please help! ic20 getting hot! SOLVED!!!

[guest]

since it is passing data
the serial in and serial out must be working
and the clock must also be working
so that only leaves the ledlatch pin

measure the resistance from pin12
to pin12 on one of the other 74hc595s

[tupinamba]

I think you have it right and we are getting close...

Resistance on pin 12 between other 74HC595 ICs is 0
Resistance between IC4 pin 12 and other 74HC595 pins 12 is 1

... What do I do ? Connect IC4 pin 12 to another pin 12 from another IC ?

[guest]

you can solder a jumper wire
and see if it fixes it

[tupinamba]

I put a jumper wire between IC4 pin12 and IC5 pin 12.
Tempo, "C", "run", "next", steps 1 et 2 leds are working. That's great ! But...
"prev" and "chain" leds still not working;
Steps 4, 5 and 6 leds not working although they were working before... That's strange, isn't it ?

[SubStyler]

hi tupinamba,

you told me that you have to desolder IC4 after it was soldered backwards.
please check all the traces around IC4, maybe there are one or more broken trace on the PCB from desoldering?

cheers
Sub

[guest]

prev usually doesnt light up
perhaps in pattern edit mode

remove the jumper
and see if 4 5 and 6 come back to life
if they do not
then start checking the chip they are connected to
to see if its outputting 5v

[tupinamba]

OK it almost entirely solved and I can fully use this great instrument at last !
Remaining dead leds were due to... absence of resistor (I forgot 2 of them while changing from 1k to 10k ) and bad solder joints. I was even able to remove the jumper wire as the extra solder made the connection effective again.

There is only one thing remaining but it is far from vital :
When I power on the x0xb0x, "prev" and "next" leds are not lit. IC4 pins 3 ("prev" led) and 4 ("next" led) provide 0v.
But if I press "next" in Pattern Edit Mode then "next" led light up and stays this was (5v on IC4 pin 4).
And if I press "prev", nothing happens, and "next" led is still on. IC4 pin 3 never provides 5v when "prev" pressed.
I checked connections between IC4 pin 4, resistor and led, and between led and ground.
It tested the led which is working.

Weird, isn't it ?

Anyway, thanks a lot for your help, I would never have done it without it ! Now my x0xb0x is starting to play with my sequencer and my MB6582 and I think they get along pretty well...

[guest]

the prev button may not light up
and i think the next button is supposed to stay on
so it sounds like its working correctly
congrats

[tupinamba]

Great ! Thanks again !