HP F4180 stopped working please help troubleshoot

[flat-earther]

I was doing a large print job with my HP Deskjet F4180, and after about 50 pages the printer stopped in the middle of a page and the black ink light started flashing.
So I went to refill the black ink cartridge with a syringe, but found out it still had a lot of ink.

I tried to print a page again but every time it would print only a bit of the page and immediately stop with the black ink light flashing again.
I tried two other black ink cartridges, and the problem still endured, so I knew this problem had to be with the printer itself.

I ran HP Print and Scan Doctor on my computer and it said it found a problem(don't know what) and fixed it. But again, the problem didn't go away.

Then I removed the black cartridge and tried to print one page with only the color cartridge in the printer, and it successfully printed the entire page!

But then, without doing anything after that one successful page, all of a sudden, the printer stopped working. And since then when I turn the printer on, only the scanner moves during startup, but the print head or paper roller motors do not move, and all lights flash on the control panel, which I found in the HP manual means a ''fatal error'' condition.

I suspect something on the motherboard has broken, but I'm just a layman and not sure how to find it, so I will appreciate if anyone helps me troubleshoot this problem. Video of the problem: https://rumble.com/v6t892t-hp-deskje...r-problem.html

[flat-earther]

This printer has an external power supply which supplies the printer with 16VDC and 32VDC. I confirmed both voltages from the PSU are working.

I opened up the printer and visually inspecting it didn't find any obvious problem. See video: https://rumble.com/v6t8bld-hp-deskje...nspection.html
Looks like it would be a lot of work to remove the motherboard, it's on the bottom of the printer under everything else, I would have to disassemble almost everything to remove it.
There is some space to inspect part of the motherboard without disassembling everything.
I have a multimeter, from the components visible at this stage is there any I should test? or do I have to remove the motherboard?

Because I don't want to disassemble unless necessary because those ribbon cables design is very delicate, I removed the control panel's ribbon cable from the motherboard and when reinstalling it, it was almost impossible to push it back in because the ribbon cable bent and blue plastic tab on its end fell off, I tried to glue it with super glue but it detached when pushing it back and the cable bent again, very frustrating this connector design.
If I disconnect the ribbon cables I'm worried whether I will succeed in reconnecting them.

[stj]

what does it do with the waste ink?

[flat-earther]

what does it do with the waste ink?

What do you mean? It's not printing so it's not creating any waste ink.

[flat-earther]

I found a photo of similar motherboard online, I labeled the connectors, maybe it's helpful for anyone.

[flat-earther]

I have finally removed the motherboard.
I will attach photos of it.
Can anyone advise me how to troubleshoot it?

[flat-earther]

I plugged the power cable into the motherboard.

I found that the 32V from the cable gets through a mosfet and successfully gets to the print head connector(see photo), so looks to me that the motherboard is receiving the 32V normally.

But then I found another mosfet that receives the 16V to its center pin(see photo), but the 16V doesn't pass through the mosfet when I measure its output pin(see photo).
Could that be the problem, that the motherboard isn't receiving the 16V?
Is it a broken mosfet, or something not allowing the mosfet to turn on? or what's going on? I'm just a beginner so it's difficult for me to draw conclusions from all this.

[CapLeaker]

No. It’s a BJT.

[flat-earther]

No. It’s a BJT.

Alright thanks.

[flat-earther]

Can anyone suggest how else to troubleshoot this board?

[flat-earther]

Any suggestions on what to check on the board?

[flat-earther]

The 16V bipolar junction transistor is NPN, and the 32V transistor is PNP.
On both measuring in diode mode between base and emitter in one direction is about 0.6V and OL in the other direction.