Sanyo M9998K audio fault - random crackle and boom noises

My second M9998K was given to me by local member Dan. It had a dead right channel that was fixed with a switch and pots clean. Unfortunately, it has now done the usual Sanyo thing and developed another fault.

This audio fault occurs on all modes including tuner, deck and RCA line in. On low volume, the random 'crackling sounds' occur. As you turn it up, the 'booming sound' kicks in - very loud and annoying. Originally, only right channel was affected but it's now occurring on both channels. All switches, pots and connectors have since been cleaned including the tuner and amp board interface connectors but with no improvement. Both amp chips have also been reflowed. Flexing the main board or tuner board can cause the sound to worsen.

I'm pretty keen to find the cause of the fault as today, I've discovered my number 1 fully working M9998K has developed the same fault! :-(

Any ideas??

Quick video demo of fault: https://m.youtube.com/watch?feature=youtu.be&v=r8pdmGbAtQA

A couple possibilities.

A- check the voltage at the amp chips during operation and see if chips are getting adequate voltage without droops.

B- check the amp chips, they might be toast. I once fixed an M70 for redbenjoe that was like that. Replacing the output amp fixed it. Did you check the line-outs and does the output signal sound clean or the same? If line out sounds good, then bad amps possibility is reinforced even more.

Superduper said:

A couple possibilities.
A- check the voltage at the amp chips during operation and see if chips are getting adequate voltage without droops.
B- check the amp chips, they might be toast. I once fixed an M70 for redbenjoe that was like that. Replacing the output amp fixed it. Did you check the line-outs and does the output signal sound clean or the same? If line out sounds good, then bad amps possibility is reinforced even more.

Click to expand...

Hi Norm,

On line out, the output level is very low and the crackling sound is still there. You can make the sound get worse by gently flexing either the tuner or main boards. It occurs on all function modes.

I'm getting ready for bed as it's almost 2:00 am here, but I'll take a look at the circuit diagram when I get a chance tomorrow, although if you think that flexing the board is related, you may wish to reflow all solder joints. On the other hand, the main and tuner boards, in addition to all the cabled connections also has a couple of board mounted connectors which if I recall, are jointed at 90 degrees. Flexing either of the boards might really only have accomplished to deteriorate the connectivity at the joints and those 2 boards need good connections to function at all... just ask Royce. Based on your symptoms, you need to look for something common to both channels and since the problem seems fore of the output amp, then it may be related to a preamp, perhaps an IC if it is a dual-preamp? Less likely if the preamp chips are mono since that means both chips would need to be bad which while not impossible, is less likely than a single culprit common to both channels.

Never had a hum issue with M9998.

The connector I had issue was mounted on the boards. Female connector was on the amp board and male on the tuner. The rest were all flexible connectors and ribbon wires.

This hum could be from some ground lead malfunction. That is a general statement!

James, you know better!

I would check the leads of the chip that is connected to the heat sink, and that area of the board.

Have you tried batteries in unit? Possible AC hum may be going on.

I would also check the power supply filter caps.

I've amended the thread title to better reflect the strange noises this box is making - 'Crackle and boom'.
I've tried it on 10Ds with the same fault evident. I've reflowed the two amp to tuner board connectors with no improvement.

My huge pile of messed up Sanyos is growing!!

Who wants an instant Sanyo collection?

jimmyjimmy19702010 said:

I've amended the thread title to better reflect the strange noises this box is making - 'Crackle and boom'.
I've tried it on 10Ds with the same fault evident. I've reflowed the two amp to tuner board connectors with no improvement.
I've waisted more time trying to fix Sanyo stuff than all other brands combined!
Who wants an instant Sanyo collection?

Click to expand...

Meeeeeee!!!!

They say that Sanyo gear sounds best. Well, I agree but none of my present and past Sanyos are reliable enough to listen to!

Probably a dumb question but have you tried using headphones?

Yes Bill. The headphone and RCA outputs have the same issues.
It's more and more sounding like a mechanical connection issue.

jimmyjimmy19702010 said:

My huge pile of messed up Sanyos is growing!!

Who wants an instant Sanyo collection?

Click to expand...

I also have a pile that is growing!
Now I get some sleep after putting one Sanyo away from me!
Always forget to enjoy other nice boxes and struggle with the ones that got issues.

I got four sanyos and not a single one works right. Actually lasonics have been my most dependable boxes. 2 of my lasonics fell from 7 feet high and smacked into the floor and both still work even though they are held together with jb weld lol.

JVC Floyd said:

I got four sanyos and not a single one works right. Actually lasonics have been my most dependable boxes. 2 of my lasonics fell from 7 feet high and smacked into the floor and both still work even though they are held together with jb weld lol.

Click to expand...

I agree!
I have one Lasonic 975 and I love it!
Very easy to work on.
For belt replacement, it is the easiest box ever made.

My most reliable brands by far: Hitachi & Panasonic closely followed by JVC & Sharp.

The so called 'non-premium brands' have also proven easily repaired! Conion C100Fs and JC2000s always seem to be easy fixes.

The Sanyo M-X series have been ok for me with 2 out of 2 proving easily fixed and reliable.
'M' series Sanyos are currently at 4 out of 4 fails.

jimmyjimmy19702010 said:

My most reliable brands by far: Hitachi & Panasonic closely followed by JVC & Sharp.

The Sanyo M-X series have been ok for me with 2 out of 2 proving easily fixed and reliable
'M' series Sanyos are currently at 4 out of 4 fails.

Click to expand...

M stands for Misfortune!

I don't know but I've always been lucky with any of my sanyo's/Fisher's.

Jimmy, it really sounds to me like you have a voltage issue. This can be caused by some circuit failures (maybe a voltage regulator) or connectivity issues (wires, connections, solder joints, and trace fractures, etc.)

If this was my boombox, the first order of business would be to first confirm that critical circuits are getting proper voltages starting at the preamp stages. And I'm not talking about tone controls when I say preamp. I'm talking about all the stages before the line-out connection. You can see where I'm talking about by reviewing the block diagram.