cr1901 changed the topic of ##yamahasynths to: Channel dedicated to questions and discussion of Yamaha FM Synthesizer internals and corresponding REing. Discussion of synthesis methods similar to the Yamaha line of chips, Sound Blasters + clones, PCM chips like RF5C68, and CD theory of operation are also on-topic. Channel logs: https://libera.irclog.whitequark.org/~h~yamahasynths
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<andlabs>
given an alternating input, is this a simple inverter or does this somehow do some sort of delay
<andlabs>
and is the LED accidentally written backwards here
<andlabs>
the LED is listed as "LD201VR3" and the Tr 8 is ... missing from this sheet lol
<andlabs>
and I also don't see it in the service manual, but the other transistors are "2SC1740S(R,S)", "2SA933S(Q,R)", and "2SC2878(A,B)"
<qu1j0t3>
andlabs: it's just a high current driver.
<andlabs>
okay then I'm thoroughly confused
<qu1j0t3>
set it up on a breadboard :)
<andlabs>
this thing should apparently be flashing the LED at a human-visible rate but right now the MAME code is flashing it way too quickly for that
<qu1j0t3>
this switches the LED same rate as the base input (and there's a pulldown obv)
<andlabs>
or at least that's one possible reasion it's not flashing in the layout file
<andlabs>
it could just be the layout file is bugged but I'm at my wits end
<andlabs>
I'm really hating layout files now; they don't work in a sensible way and they aren't really designed for anything more complicated than early 80s arcade games
<andlabs>
this input is pulsing but the states aren't
<andlabs>
I'll look at this later
<andlabs>
also I still think that LED is on backwards lol
<qu1j0t3>
matches the same diode symbol in the NPN transistor
<andlabs>
oh
<andlabs>
I was thrown off by the fact the input is on the cathode end
<andlabs>
shrug
<tunixman>
the pulldown shouldn't affect the switching, it's a pretty big resistance. but the 10k before it might bring the control voltage down too much.
<andlabs>
this is the power on LED on the DX100 which is supposed to flash on low battery
<qu1j0t3>
tunixman: they form a divider, which is fine
<andlabs>
I actually have it now mostly working in MAME
<qu1j0t3>
tunixman: no need to drive the transistor higher than i would guess ~ 2.5v here
<andlabs>
I still need to decode the circuit diagram for the foot pedal
<andlabs>
(there seem to be no surviving service guides or circuit diagrams for the foot pedals themselves)
<andlabs>
and figure out how MAME's cassette interface works
<tunixman>
qu1j0t3: yeah, that's what I was thinking, but is 2.5 enough to saturate?
<qu1j0t3>
tunixman: i would think so
<qu1j0t3>
cba doing hte math :)
<tunixman>
oh yeah wait if it's not a MOS it's going to need that to limit the current.
<qu1j0t3>
well there is also the LED current limiter
<qu1j0t3>
so there's not much to go wrong
<tunixman>
I think the base current...
<qu1j0t3>
yeah you're right
<qu1j0t3>
so you should be down to 0.5mA base current
<qu1j0t3>
idk i'm being sloppy i should go back to work
<tunixman>
yeah, 0.5mA is a responsible base current. 5kW is a responsible bass power.
<tunixman>
at least for a car.
<tunixman>
10kW if you can swing it.
<qu1j0t3>
i don't think i can brain this even if trivial, i'd throw it into ltspice becasue lazy
<tunixman>
you never know when you'll find yourself top down in Texas during a heat wave going 95 MPH.
<qu1j0t3>
too much debugging of my own stuff D:
<tunixman>
hahahah yeah, it's always good to get the simulator's opinion. the envelope is great for closed form but not so great for impulse response...
<andlabs>
oh I see
<andlabs>
it is a layout issue but it's me not undrstanding PORT_NAME
<andlabs>
and the flashing is at an adequate speed