Yamaha AV receiver htr-6250 weird issues

[oolloo]

Hi I've had weird issues with  AV hdmi amp
Some are solved by unplug replug.

It's a 2009 I bought from someone.

2 friends have newer 2013 models one is 7.1 like mine . They don't habe tge following issues.

1 with cisco iptv 4k boxes the video will after months of use draft to tear up, then goto fine grain light snow.  Power cycle from front fixes it either for minutes, hours or months.

I'm thinking that's a hdcp hand shake issue.

It does have latest fw.

The real issue is that when switching from program to program or ch to ch. Or program playing to adverts then back to program.

The sound changes,  it will be either
muffled vocals ,
more bass,
lowered dialogue volume

From channel to channel I have to select different effects , or speaker setups or modes to get the center vocals pnly and bright clear.

My friends and i all use the same TV provider and cisco stb .

The above is year round all temps 

Could it be that dust has built up inside receiver ?

On 30deg centigrade days it does seem to overheat and act up.

Please help

[oolloo]

My friends simply leave theirs on straight Dolby digital and everything sounds great on their Yamaha av receivers , I do too but I suffer the above issues.   All my hdmi cables are new and high speed rated for 4k.

One more thing firetv 4k stick , 2020 mfg date has only the sound issue same for fta satellite unit, nothing else  has the video issue.