Symptom: Farty/bad fuzz
Cure: Remove and confirm bad transistors, then test and select better transistors
No picture or schematic for this article. Fulltone is very clear about not wanting anyone to know their secrets. I have traced the '69, but won't post it. Traced schematics do exist on the net. It may be titled under a pseudonym to hide it from Fulltone. As it is supposed to be, it is a Fuzz Face clone plus your typical Fuzz Face extra variable resistors. If you do enough reading about the Fuzz Face, you'll figure out the '69 circuit. I had done this before actually tracing one, and it was somewhat disappointing to see that there weren't any surprises inside.
I don't know about the smaller enclosure '69 pedals, but the old ones have some kind of adhesive/epoxy to keep people from messing with them. In general, I just tell people to contact Fulltone for service.
However, there was a particular '69 that the music store owned that was terrible sounding. No adjustment helped. Just bad, farty fuzz. After it sat on the shelf for too long I decided to go for it. Getting past the goop was the most annoying part. After that it was just another Fuzz Face repair.
I pulled the transistors and tested them. Horrible. These were either never good or something happened that killed them. Very leaky and not suitable for a Fuzz Face. I have heard anecdotal reports that Fulltone purchased some bad batches of germanium transistors over the years.
After selecting two suitable replacements (http://www.geofex.com/Article_Folders/ffselect.htm) the pedal sounded good again.
I used to own a '69 but I just never found it terribly useful. I favored the Fulltone Ultimate Octave (Foxx Tone Machine clone) for awhile, and eventually sold both pedals without regret.