ROLAND TB-303 IMPOSSIBLE ISSUE!!!

[mimountains]

Hi -

This is my first time posting here, but I've been a longtime lurker and hope someone might be able to shed some light on a repair that's been killing me lately.

Basically - a person gave me a Roland TB-303 to work on and said that the Cutoff knob was having no affect on the sound of the unit (i.e. - no squelchy acid sounds).

I checked it out and confirmed the issue - however, the cutoff knob actually caused a drop in volume as it was turned up. In addition, the Accent and Envelope Mod controls further weaken the sound and actually cause an audible 'thump' on each accented note. Also - overall, I'd say that the unit is quieter than I'd expect it to be.

What I've done so far:
~ Cleaned the pots with deoxit
~ Metered out the pots to see if they were damaged or off their resistance
~ Re-flowed solder to all pot traces in case there were cold joints
~ Checked the power supply/regulator
~ Re-flowed solder to the ribbon connectors (there were some cold joints)
~ Replaced a few (6) caps in and around the cutoff and resonance circuit

At this point I've ruled out all above issues and need to start poking around inside the actual circuit. I know that the TB-303 uses a 'Moog-style' Transistor Ladder filter in order to create its sound, and if one or more of the Transistors fail the cutoff wouldn't work. I've removed and tested all of the transistors in the filter and they all check out as good.

Allowing for a margin of error on my part, is there anyone out there that's encountered a similar issue or has anything else that they could recommend? I'm really stuck!!!

[Zamise]

Have you tried running it off batteries? If not and you do and it sounds and works fine I'd suspect a new power adapter may be in order. Other than a new adapter I don't have any other helpful diagnostic suggestions.