• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Yamaha CA-800 - restoration - few questions

J

Janochytron

Active Member
Hi,

I got this Yamaha. Decided to do basically full restoration.

Now I read that the two microswitches for ClassA/Normal operation are a weak point and it's a good idea to change them.

What exactly do they do? I can see red and orange cable coming from the transformer. Red brings 30V, Orange brings 13V. When I select normal operation, I can see 30V leaving the switch to the rectifiers. When I select class A, I get only 1V going away.

Thing is, the amp was working before on both operations. But I did not measure the voltages when all was still assembled so i don't know what they were with everything connected and working ( I have removed the volume,filter and tone boards, but that should not really influence these voltages.

Would this be a good replacement?
I found it as alternative to elswhere mentioned V-10-1A4 from Omron.

http://ie.farnell.com/webapp/wcs/st...3&langId=353&partNumber=1796565&storeId=10163

If somebody has done restoration on ca-800 and has a list of what they substituted, that would be much appreciated. Any tips and ideas welcome.

Thanks

Petr
 
Register to hide this ad
These voltages are for the power amps unregulated B+ / - rails.
 
Last edited:
Hi,thanks. That's what I would expect. I desoldered the switches and one of them works fine but the other is basically open for class A position.
Thanks for the link, much appreciated.
Petr
 
Switching from class A to normal ,while power up, does a job on the snap switch contacts. Pits them pretty bad from high current arcing.
 
I've refurb'd 2 CA-800 and a few CA-1000's in my early days. If I was
to do one today the list would include,

- Replace noise prone transistors 2SC458 and any 2SC1345(?)
- Check all fusible resistors, replace any out of spec with metal film
- Nichicon PW and EP caps on relay board and new relay
- Elna Silmic II and Nichicon ES on power amp boards and replace 4 trimmers with multiturn type
- Replace tantalum caps with Nichicon KL
- Elna Silmic II's for remaining caps, your choice of main filters, I've tried UCC which I thought were ok, most prefer Nichicon KG
- Bump up the main filter caps, maybe 12000uf, important bump up voltage to 63V or 80V. Orininals
were 50V, too close to the rails voltage, mine was 51.xV
- Replace class A switch as previously advised

The CA-800 along with the CA-1000 is a real PITA however it is a good amp.
Suggest you unsolder the tone board after taking numerous hi res pix. Make life a little easier.

Clean all switches while it's apart ie, speaker selector, couple...
 
Hi,
thanks very much, exactly what I needed.
It's actually only 2 cables (4wires) to be unsoldered from the filter board and I could take out filter,volume and tone boards out (these 3 still joined together)
So I was able to access the rest for cleaning. Gonna do up my shopping list now.
This is the thing now cleaned (bar the power amp boards, these will be cleaned when changing caps and transistors)
upload_2017-7-26_19-21-8.png
 
  • Like
Reactions: mbz
Janochytron said:
It's actually only 2 cables (4wires) to be unsoldered from the filter board and I could take out filter,volume and tone boards out (these 3 still joined together)
Click to expand...
Thanks for the tip, hadn't looked at it that way. Looks easier with those boards removed. I've still got one to do but have been putting it
off due to the pain and suffering I usually undergo.
 
You can see them on the picture.The brown and the green that has 3 tone wires.I was putting it off as well,took it partially apart months ago to clean the switches and adjust bias and after seeing that didn't go near it:) But like this it isn't that bad.
Thanks for the tips. Coupler switch cleaned.
 
Hi, quick question before I start taking it apart. I have finished with the recap and replacements. Now my DC offset drifts constantly up on the right power amp board. Left is stable. On both boards I have changed the caps,the 4 pots, the fusistors and the two 2sc458 on the heatsinks with 1845fta. These would be probably a place to start, but hadn't have a chance to take them out yet. I did compare resistor values and checked diodes. But maybe somebody seen it before.
 
Yeah, seen it before, will check notes. Have you checked the bias on problematic channel. Also how high dc offset
you talking...
 
Might be a grounding issue on that channel.
For general health, measure voltages with repect to chassis at wires/pads
+50, -50, +B, -B, A, B, C, S.
Also Class A or Normal operation?
 
Hi, I got the amp 3 months ago and was able to set the values as per manual then. Then it was not used for couple of months prior to the re-cap. And I did not measure it right before re-cap(my bad).
The voltages coming in are same on both channels. I am at work now but if I remember correctly: +50,-50.3,+35,-35, B and C 1.7 A I don't remember but was the same.
It was under both normal and class A.
Thanks
 
I have stable 15V between tp1 and tp2.
The offset drifts a lot,always up. With the current setting, it starts at -36mV and goes way over positive.
For the bias, it starts lower than the 0.047 and then goes up, I will need to test it for longer time if it keep going up past the mark.
 
You must log in or register to reply here.
Back
Top Bottom