mechanicflunkee wrote:Maybe there's another screen somewhere in the machine that could be gunked up?

Anything's possible... Do you mean another screen before the pump, or something between the pump and the pressure gauge? (If it were gunked up downstream from where the pressure gauge takes it's reading, then the gauge would be reading too high.

Did you check the gicleur? It should be a nice round hole when viewed against a light.
And its screen is not plugged. [unlikely]

I just watched that 2nd video and wanted to offer a couple comments, having read that you rebuilt the Group.

1) The boiler pressure is too low. Adjust the machine so that the boiler pressure is maxing out somewhere around 1.3-1.4bar
2) The brew pressure not even getting to 6 bar is probably a failed OPV (Over Pressure Valve). You found the components in your Group were trashed, and so will the internals of the OPV. Rebuilt it, and then adjust it for 10 bar on your gauge, which will give about 9 bar inside the Group during actual brewing
3) Someone else asked about the condition of the brew jet, called a Gicleur. That brass jet has a tiny orifice that gets clogged. The jet orifice needs to be "reamed" out. How clogged it is, is what determines the method used to clean it. I use a carburetor jet cleaning kit that I have as a mechanic, but there are other methods. You won't get good flow out of the shower screen, or when brewing coffee (like during that timed flow test you did) if that orifice is partially blocked.
4) Depending on how old this machine is, just replace the vibe pump and be done with it. They are inexpensive and quickly/easily replaced. I've repaired a few of them, and that's also easily done, but there's nothing like just having a nice new pump. Well worth the $20-$40 bucks.

Here's what the inside of the OPV looked like on my QM Andreja that I just rebuilt:

austinado16 wrote:3) Someone else asked about the condition of the brew jet, called a Gicleur. That brass jet has a tiny orifice that gets clogged. The jet orifice needs to be "reamed" out.

NOT recommended to ream which implies metal removal. Soaking in descaling solution should remove any build up. Hot solution works more quickly.

Gicleurs are typically 0.5 to 0.7mm and finding a brush that small is difficult.

If you're going to quote me, and use that to correct what I've said, quote me correctly.