Help identifying this schematic symbol/part?

[mkstewartesq]

Working on trying to revive an old Digitech pedal (to the extent I can within my abilities). While it is 90% SMD (definitely beyond my abilities) the caps and certain other components are through hole.

I suspect that the problem is that someone plugged the pedal into the wrong power supply so I’m focusing around the power jack. Edit to add – the pedal is not completely 100% dead – the LED lights very dimly and there is very very faint sound, but it’s so quiet I can’t even tell if the effect is working.

Nothing on the board appears to be burned out – but I can’t for the life of me figure out what these two components are (L1 and L2). Since I don’t know what they are, I don’t know if they look normal or damaged – but since the pedal’s already in the morgue, I might want to try to replace them just to see if it makes any difference. But again, I can’t even tell what the hell they are.

Here’s the schematic symbol (something I’ve never personally seen before) - and the BOM on the schematic just identifies it as “IND FBD 70 OHM @ 100 MHZ RIC200 TA”:




and here’s a couple of pictures of the actual part on the board.



Any ideas? Thanks in advance.

Mike

 

[benny_profane]

Those are ferrite beads. They’re labeled as inductors (the ‘L’ designator), but are a bit different. The specs there state the equivalent resistance at a given frequency.

Here they are mitigating EMI (like you’d see with the blocky cylindrical part of a power brick cord).

I’m not sure if those are your issue or not.

 

[mkstewartesq]

Those are ferrite beads. They’re labeled as inductors (the ‘L’ designator), but are a bit different. The specs there state the equivalent resistance at a given frequency.

Here they are mitigating EMI (like you’d see with the blocky cylindrical part of a power brick cord).

I’m not sure if those are your issue or not.

Thank you.

Yeah, I’m not gonna mess with those unless I have at least grounds for suspicion that they are the problem.

Interestingly, about a year before I started on this pedal building journey, I did some preliminary investigation to see what might be up with this pedal. At the time, I was so ignorant of electronics and timid, I couldn’t even bring myself to fully disassemble it. Today, I figured that, after a year of building in 35 pedals, I probably had the lay of the land a lot better such that I could least start to figure out what was wrong. NOPE, this was quite a humbling experience. I’m still not particularly good at reading schematics and this one is four or five pages long. (At least I recognized the voltage regulators (there are three) and the diodes and the capacitors, which is way more than I would’ve recognized when I last looked at it two years ago). But I obviously don’t have the smarts yet to start figuring out what I should be checking.

So I guess I’ll set it aside and wait a few more years and come back to it to see if I’m any smarter then than I am now. And if I’m not smart enough by that time, then I’ll set it aside for a few more years, and try, try again.

Thank you again,

Mike

 

[benny_profane]

In all fairness, this has AC power input and not something you’d come across in the typical kinds of projects we work on.

 

[chris.knudson]

definitely beyond my abilities

Somehow, I don't believe that. I think you aren't giving yourself enough credit.

 

[darwin999]

@mkstewartesq - I agree with @chris.knudson

Your original thought that the original user plugged in the wrong power sounds plausible. Is it the same power connector that our stompboxes use for 9 or 18VDC? If so, then I think it such a scenario is VERY plausible - and thus may be worth taking another step or two down that path alongside your fellow forum pals. So what's to the right on that schematic? I.e., what would get unhappy about seeing 9VDC instead of AC?

Btw, under that scenario, the ferrite beads would not be impacted - they have negligible resistance within the audio range (including 50/60 Hz power), and changing from 9VAC@60Hz to 9VDC would mean squat to them.

 

[mkstewartesq]

@mkstewartesq - I agree with @chris.knudson

Your original thought that the original user plugged in the wrong power sounds plausible. Is it the same power connector that our stompboxes use for 9 or 18VDC? If so, then I think it such a scenario is VERY plausible - and thus may be worth taking another step or two down that path alongside your fellow forum pals. So what's to the right on that schematic? I.e., what would get unhappy about seeing 9VDC instead of AC?

Btw, under that scenario, the ferrite beads would not be impacted - they have negligible resistance within the audio range (including 50/60 Hz power), and changing from 9VAC@60Hz to 9VDC would mean squat to them.

Here’s the very first page of the schematic. I’ll also attach the actual full schematic, all 9 million pages of it, just in case anyone wants some light reading.

 

[chris.knudson]

Here’s the very first page of the schematic. I’ll also attach the actual full schematic, all 9 million pages of it, just in case anyone wants some light reading.

View attachment 72116

Okay, give me a couple of weeks to get through all of this... Oh damn, now I know why you gave up. Ummmm, good luck with that!
Just messing with you -- let's tackle this!

 

[Mcknib]

Did you check what looks like a fuse or some kind of circuit protection device thingy F1 if it's a fuse it should have continuity across it that's a likely candidate for blowing

I can't quite make out the part number on it

 

[Robert]

Plugging in a DC power supply wouldn't damage it, but overvoltage could.

D4/D6/D7/D8 form a full wave bridge rectifier to convert the AC input to DC. It also acts as reverse polarity protection.


Check the power supplies.

3.3V on L3, 5V on pin 2 or 4 of U8, and -5V on pin 3 of U3.

If those voltages are all correct you can move on past the first page.

 

[mkstewartesq]

Thank you all – I’ll check out the components you’ve each listed a little later and report back.

M