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Can you help me find the right Operational Amplifier for vintage sampler looking at the schematics

Discussion in 'Troubleshooting and Repair' started by ssyniu, Aug 8, 2019.

  1. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Hi guys I wasn't posting here for a while but would you be able to look at the schematics and help me to find the right Op Amp for this (Akai MPC 3000 sampler)

    here is the schematics:
    https://imgur.com/a/OBmLWFJ

    We are looking at the record in.Which one is the Op Amp??
    I would appreciate your help very much
     
  2. Ylli

    Ylli

    193
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    Jun 19, 2018
    davenn likes this.
  3. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Hi hank you for your help
    Is it going to be the same for both channels? Left or right?
    Well I just posted on the MPC 3000 page on facebook and one of the members told me it must be OpAmp.
    The problem is when I am recording in (sampling) one of the channels (i can remember which one) is distorting and it doesn react to the record in potentiometer when i am trying to lower the record in volume
    When the secon one is working perfect it doesnt distort and i can set the level with record in knob no problem.
    Thank you for your help
     
  4. 73's de Edd

    73's de Edd

    2,643
    1,074
    Aug 21, 2015
    Sir ssyniu . . . . .


    You sort of short changed us on the schema you submitted, but do duly note that there are 3 series cascaded op amps plus an initial
    differential pair of op amps involved in your Right and Left analog amplifiers processing. Not JUST the one that you gave.
    Then, they hand off the amplified audio signal to a pair of A/D converters . . .never to be HEARD by you again . . . . . until its D/A converrsion.

    How would you like to analyze your dilemmna, without having to buy . . . .NUTTIN' . . . . . . . for testing . . . . . considering you have a pair of test leads with clips on their ends and a 0.1 thru 1 ufd test capacitor.

    Initially, do your home work, and plug in and test both R and L channels to positively confirm, WHICH one is being the problem channel.
    Then, using the confirmed good channel, additionally run SW101 thru its three positions to confirm that all work properly on playback of that testing.
    When you come back with the good channel, I will proceed on procedurials.

    RELEVANT REFERENCE SCHEMA SNIPPET . . . . .

    upload_2019-8-9_5-30-17.png



    73's de Edd . . . . .


    Map Quest really - really needs to start their directions with about # 5 . . . . . . since I'm pretty sure I know how to initially get out of my neighborhood.
     
    Last edited: Aug 9, 2019
  5. Ylli

    Ylli

    193
    34
    Jun 19, 2018
    The problem you describe is not likely a bad opamp. Might be a bad switch SW101, or other component.
    Ssyniu, I'll leave you in the very capable hands of Edd. I suspect he is going to use the good channel to signal trace the bad channel.
     
  6. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Its a left channel that is faulty (I recorded this video of my mpc)



    I wish but I can't understand what are you saying here:

    Would multimeter do the job???

    Sorry for "short changing" sir 73's de Edd ;-).

    [Mod edited for clarity -- please learn how to quote :) ]
     
    Last edited by a moderator: Aug 10, 2019
  7. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Thank you
     
  8. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    OK the SW101 checked and works properly for the right channel the left is distorting despite the position of the SW101

    No I don't have leads nor the test capacitor,but I can borrow a multimeter from my friend.
     
    Last edited by a moderator: Aug 10, 2019
  9. 73's de Edd

    73's de Edd

    2,643
    1,074
    Aug 21, 2015
    Sir ssyniu . . . . .

    Working with :

    OK the SW101 checked and works properly for the right channel
    the left is distorting despite
    / irregardless of / the position of the SW101

    and
    but I can borrow a multimeter from my friend.
    The most that might possibly do is to permit you to leave the record inputs without any input connections , and then you place the DVM in its DC voltage test mode with Black negative probe to ground and then use RED positive probe to test the same circuit points on the Right and Left channels to see if there might be a noticable difference between their voltages.
    OR you could test in differential mode, where you place a + lead on one identical circuit point of one channel and the other probe on the same circuitty point on the other channel. THEN if the voltages are being the same, no meter reading will be perceived.
    But if there is being a difference in levels, then the voltage difference will be READILY seen.



    So . . . . . its confirmed, that the units right channel is the one that is working properly.
    If you look at the marked schematic you can see that the signal comes in at the RIGHT input jack at the top right corner and proceeds towards the left, through 4 stages of amplification, until it finally connects to pin 27 of the large IC106 at the far left..

    I have maked the three different increasing levels of the audio signal as it passes from the right to the left with Right 1 . . .Right 2 . . .and Right 3 labelings.
    The same is being done with the Left channel with its Left 1 . . .Left 2 and Left 3 and its signal passig into pin 2 of that same IC 106.
    Now I don't know how that unit was being connected for your testing, with you pushing buttons for changes, as I was expecting two connectors being plugged into those two RIGHT and Left Record input jacks . . . . which they might be, but I don't relate that to the button pushing audio test session.
    Additionally, I was expecting a stable 400~ or 1 khz or middle C, audio sine wave test tone instead of that whiz-whomp-bang -whirrr-thump muzik.
    BUT if the Left channel is just being dead, instead of having some degree of distortion, I guess that a no audio at all fault, is certainly being detectable.

