Sony STR-6060 preamp repair

[spaghetti]

This is my second Sony STR-6060, I liked so much the first one that I decided to buy another one in better cosmetic conditions... but not 100% working.

It seemed to be an easy fix: the preamp drops one channel at the first stages so I thought it could be due to an open cap or transistor, but locating the issue is proving to be quite time consuming. After checking almost anything in the preamp stage I found out that C603 was not really ok: the ohmeter measured 80Kohm and the capacimeter 19nF while according to the schematics it should be 500pF.
I desoldered and checked also its twin on the working channel C703, which measured 0.7Mohm and 1.2nF.

Now, the questions: I have attached a picture of the caps: what kind of caps are they? They look bulky for the low capacitance. Can I replace them with ceramic discs like the one in the picture? I happen to have a few 470pF discs around.... thanks!

 

[spaghetti]

I spent some time on the web searching for similarly shaped capacitors. The result is that the cap could be a paper or, more probably, a mica capacitor. Mica caps are known for reliability and for stability, while ceramic caps, at least the one in the picture, are not much stable and tend to thermally drift.

I temporarily replaced the mica caps with the ceramic ones and now the muted channel works fine, so at least I know what the issue was. I will later buy better quality caps such as film or poly and close the issue.

As a side note, I also recapped the preamp board because electrolytic caps were all out of specs, while ESR was still low the capacitance was almost doubled. I did one channel a time and I also found that the recapped channel sounded a bit louder than the untouched one.

 

[Leestereo]

...After checking almost anything in the preamp stage I found out that C603 was not really ok: the ohmeter measured 80Kohm and the capacimeter 19nF while according to the schematics it should be 500pF.
I desoldered and checked also its twin on the working channel C703, which measured 0.7Mohm and 1.2nF.

Now, the questions: I have attached a picture of the caps: what kind of caps are they? They look bulky for the low capacitance. Can I replace them with ceramic discs like the one in the picture? I happen to have a few 470pF discs around.... thanks!

C0G class 1 ceramic capacitors would be an ideal replacement; they have excellent properties: they are very temperature stable (0 ppm/K); have very low electrical losses with a dissipation factor of ~0.15%; and no degradation in performance with age. They are considered by many to be superior to silver mica types. See here for a graphical comparison with polypropylene and a garden variety X7R ceramic: http://audiokarma.org/forums/index....of-a-sansui-au-717.641945/page-2#post-8541465

 

[spaghetti]

That's interesting! I'll see if those caps are available at the local shop, thank you.