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1982 Ibanez Musician MC924 Polar White

Discussion in 'Basses [BG]' started by ROWFOUR, Jul 15, 2014.


  1. ROWFOUR

    ROWFOUR

    May 1, 2013
    Good day to all!

    I'm a new proud owner of an '82 MC924PW.

    All original with a few dings and minor scratches.

    It's an awesome sounding bass in my opinion that's even with the active EQ not working.

    Do you guys have any suggestions on new replacement preamp brands/model? I think an OE Ibanez preamp is out of the picture in this case.

    Thanks as always.

    row
     
  2. Red Four

    Red Four

    Apr 4, 2011
    Missouri
    Any chance that Ibanez would repair something like this? A for-pay version of what might have been warranty service at one time?
     
  3. ROWFOUR

    ROWFOUR

    May 1, 2013
    I've inquired to Ibanez website and still has not heard from them. They do have the EQ B II/III pres available but not to the exact configurarion of the original.

    I'm a beginner bass player and very happy with the tone right now. Am sure it's even better with the EQ working.

    Thanks for the input.


    row
     
  4. Abner

    Abner

    Jan 2, 2011
    Mississauga
    Any competent electronics tech. should be able to fix it. They're not terribly complicated, and schematics for it are freely available on the web.

    First, check to make sure all the wires are connected (in the right places, of course), and if there's nothing obviously broken, start with replacing the I.C. That's really the only part that could go south and stop the thing from working. Simple dual op-amp, if I'm not mistaken.

    -Alex
     
  5. ROWFOUR

    ROWFOUR

    May 1, 2013
    Sweet. Thanks.

    I'll bring it to my trusted local tube amp tech for some basic troubleshooting.

    So far, what I have done was just checked the contacts on the connector of the board. Wires are intact, I'll check if they're on the right place though.


    row
     
  6. ROWFOUR

    ROWFOUR

    May 1, 2013
    I traced the wires and they seemed to be at the right place per the schematic.
    I noticed Green ( labeled "j" ) wire is not connected to anything, by design?

    I'll bring the board to a tech to be looked at. image.


    Thanks.


    row
     
  7. Abner

    Abner

    Jan 2, 2011
    Mississauga
    Hmmm... I don't see another "j" on that diagram, either. If you can wait a bit, I can open up my '82 MC-940 and check mine. I'll try and do it later today.

    Oh, the other thing possibly worth checking is the two diodes on the output jack (both IN4148, labeled "D" in the diagram). It's not your typical stereo jack normally used to switch actives on, as this was designed to be used with an external power supply using a stereo cable from the bass to the external supply. The diodes simply isolate the battery from the external power supply voltage (if used), but also allow the battery to be used if a regular mono cable is used and the ring is grounded.

    -Alex
     
  8. Abner

    Abner

    Jan 2, 2011
    Mississauga
    Well, Row... good news and bad news. The good news: I too have the green wire coming from one of the preamp board connectors and it goes nowhere, so it seems your wiring is correct. The bad news: since it seems your wiring is correct, you have another problem.

    After opening mine (for the first time in many years) I did notice that the foam rubber sheets used for insulation and "rattle control" have seriously deteriorated. They are falling apart and I will have to find a replacement material. So after seeing this, it occurs to me, maybe yours has also deteriorated, perhaps to the point that some portions of the EQ board are shorting on something else? One of the pots or switches, or the shield can?

    Anyway... I'll see if I can come up with a rudimentary schematic from the PC board. I'm pretty sure it is identical to the EQ found in some Ibanez guitars of the era, such as the AR500, for example.

    -Alex
     
  9. ROWFOUR

    ROWFOUR

    May 1, 2013
    I really appreciate your time and energy looking it up.

    The foam insulation on mine is still intact. It may have been replaced before since it's now a closed foam material. I did checked the leads on the board and didn't found any obvious shorts or burnt out caps/resistors.

    Thanks again.


    row
     
  10. Abner

    Abner

    Jan 2, 2011
    Mississauga
    MC-924 eq (1982). Hey, Row: Just as I thought, the Ibanez AR-500 guitar schematic I found seems to be virtually identical to the preamp in my '82 MC-940. I've modified it slightly to show the connections to the external components, labeled and colour-coded as per the wiring diagram you already have.

    Ignore this paragraph, see below: Take note that some of the values are different, and I didn't bother changing the diagram (yet), but I'm sure it's just the LCR values in the actual eq. section (tuned for bass rather than guitar), and I grayed out a pot that is not used in the bass version (that's the unused green wire).

