The third generation of video consoles Sega Mega Drive-II. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Despite the forecasts of skeptics, the 16-bit IVP "Sega Mega Drive - II" continues to amaze with its longevity. Given the availability and wide selection of cheap game cartridges, it is still a desirable gift for children of primary school age. It can also be considered a champion in terms of the number of known versions. This article discusses the history of the development of these IVPs and the distinctive features of their modifications, including the latest releases.

Japanese company SEGA Enterprises Ltd. in 1987 it was going through hard times [1]. Its eight-bit Sega Master System (SMS) was significantly behind the Nintendo Entertainment System (NES), the ancestor of Dendy, in popularity. Nintendo, which produced the NES, controlled 92% of the American and 95% of the Japanese video game market. In the United States, every third family had IVP, in the vast majority of cases - NES.

To change the situation, SEGA assembled a strong team of engineers under the leadership of Hideki Sato, tasking her with presenting a 16-bit IVP to the world in a year. The prototype was the "System 16" slot machine from SEGA. It was from him that the dual-processor architecture was borrowed: MC68000 (Motorola) and Z80 (Zilog).

The official date of birth of the "Sega Mega Drive" (MD) is October 29, 1988. It was on this day that its first copies went on sale in Japan. The presentation on the American market took place on August 14, 1989, but under the “Genesis” trademark, since the word “megadrive” turned out to be already registered by one of the US companies in its name.

The first MD sales in Europe took place in November 1990 in England. The IVP included more than a dozen games developed by Namco, Electronic Arts, and Konami. If we take into account compatibility (via a special adapter) with SMS cartridges, the total number of games available to consumers reached hundreds. Good performance, rich color palette, stereo sound, diverse peripherals - this is the list of MD advantages. But most importantly, it became the first publicly available 16-bit IVP.

Various MD variants bore the company designation "MK-1601 -xx". Regional versions were released: Japanese, American, European, Asian. All of them are in a rectangular case with dimensions of 285x225x50 mm (in Fig. 1 - IVP of the American version), differing in television signal formats (PAL or NTSC), inscription languages, external design details, power supply designed for 120 or 220 V. In European MD There was no 9-pin "EXT" connector, which in the Japanese version was intended for connecting a modem. MD was equipped with a jack for connecting stereo headphones and a slide volume control. Features of the circuit design and repair of this IVP are covered in [2].

In 1993, five years after the appearance of MD, SEGA released new, cheaper modifications of the Mega Drive-II (MD2) consoles and its American version, Genesis-2, while maintaining bottom-up software compatibility with M.D.

The main differences between MD2 and MD:

- no headphone jack and volume control;

- a stereo sound signal is output to the "A/V OUT" connector;

- the internal RF modulator is replaced by an external one;

- added buttons "X", "Y", "Z", "MODE" to the joystick;

- the procedures of "cold" and "warm" start are programmatically separated;

- it is possible to check the regional compliance of the cartridge and the set-top box.

The brand name of the MD2 series models is “MK-1631-xx”, although there are others, for example, “MK-1632-xx”, “NAA2502”, “KW-501”. In Fig. Figure 2 shows the appearance of the European version of MD2 in a unified square case with dimensions of 210x210x50 mm.

In 1992-1994. SEGA's 16-bit IVPs were at the zenith of their fame all over the world. A little later, the palm in terms of sales was seized by the IVP "Super Nintendo", then the time came for the 32-bit "Sony PlayStation". Since 1996, the center of the SEGA IVP “habitat zone” has moved to Brazil and China, and then to the CIS countries

At the end of 1997, an attempt was made to revive MD2. Majesco (USA) has released under license an ultra-lightweight version of the IVP called "Genesis-Z". It does not have a system connector, which excludes the connection of the IVP with the MegaCD, and some functions assigned to the Z80 processor are simplified. In appearance, the new model is a cross between a hockey puck and a CD player. The advantages over "Genesis" and "Genesis-2" are relative cheapness (30...50 US dollars) and the ability to work with branded Japanese game cartridges.

