test system that, frankly , didn't work very well. And now, about a million years later, I'm still trying to learn electronics!
 
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