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Slide gives only downward pitch bend
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Slide gives only downward pitch bend

by GdH on Mon Sep 17, 2018 4:44 pm

Hi guys.

Some time ago I bought a second hand xox (pcb says 1.01)
One problem it has is the slide function. As another forum user says "If i have a sequence of all Cs for example and tie them some together with slides it'll be a sequence of Cs with downwards pitch bends."
A possible solution given was checking ic12 for shorts maybe created by flux.
(I put the chip out and back in but in the other direction because I thought it was put wrongly in the first place (?) because the numbers on the chip were upside down but then I got no sound at all. Its only after that that I figured the direction is shown on the pcb)
I replaced the ic12 chip (CD40668) but the slide problem is still there.

Other problems (probably due to the reverse inserting of the ic12 chip)
-The sound from the left side of the Mix Out is no more.
-When the volume knob is above 75% the sound gets distorted while the Cut Off is set high and the Res is set low. Raising the Accents volume makes it even worse.[/b]

Cheers for your time!
Last edited by GdH on Sat Jan 05, 2019 12:59 pm, edited 2 times in total.

GdH
 
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Re: Slide issue & more issues

by antto on Wed Dec 26, 2018 3:38 am

if you've put a chip the wrong way around, you might have fried something, at least because in many of those logic chips, the power pins (GND and VCC) are located diagonally on two outter-most pins, so if you put the chip the wrong way, it'll get negative VCC
the chip might fry, and/or it may draw loads of current and then something else might fry (the regulator for example)

disconnect the two boards and test the IO board, see if it works properly, check if it outputs all the right voltages

antto
 
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Re: Slide issue & more issues

by GdH on Wed Dec 26, 2018 6:30 am

Cheers for the reply antto. Apreciate it!

GdH
 
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Re: Slide gives only downward pitch bend

by GdH on Thu Jan 10, 2019 8:54 am

I feel I know too little about it all to proceed fluently
In the meantime: Just started checking the Volts on the IO board with the ioboard release v1_0(PNG) by my side.

The IC20 (5V voltage regulator) gives 8.32V (9v)
Should'nt it give 5V? Im using a 9v acac adaptor

And what do you mean with the outputs? Of each part on the IO board? Or do you mean J3 J4 J5 J6 J7 ?

Thanx for your time!

GdH
 
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Re: Slide gives only downward pitch bend

by antto on Thu Jan 10, 2019 3:01 pm

i meant, the IO board gives power to the mainboard, there are a few different voltage rails:
+12V +6V and +5.333V for the analog side
+5V for the digital side (sequencer, EEPROM, FT232 USB-to-Serial, opto-isolator)

J4 gives the analog power rails to the synth, so check +12V and +5.333V there (also, use the GND at that connector for the measurement)
J5 gives +6V, they are only used for the headphone amplifier
J3 gives +5V to the digital side
Note: 5V innevitably goes to the FT232 chip which is on the actual IO board, that small SMD chip), and the opto-isolator (IC24)
hopefully you used connectors for all of these cables, so that you can easily unplug them

the idea was, disconnect the two boards, and roughly follow the tests in the build guide (careful with some of them because they instruct you to do things assuming the rest of the circuit is not populated yet, which shouldn't be done if it's fully populated... especially tests which instruct you to inject a voltage somewhere or so..)

so... there's damage
the 5V regulator should certainly give 5V (typically somewhere about 4.9 to 5.1V)
with 8.23V the atmega, the EEPROM, and the FT232 chips might have died (and any other chips which are powered by 5V and cannot tolerate 8.23V), i'm not sure but the opto-isolator might be okay
replace the regulator, and measure again, if you got 5V, that would be okay.. i'm not sure if it's safe to plug the USB into a computer to check if the FT232 has survived or not.. i'm guessing maybe it's safe?
if the FT232 is surely dead, it'll have to be replaced, same goes for any other chips/components that have died
but work your way out from the power supply.. like in the build guide

once the IO board gives all the right voltages, and if the USB chip and everything else on the IO board works - maybe plug some cables into the mainboard to inspect the damage there
Note: it's possible that something on the mainboard has died in such a way as to leave a short circuit on a power rail, so if you plug J3 for example, attach your meter to the 5V rail as you switch power on and if you don't see 5V there - switch it off immediately, then disconnect J3 and see if 5V is fine, remove chips from the mainboard and try again..
but i stronly suspect the atmega and EEPROM would have died

actually, a naive test you can do is to measure resistance (while there's no power) from GND to a power rail or any point in the circuit
in some situations, a dead chip might be left permanently shorting the power rail, which should read as a very low resistance
you cannot easily know where that short is, but you could then unplug chips and see if it changes
Note: you might see resistance which varies in time - this happens when there are capacitors in the circuit being measured, and the measuring device practically charges them up, after some time, the reading will relax towards a given value

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