SEGA officially stopped supporting its 16-bit IVPs in 1998. In just 10 years, approximately 30 million consoles were sold, more than a thousand game programs and three thousand varieties of cartridges were created for them.

Some original modifications are known. Among them are "Sega Nomad" - a portable MD2 with a built-in three-inch LCD, "Wondermega" - a symbiosis of MD2 and MegaCD, focused on karaoke and playing MIDI music files, "MegaPC" - a hybrid of an IBM PC-386 computer and MD2, intended mainly for development of game programs.

MD2 VARIETIES

The vast majority of IVPs common in the CIS countries are Asian and European versions of MD2. They should be called MD2-compatible, since they are not built on proprietary VLSI SEGA315-xxxx, but on copies of them from various manufacturers. Occasionally you can find licensed MD and MD2 (both versions were produced until 1995). American IVP "Genesis", including "Genesis-Z", have not become widespread in the CIS countries.

MD2 is conventionally divided into three generations according to the year of production: from 1993 to 1996. - first, 1997 and 1998. - second, 1999 and later - third. They differ mainly in the degree of integration and the number of VLSIs. For example, starting with the second generation MD2, the MC68000 and Z80 processor cores are packaged into a single VLSI “multiprocessor”. Among repairmen it is known as “97xx” or “98xx”, although in fact this is the date of manufacture of the microcircuit: the first two digits are the year (1997 or 1998), followed by the serial number of the week of that year.

It is not always possible to find out from the inscription on the bottom side of the case which generation the console belongs to. MD2 cases are unified and interchangeable, so you shouldn’t be surprised to find, for example, a first-generation IVP board in a case called NAA2502.

The easiest way to accurately determine the type and generation of the MD or MD2 being repaired is by the position designations and types of microcircuits installed on its board. Table 1 contains information about the most common options, although others are also found. Listed below are microcircuits for various functional purposes that are used in MD and MD2. The names of chip manufacturers are given in brackets.

(click to enlarge)

Central processor: MC68000P, MC68000L, MC68Н000Р (Motorola); SCN68000 (Signetics) - in DIP-64 package. HD68HC000CP (Hitachi); MC68000FN (Motorola) - in QFP-68 package.

Additional processor: Z84000 (GoldStar); Z80A (Zilog); Z80CPU (Mostek); Z80ACPU (STMicroelectronics); LH0080 (Sharp); TMPZ84C00 (Toshiba); mPD780C (NEC); KP1858BM1 (Russia) - in DIP-40 housing. Z84C0008 (Zilog); 84C00AU-6 - in QFP-44 package.

Video encoder: SХА1145М (Sony); MB3514 (Fujitsu); KA2197D, KA2198BD (Samsung) - in SOP-24 housing. CXA1145P (Sony) - in DIP-24 package. MC13077P (Motorola) - in DIP-20 package.

Audio RAM: SRM2064, SRM2A256 (Seiko Epson); MK48H64 (STMicroelectronics); TC5564, TC5565 (Toshiba); MB8464 (Fujitsu); HY6264 (Hyundai); HM6264 (Hitachi); CY6264 (Cypress); MT5C6408 (Micron); M5M5178 (Mitsubishi); CXK5863, CXK5864 (Sony); MPD4364, MPD43256 (NEC); TMM2064; HSRM2264; MCM6264 (Motorola); UM6264 (UMC); AKM6264 (Asahi Kasei); LC3664 (Sanyo) - in SOP-28 package.

Video RAM: HM53461 (Hitachi); mPD41 264 (NEC); M5M4C264 (Mitsubishi); MB81461 (Fujitsu); MT42C4064 (Micron); V53C261 (Mosel-Vitelic); TMS4461 (Texas Instruments) - in DIP-28 package. HM53462 (Hitachi) - in DIP-24 package. MSM54C864 (OKI) - in SOJ-40 package.

