Sega Master System on NTSC Model 1 MD/Gen — Intermittent Black Screen

[d020]

Is Koryuu known to produce an intermittent black screen with Sega Master System games on an NTSC Model 1 Mega Drive or Genesis? If not, I could provide details and video of testing with different consoles, transcoders and displays.

[megari]

Hi @d020!

Hmm, that doesn’t look like expected behavior. Can you tell us more about your setup, please?

I see in your video you have two screens side-by-side. I’m assuming at least the left one is connected to the Koryuu somehow, and the right one looks like a CRT of some sort? Could you describe in detail how the two screens are connected to the MD, and what hardware you have in your video path between the console and the screen(s), please?

Is the console unmodded? Asking this because region mods can affect video timings, although it seems that the output is native to the console (NTSC 240p/480i, possibly line-doubled/deinterlaced to 480p?), and there is color, implying the color subcarrier is derived from the main crystal frequency correctly.

Does the intermittent black screen only occur when running Master System games on the MD, or with MD/Genesis games, too? IIRC, Master System games may have some unusual video modes and/or timings, so that could be a factor.

Are you running the original firmware on your Koryuu? If so, would you be willing to try a newer Release Candidate version, which is most likely going to be very similar to the next official release? It has a lot of bugs fixed, and some new features, too.

I would be delighted to hear any and all reports about Koryuu behavior and compatibility with different kinds of hardware, be they consoles, retro computers, video scalers/line multipliers, transcoders, displays etc. I have been actually hoping for volunteers to pop up. 🙂

[d020]

Thanks @megari. First off, Koryuu is awesome! It produces an absolutely gorgeous picture with all the (way too many) sources I have.

Yes, normally I use a SCART distribution amplifier etc. in a setup I can illustrate at the end of this post. For troubleshooting I connected fewer devices as follows, and made a new video showing the behavior does not seem to differ much:

 ===========
 | Genesis |
 ===========
      | CVBS
      v  (stock A/V cable)
 ===========
 | Koryuu  |
 ===========
      | YPbPr 
      v  (short RG-6 cables)
 ===========
 |  HDTV   |
 ===========

Genesis: VA6 w/Sony CXA1145 video encoder chip
Koryuu : original firmware
HDTV   : Samsung SyncMaster B2330HD

At least one mainboard trace in the Genesis was deliberately cut when I added an ON/OFF/ON switch to easily select between Japan-60Hz/World-60Hz/World-50Hz. Nothing further, and I did replace the RF shielding.

The only condition under which I have seen the intermittent black screen is playing an SMS game on a Genesis. Genesis games are fine, no matter the video mode.

Beta testing with firmware would be quite interesting to try; regrettably I do not have the equipment or software. Fingers crossed, I will have some income soon.

Two things I wanted to note unsure of the significance: First, I do not have a Power Base Converter. Instead I use the Mega Everdrive by Krikkz (x5, Pro). Second, when the Genesis switches to SMS mode the vertical blanking area changes. It takes on an appearance distinct from Genesis low-res mode.

One other thing that probably *is* significant: Neither the onset, severity nor duration of the intermittent black screen behavior are constant and seem to be determined largely by unknown conditions inside the Genesis console. In other words, I might see a black screen for a solid minute with two brief moments where an image appears, or vice versa, depending on whether I just switched the console on, have been playing the same game for hours, had been playing a different game for hours and just reset the console, etc. Rock-solid on the CRT no matter what.

Please allow me to emphasize just how much I am enjoying Koryuu as-is! With the more complicated setup below I have had unqualified success with anything through the A/V selector from a VIC-20 to a VHS tape with Macrovision (!). The only way I could induce an unwanted signal drop was by playing a VHS tape and pressing FF, but that is in no way unexpected.

 ===========                 ====================
 | Genesis |                 |   A/V Selector   |
 ===========                 ====================
      | RGB/AV SCART          | RGB/AV/        | S-Video
      v  (CVBS pin 19(20))    v  YPbPr SCART   |
 ===========================================   |
 | SCART Selector / Distribution Amplifier |   |
 ===========================================   |
      | CVBS   | RGB/YPbPr  | CVBS  | RGB      |
      v        |   SCART    |       v   SCART  |
 ===========   |            |     ===========  |
 | Koryuu  |   |            +---->|   CRT   |<-+
 ===========   |                  ===========
      | YPbPr  | 
      v        |
 ===========   |
 |  OSSC   |<--+
 ===========
      | HDMI
      v 
 ===========
 |  HDTV   |
 ===========

[d020]

Congratulations on your v1.1 firmware @megari! With a recently-arrived “USBasp clone”-type programmer I was able to update the Koryuu with it and made a new video using a MiniDV camera on a tripod. Two CRT on the left, one (de-)tuned to show the vertical blanking area. Two HDTV on the right, top with Koryuu, bottom with RetroTINK-2X by Mike Chi. I will include a schematic at the end of the post.

The intermittent black screen symptom does not seem to significantly differ with the v1.1 firmware. On a more positive note I believe Koryuu remains preferable overall to the RetroTINK-2X, which with SMS games on my NTSC Genesis can produce a signal that lacks color (in the linked video it does this for the first one or two frames of some scene transitions but it can be for much longer). I would be happy to make further testing or video if it would be useful!

 ===========
 = Genesis =                 
 ===========
  | (stock A/V
  v   cable)
 ==========================================
 = Component Video Distribution Amplifier =
 =          (CVBS leads on Y)             =
 ==========================================
  | CVBS        | CVBS         | CVBS
  v             v              v
 =========     ==========     ============
 = CRT A =     = Koryuu =     = Retro    =
 =========     ==========     =  TINK-2X =
  | CVBS        | YPbPr       ============
  v  loop       v              | HDMI
 =========     ==========      V
 = CRT B =     = HDTV A =     ============
 =========     ==========     =  HDTV B  =
                              ============
 
 Genesis      : VA6 w/Sony CXA1145 video encoder chip
 Koryuu       : v1.1 firmware
 RetroTINK-2X : stock firmware 
 HDTV A       : Samsung LN32D430G3D
 HDTV B       : AOC L22W861

[d020]

Sorry to bump an older thread, but I’ve found a device that seems to completely eliminate the intermittent black screen problem. It’s an old Radio Shack brand Video Enhancer / Stereo Audio Mixer (Cat. No. 15-1961), connected between the Genesis (or distribution amplifier) and the composite video input of the Koryuu, with the slider set around 2-4. I’ve only tested it with the VA6 Genesis so far, but the image on the HDTV is rock-stable no matter how long the console’s been running. I did verify that the intermittent black screen symptom returns if the device is removed from the signal chain.

It seems the device uses discrete components for the video enhancer function; a slide potentiometer, three transistors, several capacitors and resistors, and one diode. If anyone is interested I could provide pictures or try to make a circuit diagram (but I’m far from an expert there).

edit: changed link

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