Since a few weeks I got some issues when I use my PowerPak with my AVS. 
While playing a game the screen is full of flickering black lines. Here are some examples:

 





When I use my PowerPak on another NES console it works just fine, no flickering line, everything okay as it should be. And when I try other cartridges on my AVS they all look great, no issues with them.

Any ideas or hints what this could be or what could help?

 

Try an alternate power source.

Try cleaning your PowerPak.

Take a flashlight and look inside your AVS at the pin connector to make sure nothing is stuck in there like a hair and make sure no pins are bent.

Update your AVS firmware, if its already updated run the updater again and reinstall the same version.

I'm experiencing something similar with an everdrive, but according to my tests, this started on fw b6 and still present up until b8. I've already reported this to retrouSB customer support.

I hope this isn't considered off topic, or if it is that it's not too off topic, but...

What's the reasoning/rationale behind this specific fix?  I get the idea of a bad flash causing some stuff to happen, but some of the issues I've seen this suggested as a fix on were ones that appeared as time went on versus something that was immediately obvious after a flash/update.  Is there something going on with the AVS that could cause the (what I assume to be) non-volatile firmware saves to corrupt, or is this just recommended as a matter of standard troubleshooting (akin to making sure the power cable is plugged into the system, then making sure it's plugged into the wall, etc.)?  I'm not being critical, I'm honestly curious.

Thank you. 
Indeed, there is a single pin which is bent a little bit. When I move the PowerPak around the flickering parts were more or disapeared. With some pation I can get the exact position and it is working nearly free of those flickering lines.  I'm just wondern how this bent pin could happen. 

 

Standard trouble shooting.  I was leaning more twards dirty cart or pin issue than firmware here.




I would take the AVS apart so you can really get at the pin connector and see if maybe its just popped out of place or actually bent/damaged.

I've tried to take it apart, but it seems that the upper part is stuck in the front and I couldn't get it removed. I don't want to damage the case, so any tips to remove it softly?
 

Yeah, try harder not softer.  

The power/reset button is what the hang up is. Try putting the power on so the button is depressed a little. Once you get it free it will pretty much just fall apart.