Kalamath
New member
History: this machine has never made game sounds for me. Speaker pop/thump on startup. I rebuilt the sound board with new caps, new PIA chips (IC9 AND IC10), and a new crystal. I've also tried putting in the sound board from my Robotron (with the Defender ROM chip) but nothing happens. The jumper from the ROM board is solid, and I checked for pulse during sound test on both sides of the cable, consistent results. I've also tested with 2 separate ROM boards, same results. Speaker tested out of the cab, works fine, and wiring is good (close to 7ohm at the board).
Voltages on the sound board are T1= 10.9, T2= -14, T4= 4.92, T3 (ground) has continuity.
When I run the sound test and start tracing the signal, I start at the inputs on J3. Lines 6 & 8 do not pulse, but stay on High. 2,3,4,5,7 all pulse.
Looking at IC5 (where the signals go through on their way to the PIA IC10), most of the inputs from J3 pulse, except IC5-11 which is dead. No signal H or L. Oddly enough IC5-12 pulses. I checked this like 20 times cause the logic sheet shows 11->12. IC5-6/7 both stay H.
Looking at IC10 inputs, they pulse, except for IC10-18 (from J3-6) which stays H I think, and IC10-17 (from J3-8) which is DEAD...no signal H or L.
Looking at IC13-5 to 12, no pulsing. If I poke at IC13-9 I hear static from the speaker, and can adjust the volume of said static with the volume pot.
So, whats really going on here? Are the input from the ROM boards correct, with J3-6 & 8 NOT pulsing? Is IC5 bad? Could the op amp be bad, even though the speaker pops on startup and makes static when you poke IC13-9?
Voltages on the sound board are T1= 10.9, T2= -14, T4= 4.92, T3 (ground) has continuity.
When I run the sound test and start tracing the signal, I start at the inputs on J3. Lines 6 & 8 do not pulse, but stay on High. 2,3,4,5,7 all pulse.
Looking at IC5 (where the signals go through on their way to the PIA IC10), most of the inputs from J3 pulse, except IC5-11 which is dead. No signal H or L. Oddly enough IC5-12 pulses. I checked this like 20 times cause the logic sheet shows 11->12. IC5-6/7 both stay H.
Looking at IC10 inputs, they pulse, except for IC10-18 (from J3-6) which stays H I think, and IC10-17 (from J3-8) which is DEAD...no signal H or L.
Looking at IC13-5 to 12, no pulsing. If I poke at IC13-9 I hear static from the speaker, and can adjust the volume of said static with the volume pot.
So, whats really going on here? Are the input from the ROM boards correct, with J3-6 & 8 NOT pulsing? Is IC5 bad? Could the op amp be bad, even though the speaker pops on startup and makes static when you poke IC13-9?

