Repairing a cocktail table

Spectra IV


Technical study and repairing
a deffective cocktail table.


Basically, the SPECTRA IV cocktail table is built with original Bally electromechanical features, but uses specific electronic cards. For this reason, this Pinball has the reputation of being indepannable and there are only very few still functional copies.

Indeed, the majority of failures come from the CPU cards or drivers that are irreplaceable. At the time, the majority of CPU cards used Nickel-Cadium batteries that over time, eventually corrode components (as in Gottlieb or Bally).

However, electromechanicals components troubleshooting is less problematic, since still found parts or equivalents.

Having had the hands one of these tables down, we met the challenge of the troubleshoot.

Available documentation:

Troubleshooting complexity of the CPU board

The architecture of the CPU board is quite classic, designed around 6503 (CPU), 6532 (RRIOT) and RAM 5101 circuits. Despite this apparent simplicity, several features complicate the understanding of its operation and make its troubleshooting complex.

CPU 6503 board Spectra IV

On the original map, pull-up resistors at the + had been added on the inputs of the switches (connectors J3 and J4 in the 4051 entries). It is not necessary, but we left them in place.

The board was then complete, batteries are replaced by a backup capacitor. Similarly, chemical capacitors have been changed.

◆ Addressing map and protection

A portion of the RAM (5101) is decoded on the same space as the I/O (lamps). This singularity allows you to store the status of the I/O directly in RAM and reread their state (ports I/O are write-only).

Decoding using simple logic circuits, also incorporates a protective device of the RAM in the event of voltage drop. The RAM and I/O work, this circuitry to 4098 database must be fully operational.

◆ Permanent RAM

5101 RAM is used as system RAM, the internal RRIOT 6532 serves as the "stack" of the 6503.

Its contents, saved permanently by battery, can be corrupted and prevent the system from booting. There are fortunately a particular procedure for all reset (also, only way to reset the coin counter).

◆ Watchdog

A monitoring circuit is integrated into the program through the NMI entry. It requires the presence of an AC voltage 24 volts, otherwise the program will not start.

◆ Corrupted ROM

Over time, the contents of the three ROM 82S181 can be partially clear. It is sure that to work correctly, you need good ROM !



Some ROMs that can be found on the internet (for example VPinMame) are incorrect. They contain either a bad dump, or a partial erase errors. They are characterized by a very slow count of the bonus, or the game's sounds more or less random.

Below, you will find the correct version of the 3 ROMs, where the bonus count works normally, and also the detection of rotationnal tilt.

Spectra IV ROM v11

Initialization of RAM

The RAM 5101 is powered at all times, a particular device was set up by the manufacturer to be able to reset it easily. With the table was delivered a reset key, in the form of a comb in circuit board, without any component. Although not documented in the manual, its use is simple: unplug map sound/driver, connect this key on the connector J8, and turn on the flipper.

At startup, the CPU card read briefly the port of the sound card, and if the value is the expected (encoded by the key), the RAM is reset. Once made, it is necessary to turn off pinball, remove the key and reconnect the sound card on the connector J8. Recall here that the actions of connection/disconnection should always be done pinball off.

Re-init key

Reset to restore at least, the operation of the service contacts (set/test, corner/demand). It is also the only way to erase audit counters (coin, number of gameplay, etc...). On the other hand, it is not sufficient to operate the pinball machine properly.

It is imperative also to position with the 'set' mode configuration values, in particular the number of balls by parties. Indeed, it is reset to zero, its value is incorrect since the valid range is from 1 to 5. This is also the case for the price of a game, set to zero, but with a permitted range from 1 to 6. If these values are not correct, the pinball will have abnormal behavior.

Bench test fixture

We have adapted our test bench to diagnose Valley 6503-based cards. This allows to quickly check the entire board (RRIOT, RAM5101, ROM, etc...).

As board was in need of an alternative input voltage to operate, we reused our injector for Bally module.

Bench test

The bench also allows to properly initialize the RAM5101 without using the wrench provided. The configuration settings are also positioned to consistent values without any need to go through the "SET" mode.

Spectra display 6532   Spectra display 6503

Additionnal board

On some tables, a small additional "piggy-back" board has been added on the CPU card and just plug into the circuit U10 (4093). It is not mentioned in the documentation and its function is unknown, more circuit used original RCA, is a non-standard reference "612119-1".

Additionnal board

This board is not essential for our testing, we have removed it and replaced the original 4093. After research, it turns out that the unknown circuit is actually a 4093 with generic labelling. Very probably a fix for the reset/watchdog circuitry, it is preferable to replace.

Last update of this page: August 8th, 2018

French Tech