Main RAM: HM62256, HM66203 (Hitachi); mPD43256 (NEC); KM62256 (Samsung); SRM20256 (Seiko Epson); CXK58257 (Sony); ATT7C256 (AT&T); CY7C199 (Cypress); IMS1630LH (STMicroelectronics); UM62256 (UMC); HY62256 (Hyundai); MB84256 (Fujitsu); M5M5256 (Mitsubishi); MS62256(Mosel); MCM51L832 (Motorola); GM76C256 (GoldStar); Idt71256 (IDT) - in SOP-28 housing. LH52258D (Sharp); 61256PT - in DIP-28 package, TC511632FL (Toshiba) - in SOJ-40 package.

Audio channel: NA17902P (Hitachi); MPC324C, MPC3403C (NEC); SM8652; ICPA324; KA324 (Samsung); KIA324P (KEC); LM324, MC3403P (Motorola); CA324G (RCA) - in DIP-14 package. KA324D (Samsung); LM324D (Texas Instruments); LM324M (National Semiconductor) - in SOP-14 package.

UMZCH stereo phones: SХА1034Р, CXA1634P (Sony) - in DIP-16 housing. LM358 (Texas Instruments, On Semiconductor, Philips, National Semiconductor, STMicroelectronics); GL358 (Hyundai); ICPA358; KA358 (Samsung) - in DIP-8 housing.

+5 V stabilizer: L7805 (STMicroelectronics); LM7805 (Fairchild); NY7805C; OTI7805; KA7805 (Samsung); KIA7805 (KEC); ML7805; AN7805 (Panasonic); UB7805; uA7805 (National Semiconductor); HSMC7805; GL7805 (Hyundai); UTC7805 (Unison Technologies); UC7805 (Texas Instruments).

Microcircuits for the same purpose in the same packages, produced by different companies, are usually interchangeable. With the advent of new IVP models, the list is expanding.

The first generation MD2 set-top boxes are described in [2]. The diagram and detailed repair procedure for the second generation MD2 are given in [3, 4].

The third generation MD2 circuit is shown in Fig. 3. This is not an official document from SEGA, but the result of an analysis of the structure of consoles that were in the hands of the author. The same figure schematically shows the location of the main components of the set-top box and shows the appearance of its connectors.

(click to enlarge)

In everyday life, such video set-top boxes are sometimes called single-chip, since all the main functions are performed by one VLSI U5. It interacts only with the main RAM of 32Kx16 bits (chips U7, U8) and video RAM of 64Kx8 bits (chips U9, U10). The sound channel is made on op-amp U2.2 - U2.4.

Like the IVP of previous generations, the signals SOUND 1 and SOUND2 are the outputs of the left and right channels of a music synthesizer, functionally similar to the YM2612 microcircuit from Yamaha, but located in the same VLSI U5. The SOUND3 signal is the output of the PSG (Programming Sound Generator) channel. Its four-part sound is reminiscent of "Dendy". The prototype of the PSG was the SN76489 chip from Texas Instruments. The SOUND2, SOUND4 circuits connected to the S5 "Cartridge" connector are the technological inputs of the sound channel. They serve to check it without opening the IVP.

Op amps U2.2 and U2.3 are covered by negative feedback via circuits R13С6 and R14С7. The upper limit of the bandwidth of these stages is 7,2 kHz. To expand the band, it is recommended to reduce the values ​​of capacitors C200 and C6 to 7 pF.

The S-RIGHT and S-LEFT signals are intended to be supplied to an external UMZCH. Unfortunately, in many MD versions they are not output to the CN2 "A/V OUT" connector, which does not allow you to hear the stereophonic sound of games. Operational amplifier U2.4, summing the signals of the left and right stereo channels, generates a monophonic AUDIO signal, supplied through the CN2 connector to the RF modulator or to the input of a monophonic UMZCH.

The operation of the IVP is synchronized by the generator located in VLSI U5. Its frequency (17,734475 MHz) is set by quartz resonator X1. The value is not random - the fourth harmonic of the color signal subcarrier in the PAL system. The clock frequency of the processor core (7,6 MHz) is 3/7 of the generator frequency.

The X2 resonator is installed only in American and Japanese IVP models that generate NTSC television signals with a color subcarrier frequency of 3,58 MHz. The processor clock frequency in this case is 7,67 MHz.

