This is clearly the v1 of the DMX Splitter, as the v2/v3 have only three outputs.
And the reason that v1 was abandoned was because of frequent problems with Output 4 operating.
The blue transformers had limited output current and it turned out that they would not drive all four of the spec'd RS485 chips.
If you don't have ambient-air temperature issues, you might try using either this RS485 chip ...
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The illustrations are of SMD chips, but the metadata says they're through-hole.
It also says they only draw 500 microamps, which even times four shouldn't strain the blue transformer.
I make no guarantees.
\dmc