Bootleg
From the carrying of bottles of smuggled spirit in the legs of boots.
en.wiktionary.org
A "bootleg" commonly refers to a counterfeit game cartridge, CD or system.
NeoGeo bootlegs are quite common, as SNK took years to implement security measures to avoid (or at least delay) piracy. Most are believed to originate from China and South Korea.
Over the years, multicarts gained popularity as memory chip costs decreased and decrypted ROMsets became available, making design easier and sales even more profitable.
Aside from the collection and authenticity interest, bootlegs are known to be plagued with functional problems due to low quality manufacturing and/or poor design.
Recognizing bootleg cartridges
Todo: how to open. MVS: easy, 4 screws. AES: everything snaps.
No gold plating
Original cartridge PCBs have at least gold-plated fingers (slot contacts) for durability. To reduce costs, some bootleg PCBs only use HASL (dark silver color).
This can be checked without opening the cartridge.
Uncommon chip brands
SNK had their favorite brands. If found on a SNK PCB, these chip logos are often bad news:
From left to right, top to bottom: AMD, Atmel, Cypress, Goldstar, Hyundai, Macronix, Microchip, Motorola (sometimes), Samsung, SST, UMC, Winbond, Xilinx.
Also Lattice and Intel.
EPROMs or flash memory
EPROMs (UVPROMs), chips with erasing windows, are often used in bootlegs.
Note that some original cartridges use EPROMs as P ROM revisions instead of plain mask ROMs.
Bad NGH marking
Memory chips only marked with a 3-digit number not matching the game's NGH number are certainly fake.
Sanded or rebranded chips
Some chips can be sanded (no markings, visible scratches...) to prevent other bootleggers from copying the design. Clone chips (either mask clones or PLDs) can be rebranded for the same reason.
SMT adapters
SMT adapters are small PCBs commonly found in early bootlegs and converts. They allow the use of (cheaper) SMT flash chips instead of EPROMs without having to redraw the whole board's layout.
They were often assembled by hand and therefore covered in flux barf (see below).
Uncommon board shapes
As some PCB manufacturers set their price according to the real board area instead of the smallest containing rectangle, some bootleg PCBs were made in unusual shapes to reduce costs.
All known SNK cartridge PCBs are rectangular.
Soldermask not green
Many bootlegs use yellow soldermask.
All known SNK boards use green.
Questionable markings
Meaningless "serial numbers", serif font, Engrish, bad alignment, bad logo proportions, and wrong line thickness are all signs of fake PCBs.
Sometimes, nothing is better than something (even if no silkscreen at all also means bootleg).
Paper chip labels
Paper labels are very rare in original cartridges, most manual QC markings were made with grease pencils.
Make sure you don't actually own a prototype !
Flux residue
[Flux] used for manual soldering, when not cleaned off, looks like dried barf after a few years.
Aside from eventual traces of accidental beer spills, rat piss and dust, original boards should be clean.