I bought a Sega Titan Video (ST-V) mainboard and a Darksoft multi-cart along with a CPS2 in 2018 for use at home. I’ve rarely used it, and everything I’ve done with it hasn’t been documented here. This is about to change as it seems I have opened Pandora’s box after testing a SuperGun with it.

Introduction

The Sega Titan Video, more commonly known as Sega ST-V or STV is an arcade system based on the Sega Saturn. Not only based on, but actually having the same specifications, which makes it a low-cost arcade system (Nicole Express commented on this here). A lot of information about this system can be found in the usual places, such as Sega Retro, System 16, Arcade Otaku Wiki and most importantly the Arcade-Project Forums which turned out to be an invaluable source over the years to get this thing running. You will find many links to threads of this forum in this article.

You don’t need much to use an ST-V at home, just a SuperGun and an extra adapter if you want to enjoy stereo sound.

I played around with the mainboard and the Darksoft multi-cart for a while and upgraded all sorts of things:

• MODBIOS v1.11
• Game selector with LCD
• 3D printed cases for the Darksoft cart and the LCD selector. There’s also an add-on for the cart housing that I might explore in the future.
• Stereo audio adapter for connector CN24
  1 – Left
  2 – Ground
  3 – Right
  4 – Ground
  (Another option is the Sega ST-V IO Board.)

Then I put everything in storage because other projects came up and eventually I forgot about it. For me, it was very uninteresting for a long time because I had only concentrated on the Saturn itself since the late 90s and collected a lot of hardware and software for it.

Pandora’s box

This Christmas I treated myself to a used old HAS V2 (Home Arcade System, a SuperGun) and started cleaning it up and repairing the power supply. I also printed some JAMMA keys (there are two versions, depending on whether you want to remove pins 7/8 or not). When it came to testing, I played some games on my Neo Geo MV2FS and then remembered my ST-V that was still in storage.

Right from the start it gave me problems with games not loading properly, but this was due to my impatience / not following the instructions. After some more reading on the Arcade Project forums, I found out that I had never set up the Darksoft cart properly, specifically connecting the reset line to the mainboard. This is not really a problem if you wait for the flashing process to finish, but as I said, I was impatient. I fixed this immediately and the games were flashed properly again.

I also never set up the audio connection (for the flashing start and end sounds) between the cart and the amplifier. That was the next thing I did, and I couldn’t get any audio out of it, or from a mini-speaker I had installed in the cart as a last resort. After some more reading, I finally found sound files that would play and tried a couple of games. So far, everything went fine. Then I moved on to the last game that had been modified to work on the ST-V multi-cart: Decathlete.

To my surprise, the graphics were still garbled. I then tried a couple of other games that had worked fine before, and now they all had garbled sprites. I began to question my sanity.

Diagnosis

There are two test menus built into the ST-V: The NORMAL TEST MODE is started by pressing the TEST button (SW1) after switching on. In the MEMORY TEST, IC27 immediately went to BAD statis, but everything else was GOOD.

I then went into FACTORY TEST MODE, which can be accessed by holding down the TEST button (SW1) when the mainboard is switched on. Here the MEMORY CHECK found that everything is GOOD.

But the VDP1/VDP2 CHECK showed that VDP1‘s VRAM was BAD and the VDP1 CHECK showed nothing at all. However, the VDP2 CHECKs were fine.

This confirms that there’s something wrong with IC27 (Hitachi HM5241605TT-17, 131,072-word x 16-bit x 2-banks = 4 Mbit SDRAM) which sits right above the large VDP1 (Video Display Processor 1, IC28, SEGA 315-5689).

An internet search for this problem in the forums Arcade-Project (no results), NEO-ARCADIA (with wrong information, see next section) and Arcarde Museum (not helpful, because wrong chip) yielded these results, suggesting to reflow the solder joints of various chips, from memory to VDP1 to SH1 and SH2.

Repair – Part 1

I started by reflowing IC27, but unfortunately nothing had changed. Before removing IC27, I wanted to make sure that the connection to the VDP1 was also good, so I I reflowed that too. First the top row of pins (no change) and then all four sides.

Oops, that went the wrong way. (Sorry for the jittery image, I had placed the capture device on top of the PSU to have more space on the work table.)

I then removed a short on the VDP1 that I had missed after reflowing it and everything went back to the new normal (IC27 BAD).

At this point, I should have replaced IC27 – if I had a spare – but I didn’t. So, I looked for alternatives on the ST-V board. Contrary to the hints in the NEO-ARCIA forum, the mentioned equivalents for IC27 (4 Mbit SDRAM) were wrong: UPD4502161G5-A12, HM5221605TT-17, LC382161T-17 are all 2 Mbit SDRAM chips. That’s why I had to look for other 4 Mbit chips instead, which didn’t leave me with many options. The only M5241605TT-17 or UPD4504161G5 chips left on the ST-V mainboard were IC24 and IC25 – the main RAM, which was checked at the same time in the MEMORY TEST.

But I was out of options and willing to take the risk. I removed both IC27 and IC24 and swapped them, extra precaution and tinfoil here to protect (me from) the electrolytic capacitors.

Result

And the result? Well, the system no longer booted normally (black screen), nor did it boot into FACTORY TEST MODE – I was almost expecting this as IC24 and IC25 were tested in pairs. But this gave me the final confirmation: When I put IC24 back in (and left IC27 out), I got the same result as before (IC27 BAD).

I’ve now ordered a junk Saturn to harvest an SDRAM chip and will then either continue this article or write a part 2 – depending on how much is left to do.