Sega SG-1000

[beaker]

Just bought a Sega SG-1000 II off ebay for not much money and I am having getting sound. I've tried a couple of different leads and 3 different TV's (Pioneer plasma, Goodmans CRT and Philips CRT). The only one I did get sound from (which was quite clear) was the Philips but as soon as I stored the channel it went again. Anyone got any ideas what could be happening?

[Bryce]

Where did it come from? Any chance it's outputing a different PAL version? Ireland / UKs PAL use a different sound carrier frequency than the rest of Europe. This would cause you to get a picture but no sound.

Bryce.

[beaker]

Hey Bryce,

I think despite the English on the top of the case it's a Japanese model looking at the back (It was a bit of a flop for Sega and only got a limited release in Europe and no release in America) and low and high signal switch seem to equate to 90.25Mhz and 97.25Mhz. So I guess the chances are it's outputting a NTSCJ signal and as I think your suggesting my televisions are unable to decode it properly. 

I take it my only options would something to convert the signal or modding it to composite or something?

[Bryce]

Do you have a schematic for it? If you can send me that, I'll tell you what the best picture / sound solution is.

Bryce.

[beaker]

Sorry, I couldn't find a schematic but I did find this web page where they've converted it to output RGB. Some of it looks doable but the amplifier part looks absolutely terrifying to me
RGB + Synch Amplifier Circuit for Sega SG-1000 II (Mark 2) | nIGHTFALL Blog /

I think I'll give up before I even begin and just use it as a paper weight 

[Bryce]

It's a great looking device. It oozes retro. If you have any games for it, I'd definitely use it. SCART and cinch audio makes it quite interesting.

Bryce.

[MacDeath]

Is this a console or a real computer ?

[beaker]

@MacDeath - It's a console but there is an edge connector on the front to add a keyboard, printers and a cassette player. It can also read the same Sega card games as the original Master System that came after it with the right adapter.

@Bryce - Your right hey. I have a couple of games for it but I was looking at getting Congo Bongo, Sega Ninja and ahem Girl's Garden (it's supposed to be good...) and the mod would mean it could be used on modern TV's AND it seems quite rare looking on ebay... I don't suppose you fancy a new project at some point?  I can't read a schematic to build the amp and my soldering iron is pretty crap 

[TotO]

It can also read the same Sega card games as the original Master System that came after it with the right adapter.

Sure, the SG-1000 can read the thin "Sega My card" through the adapter, as those games only require the original TMS9928A screen mode.




Later, some Sega My Card will be Mark-III/SMS only compatible (printed on the top) before switching to the full cartridge system to increase the ROM capacity and allow saves (Phantasy Star).

Spoiler: ShowHide

[Bryce]

@Bryce - Your right hey. I have a couple of games for it but I was looking at getting Congo Bongo, Sega Ninja and ahem Girl's Garden (it's supposed to be good...) and the mod would mean it could be used on modern TV's AND it seems quite rare looking on ebay... I don't suppose you fancy a new project at some point?  I can't read a schematic to build the amp and my soldering iron is pretty crap 

Building the AMP part is simple, if you are willing to make the connections to the Sega PCB. The AMP is simple enough to make on a protyping board. If not, you could always send me the Sega PCB.

Bryce.

[beaker]

@Tot0, thanks for the information, I didn't know that 

@Bryce, thanks for the offer. I assume just the PCB to reduce the weight? I don't suppose I could be really cheeky and ask I could send the whole thing over for you to work on if you have the time as the entire console only weighs 595g, plus I think I may have at least one more issue other than the sound, or is that pushing it?

The reason I ask is firstly it would be great to have it professionally done, and secondly I am not confident that I wouldn't mess it up and it would cost be 3 to 4 times what I paid for it to replace it looking on ebay not including postage from Japan. If it was more common I wouldn't mind so much...

The other issue mentioned earlier is I noticed that the pads don't seem to be working very well and I ended up using one from my master system last night while playing around with it properly for the first time. Would you be able to look at the controllers as well? I opened one up and one of the plastic holders for the screw fell out after breaking off (hopefully prior to me turning the screw to undo it). This suggests to me I would be better letting an expert look at it.

Probably should also mention I've been thinking about it today and was thinking about putting an 8 pin DIN socket on the back of the console as they used in the Megadrive and Sega Master System so we can use those scart leads rather than have one permanently attached but can discuss it more later...

Thanks in advance,

Beaker

[Bryce]

Seeing as you would be paying the postage, you can send as much or as little as you want

Let me know the pinout of the 8pin DIN if you want it to be compatible. I can look at sound / controllers etc while it's here. But don't forget to send me at least one game to test it with.

Bryce.

[beaker]

Cool, thanks Bryce 

I'll send you my entire collection of all two games and my Megadrive RGB scart.

This site seems to show the pinouts:
Game Console RGB SCART Cable Diagrams

Let me know how much you want for doing the work when you're ready and I'll paypal you the money 

Thanks again,

Beaker

[MacDeath]

This machine was womewhat a proto MSX1...


the "Sega1000" specifications were somewhat the technical basis for the MSX standard, still those are not really compatible.

[Bryce]

This site seems to show the pinouts:
Game Console RGB SCART Cable Diagrams

Does your SCART cable also have those resistors and capacitors inside the connector? If so, I'll have to make the RGB Amp slightly different. Not an issue though.

Bryce.

[TomEtJerry]

Hi

Sg-1000 is a console, but Sega has done later a computer based on the same hardware, the SC-3000 (Yeno SC-3000 and SC-3000h in France). I think the games were compatible with the SG-1000.

Maybe we can consider it as the japanese CPC, as you could connect a 3 inches disk drive in the computer if you were rich(SF-7000 interface).

