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Re: Dreamcast Black Screen - No Audio or Video
Posted: Fri Mar 26, 2021 11:26 am
by nononymous
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.
Re: Dreamcast Black Screen - No Audio or Video
Posted: Fri Mar 26, 2021 3:09 pm
by ShadowGeist
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 .
Re: Dreamcast Black Screen - No Audio or Video
Posted: Sat Mar 27, 2021 5:10 pm
by ShadowGeist
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!
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...
Re: Dreamcast Black Screen - No Audio or Video
Posted: Tue Mar 18, 2025 8:15 pm
by victorstk
ShadowGeist wrote: ↑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!
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...
is there another way to fix this? I don't want to cut a trace on my dreamcast just to find out that the fan was not a problem
I'm having the same issue, I turn it on, at the first time i could see the logo for a few seconds then black screen, the vmu beeps and shows nothing, and the gdrom tries to read a disc but stops quickly
I have checked the PSU and the voltages are correct, I have tried resoldering the fan connections and they're fine too, I have checked the mother board and there's no "long screw damage" to the traces
I think this one is dead for sure
Re: Dreamcast Black Screen - No Audio or Video
Posted: Tue Mar 18, 2025 9:58 pm
by xzer0PL
Just do it. It is high chance that is only fan issue. Cut trace, put short wire. If vmu is working, there is logo that means processors are ok.