Persistent Dreamcast Issue in 2023: Black Screen with Working Audio - Seeking Solutions. SOLVED!!

[megavolt85]

ZD - zener diode
FL - filter

[CrisMod]

ZD - zener diode
FL - filter

Sorry Megavolt85 , where they are? Do you mind to guide me a bit more with infos, please.

In mean time, I don't know if the below informations are relevant but with Thermal Gun I have around two resistors more hotther about 8/10 °C.

Please, watch the below pic.

[megavolt85]

this is not resistance, these are filters, those that heat up are marked FL401 and FL402

[CrisMod]

this is not resistance, these are filters, those that heat up are marked FL401 and FL402
Снимок экрана от 2023-10-08 20-23-20.png

Thank you for the info megavolt85!!

I will check it tomorrow , this part it's what you were referred to me about ZD - zener diode and FL - filter? Or I also should check some where else?

[megavolt85]

There is nothing else to check, if the problem is not in the filters or zener diodes, then the problem is in the DVE (IC401)

[MoeFoh]

Double-check IC401 for bridges or poor solder joints. Reflow if needed.

IC401

[CrisMod]

I've done it!!!!!!!!!!!!

Thanks to the guidance and assistance of megavolt85, I've finally resolved the persistent issue with my Dreamcast. Hooray!

First and foremost, the problem was tackled by replacing the IC401 chipset, as advised by megavolt85. IC401 is responsible for the video output, and as megavolt85 cautioned (seriously, be careful to avoid any shocks), the chipset instantly burned my finger, indicating it was completely dead. When replacing it, I used a hot air soldering gun due to the age of Dreamcast motherboards, which are now approaching 30 years old. Extra caution is paramount with these vintage components.

While redoing the soldering, before attaching the IC401 pins, I noticed that some solder joints had detached from the pins. This caused flickering and strange lines on the screen, sometimes with small black circles in the background.

As megavolt85 rightly suspected, the problem might have something to do with the ZD - zener diodes. Upon further research, these diodes seemed responsible for interlaced and progressive video output, refresh rates, and more. Before replacing the ZD - zener diodes above and below the motherboard in the IC401 area, I used a macro camera to inspect IC401. With the macro, I noticed that in certain areas of the newly soldered IC401, some solder bases had shifted outside the pins of the chipset, potentially causing poor contact. I've attached a photo below as an example.

Indeed, by resoldering the bases and bringing them closer to the IC401 pins, the Dreamcast sprang back to life, eliminating those pesky flickers and image misalignments, along with the black circles in the background.

But I still had an issue with incorrect color tones, and the FL401 and FL402 (FL - filters, as megavolt85 taught me) were running hotter than the others. Before proceeding with replacing the FLs (hoping it was just that), I noticed that the solder joints on the side of the filter had ground connections, as indicated in the circuitry technical sheet sent by megavolt85.

These ground connections had a severe lack of solder and showed signs of aging. So, I thought one of the issues might be the aging filters with potential cracks in the solder joints (before replacing them). What I did was add solder to all the filters in the video area. I observed that the solder had adhered to all four corners and was much more visible. Crossing my fingers, I powered up the Dreamcast, and it returned to its former glory. I was ecstatic! The temperature difference I had previously experienced of 8-10 degrees Celsius (from the rest of the FL) had now reduced to a mere 1.5-2 degrees Celsius. The image now displays perfectly, as shown in the photo below.

What can I say? The Dreamcast is undoubtedly showing its age, and we must face unexpected challenges. However, with the help of special individuals like megavolt85, I can continue to enjoy my cherished console endlessly. Thank you infinitely.

Possible Cause of the Problem:

The issue seemed to have arisen from frequent cable changes between my various monitors and my Dreamcast. Given my penchant for experimenting and testing, I found myself swapping cables quite often.

Using cables from the Dreamcast to VGA connections, I noticed that they were slightly stiffer, and the act of connecting and disconnecting them multiple times might have strained the solder joints in the Dreamcast's video connection. Then, the unfortunate incident occurred when, with the Dreamcast powered on, I disconnected a cable to connect it to another test TV. It's possible that amidst the various bends and flexes the motherboard experienced in that area, the solder joints began to crack. Additionally, the cable, in its unplugging process, may have inadvertently caused a pin cross, potentially damaging the IC401 chipset. Alternatively, it could have simply succumbed to the effects of aging circuitry, which is an unfortunate reality we face with these aging consoles.

[CrisMod]

Double-check IC401 for bridges or poor solder joints. Reflow if needed.

ic401.png

Thank you, MoeFoh. Yes, in the picture, it may appear to be a soldering in that area, but it was actually the flux that created this translucent effect with the angle of the picture. As I mentioned earlier, I've already addressed this in my explanation above. Thank you.

[megavolt85]

Using cables from the Dreamcast to VGA connections

Let me guess, are you using a Chinese VGA cable?
the problem is that the Chinese cable does not have coupling capacitors, which are needed to prevent DC voltage from passing through, never connect such a cable with the console or monitor turned on

[CrisMod]

Using cables from the Dreamcast to VGA connections

Let me guess, are you using a Chinese VGA cable?
the problem is that the Chinese cable does not have coupling capacitors, which are needed to prevent DC voltage from passing through, never connect such a cable with the console or monitor turned on

I can't hide anything from you, you're the wikipedia of Dreamcast (WikiDreamcast) .

Yes, exactly, I use a Chinese VGA adapter which apparently seems well made but as always, they are always hiding something.

So, in this case, surely when I changed the cables in between the 2 Monitor/TV and console turned on caused the chipset to fry.