TB303-Pitch mode problem

[kbo]

Hello,

I have some mistake on my tb303 and i need some help to resolve it.

Here a video
.https://www.youtube.com/watch?v=8aadRmKy0jw


C,D,E,F#,G#,A#,C key work fine only C#,D#,F,G,A,B keys have this problem.

I have change RAM chips. All IC are correctly powered.
No battery leaking . SN 274900

I think it's not a common problem :)

Thank a lot :)

[mmm]

Let me explain what - probably - happens here.
The lowest bit of DAC goes "high" occasionally for the notes where it actually has to be "low". That's why the problem happens for every other note (like in a whole-tone scale).
Why the bit goes high - I don't know. You can measure this at IC9 pin 4 (Input) and pin 5 (output). If pin 5 stays low when pressing the offending keys repeatedly then IC10 is probably to blame. If pin 4 stays low but pin 5 goes high then IC9 is probably faulty. If pin 4 goes high the problem probably comes from the processor.

[kbo]

Thank a lot for your response :)


IC 9 C# pressed repeatedly


note good PIN 4 0v PIN 5 0v
note false PIN 4 2,15v PIN 5 5,32v

In pin 4 I have a 2,15v in continious
When i push (c#key) the first time pin 5 drop to 0v and up slowly to 2,15v, but when i repress it the voltage stay at 2,15v

I have changed and socketed IC9 IC10 IC13 and IC2

The problem can be come before the cpu ? switch board with a faulty Q or D
Ram M58981P-45

[mmm]

You could try to measure the situation at pin4 without IC9 installed. If it then also goes to 2.15V the problem lies probably within the RAM or the processor.

[kbo]

Hello,

C key (work fine ) When i press the key the voltage is 5,36
C# key ( work not fine) when i press the key the voltage is 2,28 and drop to 0 ( first press) but don't stay to 0 it go to 2,28 and stay to 2,28
Exemple sequence key stay pressed 3second
C, C#, C, C#, C#, C#
5,36, 0->2,28 5,36, 0->2,28, 2,28 2,28 IC9 pin4

I have removed IC3, IC4, IC5 the problem is always here

[kbo]

MMM where are you ^^

[mmm]

Well, we have more or less eliminated many other possibilities, so right now it points at the processor. I'm not 100% sure about the other voltages though - I believe the signals coming from the processor should be closer to 6V (not 5.36V) - but it's been ages since I last worked on a real 303.
It might be useful to check/exchange R43 (and perhaps R42, R49 and R50, too); if that one has intermittent contact to ground I could imagine a similar scenario.

[kbo]

Hello, no problem with résistor.

All my problems go out after replacing the old cpu with a qs303 .
Faulty cpu or cold soldering i don"t know but i'm very happy :)

Sorry for the late and thank for your help :)