Yamaha A-500 recap

bazarimajom

Member
Hello All!

I just successfully finished partly recapping my new little amp but there is a concern I have. Can I replace polarized electrolytic caps with Wima MKS2 PET films? The caps in question are 0.22uf and 0.47uf 50Vs, there are 6 of them of each capacitance. Here is a link to the Wima caps in question and the service manual.

The amp is in very good condition, DC offset is 5mV for left and 10mV for right channel.
 
Those MKS2 caps are real nice. I've started replacing everything 6.8µF and under with them. The 6.8µF are still not too expensive. There are also 10µF that I use in a few places in the signal path but they are pretty expensive and can be a bit to large to fit in some places. Go for it.

Cheers,
James

Edit: Nice amp btw. I hope that you enjoy it.
 
Thanks, I've already ordered the filter caps from ebay, probably fake ones, but I will give it a try. Hope they not will not blow in my face :)))
 
Yesterday I was out for some beers and left the amp on, about 6 hours later when I arrived I smelled that something electronic was burnt. When I looked at the amp it was shut down....I took the cover off and the main switch fuse was blown. I won't be home this weekend to check it, but I would appreciate if someone could tell me what should I do with it before putting in the new fuse :) I couldn't see anything else that was burnt on the board, but I will check on Sunday or Monday. It was working 20-30 hours since recapping, is it possible that the fuse was too old?
 
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I'd do a really thorough inspection to see if you can spot where the smell came from. Use a magnifying glass and your nose. Usually burned semiconductors stay stinky for quite a while after the smoke has escaped.
I have seen older fuses give up the ghost but never with a smell that I could detect. If you can't see anything I'd say replace the fuse and only bring it up on a dim bulb tester so you don't potentially do any more damage. If the bulb stays bright then you've got some troubleshooting to do. If it dims down and the relay clicks then you should be safe to go with full mains though again I wouldn't even plug it back in until a good looking over.
 
Thank you Avionic! As I understand anything that matches in size and has greater rating in voltage and current should be ok.
 
Finally the parts arrived, I have soldered the rectifier in and plugged the amp to a DBT (the best idea). Unfortunately the bulb was bright, so I checked the outputs. One of them got fried but I just noticed it now... it is a 2SC3284. The others seem intact and tested OK (de-soldered them all). (The fried one tested OK too, is it possible?) Now I would like to ask again for help, to find the best solution to replace the output(s). Should I try the bay from china or what other replacement parts would you suggest? Thanks in advance!
 
I checked some resistors too and it seems 2 of them have out of spec, 2 bigger gray 1.5K Ohm metal oxide resistors (R257-258 according to the manual (2P 1.5KOhm)) are just 0.9K. But again, I'm not sure what wattage are these, and what is a suitable replacement? Could you tell me please? Thank you! :)
 
Thank you Avionic! I suspected 2P denotes the watt rating but I wasn't sure. The parts are ordered, I'll upload pics when the amp is fixed!
 
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