Thanks André

You're right! I need the famous "Q*Bert" strange voice

I'll check how I can add them (probably a sample to add, but not sure).
I got a Q*bert boot, but still not working. It freezes when you start a game or after a certain time (30 sec to 1 minute...sometime more), even if you do nothing.
Because I have a Q*bert->Jamma adapter, I tested it on other jamma cab, in other to exclude the power supply. But I don't know how to fix or even localize the problem

Oh, regarding the Q*Bert voice, I'm wondering if it wasn't an *add on* board to allow the speech synthesizer (like the extra add-on board who gives voices in Disc Of Tron) ? Mhhh maybe not (from WIKI page) :
A MOS Technology 6502 chip that operates at 894kHz and a speech synthesizer generates the sound effects and Q*bert's incoherent expressions respectively.[1] The audio system uses 128B of random-access memory and 4KB of erasable programmable read only memory to store the sound data and code to implement it. Like other Gottlieb games, the sound system was thoroughly tested to ensure it would handle daily usage. In retrospect, audio engineer David Thiel commented that such testing minimized time available for creative designing.[8]
"We wanted the game to say, 'You have gotten 10,000 bonus points', and the closest I came to it after an entire day would be 'bogus points'. Being very frustrated with this, I said, 'Well, screw it. What if I just stick random numbers in the chip instead of all this highly authored stuff, what happens?'"
David Thiel on the creation of Q*bert's incoherent swearing.[5]
Thiel was tasked with using the synthesizer to produce English phrases for the game. However, he was unable to create coherent phrases and chose to string together random phonemes. Theil also felt the incoherent speech was a good fit for the "@!#?@!?" in Q*bert's speech balloon. Following a suggestion from technician Rick Tighe, a pinball machine component was included to make a loud sound when a character falls off the pyramid.[5][6] The sound is generated by an internal coil that hits the interior of a cabinet wall. Foam padding was added to the area of contact on the cabinet; the developers felt the softer sound better matched a fall rather than a loud knocking sound. The cost of installing foam, however, was too expensive and the padding was omitted.[7]I'll investigate on this.