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Are these MIDI-related IC's?

Discussion in 'Datasheets, Manuals and Component Identification' started by FuZZ1L0G1C, May 25, 2019.

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  1. FuZZ1L0G1C


    Mar 25, 2014
    While having a MEDELI M1 musical keyboard stripped down, I decided out of technical curiosity and self-teaching of how a MIDI keyboard works, to attempt to trace the MIDI part of the circuit.
    Besides that, I am also tracing the (faulty) power supply, and the amplifier section.
    Wondering which IC controls the MIDI data, as it has multiple voices, rhythms, MIDI record and playback, as well as MIDI-out to the DIN port.
    The only 2 IC's are on the main board, silk-screening on IC typed below.
    When I Googled data spec-sheets on these IC's, found that these are amplifiers.
    MC4558 = op-amp and TA822PL = 2.5W dual power amp.
    So I scratch my head, thinking "where the heck is the ROM or EEPROM for wavetable and MIDI?"
    Going onto MEDELI's HK website, they apparently manufacture their own keyboards, and some IC's, or have them custom-made by UTC, which is obviously the case here.
    So, as these are the only two chips on the entire keyboard, could one of these be the ROM or MIDI controller, perhaps by coincidence having the same part number after the UTC S*A*?
    On UTC's website, (where they list these as amps), the bottom 2 characters are date codes, but the SLA2 and SKA prefixes are not listed by them.
    PS- The Kyb owner reversed his 12VDC polarity after damaging & re-joining the wall-wart cable, blowing the 2.2mF 25V cap and 1N4001 diode.
    Circuit still works on "battery" 9V DC power, tested with my DC supply.
    Still tracing circuit...
    One of my reasons for trying to source the actual MIDI IC is to pair it correctly in Frooty Loops Studio 20 (Controller Device is .......) .. eg Yamaha XYZ.
    Otherwise 'New USB Audio Device' is the generic / default.

    medeli m1:
    C10 = 2200 u 25V ESR 1" x 0.5" (open cct)
    D1 = 1N4001 silicon (open cct)

    U2 = DIP-8 package.
    UTC SLA2

    U5 = DIP-12H package.
    UTC SKA.
  2. davenn

    davenn Moderator

    Sep 5, 2009
    probably just some sort of manufacturing code .... irrelevant as you already have the actual part number

    well there must be another IC or more somewhere on the PCB

    how about some photos
    Last edited: May 27, 2019
    FuZZ1L0G1C likes this.
  3. FuZZ1L0G1C


    Mar 25, 2014
    Thanks for reply.

    Searched all PCB's - only those two listed - not life-threateningly important - was just to see if I could match Frooty Loops input to a 'known' listed MIDI device.
    The downloaded MEDELI M1 PDF user manual says "New USB Audio Device" should show when connected.

    Will upload ASAP, when I get Pentax up & running again - some intermittent problems with it. (Second-hand DSLR).
    Cellphone is too un-sharp for clear pics of components.
  4. FuZZ1L0G1C


    Mar 25, 2014
    Some not-so-sharp photos taken with cell phone camera at it's closest focusing distance.
    Reduced size 37% from 1600*1200 to lessen forum footprint.
    The 2 IC's marked with red "+":
    The 8-pin DIL (MC4558L) is shown top center and the DIP-12H (TA8227PL) is left, under it's heat-sink.
    Temporarily removed heat-sink to check part no.
    022.jpg 029.jpg 034.jpg 035.jpg
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    What about the keypad matrix connector pcb? Any components on the back of it?
    FuZZ1L0G1C and davenn like this.
  6. davenn

    davenn Moderator

    Sep 5, 2009

    what makes you think that C10 is blown ?
    looks perfectly fine to me
  7. davenn

    davenn Moderator

    Sep 5, 2009

    how did you measure that ?
    a decent cap meter and cap out of circuit ?
    FuZZ1L0G1C likes this.
  8. FuZZ1L0G1C


    Mar 25, 2014
    Yes, I peered closer in daylight, saw at least 2 IC's and dozens of SMD components on underside, all low-profile.

    I have two DMM's that have Capacitance functionality, a Major-Tech MT1879 Industrial Multimeter (auto-range CAP), and an ANENG DT-9205A (cheaper meter) which only reads "F" manually from 20n scale (200 pF miinimum) to 200 μF max scale, 1.99 mF max C.

    2200 μF cap reads around 300-400 nF (0.3μ<>0.4μ) on auto-ranging MT1879, and reads over-range (1) on the DT-9205-A.

    /Obviously out of circuit. to avoid false readings. :confused:;)

    Later (after sleep), I'll do the oscilloscope cap-value test, which I trust.
    I must check the Major-tech's 9V battery, although the "batt" warning does not display (yet).
    Last edited: May 28, 2019
    davenn likes this.
  9. FuZZ1L0G1C


    Mar 25, 2014
    Sorry, in above post, I stated that the ANENG DT-9205A DMM can read maximum 1.99 mF (1999 uF).
    This was an error on my part, as I seldom use this meter (mostly lives in car's boot).
    Looking up the specs in the manual, the displayed scale is the maximum for that scale.
    So this DMM ranges from 0.2 nF to 200 uF.
    Scope test temporarily on hold, until I complete running a proper ground/earth point to the workbench.
    (Very Noisy trace).
    Will update..
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