Terra Cresta Repair Logs

Repairer: Paul Swan

BOARD NO: 0111
GAME: Terra Cresta
MANUFACTURER: Nitchibutsu
DATE: 1985
HARNESS: NITCHIBUTSU-S

SYMPTOM (21/07/96)

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No initialization.

SOLUTION

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Using a scope to have a look around the 68K indicated that all the address/data pins were floating. Using a pulse injector on the 68K RESET pin 18 started the game but the game would not start from power on. The 68K reset line was output from an LS14 hex inverter at location 3A and the complete reset circuit as it was on my game is as follows:-

 Vcc                                     3A
  ^                                    13|\  12
  |                                +-----| >0----->RESET1~ (to 68K)
  |         R3                     |     |/
  +-------/\/\/\-----+             |    LS14
  |        100R      |             |
  |                  |     3A      |     3A
-----       R4       |    3|\  4   |   11|\  10
|PST|-----/\/\/\-----+-----| >O----+-----| >O----->RESET2~
-----      10K       |     |/      |     |/
  |                  |    LS14     |    LS14
  |         C2       |             |
  |        |  |+     |             |     3A
  +--------|  |------+             |    9|\  8
  |        |  |                    +-----| >O----->RESET3~
  |        100uF                         |/
  =                                     LS14
 GND

The three legged device "T518B" designated PST is presumably a three terminal reset generator chip. This circuit, as it stands, won't work very well and what has probably happened is that R3 and R4 have been swapped accidentally during manufacture. Swapping R3 and R4 over fixed the game completely. It's possible that other board sets in the same production run may have the same error and for reference the serial number of my board is "CA2906" and "85-06080"