Dreamcast Black Screen - No Audio or Video

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nononymous
noob
Posts: 1

Re: Dreamcast Black Screen - No Audio or Video

Post#11 » Fri Mar 26, 2021 11:26 am

I have (mostly) the same issue : DC power up, boot screen appear with sound, power led, logo on VMU, fan and disc spin but then no output and disc stop spinning, and if i unplug and replug the controller, i have no more the logo (still power led and fan spin)

I have change the capacitor on the power supply, resolder the fan connector and the capacitor next to it but still the same issue.

and if i boot up the console without the GD-ROM Drive, i have a black image and them the Dreamcast logo for 1-2 sec and no signal again.

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ShadowGeist
undertow
Posts: 30

Re: Dreamcast Black Screen - No Audio or Video

Post#12 » Fri Mar 26, 2021 3:09 pm

nononymous wrote:I have (mostly) the same issue : DC power up, boot screen appear with sound, power led, logo on VMU, fan and disc spin but then no output and disc stop spinning, and if i unplug and replug the controller, i have no more the logo (still power led and fan spin)

I have change the capacitor on the power supply, resolder the fan connector and the capacitor next to it but still the same issue.

and if i boot up the console without the GD-ROM Drive, i have a black image and them the Dreamcast logo for 1-2 sec and no signal again.


Sounds all too familiar...

Read my post concerning IC601 in this thread HERE .

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ShadowGeist
undertow
Posts: 30

Re: Dreamcast Black Screen - No Audio or Video

Post#13 » Sat Mar 27, 2021 5:10 pm

IC601 is a Fail-Safe device. Interference between the fan tachometer and this chip will cause the DC to shutdown approximately 10 seconds after initial boot to protect components from possible damage caused by overheating even if the fan is running.

It's possible to diagnose an issue by connecting points located at R627 without cutting trace and testing.

Taken from Nold's guide...

Nold's Alternate Dreamcast Pinouts & Workarounds

Faking the FANs PWM-Signal
Why use Arduinos or 555's... damn... just use some solder!
Image
Some background: The DC uses IC601 (a multivibrator IC) as some kind of ADC (Analog-Digital-Converter), to convert the PWM-Signal from the fan (up to 2.5v), to 3.3v (= logical "true"). So when there's no fan, it'll put out 0v (= logical "false"). So all we need to do is pull-up the output signal of the IC & done! How nice Sega prepared this mod for us & gave us some free solder-pads.. (It might be safer to use a resistor here, but it should even work without the IC, anyway; also there is a capacitor, protecting a possibly connected fan.)

Controllers & RTC

Every pair of filters is for one controller. They are connected to pin 1 & 5 of the controller. DON'T remove these filters! (There are connections on both sides of them).
The RTC voltage is connected to pin 2 of the connector, using a 10Ohms 1W resistor. Don't use a 3.3v Battery here! (The Dreamcast uses rechargeable batteries).
Last we have the PWM-Signal coming from the FAN. It's required for the DC to boot, but we won't need it...
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