My first Build - portable Megadrive

[ManicMan]

I've gotten to a stage I'm happier doing this kinda information about it.

I'm working on a Portable Megadrive (Known as Genesis in American only, due to Copyright back in the 80s) as my first (and probably only depending what I feel like) portable console. The Base Console is the European Megadrive Mk2. This was smaller then the Mark one, and it added Stereo sound but, it lost the 3.5mm Stereo headphone jack with Volume control so it's debatable if it was an improvement or not.

The Screen is a cheapo Car screen which, after some problems noted in the screens sub-forum, came to be used. Main problem right now is that screen, while designed for Sound, doesn't seam to come with Speakers. While I can just use spare set I got, I will probably have trouble connecting them up to the screen's board so I can reuse the inbuilt volume control.

My battery source is a Lit-ion rechargeable battery which outputs 12.6-10.8vDC with about 6800mAh.

Being a bit of a retro fan, I don't want this super small and I won't be, but correct expectations would be able the size of the Megadrive Mk2 (I don't know if I feel happy enough cutting the board in half and wiring it up to make it smaller).

Progress isn't expected or even planned to be that fast as I'm doing it in what is laughable called my spare time.

Current stage is checking all parts will together on there own. The Screen works with the Megadrive, the Screen works on battery. I need to split the battery cables to power the Megadrive at the same time, and work on the speakers for audio. Once this is completed and tested, I'll move onto the next stage which is involves cutting and soldering. When it comes to the Megadrive Mk2, It is pretty safe to cut off the side with the expansion slot, but there are only smaller other bits which can be safely cut without any danger.

Due to how hard the Sega Solder is (I can't get the stuff off), I might end up with a cheap old Game Genie as a way to relocate the Cartridge slot, though this is NOT ideal. cutting and adding wires with that amount might be tricky for me as I have large hands and fine tiny soldering a real pain.

 

[ManicMan]

Re: My first Build - portage Megadrive

Spilt the Power cable, Both parts successfully power up together.

To do- Get Speakers installed and audio working.

 

[ManicMan]

Pretty sure I can't add Speakers to the Board due to missing Chip.. but not fully sure. Will post hopefully decent image later.

Carefully undoing the tape holding the control board to the screen, the composite cable bit is labelled but I currently do not know what each one means.. the 12 connections only have 10 labelled too.
1- +12v {the Positive power line}
2- GND {the Ground/Negative Power line}
3- AV1 {The first Composite video line}
4- CND {no cable attached, unknown}
5- AV2 {the Second Composite Video line}
6- Back{seams to be connected to the Trigger Line}
7- RR {no cable attached, unknown}
8- AV3 {no cable attached, Third Composite Video line}
9- LL {no cable attached, unknown}
10-GND {no cable attached, ground line}
11- Unlabelled
12- Unlabelled

While it might be possible to add the missing chip.. the only one I got that seams to fit would be one labelled 'LA7217 6N9'. This means nothing to me and i'm unable to find a matching chip to know what it is.

EDIT:

right. What I believe is for the sound would be the four pins holes on top right (white with wire line broken) that would be where the input connects, (the connector under it is the Screen buttons). Then at the bottom Right, two sets of two, I believe at Left and Right Speakers. above them, is a space for a 16 pin chip which is believe to be the main part missing that I need. I'm of sure if a battery or capacitor is needed there as I can't see any connection to any other part of the board.

finally found that chip (i'm having bad luck with location information of late ¬_¬). it's just a video chip.

 

[ManicMan]

As unsure with Screen's volume Hooked up a pair of speakers from a dead Screen to a Turn wheel Rheostat, and to test, a 3.5mm Headphone Jack. Works.

Next stage to check when it is instead connected to the Megadrive.

 

[ttsgeb]

You might want to invest in a higher wattage iron. I imagine if you can find an electronics chain (IDK what the UK has to offer there), you can find a 30/45 Watt adjustable iron for around 20 pounds. If you're trying to do this with a 15W iron, you're just gonna keep running into headaches with solder not melting.

