Yamaha CA-810 drama

[aural junkie]

Hi all. New here and I need some help.

I finally got my hands on some vintage Yamaha gear, namely a CA-810 and a CT-810. The tuner is great but the amp has some problems.

Namely, output in both channels sounds terrible through my speakers. Specifically, it sounds like sound is coming from underwater, with the lows, mids and highs all off.

I don't think the issue is the pre-amp, as connecting the pre-amp out on the yamaha to my denon pma700ae produces incredible results. I mean music sounds freakin amazing in that set up.

I tested the DC output to the speaker pots on Yamaha before I bypassed it through the Denon and there doesn't seem to be a problem - 4.5mV on the left channel and 10.5mV on the right.

The volume pot is flawless (not scratchy) and the balance and treble pots are the same. The bass pot is a little scratchy but I know how to fix that with a bit of deoxit.

On close inspection, the board inside doesn't appear to have blown anything.

I've used the google but to no avail. Any ideas where I start?

 

[dksp]

Hi!
Did you check the Loudness button and pot too?

EDIT: Just realized the problem doesn't appear when you connect the Yamaha as a preamp to your Denon, so the problem should be somewhere in the amplifier section.

 

[avionic]

Try cleaning the speaker select switch.

 

[avionic]

Also remove the two pre-out/main-in jumpers on the rear panel. Wipe them off with alcohol. Then reinstall them.

 

[aural junkie]

Speaker select cleaned, jumpers cleaned and loudness checked and cleaned. Still very poor sound from the amplifier section on the amp.

Any further ideas guys?

 

[mbz]

OK, so the power amp stage is not producing the goods. Both channels affected (same through headphones?) so probably power supply issue.
Check power supply voltages, state of main filter caps, C363, 4 12000uf/58V, any sign of physical distortion or leakage, bias should also be checked, it
won't be the cause (very unlikely, again 2 ch) but may point to the issue.

Voltages to check are pin 3 and 8 on the main amp board, expecting +/-51Vdc or there abouts. They will be OK as the psu is just a rectifier and filter
caps. If you have plans to refurb it would be a good time to replace the main caps.

D401, 2 would be next on the check list.

 

[avionic]

Out of tolerance fusibles in the PS ? Bad solder connections on the pass transistors ? At least its easy to get to.Mate mbz has got your 6 .

 

[avionic]

Pass transistors are heatsinked. TR805 and 806.

 

[aural junkie]

Both L & R are affected, but primarily the L output, its freakin horrible. Headphone output is fine though which is a little weird isn't it?

I'm on to that checklist now. Cheers mbz & avionic

 

[mbz]

Headphone output is fine though which is a little weird isn't it?

Yes.

One school of thought is that the headphones don't load the amp down as much since they are normally higher impedance than
your "8 ohm" speakers. While I agree I think that there are many other more likely possibilities. However dying main filter caps
would fit the scenario also a transistor being asked to work harder than what it likes.

Couple of more things to try.

Play the amp very quietly through the speakers, is the sound still distorted?
The speaker switch is still a key suspect, despite the cleaning. Have you tried connecting the spkrs to "B"

Both L & R are affected, but primarily the L output, its freakin horrible.

The fact that L&R are not equally affected suggests it's not the common aspects of the power supply.

Please also resistance check the fusible resistors in the power amp, FR401,2,3,4,5,6,7,8,11. In circuit should be fine.