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  • May 14, 2020 at 6:29 pm #86263
    piamp
    Member

    Hello!
    I have an electric mistress on the bench,
    it’s a V2 according to this page :
    http://www.metzgerralf.de/elekt/stomp/mistress/electric-mistress-v2.shtml

    I get no sound at all when the pedal is engaged.
    Seems i have no V+ :
    Taking voltages at the BC309 : 14.13V on the base of B309 ; 14,81 on the emitter, but only 0,6 on the collector !
    Also the 33uF cap is missing (seems it’s been clipped?)

    Any help ?
    Thanks :)

    May 15, 2020 at 9:38 am #126077
    Scruffie
    Member

    And the 741 voltages are…

    You’ll have to put the 33uF back then.

    May 15, 2020 at 9:56 am #126078
    piamp
    Member

    the 33uF is here, it was on the other side of the pcb :)
    there’s no zener, but a transistor instead : 2N3563
    here’s a picture :

    https://ibb.co/xh2pVDD

    about 741 voltages :

    pin 1 : fluctuating 1 to 2 v
    pin 2 : 6,84V
    pin 3 : 0,439V
    pin 4 : 0V
    pin 5 : fluctuating 0.7V / 1.5V
    pin 6 : 13.6V
    pin 7 : 14.7V
    pin 8 : 0V

    May 15, 2020 at 1:15 pm #126079
    Scruffie
    Member

    Oh, if there’s no Zener that’s the early power supply variant which is prone to failure.

    Here’s the EH service note that was sent out.

    1)Replace the 2N5087 or BC309 transistor with a 2N4353 transistor.
    2)Replace the 2N3563 transistor at pin 2 of the 741 with a 6.8V Zener.
    3)Replace the transistor or Zener at pin 6 of the 741 with a 47k resistor.
    4)Replace the 18k resistor with a 22k resistor.

    So put simply you need to make it look like the version in the schematic on the metz site.

    But there’s also a possible short somewhere in the circuit, I would test the 33uF & 100uF caps for continuity and if the 4013 is in a socket, try popping it out and seeing what happens to the supply voltage then.

    May 16, 2020 at 6:27 pm #126082
    piamp
    Member

    thanks,
    i cant find any 2N4353
    can it be replaced by any modern transistor ?
    i have some 2n2905a

    May 18, 2020 at 1:58 pm #126086
    piamp
    Member

    small progress here…
    i changed the LM471 and now i have a V+ !!!

    But still no or bad sound
    so i began the troubleshooting procedure : http://www.metzgerralf.de/elekt/stomp/mistress/repair.shtml

    Turn on power supply and check for 18.0 V at pin 7 LM741
    -> ok

    Check for 12 V (12.0 – 13.5 V) at pin 8 4885, pin 14 4013, pin 3 LM339
    -> ok

    Check for a low frequency (~0.05 – 20 Hz) sweep about 0.5 to 9 V at pin 2 LM339 – frequency controllable by RATE pot
    -> it’s stange here : i have about 9V and once every 10sec it drops to about 3v for a glimpse and then goes back to 9V. is it what is expected ??

    Check with oscilloscope for clock output at pin 1 of LM339 (~40 kHz to 400 kHz)
    -> i do have something that looks like a clock (9V that goes to 0v at a Khz frequency)

    Switch to FILTER MATIX mode. Clock frequency must be controlled by RANGE
    Check with oscilloscope for square wave output at pins 9, 12 and 13 of 4013 (~20 kHz to 200 kHz)

    -> it’s totaly flat at thoose pins :(

    strange things on my unit : pin 4 of the 4013 goes straight to pin 2 of the LM339 ?

    I had 2 red tantalums between 2 and 4 of the LM339, one 1uF, the other no reading ? changed for what i had on hand (parralel 2.2uF and 50n)

    May 18, 2020 at 2:53 pm #126087
    Scruffie
    Member

    Sorry, that should have been 2N4354.

    I suspect your 4013 is busted, post voltages or just replace it.

    Pin 2 connecting directly to pin 4 of the 4013 is fine, the circuits varied over time.

    As for the tantalums, maybe they were out of N.P. 2u2 caps that week.

    Pin 2 of the 339 should have a triangle wave on it.

    May 18, 2020 at 2:57 pm #126088
    piamp
    Member

    here’s what i have at pin 11 of the 4013:
    https://ibb.co/PxXygQN
    pin 13 is roughly the same inverted, pin 9 and 10 are flat. will buy a new 4013 tomorow (with a 339 too!)

    why is there 2 parraleled 2.2uf and 50n caps across pin 4 and 2 of the 339 ?

    also, my unit does not have any 100uF at V+ near the SAD1024. Does it need it ? Why a 100uF here ? it’s parralelled with the 33uF at the collector of BC309 ?

    May 25, 2020 at 12:34 pm #126105
    piamp
    Member

    So, after new ICs (339, 4013, 471) and new eletrolytic, the mistress sounds great !!!
    My only concern is in non sweep mode, i get a bad oscillation sound when range goes to about 80% and no effect at all after 80%. From 0% to 80% it sounds ok…
    In sweep mode, all range pot range is good.

    I performed the alignement procedure.

    Is it normal ?

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