Wait what ucan downgrade ps4? Or is rhis just changing the mobo?
Software downgrade is not possible for now, and technically - no, this is not just changing the motherboard, this is much harder procedure. The whole process must be like this:
1) desolder APU chip and memory chip from donor motherboard with old firmware and reball the APU.
2) take out bd drive board from the same donor unit.
3) desolder APU and memory chip from target motherboard.
4) solder the APU from donor unit to target motherboard.
5) swap bd drive board from donor unit to target unit.
6) assemble the console
This process is safe if the engineer, which will do the job, is skilled enough, but many things can go wrong if unexperienced person will try to do this. But all in all, this is not what you should be worried about.
The real place to worry for is the origin of donor components. Judging by experience in previous generation of consoles, the most common reason for hardware faults like rrod on xbox 360 an ylod on ps3 is bad solder joints (solder balls) between APU/GPU crytal and PCB of the chip, and less common - bad solder joints (solder balls) between APU/GPU chip PCB and main PCB. In later case desoldering the chip, reballing it and soldering it back (same process as swapping APU from one motherboard to another) fixes the problem and system works well and stable after that, but in former case reballing helps only for some amount of time (heavily varies, can help for only couple of days or can help for half a year, but nonetheless problem will reapear after some time). Also reballing APU/GPU crystal is impossible (well, may be possible at factory, but not at repair shops). Of course, bad solder joints isn't the only possible reason for hardware fault - if the fault was in power management systems or with practically any other component on mainboard except for apu and memory chip then this parts (I mean APU and memory chip) will be ok and swapping APU and memory chip from your console to this parts will give good results and your system will work well. But if the APU and memory chip will come from donor motherboard where the problem was in bad solder joints between APU crystal and APU PCB - then after working for some time your system will break.
Imo, $80/$120 is real cheap for this kind of work, so if you trust this service then the price is really good.
Sorry if this post is confusing, if you have any questions - just ask, I'll try to answer them. And sorry for my broken English.
