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Thread: BOSS SYB-3 Bass Synthesizer No dry signal in Mono out

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    BOSS SYB-3 Bass Synthesizer No dry signal in Mono out

    I have a Boss SYB-3 Bass Synth pedal that only outputs the effected signal when using the OUT A (MONO) jack. If I plug another jack to the OUT B it works as supposed to (OUT A: FX, OUT B: DRY). Iīve traced the dry signal and it stops right at Q7īs pin2, no more dry signal at Q7īs pin1. I donīt know if Q7 (2SK880) is fried or if it is another part related to the switching circuit. All Smt components BTW. Can someone help me fix this problem? Iīm attaching the schematic for reference...Thanks!!!

    BOSS SYB-3_SN.pdf

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    Not too sure what the issue is that you are describing.

    ● Is OUTPUT B connected?
    Sounds are output only from the OUTPUT
    B jack when the effect is switched off
    while a plug is connected to the OUTPUT
    B jack. When the effect is off, the output
    from the OUTPUT A (MONO) jack is
    muted, with no sounds being output.

    https://media.sweetwater.com/store/media/syb-5_om.pdf

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    No, only the A output is connected. Also Iīm referring to the SYB-3, not the SYB-5 as you linked. When the effect is engaged, there is no dry signal coming out of the output (A - MONO mode), only the effected signal. Bypass works ok. Q7 is not letting the dry signal go through, Iīve replaced it with a 2sk117 but still the same problem. Measured the diodes and caps around that part of the switching circuit and they appear to be ok (tested in circuit).

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    don't forget the joker g1's Avatar
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    Q7 gets it's switching signal from Q11. Is Q11 collector switching?

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    Quote Originally Posted by g1 View Post
    Q7 gets it's switching signal from Q11. Is Q11 collector switching?
    How do I find out? What do I check for? Iīve replaced Q7 with a 2SK117 but is the same...I thought about Q11 but I donīt know what/where to measure...

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    Measure DC voltage at Q11 collector (junction of Q11, R45, & R43) when effect is engaged and disengaged.
    Also check at pin7 of IC10.

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    Quote Originally Posted by g1 View Post
    Measure DC voltage at Q11 collector (junction of Q11, R45, & R43) when effect is engaged and disengaged.
    Also check at pin7 of IC10.
    Here are the voltages
    Q11C ON: 8.22V
    Q11C BYP: 0.0015V

    IC10 PIN7 ON: 0.001V
    IC10 PIN7 BYP: 4.97V

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    Quote Originally Posted by pickups_cba View Post
    Here are the voltages
    Q11C ON: 8.22V
    Q11C BYP: 0.0015V
    Ok, looks good, do same test at pin3 of Q7.

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    And after doing that test, repeat tests with a 1/4" plug inserted in output B. (if previous tests were done like that, then repeat without it)

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    Quote Originally Posted by g1 View Post
    Ok, looks good, do same test at pin3 of Q7.
    Iīve got 0.050V and 0.100V (aproximately, values were not stable)

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    Man this thing itīs driving me insane!! Now there is no bypass signal!!! Q5 had the same symptoms as Q7, the rest of the switching components appear to be OK. Original transistors are 2SK880. If I use 2SK117, I canīt make them turn on, if I use J201 they remain on and canīt be turned off. I am very close to send everything to hell, put some jumpers and convert it to true bypass...I mean I want to keep the original functions, but the pedal appears to be self destructing!!

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    Are you positive you have the K117's oriented the right way around?

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    Quote Originally Posted by g1 View Post
    Are you positive you have the K117's oriented the right way around?
    Yes, from the start I even soldered wrap wire to both transistorsī pads on the board, and the other ends of the wrap wires are placed into a breadboard, so I can try different transistors and pinout without destroying the PCB. Iīve tried every possible configuration and it doesnīt work

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    Here's a diagram of what it should look like from above. Measure gate voltage at middle pin and make sure it is changing from off to on. Then measure resistance between S & D for on and off states. Should be low resistance in one mode, high resistance in other.

    Click image for larger version. 

Name:	k117.jpg 
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    g1 thank you very much for the guidance, Iīve really tried but due to time constraints Iīve decided to make it True Bypass by jumpering Q7. I used a breadboard fixed to the pedal case with a small DPDT switch and millenium bypass. It works great. Maybe in a while when I have some spare time Iīll try again to make the original bypass system work, but I really needed the pedal working ASAP. Since Iīm not going to use both outputs at the same time, I wired the normal boss on/off switch wires to the Output B jack, so I still can have access to the Synth Hold function by using an external footswitch. Iīve thought about wiring this jack to the cutoff pot, but I didnt know if it was a good idea since the ground of the pot is digital ground and the jack sleeve is connected to the chassis (analog ground). Was I too cautious?

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