midi in issue

[mp19]

Hi!
I have finished my third xoxbox and i have a problem. Everything works fine except the midi in. Without anything plugged midi in works, but when i plug a jack in the mix out it stops working. Also when there´s a jack plugged you can hear the tick of midi clock and midi notes ticks thru the speakers. Midi play mode don´t work too. Could it be R16 the problem?
Thanks

[mp19]

i´ve changed R16 and the problem persists. When i plug the audio jack in the mix out and the tip is touching the ground i can hear the midi clock code thru the speakers.It´s like they were linked.

[guest]

leave the midi cable plugged in
but turn off the x0x
and then measure the resistance from ground on the x0x
to all points on the midi cable
including the sleeve

im guessing there is a short around ic24

[mp19]

the points at the corners don´t show any value.
the three central points show values from right to left at the bottom of the Pcb
1 - 212 ohms
2- 351 k
3 -1313 k and oscillating very much
Thank you for your answer!

[guest]

does the shield have any resistance to ground

it looks like pin1 of ic24 might be shorted to ground
check the resistance to ground from all pins on ic24

were an audio cable and a midi in cable
the only things you had plugged into the x0x

[mp19]

pin 1- 2 ohms
pin 2 - 1228 k and oscillating
pin 3 - 0
pin 4 - 0
pin 5 - 13 k
pin 6 - 148 ohms
the shield is central pin of the connector, isn´t it? it shows -345k, a negative value.

[guest]

ok
it looks like pin1 is shorted to ground
try rehitting the solder joint
and look around for bits of copper touching

the shield is the metal ring around the whole connector

[mp19]

Ok,today i rehitted some solder joints and with a Kawai drum machine the midi in works fine. But when i connect the kawai output to the xoxbox´s mix in the sequencer stops working.
When i tried to sync the xoxbox to the computer without a plug in the mix out works fine but when i plug the jack the sequencer suddenly stop.
There´s no copper bits and solder joints are ok.
At the shield, the resistance doesn´t show any value-
Strange problem ,isn´t it?

[guest]

does it still measure 148ohms
from that one pin

it could be the short is inside the chip
and the chip is bad

[mp19]

The midi in works fine without anything plugged at mix in or mix out.
The problem is when you plug a jack, the sequencer suddenly stops.
Do you think it could be a short inside ic24?
Could it be a bad diode?
How could i measure the diode for a bad one
I´ll look this afternoon the 148 ohms,
Many thanks guest for your answers.

[guest]

a short inside would cause this problem
basically there is a grounding issue
and midi should be completely isolated
but instead the ground is getting shorted
to a point on your midi line

[mp19]

Could i use 4n28 insted 4n37?

[guest]

i dont know whether it will work
but it wont hurt to try it
its the same pinout

you can also try plugging the midi in
into the midi thru jack
and see if the problem goes away

[mp19]

ive changed optoisolator and problem persists. Ive used another 4n37.
Midi thru works for start - stop message and time code, but don´t work for midi play mode. I can´t hear any note. I don´t know if this is normal.

[guest]

does using midi thru
still give the pop sounds

there is probably a microshort
on pin1 of ic24 or r19 or d48
measure the resistance to ground at this point