He visto ese fallo antes, y las conclusiones a priori son que tu Dreamcast se ha suicidado. Os cuento...
Al conectar la DC hace los sonidos clásicos, es decir hace booting perfectamente y ademas carga los gd/cd con absoluta normalidad, con la unica excepción de que no muestra ni audio ni video. En una palabra la consola funciona pero el A/V está kaput.
De mano podriais revisar todos y cada uno de los pines del conector A/V de la DC, ya no se trata simplemente de limpiarles la roña que acumulan sinó de comprobar uno por uno que tienen continuidad y que no estan doblados, sueltos, rotos.... etc
También no estaría de mal probar con varios cables y de paso alguna VGA / Box para DC.
Otra cosa es sacar el audio desde las conexiones internas de la DC con eso se podría contrastar que aunque se saque la señal directamente de la DC esta misma continua con los mismos síntomas, es decir ... suicidio
Intenta hacerte con otra DC y esa déjala para piezas y repuestos así siempre alargarás la vida de tu DC, parece ser que el arm7 y el PowerVR2 tienen un problema en el bus de salida o bién el controlador se ha dañado, lo que no impide que el SH4 y la demás electrónica de la DC funcionase como si nada.
TROUBLESHOOTING
Dreamcast doesn't power on.
Check that the Power Cable is firmly plugged into the back of Dreamcast and also into the outlet.
Make sure your outlet works.
Make sure you are using only the Sega authorized Power Cable (part #MK-50158).
Firmly press the "POWER" button on the left side of Dreamcast.
There is no video and/or audio.
There could be a number of reasons for this. Check the following first:
Make sure the brightness adjustment on the TV is not turned down.
The Power Cable should be firmly plugged into the back of Dreamcast and also into a working outlet.
Make sure your TV is plugged into a working outlet.
Make sure Dreamcast and the TV are turned on.
If you're using the Stereo A/V cables:
Make sure the Stereo A/V cable is firmly plugged into Dreamcast. Make sure the other end of the Stereo A/V cable is correctly plugged into the audio/video terminals on the back of your TV: yellow plug to yellow video terminal, white plug to the white (left) audio terminal, and red plug to the red (right) audio terminal. If your TV has only one audio terminal, use the white plug in the audio terminal and leave the red plug unplugged.
Make sure your television input (Television/Video switch) is set to Video.
Only use a Sega authorized Stereo A/V cable (part #MK-50157), RF Unit (part #MK-50159), and Power Cable (part #MK-50158).
If your TV has more than one set of A/V input terminals, try different A/V input terminals. Make sure to set the TV to the correct auxiliary setting. Refer to your television's operating manual to ensure you have made the proper settings. If necessary, try different A/V input terminals. When doing this, be careful of electric shock. Unplug both Dreamcast and the TV before checking the plugs and terminals.
If you're using the RF Unit:
Securely plug the TV OUT cable from the RF Unit into the TV and the A/V IN cable from the RF Unit into the A/V OUT terminal located on the back of the Dreamcast console. Make sure to set the TV to the correct channel.
There are unusual /images or characters on the screen.
Turn off your Dreamcast and do the following:
Try reconnecting the controller.
Make sure all system connections are firm and correct. You may want to try reconnecting the A/V cables or RF Unit and the power cable.
Re-seat the game disc on the spindle, label side up.
Make sure all controller peripherals (i.e. Jump Pack, VMU) are seated firmly and correctly.
Make sure you are using only Sega authorized accessories. Unauthorized products may not be fully compatible with Dreamcast.
The Date/Time or Language settings reset each time Dreamcast is started.
The rechargeable battery has lost its charge. Power on your Dreamcast and leave it on for at least two hours to charge the battery. If that doesn't do it, the rechargeable battery is likely dead. To have the battery replaced, please follow the directions for repairs before sending or bringing your Dreamcast to an authorized Sega repair center.
Dreamcast does not work with my TV even though other game consoles do.
Make sure the auxiliary channel is set up correctly on the TV. Consult your TV user manual for details.
RF Units that were intended for other game consoles may not work. Use an authorized Dreamcast RF Unit (part number MK-50159), which was not included with the Dreamcast. It is available for purchase at
http://www.sega-parts.com.
Dreamcast is too hot to touch.
Your Dreamcast is not cooling effectively. The first thing to do is to turn off Dreamcast and unplug it until it cools down. Then check the following:
Make sure the air holes and vents in the back and side of the Dreamcast are not blocked.
Make sure that the Dreamcast console isn't near anything hot, such as a heater, or on top of a TV.
Make sure Dreamcast is placed in a flat location.
Make sure that air is coming out of the fan vent on the side of Dreamcast. If no air is coming out, shut Dreamcast down. The fan may be broken and need to be repaired.
Error message: "This game does not support the A/V cable currently connected to the main console. Turn off the power and replace the cable."
The software does not support the type of A/V cable currently connected to Dreamcast. This usually occurs when you are trying to use a VGA Box on a non-compatible game.
Please remove the A/V cable you are currently using and replace it with the Sega authorized Stereo A/V cable (part #MK-50158).