1982 Boss BF-2 resurrection

[NippleWrestler]

a non-working pedal came to me a few days ago. A 1982 MIJ BF2 Flanger. Beaten up and dead.

I plugged it in and the guy was right, it didn't work either in bypass or when engaged. Interestingly the LED went on and off with the switch leading me to conclude the power supply itself was still ok and the switching system was working (Boss use JFET switching systems).

To save money Boss used really inadequate filter caps. The pedal takes 12v, but 18v caps are used. On the opamp bias line (half of supply) they use 6.3v caps for what equates to a 5.2v rail (12v becomes 10.?? after diodes have dropped the voltage, half of that is the bias voltage for the 2 x 4558s) so I wanted to check out the power supply and anything related to it, presuming something in the signal path (there's 11 transistors, 5 opamps) wasn't getting the juice.

Here's the backside.



Here's topside after some component changes (anything blue):



When I opened up the back a transistor fell into my lap. Q6. It had totally broken off at the body. I took out the legs and installed a 2n2222 in its place, bearing in mind the pinout is different so 2 of the legs need to be twisted.

This didn't solve it. There was also some brown corrosion on 2 of the nearby resistors, so I replaced those with metal films while I was in there. Still no dice.

Then I replaced all the caps in the power supply network, along with the 11v zener. If someone used the wrong power supply these components may have died, plus they're all 41 years old and, as mentioned, underspec'd for the job. I used modern replacements rated at 50v.

Still no dice.

Then when I ran the voltages of the opamps I was getting weird readings at the outputs. It was 1.3v while the supply is 10.4v. It should be half of supply (~5.2v), not a tenth. I wiggled some stuff around to find the supply voltage but couldn't get a reliable reading, then when I checked the output voltages again to see if I'd made a mistake the voltages would fluctuate from 1.3v up to 6v and back down again. Checking the schematic, there's a voltage divider network of R34, R35, and C25 which bias and filter the opamps. Interesting.

I pulled all these components and found a lot of white crusty flaky gunk under C25. I cleaned it all off, installed brand new components (a 50v cap in place of the 6.3v rated stock cap), and now it works.

Along with 2 transistors everything blue is a new part:



Serial:



Behold the majesty:



It's good to know my brain is not as calcified as I thought.

[StrummersOfThunder]

That’s awesome man. These sort of victories are great. To me, the serviceability and trouble shootable nature of analogue gear remains a massive appeal.
Nice patina on the case
Do you think the under-gunned spec cap ratings were due to just using what was on hand ? Mostly running on battery so no chance of voltage spikes ? Cheap?

[NippleWrestler]

That’s awesome man. These sort of victories are great. To me, the serviceability and trouble shootable nature of analogue gear remains a massive appeal.
Nice patina on the case
Do you think the under-gunned spec cap ratings were due to just using what was on hand ? Mostly running on battery so no chance of voltage spikes ? Cheap?

All of the above. I suspect they had millions and millions lying about and back then a 33uf/50v cap would be much bigger than the same cap now some 40 years later and of course room is an issue, especially on a packed board like this. They would work in the circuit (and they apparently did), but them dying is a question of when and not if. They're also shit quality parts which doesn't help.

And yeah, people can use batteries to avoid spikes/surges, but I don't know a single person who still uses them... I don't even include battery functionality in my builds because it's just redundant tech that does nothing but go in landfills and bleed shit for 1000 years. With all that said, Boss dropped the ball with weak components running so close to their limit from day 1.

[StrummersOfThunder]

That’s awesome man. These sort of victories are great. To me, the serviceability and trouble shootable nature of analogue gear remains a massive appeal.
Nice patina on the case
Do you think the under-gunned spec cap ratings were due to just using what was on hand ? Mostly running on battery so no chance of voltage spikes ? Cheap?

All of the above. I suspect they had millions and millions lying about and back then a 33uf/50v cap would be much bigger than the same cap now some 40 years later and of course room is an issue, especially on a packed board like this. They would work in the circuit (and they apparently did), but them dying is a question of when and not if. They're also shit quality parts which doesn't help.

And yeah, people can use batteries to avoid spikes/surges, but I don't know a single person who still uses them... I don't even include battery functionality in my builds because it's just redundant tech that does nothing but go in landfills and bleed shit for 1000 years. With all that said, Boss dropped the ball with weak components running so close to their limit from day 1.

Good info
Thanks for sharing the gut shots . I love that stuff

[FuzzMonkey]

I assume you kept it ASA spec'd?

[jeremyb]

Sweeeet, what did you think of the sound of it? these are highly regarded!

[NippleWrestler]

I assume you kept it ASA spec'd?

12v DC direct or part of a 9v daisy chain and it runs perfectly but I probably will convert it to PSA since it only involves jumping 2 things.

[NippleWrestler]

And yep, just converted it to non ASA spec. While I was in there I lowered the clr from 3k9 to a 1k5 for more led brightness as it was rather dim.

I also dialed in the trimpots and this is a whole lot of fun, capable of great clangy madness or subtle motions swirling underneath the music.

[FuzzMonkey]

12v DC direct or part of a 9v daisy chain and it runs perfectly but I probably will convert it to PSA since it only involves jumping 2 things.

Easy to undo when jumped for those who want the OG specs.

[NippleWrestler]

Sweeeet, what did you think of the sound of it? these are highly regarded!

First I hated it. It was distorting every note like a dying fuzz pedal and clipping at the extreme range of things.

I opened it up and dialed in the 3 trimpots and now it's really good. Warm, thick, colourful, doesn't sound sterile or digital or cold or whatever else, just pleasantly swirly but it is capable of insanity if you dime the resonance control and it will almost oscillate (the trimpot inside controls how mad this control can get) into whale noises or police sirens if you want. I dialed it back internally to just before that happens so the range is all what I want to hear.

It's cool. Well worth the $8.

[NippleWrestler]

And here's a handy diagram I made myself comprised of my photo and the board layout from the service manual which I flipped and overlaid to better identify what is what from the solder side. May it help visitors from the future.

LGdnKl7.jpg (465.89 KiB) Viewed 16638 times

[FuzzMonkey]

It's cool. Well worth the $8.

Nice!

[NippleWrestler]

It's cool. Well worth the $8.

Nice!

Because it was 99% dead and the fix was reasonably involved the guy let it go for the cost of shipping. Someone has already offered me $200 for it.

I replaced all the other electros last night as I don't trust them, being as old as they are.