No video/audio through Super CD-ROM² output

[Raulie]

Hi guys,

I bought a Super CD-ROM² with no sound, and when I tested it out there was no video/audio through Super CD-ROM² output.

If I connect the A/V cable to the Core Grafx, the games play perfectly, but obviously with no CD audio. I’ve replaced all the capacitors and there’s no difference.

The volume balance IC (M51131L) has only 0.77V as supply voltage.

I would be happy, if I could fix just the audio. For video, I can have the RGB mod.

Any ideas?

Regards,
Raulie

[pnauts]

Here are the Values I measured once for a fixed one:

1: 8V (V supply)
2: 3.4V (input 1)
3: 3.1V (output 1)
4: 5.52V (Vréf)
5: 8V (Low pass filter)
6: not connected
7: gnd
8: 5V (volume control)
9: gnd
10: 2.8V (Balance control)
11: gnd
12: 5.52V (wire to 4)
13: 3.1V (output 2)
14: 3.4V (input 2)

It seems that you have to check the traces on your supply pin.

[Raulie]

Thanks for your response pnauts!

There was a broken trace between C305 and R306. Now, I have video, but still no audio.

I've checked the values of every pin and now they're pretty similar to your values:

1 = 7.97V
2 = 2.96V
3 = 3.09V
4 = 5.58V
5 = 7.70V
6 = 0V
7 = 0V
8 = 4.92V
9 = 0V
10 = 2.72V
11 = 0V
12 = 5.58V
13 = 3.1V
14 = 2.95V

At least, now I know that the M51131L is fine.

[Raulie]

I turned up the volume, and there's sound! Low crackling sound though.

I read that was your problem pnauts. So, I think I just need to clean the pcb. Let's see...

[pnauts]

Check pin 4 on CN103 connector, the voltage should be as low as possible to 0V. According to the result, probably the 1000µF capacitor next to the heatsink leaked on a via located under this cap.

[Raulie]

Hmm... Right now, it's 1.02V. I removed that cap, and it was pretty clean. I cleaned it again though.
It made no difference.

I'm going to verify all the traces related to that pin.

Thanks!

[pnauts]

you should have twice less minimum at cold, and a decrease as soon as the time goes by.
Follow the trace from the via under the cap and clean it, there is perhaps another issue.

[Raulie]

What a maze! I finally found where pin 4 is connected. It's connected to 2 diodes, which are connected to some transistors, near the 1000µF cap:



That's it for today... LOL!

[pnauts]

I should have a complete scheme for this one, but I can't have a look before next week.

[Raulie]

I got desperate, and I washed the pcb using a hose, a toothbrush, and Palmolive. Now, the sound is perfect! 

[thesteve]

lol
dishwasher works too

[pnauts]

I think it's better to use isopropylic (exact english name?) alcohol, but nevertheless it works.
I hope for you it'll keep this way.

[thesteve]

sadly alcohol doesnt work as well as high temp detergent

[pnauts]

mmm... I would worry about cleaning old parts this way for long terms issue (porosity ? humidity ?) perhaps for no reason

[thesteve]

Porosity is one reason it's necessary

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