[beaker]

@Bryce, it's from Retro Computer Shack. The ebay listing below says it has additional components fitted inside the scart plug to ensure the highest quality picture which I take to mean it does but I've emailed them through ebay to confirm (hopefully they'll get back to me)...

Sega Megadrive 1 High Quality RGB Gold Scart Lead TV AV Cable - Stereo - NEW |

Edit: Ian (of Retro Computer Shack) just got back to me:

This lead just contains the resistors to attenuate the RGB signals to Scart level. Doesn't contain any capacitors, as I have never found any need for them.   May not work with a modded SG-1000 as the RGB TTL levels may be different.

@TomEtJerry. Would probably be cheaper going for the SC-3000 if I ever want a keyboard. The cheapest I can find the keyboard for the SG-1000 is €190 from France!!! 

SK-1100 Keyboard Clavier Pour Sega Sg-1000 | eBay

[TomEtJerry]

Hi,

SC-3000 hardware is not cheap too :-( so...  In addition, the SC-3000 has a big lack, its cartridge connector. I don't kow if it's the same for the SG-1000, but that's quite annoying (connector pins are not flexible enought). That's a pity because it's a nice little computer.

[Bryce]

Hi Beaker,
        just thought I'd let you know (to your relief), that the SG-1000 arrived here today. Wow, it really does Oooooze retro, what a great piece of kit. As always I couldn't wait to rip it apart carefully disassemble it

Here's what it looks like inside:

[attach=2]

So what's inside: Starting from the left there are two MB81416-12. These are 16K x 4bit dynamic RAM ICs (NMOS parts!). The rather large heatsink is for the 7805 (5V voltage regulator). Under its left "wing" is the TV modulator, under the right side is a 74LS257, this is a data separator / multiplexer, probably to allow the video IC and CPU to access the same RAM. The other small IC on the top right is also a 257 (you need two of them for 8 bits). The big IC below the heatsink is some sort of Sega custom IC. Then there's the Z80 (above the cartridge slot) and lastly a Toshiba TMM2009, this is a static RAM IC as far as I know, but I need to check my datasheets to be sure. It's a single sided PCB with a crazy amount of bridges.

The power switch (bottom right) is a work of art.

As soon as I have time I'll try one of your games out and measure what video signals are available. Then I'll see what the best solution is to get a sharp picture out of it

Stay tuned,

Bryce.

[Sykobee (Briggsy)]

Looks like you'll have to correct the specifications here: http://en.wikipedia.org/wiki/SG-1000#Specifications


Very simple design really.

[beaker]

Phew... faith has been restored in the postal service again 
It does look positively vintage hey, I am half expecting to see a couple of vintage glass tube amplifiers on the board. I've already started making a list of games I want for it. I take it the bridges you mention are the things that look like staples?
What state are the caps in? Hopefully they used better ones than in the Gamegear 

Sorry I forgot to include the Sega TV hookup, although truth be told I am still trying to work out how to connect it to my TV....

[Bryce]

@Briggsy: I'm not sure the specs are wrong on Wikipedia. Beakers device is an SG-1000 II not the original SG-1000. Maybe it had different specs. They definitely moved from NEC to Sharp on version 2 and the PCB layout is also completely different, so the RAM may have been upgraded too. Maybe it's the 6128 of the SG-1000 world

@Beaker: Yes the "staples" are bridges to cross over the tracks beneath. Essentailly doing what the second layer on a two layer PCB does. The capacitors all look fine to me, but I'll test them while I'm at it anyway. The TV hookup is only a cheap UHF switch. You won't ever need it.

It would be nice to have a schematic of the device, but I can't seem to find one. It shouldn't be a problem anyway, I can work out where to take the signals from without it.

Bryce.

Edit: I've just found the original Sega Specs here: which also claim that it only has 1K RAM and 2K Video RAM, but the 2x 81416 is definitely 16KB (not 16Kb) of RAM, so:

A) They only use part of the RAM available
B) They intended having more and then did a turn around?
C) It's been upgraded or repaired by someone.

I can't find any other pictures of the device online, so I can't see if other devices have other ICs in these positions.

[beaker]

The capacitors all look fine to me, but I'll test them while I'm at it anyway.

Cool, thanks.

The TV hookup is only a cheap UHF switch. You won't ever need it.

he he, just as well the metal prongs are pitted and turning blue... I actually have an identical Euro one with the aerial connections on it but nice to keep this version for completeness. 

It would be nice to have a schematic of the device, but I can't seem to find one. It shouldn't be a problem anyway, I can work out where to take the signals from without it.

I couldn't find anything on the web either. The only thing I found was the link on the previous page which appears to be the same PCB revision (assuming there were any others in its short lifespan). It would be nice to chuck everything including the kitchen sink at it in terms of signal output so RGB, s-video, composite if possible but I don't know how practical it is?

[Bryce]

Well I've ordered the parts for the RGB amplifier etc already, and that will give you the best picture plus decent sound through your TV (Dual Mono). Adding S-Video is possible but pointless when you have RGB and the correct cable already available. It would also mean using an AD724 or CXA1145 to produce the S-Video signal from the RGB (it's not available on the PCB) and I'd have to order those parts from China.
I will use a slightly modified version of the RGB amplifier circuit you linked to. I need to make some changes because the circuit is not 100% tuned to the SG-1000 output and because your SCART cable seems to have some internal components that aren't taken into consideration in his circuit.

Bryce.

[beaker]

Excellent, thanks, yup it was RGB I'd prefer 
Not a problem with the s-video (I was thinking it may be like the Master System 2), I was just wondering if it would ever be used on a TV without RGB scart... just me going off on one as normal