I was in the same boat as you, but I decided to buy the Siegcraft testing fixtures instead of a Rottendog.
The reason I went that way was is because I have 3 sys6 CPUs and 2 driver boards.
My boards are not as good as your pictured CPU.
I learned a lot about troubleshooting these in the past couple of weeks.
First thing I learned is that the game ROMs ARE ABSOLUTELY WORTHLESS for troubleshooting a board who's past is unknown.
If there is even the smallest defect those ROMs do NOTHNG except flash the LEDs briefly and then lock on.
You REALLY must acquire a test ROM to make any progress on boards with defects.
I used the Andre v2.0 test ROM (sys7.bin - 2716 ROM) most since it has pretty comprehensive tests for major components.
(and it runs EVEN IF there are several defective components and the driver board does not have to be attached to test only CPU components)
You can leave the other ROMs in, just put the test ROM in the IC17 location.
You need to make the little LED board that the Andre v2.0 manual describes. (I think it took me 10 minutes to make one)
Once you have all the Andre tests passed (except PIA V sys7 only) you can think about putting the game ROMs back in.
I highly recommend switching the six ROM configuration to the three ROM configuration. (2732 with FPcombo.732)
linked here: https://pinside.com/pinball/forum/topic/firepower-tech-repair-and-restore
Then the Siegcraft boards (display tester, diag. switch, and lamp matrix PCBs) show that the game runs and you can step through the standard tests.
This is all SO much easier on the bench instead of in the backbox.
Right now I have all three CPUs and one driver board working properly, one driver board is still not working, parts ordered.
Just things I wish I could have known about BEFORE I started down the sys6 board repair road......