QUAD 306 - Distorted Output: Cap Replacement?

Hi everyone,

I recently bought a second hand Quad 306 and have been using it successfully with my Yamaha NS10m’s for about 4-6 weeks.
Sadly, the left output has now started distorting - quite badly, so it’s unusable - and I’m wondering what the best thing to do might be.

I’ve been hearing that it could be that the caps need replacing. Although, the seller - on eBay - said that he’d replaced them recently, but that’s not to say that he’s telling the truth or even if that’s the issue. I’ve also heard that replacing the TR8 (transistor?) could be a possible culprit.

Any suggestions?
Also, if it is the caps, is it something that someone with limited soldering experience can manage? (I’ve changed guitar pickups etc).

Thanks!
James
 
Here are a few photos.
It was working fine at first so - forgive my ignorance - presumably, that would suggest they were put in correctly.
I'm no expert though, so please let me know if I'm wrong!
 

Attachments

  • IMG_0215.jpg
    IMG_0215.jpg
    437.1 KB · Views: 112
  • IMG_0213.jpg
    IMG_0213.jpg
    531.8 KB · Views: 106
  • IMG_0214.jpg
    IMG_0214.jpg
    566.5 KB · Views: 90
  • IMG_0215.jpg
    IMG_0215.jpg
    437.1 KB · Views: 107
  • IMG_0216.jpg
    IMG_0216.jpg
    489.9 KB · Views: 95
View attachment 1188334

I thought these capcaitor polatitiy looked suspect, but they are correct based on service manual.
you can find it here : https://www.dadaelectronics.eu/uploads/downloads/02_Quad-Service-Manuals/Quad-306-Service-Manual.pdf


Might be worth checking for simple mechanical fault like dry joints?
Is the capacitor on the right touching the power resistor? The heat will kill it very quickly.
The low value brown capacitor in the middle of the photo is folded over - a very strange thing to do
 
Capacitors are rarely the cause for a sudden onset of distortion, that suggests a fried semiconductor or loose connection or failed power rail. You can sometimes get RF oscillations due to aging capacitors, so its possible. In many amps failing electrolytics go unnoticed until the power-on mute and safety circuit starts misbehaving.

Typically we're talking many decades before aging electrolytics become a show-stopper.

First step when working on an amp is be safe, next is looking (sniffing) for any obvious damage/overheating, and then checking the DC power rails are all present at the correct voltage (don't connect expensive speakers to a suspect amp, BTW, some cheap set will do)
 
Thanks for that, Mark!
To be honest, I think all of this is above my station really. I wouldn't really know what I was looking for with any of this; I think it might be time for me to bite the bullet and get a professional involved.

I was hoping if it was just a very obvious, quick fix, I might be able to do it. Sadly, there is needs to be someone experienced to fully check it over and diagnose it.

Thank you for your help!