Home › Forums › Help/Technical Questions › Vintage Soul Preacher Works on AC adapter but on battery I have a problem

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  • January 10, 2013 at 8:05 pm #82794
    csiegel
    Participant

    I have excellent soldering skills and some knowledge on electronics but need some help. This should be a easy question to answer for you techs.

    I have a Vintage Soul Preacher. It is the year that has the 1st version knobs, battery access door, and has a green chicklet cap and a resistor on the underside(soldered) side of the PC board.

    The pedal operates absolutely perfect when it is powering off of the 3.5mm +tip 100mA AC adapter plugged into the AC outlet.

    The problem is: When I power the pedal off of a new and tested 9VCD(reads 9.3VDC on meter) battery. The pedal works when I first install the battery and plug it in and start to play it. At first the pedal seems to work properly and then the output volume of the pedal decreases in a linear fashion to the point where, even with both knobs full CW, the output of the pedal diminishes to total silence (no sound coming out). It takes approximately 2 minutes for the pedal to go from full output to zero output. This happens whether or not the AC adapter is plugged into the pedal and disconnected from the AC outlet. So, this rules out any type of problem with the AC adapter jack on the pedal malfunctioning. I also inspected the pedal for any cracked solder joints and checked all of the obvious things that could be seen with the eye or troubleshot. Checked out good 100%.

    My best guess is that I have one or several capacitors that are bad and need to be replaced.

    Could you tell me which capacitors would only be in the portion of the circuit that the battery is tied to?

    Since there are no issues when the voltage is coming from the AC adapter 3.5mm jack, I only want to replace the capacitors that are in the portion of the circuit that is tied to the battery and not in the AC adapter jack portion of the circuit.

    I just need to know which capacitors to replace. If you could tell me which capacitors on the schematic in this link to replace: http://www.montagar.com/~patj/soulprch.gif

    You can email me any info that would help to this email: christophersiegel1@msn.com

    Thank You!

    January 10, 2013 at 8:25 pm #118630
    The EH Man
    Moderator

    100uf, 10uf, and 1uf in the upper left

    January 10, 2013 at 8:39 pm #118631
    csiegel
    Participant

    Do you recommend I just go ahead replace all of the electrolytic caps while I am at it? They may have all dried up if the pedal has been sitting for years? I think there is only a couple more electrolytics other than the ones you already pointed out?
    Also, is there a particular manufacturer you recommend to maintain the sonic character of the capacitors being replaced? Can I purchase them from Electro-Harmonix?

    January 10, 2013 at 8:43 pm #118632
    The EH Man
    Moderator

    It’s not going to hurt to replace them all. I wouldn’t worry about brand as long as they’re new.

    January 14, 2013 at 3:43 am #118658
    ranjam
    Member

    To me, if it works fine on AC but not on a battery, it has to be a problem with a component that is exclusive to the battery ‘circuit’. If you check the power supply section, I’ve circled the one cap that could affect the battery ‘circuit’, especially if it is leaky;

    soulpreacher_zpse5aa8862.jpg

    I doubt anything else would be ‘bad’ and still let the pedal would work perfectly with an AC adapter. But changing all electrolytics is never a bad idea. Just for fun, if you have a cap meter and an ESR meter, check the original caps as you change them. If that 10uF I circled is leaky, you can thank me. Or not.

    January 14, 2013 at 8:25 am #118659
    csiegel
    Participant

    Thanks. I don’t have an ESR meter or cap meter. I am open for suggestions on good and inexpensive ones. I will replace the cap you circled first and the test the pedal to see if you are right. I will post results when I receive and install the cap.
    Thanks again.

    January 15, 2013 at 1:40 am #118665
    ranjam
    Member

    I could be wrong, but it makes perfect sense to me. The only other possibility is the input jack has a bad/corroded contact from the battery. Follow the negative lead. The positive lead goes to the base of the 2nd transistor and the 10uF capacitor. It’s a stereo jack that connects the battery ‘-‘ lead whenever a cord is plugged in. You could put a fresh battery in, and measure the voltages as indicated in the schematic. Go to the 2nd transistor and measure the +9VDC and the +4.5VDC. You could leave your meter clipped on to the board and leave the measurement showing on your meter. Now you can wiggle a few wires, hit caps or resistors with a hair dryer or freeze spray, and wait for the voltage to drop to ‘0’. There’s the problem.
    Cap meters usually come ‘free’ with many DVM’s, but of course you can buy a dedicated cap meter. ESR meters are a little expensive, but worth it if you plan to do a lot of your own work. They can find bad caps ‘in circuit’, so they are great time savers as opposed to unsoldering a capacitor to measure it, or changing every capacitor.

    March 6, 2017 at 10:58 am #122663
    Austwide
    Participant

    Hi guys

    Totally amazed, just picking up the guitar after 30 years and I find my old Soul Preacher. Trouble is I lent it to my brother way back then (he doesn’t recall) and he pinched the stomp switch out of it and lost the back cover.

    Well I found this thread with the circuit, thanks to the poster of it, saw where the wires and another wire or 2 that had broken off went quick solder job and fired it up.

    It sort of works but when the volume (input signal?) builds up, the output volume goes to zero and slowly returns over the next 2 or 3 seconds, strum again and back to zero. Same result on battery or adaptor. I don’t know if this is a new fault or the reason he pinched the stomp switch.

    All of the pots and switches seem to do as expected and I have triple checked where I put the replaced wires.

    I never expected to find the circuit, I posted this here so is anyone can actually follow one beyond where the wires go, they can easily refer to it.

    Can anyone help me out – I need something to cover my lack of guitar skills.

    Thanks
    Andy

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