Resonators X1 and X2 and television standards are switched using jumpers J5.1, J5.2 and a group of jumpers J4. The purpose of the latter is as follows:

• J4.1 ("O/J") - removed in Japanese IVP models;
• J4.2 ("N/P") - NTSC or PAL standard;
• J4.3 ("TV N/P") - color subcarrier frequency 3,58 or 4,43 MHz;
• J4.4 ("6/5") - frequency of television fields 60 or 50 Hz.

The Schmitt trigger on op-amp U2.1 controls the voltage in the +5 V circuit. If for some reason it drops, capacitor CE2 is quickly discharged through diode D2, and after the voltage is restored, it is slowly charged through resistor R11. A negative reset pulse with a duration of 2.1...0,2 s generated at output U0,3 is sent to pin 158 of microcircuit U5. This prevents the microprocessor system from freezing during power failures. By closing the WDOG circuit (pin B2 of the S2 "Cartridge" connector) to the common wire (GND), you can restart the IVP.

In table 2 shows a list and purpose of all circuits connected to connector S2.

The supply voltage of the IVP is stabilized by the Q1 L7805CV microcircuit (STMicroelectronics). Diode D1 protects against accidental supply voltage of incorrect polarity.

Structurally, the set-top box consists of three printed circuit boards connected to each other by ribbon cables. The side “System” connector is absent in this model, as in the “Genesis-Z”. It should be noted that although MD2 of the first and second generations has a 60-pin system connector, it often happens that not all the circuits necessary to connect the IVP to the MegaCD module are connected to it.

REPAIR FEATURES

Approximately 70% of MD2 malfunctions of all generations are due to failures of the +5 V voltage stabilizer microcircuit and wire breaks in the network adapter cord, in the windings of the power transformer, in joystick cables, in inter-board connections. These defects are easily found by “testing” the wires with an ohmmeter and measuring voltages with a voltmeter. In particular, the voltage at pin 1 of the integrated stabilizer Q1 (see Fig. 3) must be at least 8 V, and at its pin 3 - 5±0,15 V.

When searching for MD and MD2 defects, you can use MFD tables related to the cartridge socket, main and video RAM [3]. Very often, the criterion for the serviceability of a microcircuit is the temperature of its case. If, a minute after turning on the IVP, any of the microcircuits can no longer be touched by hand (it is very hot), most likely the microcircuit should be replaced. The exception is the +5 V voltage stabilizer.

As already mentioned, in the third generation MD2 the main functions are performed by VLSI U5. However, even if it partially fails, you can try to restore the operation of the IVP. For example, in [5] there are schemes for replacing the OE and CS signal conditioners located inside the VLSI with very simple cascades on conventional logic chips.

In Fig. 4 shows a diagram of a unit that allows you to select games in cartridges that are switched by a reset signal.

Scheme in Fig. Figure 5 shows how you can temporarily restore the operation of the IVP in the event of a faulty supply voltage control unit at op-amp U2.1 (see Fig. 3).

The circuits of the IVP processor board, which should be broken by cutting the printed circuit conductors, are shown in Fig. 4 and 5 are marked with crosses.

A common malfunction of video set-top boxes is poor soldering of VLSI pins to the contact pads of the printed circuit board. To search for such defects, you need a magnifying glass and a thin needle, which is carefully, without strong pressure, passed over all VLSI pins. A poorly soldered pin reveals itself by wobbling. To restore functionality, just use a soldering iron tip (cleaned of excess solder!) to press the lead to the contact pad and warm it up for 1...2 s.

Literature

1. Pettus S. SegaBase Volume 3 -Genesis/Megadrive - .
2. Ryumik S. Features of the circuitry of 16-bit video consoles. - Radio. 1998, No. 4,5,7,8.
3. Ryumik S. Repair of the Sega console using MFD tables. - Radioamator, 2001, No. 12. p. 28, 29, 32, 33; 2002, No. 1, p. 28, 29.
4. .
5. Ryumik S. Analyzer of the logic of decoder operation. - Radio, 2002, No. 4, p. 20.21.

Author: S.Ryumik, Chernihiv, Ukraine

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