HEAD ON ( & SI) sound problems

[vernimark]

I'm restoring a strange japanese cocktail called "Twin". It has a board similar to Sega/Gremlin head on but with 2 boardsets. you can select space invaders or head on through a switch.

It has 2 sound boards, one for each game. both have problems and I'd like to start with Head on.

As you know this game produces two "screech" sounds; one for "my car" the other for "computer car".

So these two sounds are ALWAYS on.

I attached the sound board schematics related to those sounds.

- cutting pins 9 and 5 of U10 (4069) both sounds stop, but these sound will be deactivated forever
- removing/substituting Q13 and Q14 nothing changes (always sounds on)
- cutting (6) and (7) wires from the motherboard nothing changes (always sounds on)

Note: U13 5837 noise generator in this cocktail is powered by +12 and -5 instead of +12 and -12

any idea?

[ajhippel]

try removing the cable of pin 6 and 7 of the connector and wire these pins of the soundboard to gnd or +5v

when this switches the sounds on / off check or replace u16 (ls374)  on the game board

[vernimark]

good idea thank you

[vernimark]

done. If I "force" the input signal to ground, sound stops but connecting to the board component sound starts again. I substitute the component and I forced the input to 0 but nothing changed.

THis pcb is different from the original head on. It supports two sound boards and the outputs come from a 74175 instead of the 374

[ajhippel]

try forcing the output pin of the 175 to gnd... if the sounds does not stop, there might be a problem with the connection (cable) between the two components.

[vernimark]

I spend some time on the board.
I have less than 12V on the board and probably this difference was enough to force the bases of both transistors to stay closed.
I changed R64 and R67 from 10k to 18k and now all sounds are ok.

thank you for the help

[vernimark]

ah... I repaired the SI sound board too...
2 sounds were missing:
- explosion
- missile

In the beginning I thought the problem was in the noise generator because both of them use that circuit but after an easy check I found a couple of faulty LM3900.

I'll post soon pictures of this strange cocktail.