 

[ManicMan]

I checked, I got a 30watt iron and a 100 watt gun. maybe It just wasn't heating up enough or the heads need a Dang good clean. ^_^;

and in this area of the country at least, the electronics shops are bad.. the closet to me is about.. 3 towns over (well.. 2 towns and a village cause I'm basically in a village).. It would basically be a order online job on the whole.. there are a couple of close-ish places the other end of town but they are kinda.. erratic on opening times..

I don't refer to my area of the country as a backwater for nothing.

Oh, but the best UK chain these days is Maplins.. (what it in the US, since RadioShack has had bad Customer service for years and is now closing?)

 

[ttsgeb]

Well, assuming that Radioshack fully disappears, the electronics store is going to become http://www.amazon.com

 

[ManicMan]

Shame.. one thing that annoys me is having to shop online cause you can't get it locally.. this means a while waiting and sometimes, for small bits, over 100% shipping costs (even if it's not fantastical high, it annoys me).

Haven't tested the Speakers on the Megadrive yet as my first test with a 3.5mm jack had them a bit quite, so I'm putting in an amp. Waiting for blank circuit boards.

Luckily, old screen which I took the speakers from, has all the parts for a amp. a TDA2822M amp, some 220mF 16V capacitors and some resistors.. BUT, my guide says two 22k 1/8 watt resistors, 1x220mF 16v capacitor, and 2x47mF 16v capacitors. The board uses Chip resistors, with.. I can make out 101 (or 107) but not others.. so i'll probably have to get some in.. and an the Capacitors are 220mF without the 2x47mF.. So I decided to give up the idea and brought a TDA2822M Kit. probably get here end of week, start of next.

minor change I might make (I think I would be a good idea) is to add a Headphone jack.. I'm not quite sure where to put the jack though. Since it should shut off the speakers when in use, I would make sense to put it so the channel outs go to the jack, and THEN to the speakers.. But i'll need to figure out the model to get the pin outs for it..

EDIT: Dang.. idiot time again.. the Kit comes with headphone jack and volume control... oh well.. Live and learn.

 

[ManicMan]

Okay, got the Amp a couple of day ago but haven't had too much time to work on stuff.. Might not have time to test it for a couple of days.. the best idea for powering it (5V) that I think should work is to connect it to the Megadrive's Own 5volt regulator. It shouldn't affect current much. If I remember right (need to check when I got the time), the Megadrive uses a 78XX 5 volt regulator attached to the huge Heat sink. It is a type I'm familiar with so connecting up with it shouldn't be a problem (even if I wasn't it's a simple bit of kit)

 

[ttsgeb]

Yep, it's a 7805.

You should consider replacing it with a modern switching regulator, though. 7805s are pretty inefficient.

That said, you shouldn't have any problems powering an amp off it it as well as the SEGA. You don't find these things in everything for no reason.

As far as the headphone jack goes, you're going to want to wire it between the amp and the speakers. Switching jacks are pretty easy to come by, and if you grab one with a clear casing, you can just look at it to figure out where to wire things.

 

[ManicMan]

sounds good.. Not sure what better regulator to switch it to though.. so for safely it might leave it.

Turns out the Kit comes with a headphone Jack so that bits fine ^_^

the main wonder I got about powering the amp is.. shouldn't it go from a capacitor after the Regulator before I put it into the power line? The Amp just goes from the power in to the Amp chip So would it be fine to just connect straight from the Regulator out?

 

[ttsgeb]

The TDA2822M can operate anywhere from 1.8v to 15v, so while it may not be the *best* solution, it'll probably be fine pulling power directly from the 7805.

The datasheet has a few example schematics if you want to crosscheck with what you're using though. They all include a capacitor to ground in parallel with the amp, so that's probably worth considering.

Figure 16 is likely your best reference here.

http://www.mouser.com/ProductDetail/STM ... 9uBQ%3D%3D

 

[ManicMan]

Bit of a delay due to busyness and minor health issues (nothing to worry about, just a fair bit of pain ^_^ ).

attached audio amp and so far, nothing of note sound wise but some buzzing.. should be sorted out in a few days I think.. or at least get to a stage where more help is required.

 

[ManicMan]

okay, i'm an idiot again.. no power is going to the amp.. it seams I might have been stupid with my big hands and soldered the ground wire to both the ground. and the amp's input pin.

hopefully get time to look at that and see if that is the problem more later.

