Boss sd1 mod problem !

[TimWaldvogel]

I am modding a sd1 for a friend and I am having trouble. I only changed d4 and d6 to a 1n400x and it's not working right. They are orientated the right way. Bu now when I plug it in it sounds circuit bent. Or fuzzish. Is very raspy and fuzzy and cuts out a little when I strum. One o the copper pads came off while desoldering. How do I fix this

[flintstoned]

Follow the trace with the missing pad to the next component and use a jumper. Ideally you'd use the lead of the component you just installed, but i bet its too late for that. If the trace has a few components together in the same lil area where you lost the pad, this is when a solder bridge can be a good thing!

[Renegadrian]

Use this old topic instead of opening a new one...

Got a SD1 to get it modified, didn't try if it worked before I changed parts. Now I got problems with it, no sound both in bypassed an on position. Audioprobed, the signal stops at the input buffer, signal at the base but no signal at the emitter.
Tried to change that transistor with a 2n5088, bending the pins to make it bce like the original tranny. no result...
what do you suggest?!

[Electron Tornado]

Audioprobed, the signal stops at the input buffer, signal at the base but no signal at the emitter.

Are you getting voltage to the collector?

[Renegadrian]

The collector is tied to the main 9V trace, that trace and all components on that trace have the right voltage.

I'll try posting some voltages...

battery 9 V tied to the dc jack

Q5 (input buffer)
B 2.38
C 9
E 3.15

IC (socketed a 4558D)
1 5.15
2 5.15
3 5.10
4 0
5 4
6 4.46
7 5.15
8 9

Q6 (output buffer)
B 2.02
C 9
E 3.02

Q2
4.20
0
2.22

Q1
4.40
0
4.40

[duck_arse]

both Q5 and Q6 show the base V lower than the E V. is this correct? and both those bases are tied to the same Vref as pin 5 of the opamp, so they should be about V/2. also, Q1 and Q2 channels are pretty much connected to each other, but one of your volts is 2.22.

hmm, the circuit I'm looking at is not 100% clear as to where the fet channels get their bias from, just R13 and VR2?

[Renegadrian]

yes both buffers B and IC pin 5 are tied to vref via their resistor, obviously the voltage after that resistor varies as those resistors haven't got the same value. (i upped input buffer res. a bit, originally is 470k, so it's correct that is close to Q6 B voltage) - fet drains are tied one to R13 and one to the volume wiper.

[Renegadrian]

You know what's really really strange!? It DOES work...if I just turn down the guitar volume to 6!!! It just cuts the sound at full volume...that is sooooo strange...suggestions!? HELP ME PLEEEEEEEEEASE!!! 

[duck_arse]

I still say you got a problem with those B-E readings. the E should be lower than B for the transistors to work. retrace your pcb, re-re-re-check you pinouts for replacement and original parts.

photos?

[Renegadrian]

Now I replaced R2 back to stock value (it's the resistor feeding the input buffer)
I got a stock SD-1 and made a table with the voltage readings...
stock one is obviously working as it should.
buffers on the stock one are smaller 395 trannies, "strange" one has regular c2240

   stock   mod
q5      
b   2,8   2,7
c   8,8   8,8
e   3,3   3,1
      
q6      
b   1,9   2
c   8,8   8,8
e   2,9   3
      
ic      
1   4,5   4,5
2   4,5   4,5
3   4,4   4,4
4   0   0
5   3,9   3,9
6   4,4   4,4
7   4,5   4,5
8   8,8   8,8

q2      
   4,1   4,1
   0   0
   2,2   2,2
      
q1      
   4,3   4,3
   0   0
   4,3   4,3

[duck_arse]

well that looks like both pedals are not working. something is screwy here. do you have a circuit diagram you can link too? and what is the full # of the "395" 's yr putting in?

[Renegadrian]

strange yeah..but the other one, the stock one, is alive and kicking, and that other one is not...
schem is this one http://www.geocities.ws/cibonato/img/Sd1.gif which has the same numbering on the pcb.
those mini trannies read 395 27F

[duck_arse]

is this your board, are those your transistors?

[Renegadrian]

yep, the same board. The stock one working has a copuple differences from the schematic linked and other sd1's I had here for mods. 47n at c12 not 10n (not very important I guess, is at the switching block) and those trannies at q5 and q6 (in and out buffers)

[duck_arse]

weeeeellllllllll ........ I dunno. lift C9, see if the fets messing up, C2 see if that's bad? if the transistor has same volts as good unit, maybe it's AC parts messing about.

[Renegadrian]

ok i'll try and check c9...even if the voltages at its ends are right

[Renegadrian]

I just don't know what to do...holy cow...obviously c9 is alright...c2, c3 too...

[duck_arse]

isolate the input buffer from the rest of the circuit by lifting both C2 and C9 (you must be sick of de/soldering them by now). feed in yr guitar, and take the buffer output to some external monitor, whatever you use for audio probings. does it still cut out at +6? sound right? if yes, well, you've eliminated the input buffer.

(I'm all out of ideas or methods.) check for dc at both ends of R1, guitar plugged in, guitar plugged out.

[Renegadrian]

right i'll try thx