    With this schematic, any competent tech. should be able to get it up and running. Let us know how it turns out.

    -Alex

    Edit: I have updated the image to show the values actually used on the basses rather than the guitars. Inductor, capacitor, and resistor values in the actual e.q. section are slightly different.
     
    Last edited: Aug 25, 2014
  11. ROWFOUR

    ROWFOUR

    May 1, 2013
    Thanks again, Alex.

    I brought the bass to a guitar repair shop, they've contacted Ibanez, it took days for an answer then was advised with a Bartolini replacement.
    I mainly play drums and have not had any experience on after market pres for a bass, I like them stock.

    The tech confirmed that it would be a straight swap, no additional pots or switches.

    Since I can't compare the tone of the original pre, I'm hoping that the Bartolini will sound good.

    Thanks everyone!


    row
     
  12. Abner

    Abner

    Jan 2, 2011
    Mississauga
    Without even attempting to swap the one 8-pin chip on that board? Sounds to me like they just want to make a sale of a new preamp. I'd be looking for a different tech.

    Good luck with whatever you decide, and hope you getting it working one way or another.

    And still, would love to hear the outcome however it goes. :)

    -Alex

    Edit: Oh, and if you decide on a new preamp, think about sending me the original one. I'm sure I can fix it.
     
  13. ROWFOUR

    ROWFOUR

    May 1, 2013
    My apologies.

    Let me clear it up a bit, the OE pre and pots will be replaced and the wiring will be redone. All original parts will be kept in case I found a working preamp or when I get the original fixed.

    Should be the same configuration when done, per the tech.

    Still a good idea? Or find a different tech or different route?

    Thanks.


    row
     
  14. wvbass

    wvbass Supporting Member

    Mar 1, 2004
    West Virginia
    Pots, electronics, blah, blah blah. This thread is two weeks old and still has no pics of an Ibanez MC924 in Polar White. This thread should be closed on that basis alone.
     
    punchdrunk likes this.
  15. Abner

    Abner

    Jan 2, 2011
    Mississauga
    But... it has diagrams of her innards! All nekid, like! :D
     
  16. Abner

    Abner

    Jan 2, 2011
    Mississauga
    Row, I guess it's up to you. Replacing the entire preamp, harness, and pots may be the sure thing, and heck, it might even sound better than the original. But I bet that's also the more expensive option.

    The other criteria is if you want to keep it original (personally, I think that option is overrated in some cases, but not all), then I still think fixing this one is worth it, and cheaper than replacing the whole harness.

    Take the P.C. board to an amp technician, ask him how much to replace the op. amp. If it still doesn't work, you're only out a few bucks.

    (I'd post another pic of mine, but I don't have a white one.) :(

    -Alex
     
  17. ROWFOUR

    ROWFOUR

    May 1, 2013
    Ha! I hear you wv.
    I'll post the photos as soon as I get the bass back, hopefully by Monday.

    Total investment would be ~$500, including the new Bartolini pre.
    Not sure of the exact model as of yet.

    Thanks.


    row
     
  18. DanAdams

    DanAdams Supporting Member

    Nov 3, 2013
    Maine
    As the proud owner of 2 mc924 basses I would not consider paying anywhere close to $500 for a new preamp. Mine both have good preamps and they don't add a whole lot.
    I would happily use it passively. Each of my basses with working electronics cost under $500 so that cost for a preamp only seems nutzo.
    For me I'm trying to find a suitable replacement for the bridge pickup. mine are noisy and as a sound engineer I want the bridge pickup to be dead quiet. I haven't found a good fit yet.
     
  19. Abner

    Abner

    Jan 2, 2011
    Mississauga
    Well, it depends. It's a 3-band eq. Some might find that useful. Earlier versions also had a variable boost.

    And $500 for a preamp? I was thinking the same thing at first, but...

    I think he means total of the used bass and a new preamp is around $500. That's not bad.

    (Still, I think it's worth a shot to replace the chip. Couple'a bucks for the part, a few dollars labour, and we're done. And it plugs right in, no rewiring necessary.)

    What's the scoop Row? Any progress?

    -Alex
     
  20. ROWFOUR

    ROWFOUR

    May 1, 2013
    Here it is. Picked it up as soon as I got back in town.

    Yes, total with repair is $500 and some change.
    image. image. image. image. image. image.
     
    Abner, wvbass, Pelham Bleu and 2 others like this.

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