Yes, that's exactly it.

In fact Gottlieb remained very "old school" concerning the electromechanical part of the SYSTEM 80 / 80A. Bumpers are stand-alone systems, which do not depend on the CPU (or DRIVER board).

Gottlieb has just added "pop-bumper" boards, which allow:
- to calibrate the pulse time sent to the coil, whatever the duration of the contact
- to use a low voltage in the contact (logic "5 volts") rather than the traditional 24 volts, thus avoiding having sparks of rupture. Thus the washer of the contact on the bumpers undergoes less wear, and it reduces the electromagnetic disturbances.
They are activated by the contact on the bumper, and it's all ! Of course, the 24 volts power is cut/allowed by the Q (Game over) and T (Tilt) relays. It is a legacy of the electromechanical era.

The search for the breakdown is therefore quite simple.
Caveman_Bumpers (resized).png
The problem could come from a power failure in 24 volts lines (relays Q or T, fuses F13, F14, F15), or deceptive of all pop-bumper boards. But these options are to be excluded, because it is rare that the three boards or fuses toasted at the same time, and if the other works (pinballs, kicking targets), then there is 24 volts present.

In fact, the most likely is that all pop-bumper boards should no longer be powered with 5 volts.

Unplug one of the pop-bumper cards and verify that there is 5 volts between pins 5 (+) and 2 (ground) of the connector. You can also use the pin 6 for ground, as this one goes to the A1 (CPU) board. Pin 2 is also a ground, but goes to the bottom of the cabinet (main ground, on power plate).
If the 5 volts does not arrive, check the connector A1J6 on the CPU (the +5 volts comes from the connector of the switch matrix).
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OK, a little technical explanation of how the Caveman works is necessary:
The Caveman is the first SYSTEM 80A designed (prototyped on a Black Hole, and the first marketed was Devil's Dare): unlike the other pinball machines in the series, this one has not two but three independent systems.

There are :
① The CPU board (6502)
② The SOUND board (also built on a 6502 architecture)
③ The VIDEO board (built on an Intel 8086 architecture, developped in Europe )

These three independent systems communicate with each other.
► Between the CPU board and the SOUND board, the communication is unidirectional (CPU → SOUND) via the A3J5 (CPU / DRIVER) connector.
► Between the CPU board and the video board, the communication is bidirectional. As there was no dedicated bus, the designers used "lamp" outputs for the CPU → VIDEO direction and "switch" inputs for the VIDEO → CPU direction.

The video board (more exactly the ROMs) is multilingual. By default, it starts in German (no wonder ... when we know where it was developed! ).

◊ When the CPU starts, it sends a command to the video board, asking it to switch to the correct language. But what is important is that unlike AUDIO commands that are not acknoledged, the VIDEO commands are. The CPU board is waiting for a feedback from the VIDEO card and if this acknowledgment does not arrive, the game can not start.

Since the game remains in German, it is obviously that the initialization command does not reach the video board. It seems that the problem is at the level of the command (lamps) and not of the acknoledge (switch matrix). Since the command does not arrive at the video board, it never returns acknowledgment and the CPU can not start correctly. As the It is necessary to follow the signals of the lamps.

The causes can be multiple/complex:

• It can come simply from a bad connection (oxidized connectors).
• A failure on the CPU or the DRIVER that no longer controls the lamps properly.
• A failure on the input circuit in the video block.

If the game worked before, then it's most likely a connector problem.

The lamps L4, L5, L6 and L7 are used only to indicated to the video board, the player active (1...4). So the issue is probably not here.
The lamps L12, L13, L14, L15 are the command sent from the CPU to the video board.
The lamp L16 is the strobe sent from the CPU to start the command.
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Check the connections at A3J3 and on the video block (P2 - A23J2).