[sdiy] TB-303 terror

[mark verbos]

Hi all,

if anybody cares, I got the 303 working today. It turned out to not be 
the RAM. It was the chipforbrains replacement switchboard. The board was 
very high qaulity, even including some headers to mount the board in the 
303 for easy replacement, should you need to again in the future. 
However, resisters R201, R202, R221 and R227 were all 1.7K insted of 
47k. I guess this was draining the outputs from the processor because 
when I switched them with the resistors from the old board, everything 
works fine. It drove me nuts for a while, but I finally figured it out 
when I took the 3 RAM chips out and switched them around. Nothing 
changed. Then I pulled the 4 pin header for wires 19-22 out and it 
worked fine (except those LEDs didn't light, obviously)

anyway,

Rock on guys,


Mark



Byron G. Jacquot wrote:

>>I am working on this TB-303 that has a wierd issue. When I go into
>>proram mode I can play any note from the keys, but when I play back
>>from the memory, every note is one of the lowest 4 on the keyboard.
>>Also slides and accents don't record, but octave up and down do.
>>
>>Is there a bad memory chip? Has anyone had this problem? I have been
>>running over and over it all day.
>>    
>>
>
>That's an 8-bit RAM chip, right?  Check the data outputs from it with 
>a scope probe, while playing back.  You might also watch the !RE 
>line(s) to it, as well as the address lines.
>
>If it's two 4-bit RAMs, then there may be a problem in decoding the 
>even/odd addresses, or one of the chips has gone bad.
>
>IF it's like the TR606, with 2 4-bitters, you could try swapping the 
>RAMs with each other and see if the problem moves with 'em.
>
>Byron Jacquot
>
>  
>