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Author Topic: Sound problem on Micro Genius famiclone  (Read 1302 times)
pirate
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« on: April 26, 2012, 07:04:05 PM »

Hello,

there is a sound problem on my Micro Genius IQ-502,it is a NOAC based famiclone.
Only on some games volume is  very low and also some weird sounds.
Is there a way to fix it?
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133MHz
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« Reply #1 on: April 26, 2012, 07:45:30 PM »

Are you testing through RF or AV? If you're using RF, the sound carrier might be misaligned, in that case try AV.
If it also sounds bad on AV, it could be any single one or a combination of these:

  • Faulty power circuitry (AC adapter, power switch, voltage regulator, filtering capacitors) causing low or dirty voltage which can muddy or distort the sound.
  • A bad capacitor or other passive component along the audio path from the NOAC to the Power/RF board.
  • A bad 74HC368 chip can cause severe audio distortion, usually worsening as the machine warms up.
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pirate
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« Reply #2 on: April 26, 2012, 08:34:03 PM »

First , thanks for help.

I use AV,there is problem only some games.Volume too low,and some games has weird distorted sounds.

Faulty power circuitry (AC adapter, power switch, voltage regulator, filtering capacitors) causing low or dirty voltage which can muddy or distort the sound.
AC adapter is original,i think other parts you mentioned original.Audio and video jacks opposite wired,is this caused a problem ?


A bad capacitor or other passive component along the audio path from the NOAC to the Power/RF board.
This is woth to check.


A bad 74HC368 chip can cause severe audio distortion, usually worsening as the machine warms up.

If it is,probably no way to repair.

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80sFREAK
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« Reply #3 on: April 26, 2012, 10:48:21 PM »

Quote
NOAC based famiclone.
Quote
74HC368 chip
Does not compute... Huh

2 pirate How old this unit? With "high quality" of clones anything is possible. Especially quality of el capacitors
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pirate
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« Reply #4 on: April 26, 2012, 11:47:14 PM »

From late 90's,not used much,it was NOS when i bought.
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80sFREAK
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« Reply #5 on: April 27, 2012, 02:10:44 AM »

Ah, that's it! Recap it first.(IMO doesen't worth)
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« Reply #6 on: April 27, 2012, 05:11:55 AM »

A bad 74HC368 chip can cause severe audio distortion, usually worsening as the machine warms up.

Actually this part caught my attention, I too have an old famiclone which makes squeaky (high pitched noises) sounds sometimes. Is there any explanation on why the 74368 should be distorting sound?
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« Reply #7 on: April 27, 2012, 09:24:56 AM »

maybe missing low-pass RC filter on sound circuit before the buffering stage. (you need to add a capacitor, value depends on which cutoff frequency you would like to built the filter.

as for me, i use 5 kHz cutoff frequency.

f = 1/(2*pi*r*c), where r - is the resistance, c - capacistance in SI units. Most of crappy famiclones/segamegadriveclones affected by this issue)

so, need very detailed PCB pictures of this famiclone where every track is recognizable.
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80sFREAK
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« Reply #8 on: April 27, 2012, 10:25:33 AM »

A bad 74HC368 chip can cause severe audio distortion, usually worsening as the machine warms up.

Actually this part caught my attention, I too have an old famiclone which makes squeaky (high pitched noises) sounds sometimes. Is there any explanation on why the 74368 should be distorting sound?
Explanation - mic in pad2 and non-shielded cable.
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pirate
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« Reply #9 on: April 27, 2012, 11:36:06 AM »

Thanks for all responds.
I will replace caps,but i cant understand why there is not same problem on all games ?
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80sFREAK
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« Reply #10 on: April 27, 2012, 01:06:55 PM »

How you can explain
Quote
weird sounds
Huh Is the sound distorted like volume overload? You should upload some sound samples(wav not mp3!!!)
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« Reply #11 on: April 27, 2012, 05:43:01 PM »

mp3 is enough
it depends on the game, because not of all games use DPCM sound channel
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« Reply #12 on: April 27, 2012, 06:24:54 PM »

A bad 74HC368 chip can cause severe audio distortion, usually worsening as the machine warms up.
Actually this part caught my attention, I too have an old famiclone which makes squeaky (high pitched noises) sounds sometimes. Is there any explanation on why the 74368 should be distorting sound?

The audio passes through one of the gates of the 74xx368 chips, most likely for buffering.
What I can't explain is why the '368 tends to fail in such a way to distort the audio as a result, usually getting worse as the system warms up. To date I've had three Famiclones with the same problem, replacing the '368 has fixed the problem in every single one of them.
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80sFREAK
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« Reply #13 on: April 27, 2012, 08:34:30 PM »

2 133MHz could you specify xx for 368' which gives a problem
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« Reply #14 on: May 02, 2012, 05:53:58 AM »

The audio passes through one of the gates of the 74xx368 chips, most likely for buffering.
Thanks I'll try to replace it in my famiclone!

@80sFreak - my famiclone doesn't have a microphone... actually I have never seen a famiclone with a microphone here in Europe.
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