 

[ManicMan]

mm.. I need a decent voltage checker but.. the Megadrive's 5v regulator has the three pins which the circuit board labels as Input ground and output.. Attaching the ground to ground and the output to input (on the audio amp).. I don't seam to get power.. attaching from underneath.. I wouldn't have thought the current was too low... gonna need more testing ¬_¬

 

[ttsgeb]

Have you tested the amp independently of the megadrive?

 

[ManicMan]

only basically so far.. I got a 9V battery connector hocked up to a 5V regulator for power but the battery might have been flat, and I need to put new wires on a 3.5 jack to check Audio or see if the headphone jack is weird.. I would have expected, as it looks like a standard connector, I could just connect up to the input lines to allow it to work as a headphone port (or if no headphones connected, straight to the speakers) BUT it's possible.. I guess, that for some reason, it only works as a in port.. easy to check that with a microphone of course..

I'll set it up tomorrow and see...

 

[ManicMan]

can't seam to get it to work on battery either..

I seam to have constructed this right.. so I wonder what's up.. the 5v regulator on the battery doesn't seam to get warm when on the circuit so i'm wondering if it's even drawing from it.. I think I got a spare amp and I guess I could just take this apart and instead of using the printed board, try a blank board in case I've damaged it somehow..

: EDIT:

Not long after the problem, I was given an old working 'travel speaker for Ipod and Iphone'. 5V power supply. I think I got a nice new amp ^_^

Two 15W speakers, a headphone jack for IN which i'm sure can be rigged for out as well (or just replaced). a board for power and volume.. I think I can do something with this.

EDIT 2:
oh, by the way.. trying to work out the pins for setting this up.. the Headphone jack is only in by the looks but it's a standard connector. the Ipod connection thing is attached to a board so I can't use the pinouts to work out the audio connectors.. the cables are labelled but I'm trying to figure them out..

5V and Ground are simple.. ID, 3.3v are possibly what they sound like, though why it needs the ID I don't know.. which lefts RX and TX and a unlabled one.. not sure what they are.. . those cables all go to the control board (volume +, volume - and power), BUT on the other side of the board is three which are Left, Ground and Right, which go to a second board which is the Amp.

I'm hoping the one with the 5V,ground,ID etc isn't important or for Iphones, so they are 'spare'.. this thing at least draws power from Batteries OR mains.. maybe it also takes from the Ipod or whatever if needed.. interesting..

 

[ttsgeb]

Okay, it took me a while to decipher that post.

On the iPod connector board, you have two sets of ribbon cables, right? The one with R,L,G matters. That's an audio in. The one without doesn't.
That said, I would remove the headphone jack and wire the sound up there, then if the jack is switching, you could wire it between the amp and the speakers to use as a output jack. You should note, however, that it'll probably royally *Can'tSayThisOnTV* whatever headphones you attach to it, so start out with something you don't care for, and be sure to check the impedance of the speakers to ensure your phones can handle it.

Pictures are also super useful for us. Imgur is a great free image host that doesn't throw a world of *Can'tSayThisOnTV*ery at you as soon as you get any kind of traffic.

 

[ManicMan]

sorry, been a bit busy today, working on it in a couple of spare hours.

I'll try to get some photos taken tomorrow.

not ribbon cables but yeah. two sets, one that is the RLG. Connected and works (a bit of static but that's cause I just touched to test more then soldering and protecting).

There are two power source options.. 5V adaptor or Batteries. I don't think it makes too much difference but I'll try to connect the battery ones up to the Megadrive's 5V. it's easier just cause the adaptor jack has 2 ground lines (and the battery ones have longer cables).

So... remove Headphone jack. connecting it between the amp and speakers might be a bit tricky cause it's a quite compact board.. though I can have the speaker wires go to a blank board which i put the jack on, and then out to the speakers..

but like I said, Tomorrow I can get some images.

Oh and stupid question probably but.. the little press button has, of course, two pins. If I just bridge them, that would bypass the power switch? it's fair enough to have 2 power switches (I got one for the battery and one for the Megadrive) but I really don't think I need a third one for the Speakers. (speaking of which.. still need to fully look into that trigger line on the screen)