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skate323k137

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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.
 
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are there any film caps involved - specially mylar ones?
 
I don't believe so. There are a couple ceramic caps in the support package. If you google PX4460 you'll find a repair log mentioning it. That little package chip seems to be very elusive.
 
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:

LA4460+Audio+Amplifier+Circuit.png


Then look at the PCB:

snowbros_toaplan.jpg


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.
 
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Now we're getting somewhere.

Snow bros seems to follow this schematic exactly:

12W%2BAF%2BPower%2BAmplifier%2Bfor%2BCar%2BRadio.png


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.
 
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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 LA4460 amplifier (mostly resistors and capacitors), the latter embeds an OP-AMP for pre-amplificatiom of sound
 

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Wow! Awesome work!

I think for this board since there are spots for all the components themselves I'll just eliminate the chip, but that is awesome news for other boards!
 
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)

20180122_135625.jpg


And here's a complete audio section!

20180122_141925.jpg


Time to go PLAY this game :D
 
I have a Snow Bros with this same issue, sound is working but really low so I removed the amp support custom and installed the discrete components - result is a massive improvement!

Thank you for the guide :)
 
I have a Snow Bros with this same issue, sound is working but really low so I removed the amp support custom and installed the discrete components - result is a massive improvement!

Thank you for the guide :)
Thanks for letting me know, it's always nice when a guide helps someone out. It certainly does sound nice with these parts.

Cheers!
 
Just did this same repair on an Air Buster that had low audio. The locations and labels of the parts were a bit different, but it fixed the issue and sounds great. Thanks for posting the details!!
 
That's why I did it. A trip to "the shack" is way easier than reversing an IC (not that reversing it is not the next logical step in case of missing traces). You are fully welcome and thanks for posting up to let me (or future people) know.
 
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.
 
I’d post this in a separate thread to get more exposure, but it kinda sounds like your video ground may have an issue.
 
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)
 
I don't think C10 is part of the amplifier circuit

It sounds like you've added an incorrect resistor somewhere if you're getting yellow instead of white where it was white previously. This mod shouldn't be changing any colours at all.
 
I have a snowbros boot I got today which has sound but it's low and very noisy. I can't find the Px4460 but can see a mb3712 near the audio circuitry... I'll work on this when I have some more time but I think even though I have a boot, I will find this forum post v useful. A lot of the components from a genuine board appear to be in place on this boot.
 
If you have a boot, then you just need to replace the caps in the audio section
Thankyou @xodaraP, but Tried that, same thing. The old caps were out by quite a bit more than their stamped % but volume still very low and no different to before.
The volume pot is functioning OK. I have some spare aliexpress audio amps, I could maybe try one of those instead, but it would be nice to use the original through-holes and keep it old school (albeit a bootleg)
 
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