TB-303 :: CV gone bonkers

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donfuego
 
Posts: 41
Joined: Fri May 27, 2011 11:51 am

TB-303 :: CV gone bonkers

Post by donfuego »

Hooked up my old trusty box yesterday only to find it had gotten ill...

What happens is this: As soon as I power it up, the CV (and note pitch) starts from normal and slowly drifts up to 8-9 volts (it probably would keep on if I didn't turn it off at this point). It takes about 30-60 seconds to reach this level but it doesn't drift smoothly though, it goes up and down a bit and occationally drops down several volts.This happens regardless if it is playing a pattern or not.

CV at R90 is NORMAL! I guess it could be the IC11 AN6562, but how can I rule out other possibilities? What about all the transistors, or the R100 or even the diodes?

Luckily I built a x0xb0x a year ago which suffered from pitch problems (I owe big time to guru/hero 'guest' for helping me out) so I'm not all green to this, except this time it's a real 303.

Any thoughts?

Regards

Don

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mmm
 
Posts: 517
Joined: Tue Apr 24, 2012 1:51 am

Re: TB-303 :: CV gone bonkers

Post by mmm »

donfuego wrote:Hooked up my old trusty box yesterday only to find it had gotten ill...

What happens is this: As soon as I power it up, the CV (and note pitch) starts from normal and slowly drifts up to 8-9 volts (it probably would keep on if I didn't turn it off at this point). It takes about 30-60 seconds to reach this level but it doesn't drift smoothly though, it goes up and down a bit and occationally drops down several volts.This happens regardless if it is playing a pattern or not.
My guess is that indeed IC11 is the culprit here. You could remove D31 and TM5 to make sure (theoretically also IC12 could play a role but I doubt it).

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donfuego
 
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Joined: Fri May 27, 2011 11:51 am

Re: TB-303 :: CV gone bonkers

Post by donfuego »

Hi guys!

It took me a while to actually pull myself together, source the part and replace it, and wham! as good as new :D

A peculiar thing, it seems like the 6562 had completely died while the 303 been sitting on the shelf for a year or so. Today when powering up, before replacing ic11, there was no sound at all. CV was there (and still goofy) but I could only hear a very faint gate noise when playing, so I was worried that something more had died in there, but it turned out to just be the 6562. Yay!

A late Big Thanks to MMM for the response! :wink:

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