Audio Circuit (PC Engine Duo)

the pc engine duo has a sound system that mixed audio from various sources i have yet to reverse engineer the entire circuit, but have done a good amount of it overview a lot of the circuit users op amps, and a good replacement is the texas instruments rc4558 audio can be provided from hu6280 (pin 17 left out, pin 18 right out) hucard (pin 2) super cd engine in short, many 4558 op amps feed audio through a multiplexer (bu4053bcf) to mix the various sources together, and they get sent out to the headphone port through an op amp and to the av port through an op amp typical issues a quick overview of the typical issues i have encountered are nec d91317gd pin 81 which should enable the bu4053bcf enable pins 9/10/11 sometimes doesn't go high in which case just wire pins 9/10/11 to 5v (not 7v) dead 4558 op amps (any of them) are dead ic503, ic521, ic506, ic203, ic202 rotted traces under the op amps from capacitor leakage audio sources there are several places the audio is generated from i will cover them below hu6280 the hu6280 is the pc engine hucard system, and it generates audio for that part of the system the audio comes out of pin 17 (left) and pin 18 (right) they travel over the ic506 and connects to the ic506 amp that drives the av port out right (pin 18) > c879 > r612 (1k) > c6235 > ground right (pin 18) > c879 > r612 (1k) > r613 (5 1k) > ic506 right in (pin 6) left(pin 17) > c878 > r611 (1k) > c6234 > ground left (pin 17) > c879 > r611 (1k) > r631 (5 1k) > ic506 left in (pin 2) hucard the hucard through pin 2 sends audio directly through c883 > r616 (3k) which then goes through several places like r613 (5 1k) to the ic506 right in pin super cd bios i have not yet tracked back where super cd audio comes from av port audio the av port op amp is a 4558 it is the ic506 av port amp (ic506) this amp is right before the av port av port left audio in ic506 left in (pin 2) goes through several paths r689 (6 8k) > +c613 > ic505 m51131l volume balancer pin 3 out1 mixing with right in via r627 (15k) and r629 (15k) av port right audio in ic506 right in (pin 6) goes through several paths r690 (6 8k) > +c614 > ic505 pin 13 out2 which is an electronic volume balancer (m51131l) r630 (15k) > right audio out bu4053bcf pin 1 y1 mixing with left in via r627 (15k) and r629 (15k) av port right / left channel mixing the ic506 left in and right in join together through two resistors r627 and r629 and the center of those two resistors taps off and goes to the mono audio output z0 of the bu4053bcf (pin 5) av port audio in+ ic506 left in+ (pin 3) and right in+ (pin 5) goes through three paths +c323 > ground r323 (10k) > +c306 > ground r324 (10k) > ground +c884 (near volume wheel) > audio ground (hu6280 pin 20) av port left audio out the ic506 left audio out comes out (pin 1), joins back to left (pin 2) through r691 (1 5k) , carries on through +c610 > r607 (47k) which pulls to ground the signal out of c610 then carries on through r610 (1k) > l601 (inductor on top side) > left pin av port also, a npn transistor q604 is connected to the left audio output collector , and emitter to ground, so basically pulling the left audio signal to ground , when the q604 (base) is high av port right audio out the ic506 right audio out comes out (pin 7), joins back to right (pin 6) through r692 (15k) , carries on through +c604 > r604 (47k) which pulls to ground the signal out of c604 then carries on through r608 (1k) > l602 (inductor on top side) > right pin av port also, a npn transistor q603 is connected to the right audio output collector , and emitter to ground, so basically pulling the left audio signal to ground , when the q604 (base) is high av port audio disable path in short, sending q604 base high will disable left audio by physically sinking the left audio out on the av port sending q603 base high will disable right audio by physically sinking the right audio out on the av port both disable signals meet at d601+ the left audio q604 (base) goes through r605 (2 2k) through d601+ the right audio q603 (base) goes through r606 (2 2k) through d601+ the d601+ goes to several sources the primary one being the pnp transistor q308 the pnp transistor q308 ultimately pulls q604 (base) and q603 (base) high disabling audio the q308 (collector) connects to the d601+ the q308 (emitter) > d303+ > 5v output of ic302 > +c310 > ground keeping the emitter high ready to send it to the collector also, q308 (emitter) > +c325 > ground so, when the q308 (base) is low it will turn off audio the q308 (base) > r315 (10k) > +d306 > 7v the q308 (base) > r315 (10k) > +d306 > 5v (ic304 vreg) so from what i have currently traced, the audio should never turn off unless the 5v and 7v rail are down or traces are damaged headphone port the headphone port has left and right audio and ground there is no separate spring switch that disables anything headphone amp (ic507) the amp by the headphone port sends the audio out to the headphones headphone left out todo headphone right out todo headphone audio disable as well as turning off the av port audio, the headphones are also shorted to ground via the same trigger (q604 base going high) as input to +d602 > r609 (2 2k) > q608 (base) so q608 emitter to ground, collector through l604 to headphone pin left, meaning headphone pin sinks to ground at the same time as the av port does final headphone output also has resistor r601 (10k) and capacitor c683 to ground as input to +d602 > r624 (2 2k) > q609 (bas) so q609 emitter to ground, collector through l605 to headphone pin right, meaning headphone pin sinks to ground at the same time as the av port does final headphone output also has resistor r602 (10k) and capacitor c684 to ground unknown amp ?input maybe? (ic503) another amp that receives audio, but i haven't traced yet to where it goes is ic503 it is a 4558 op amp pin number name description 1 1out 2 1in audio in (from bu4053bcf z pin 4) 3 1in+ 4 vcc ground 5 2in+ 6 2in audio in (from bu4053bcf z pin 4) 7 2out 8 vcc+ 7v unknown amp (ic521) another amp that receives audio, but i haven't traced yet to where it goes is ic521 it is a 4558 op amp pin number name description 1 1out 2 1in left audio in (from bu4053bcf z1 pin 3) 3 1in+ 4 vcc ground 5 2in+ 6 2in right audio in (from bu4053bcf y0 pin 2) 7 2out 8 vcc+ 7v unknown amp (ic203) another amp that receives audio, but i haven't traced yet to where it goes is ic203 it is a 4558 op amp pin number name description 1 1out audio out (from bu4053bcf x pin 14) 2 1in 3 1in+ 4 vcc ground 5 2in+ 6 2in 7 2out audio out (from bu4053bcf y pin 15) 8 vcc+ 7v audio mixing (bu4053bcf multiplexer) the audio sources come into the bu4053bcf multiplexer x = ?? (enabled by a) y = right audio (enabled by b) z = left audio (enabled by c)\\ all three enable pins are sent high by the nec d91317gd pin 81 pin number name description 1 y1 (out) right ic506 r630 (15k) > ic506 pin 6 (av port right audio in ) 2 y0 (out) right ic521 r625 (15k) > ic521 pin 6 right in r625 (15k) > r626 (15k) > z1 (mixing l/r) 3 z1 (out) left ic521 \+ vol balance r623 (15k) > r621 (15k) > x0 r623 (15k) > left in ic521 pin 2 r695 (6 8k) > left out ic521 pin 1 r695 (6 8k) > c617 > volume balance left in pin 2 r626 (15k) > r625 (15k) > y0 (mixing l/r) 4 z (in) left ic503 r655 (8 2k) > c621 > ground r655 (8 2k) > r654 (8 2k) > c653+ > r687 (270k) > ic503 pin 6 r655 (8 2k) > r656 (8 2k) > ic503 pin 2 r655 (8 2k) > r656 (8 2k) > c322 back to input z pin 4 5 z0 (out) mono goes to both ic506 left in and right in through resistors r627 and r629 6 inhibit ground 7 vee ground 8 vss ground 9 c c = high turns on z output enabled by nec d91317gd pin 81 10 b b = high turns on y output enabled by nec d91317gd pin 81 11 a a = high turns on x output enabled by nec d91317gd pin 81 12 x0 r621 (15k) > z1 (left ic521 + vol balance) 13 x1 r628 (15k) > r689 (6 8k) > ic506 pin 2 (av port left audio in ) r628 (15k) > r627 (15k) > mono point going to ic506 left in & right in 14 x r213 (1 8k) > ic203 pin 1 r213 (1 8k) > then many more places i'm not going into \ p 15 y r212 (1 8k) > ic203 pin 7 r212 (1 8k) > then many more places i'm not going into \ p 16 vdd 7v volume balancer (m51131l volume balance) the volume balancer is responsible for balancing the audio coming in from ic203 (yet unknown where its input comes from) it then sends volume controlled audio out to the av ports amp ic506 right in and left in i have yet to track all these pins to where they go