Fixing a stereo amplifier

[TGV]

Hi. After a few years of not using it, I fired up my 30+ year old stereo amplifier, a QED A240SA. It was a decent amplifier, a bit pricey even. But when I turn it on, it behaves ... odd. The music fades away in one of the channels, and then comes back, and it also seems to sound rather shrill. Since I had hooked it up to a new device, a TV settop box, I blamed the settop box, but to my surprise, after a while it started playing normally. The next day, I repeated with a CD player, and the same scenario played out: it took a while, and then it played fine. So, today, I opened it up, and armed with my tiny knowledge of electronics, I expected to find a bad capacitor, but it looks as if everything is fine. I've attached a picture.

So my question to you is: is there something I can do to find the root of the problem, or is this something for an expert? Or is a warming up period normal for such an old amp, even though it never had to warm up before?

Thanks in advance.

 

[Harald Kapp]

I expected to find a bad capacitor, but it looks as if everything is fine.

That is my guess, too. Typically the electrolytics will have lost their capabilities over the years. This will not necessarily have left a visible trail.

Or is a warming up period normal for such an old amp,

No, it isn't. What happens is that what little capacitance is left in the electrolytics is partly restored once you apply power.

I suggest you replace the electrolytics. It's only a dozen or so and they are easily accessible.

 

[Ylli]

https://www.hifiengine.com/hfe_downloads/index.php?qed/qed_a240_series_2_service_sheet.pdf include schematics. You will have to register at HFE before downloading, but they do not spam or push any ads.

 

[TGV]

I suggest you replace the electrolytics. It's only a dozen or so and they are easily accessible.

Thanks! I'll give it a try.

 

[TGV]

https://www.hifiengine.com/hfe_downloads/index.php?qed/qed_a240_series_2_service_sheet.pdf include schematics. You will have to register at HFE before downloading, but they do not spam or push any ads.

Unfortunately, they don't let me register. It says "Sorry but this feature is not currently available in your region". I did find something at another site, though: https://elektrotanya.com/qed_a240_series_2_service_sheet_sch.pdf/download.html. Doesn't require an account to download, only a recaptcha. The cover sheet says it was written by QED, so I guess it's the same or very similar.

Thanks!

 

[Ylli]

I did find something at another site, though

Same thing. HiFiEngine and Elektrotanya typically have the same data.