akai ax80 midi out not working

[mirt]

midi in and thru is working but on midi out there is something about 15v, imo it is fried some chip but where to find proper one. any ideas?

[rhino]

speaking as one who has slogged his way thru the AX80's guts, my first guess is IC 32, a 74LS08 quad AND.
no scanner handy, but this chip is in the back left corner of the CPU board, near where the cable to the jacks plugs in. keep us informed

[mirt]

thanks! i'll try to check it. do you know what voltage should be on outs of this gates?

[rhino]

since MIDI is a digital logic signal, if you scope the output you sholud see square wave pulses at about 32 kHz.
if the output is 15 volts DC, sounds like one of the stages is locked up. let me find the schematic again and i'll get back to you

[mirt]

ok. i've check everything, voltage on out is about 5.42v (so this is probably power of digital part). i have some pc scope but i have some problems with calibration, i've check ic32 with voltage meter and on out of first, second and third gate is 4,8v and on out of last one there is 0,05.

ok there was some saw on monitor when scope was conected to out of synth, so it should work, but after connecting to pins of ic32 (ground to pin 7 and positive to pins 3,6,8 or 11) there was no puls on screen.

[rhino]

pins 9 amd 10 of IC 32 are connected to pin 17 of IC 2 (one of the CPUs). this should have pulses.

pin 8 of IC 32 is the MIDI out (to scocket) this should have the same signal. there is nothing else in that line excepuy a 220 ohm resistor and a 0.001 uF bypass cap to ground.

at the MIDI out socket, you should have GROUND, +5 volts, and a pulse signal.

chesk to see: MIDI socket bad...bent pins.

receiving synth set on correct MIDI channel.... NOTE AX80 resets to channel 1 on power-up

bad solder joints

bad connection between main board and MIDI jack board.

it is very unlikely that a failure in the CPU IC could affect only the MIDI out.



bill