Repair Log: Snow Bros PCB Audio (PX4460 removal/alternative)

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    • Repair Log: Snow Bros PCB Audio (PX4460 removal/alternative)

      Got a Snow Bros PCB in a trade a while back... it plays fine, but the audio has always been quiet. Like, really quiet. Max out the volume pot on my cabs that never go past 40% quiet lol.

      Anyway so far I have:

      Replaced all 4 electrolytic caps
      Replaced the 4558C Op-Amp
      Replaced the LA4460N amplifier
      Verified the amp is getting proper input voltage
      Checked the volume pot - it's labelled 10k but is only really 7k. But it runs smoothly and the (extremely quiet) audio follows it as expected.

      I'm really hoping it's not the PX4460 support chip for the amp. Mine is present, but I'm not sure exactly what it's supporting on the amp, or if it would cause this particular problem if it were faulty. Any insight is appreciated.


      EDIT


      This was fixed by replacing the PX4460, but not actually replacing it. Toaplan left traces and plated holes to use individual caps and resistors for the audio amp instead, so that's what I did. It's documented in the posts below.

      The post was edited 2 times, last by skate323k137 ().

    • stj wrote:

      are there any film caps involved - specially mylar ones?
      So actually it seems you are on to something, the manual for the amp recommends poly film caps so maybe that is what's in this kaneko chip.

      It seems like the board has alternate markings and PCB holes to do the same functions with individual components to replace the support package chip (PX4460). I wonder if that is the case. For example look at the schematic for the audio amp LA4460:



      Then look at the PCB:



      if you look, c16 c17 are marked for pf cap. then r20/r24 to ground. This follows pin 7 / 9 of the amp schematic.

      That covers pins 7 and 9 of the amp, with one pin for ground that leaves 2 pins on the support package for pins 4 and 5. Once I figure out the correct locations for those replacement components I'll probably give this a shot. It seems a lot of repair logs are looking for this support package, so this could be useful for others too.

      The post was edited 1 time, last by skate323k137 ().

    • Now we're getting somewhere.

      Snow bros seems to follow this schematic exactly:



      PARTS LIST:

      1x 1.5k resistor R25
      2x 4.7ohm resistors R20/R24
      2x 47uf axial caps C13/C15
      2x .033u poly film caps C16/C17
      1x .01u poly film cap C14

      With these you should be able to remove the PX4460 entirely and never need one again for this game.

      The post was edited 2 times, last by skate323k137 ().

    • I reproduced both PX4460 (and his "companion" LFP6K), I will receive bare PCBs in next days.
      The fist contains part of typical application circuit of the LA4450 amplifier (mostly resistors and capacitors), the latter embeds an OP-AMP for pre-amplificatiom of sound
      Images
      • LFP6K.jpg

        9.75 kB, 149×118, viewed 492 times
      • PX4460.jpg

        6.15 kB, 136×113, viewed 494 times
      • DSCN2472.jpg

        221.88 kB, 800×600, viewed 136 times

      The post was edited 1 time, last by caius ().

    • I'm happy to report my snow bros is alive, well, and no longer has any need for the PX4460.

      I used a bit overkill for voltage rating on the caps to say the least, but the audio is crisp clean and LOUD.

      In case anyone else wants to do this, the above diagram and parts list covers it, and here are pics to piece it together. Hopefully you order appropriately sized (smaller) parts.

      Here are all the thru holes to clear (only need to clear left most leg of the old PX4460, or it has alternate pad by marking IC53)



      And here's a complete audio section!



      Time to go PLAY this game :D
    • I just got the same board for 125 US. I am fairly new and it is my second board... other is just Neo-MVH MV1FT.

      I noticed that the brightness low and the screen is not crisp. I do not have a Supergun, waiting for RGB.... I just connected it to the shitty Jamma connector on the CMVS from Aliexpress.

      I will reply the Dip Switches and Capacitors soon.
    • That was exactly what i was looking for, thank you for sharing that.
      I have 3 Snow Bros, after the typical dram issues they have, i did this mod for the px4460 and i have found that all of them were working fine on the very first boot, then they just went mute like before...
      I also noticed that, strangely, the boot screen changes from white (with no mod) to yellow (after the mod).
      I have checked my work on all of them and i followed this method exactly as it should, but they just work the first time. I have not changed the amplifier and op amp but, could it be that on all of them??
      Also, position C10 was rated 470Uf but i just noticed that you installed a 1000Uf, but i don't think that matters (also diode on D1 is missing)