    You certainly will need to find a source of the mentioned range of permissible values of a paper or ceramic or poly cap, that would exhibit almost no degree of DC leakage as an electrolytic capacitor would.
    So you need to think of any of any electronics that you have that could supply a salvaging and temporary use of one of those caps.
    OR you may have electronics inclined friends that could loan you one, or you buy one from a local supplier or a contact ham radio person, possibly for a freebie.
    The clip leads just enable you to clip that capacitor into circuit, with out you having to solder it in.
    HOWEVER, considering that you are being a soldering person , two adequate length wire leads, used as exttensions to the caps leads and two end solder connection into solder points in the circuit . . . . would then get your capacitor connected into circuit.

    HERE IS YOUR TEST CONCEPT:

    You now know that all is being correct with your right channel performance, so we will use it to ADDITIONALLY inject its GOOD audio into specific, like level test points of your quirky Left channel.
    You would have an audio input going into the units RIGHT record input jack and, initially, we go way down to its extreme end at marked on R3 test point.
    Your Left record input jack, you leave without any thing being plugged into it.
    You connect our required capacitor between R3 and L3 test points.
    Now when you do a test recording session, the good audio of the RIGHT channel will pass down, just as it always did, but will ADDITIONALLY cross on over, thru the test cap, to also feed its good audio signal, into the A/D input of the IC102 at its pin 2.

    If all is well in your test recording session, the right channel should still record good as expected, BUT additionally the Left channel audio should also be good, since it was ACTUALLY being the flawless RIGHT channels audio.

    Considering that being a successfull testing, you would then move the test cap from where you had it , to then being between R2 and L2.
    Do the same test recording procedure, if it is successful, you then have eliminated Left channels IC 105 as not having a fault.

    If all is well, then you move the test capacitor between R1 and L1 to see if 1/2 of IC 104 is being good.

    I stop at this point for feed back or any ?'s from you . . . if so being needed .

    OBSERVATION . . . .
    On your units display . . . the right halfs brightness appears to me, to be appreciably brighter than the left side.
    Assuming that incand lamps or LEDS might be used for backlighting illumination, the left side might have an outage.

    73's de Edd . . . . .


    HEY ! . . . All you AUSSIE fellers . . . . REMEMBER ! . . . . .that in the dreaded Australian outback . . . . anything that doesn't eat you TODAY, is merely saving you for tomorrow.



     
    Last edited: Aug 10, 2019
  10. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Its called funk

    Right so I need to get capacitor
    I will come back on this.

    Tank you so much Incredible help sir Edde


    [Mod edited to show quoting]
     
    Last edited by a moderator: Aug 10, 2019
  11. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Sorry Ive missed this one:
    β€œOn your units display . . . the right halfs brightness appears to me, to be appreciably brighter than the left side.
    Assuming that incand lamps or LEDS might be used for backlighting illumination, the left side might have an outage.”

    This is quite old recording at the moment the backlight is completely gone from sometime appreciate your help friend I will do the test and comeback with the feedback.
    All the best
     
  12. Ylli

    Ylli

    193
    34
    Jun 19, 2018
    Edd, I think this is an artifact of the external lighting. The left side of the display brightens up when he pans the camera to the left.
     
  13. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Manage to get this one.
    Is it good (for the test)?
    https://ibb.co/X5028hC
    Just need to get crocodiles ;-) hopefully I will get them today.
    All the best!
     
    Last edited: Aug 12, 2019
  14. 73's de Edd

    73's de Edd

    2,643
    1,074
    Aug 21, 2015
    " Just need to get crocodiles "


    I think that those, would be MUCH - MUCH too large for getting down into and doing any connecting . . .mini clips would be more in order . . . .

    [​IMG]

    or else, twisting on appropriate length stranded hook up wire leads to the cap leads and solder tinning the wire ends and temporarily solder tacking to the circuit test points.

    I checked out the units backlight lighting . . . . . and they are using . . . . NO . . . . . incand lamps nor LEDS, but a custom low voltage electroluminescent backlighting strip . . . . . now being categorized as . . . . .unobtanium.

    73's de Edd . . . . .


    Don't be so open-minded that your brains fall out.



     
  15. ssyniu

    ssyniu

    29
    0
    Sep 20, 2017
    Thanks for checking.Actually I was discussing this matter some time ago with one of this forum (inactive anymore) member and he suggested something like this to attach two rectangular LEDs (hot-melt glue) onto the edge of the LCD pcb (two at either end) and a simple series resistor"??? Or I have also option to get one of this when I am done with the recording issue with which you are helping me at present:
    https://www.ebay.co.uk/itm/AKAI-MPC3000-and-MPC60mkII-LED-SCREEN-LCD-display-NEW-LAST-TWO-LEFT-LOW-PRICE/253905983249?hash=item3b1df9d711:g:QQoAAOSwTmtZ6Hwi&fbclid=IwAR1eCciaGecXixR8TFpsFZqoDRSyfCMo63QheSUeCq0Bs4VvORpyFPD6SnA


    Probably I will choose the first option and ask local engineer(the guy who is fixing the TVs basically) if he can do that to fit those LEDs and "use a resistor to suit both the LED/colour chosen AND whatever power pick-up point they chose from the internal circuitry".

    What do you think about this idea by the way??

    All the best.
    Ill comeback as soon as I got the testing done with the feedback.
    All the best sir 73's de Edd
     
    Last edited: Aug 14, 2019 at 8:01 AM
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