GBS-8220, 23DB Connectors and Leads

[Johan1973]

You can use the same solution for your power supply.

Measure the ends of the inductor (its just a transformer really) so that you know which end connects to which. Then wire minus in to one side on one of the transformer coils, and then minus out on the other. Then wire plus in on the other transformer coil, and then wire plus out on the other side. Then you connect caps in parallel with + and - on both sides of the transformer (which now acts as an inductor). You can use any old transformer, for example from ATX power supply etc. That is small enough. The value of the inductor is not so important, since it is just to even out the variations between + and - in the voltage. The caps acts as filters to further smooth out the voltage. And I would recommend getting some 1000uF or so. Seems to be pretty good value.

UPDATE: Forgot to mention that the caps should of course be elctrolyte, so do not put polarity wrong.

Originally Posted by MacDknife

Hi Johan!
I'm new to this retro computer scene (even if I am almost 60), as I am helping my son, who has decided to start collecting retro consoles. Imagine if I had seen this forum before I bought the GBS-8220. Still I got it up and running and got a great picture except for those spots. The higher the resolution, the worse they are.

This is apparently something you have solve by applying a "filter" to the power supply. I bought a cheap adapter at ELFA that gave the 5V/2A I required. Could I apply the same solution to my board with this adapter?

I am afraid I don't really understand your schematics above, but as I understand it, all I have to do is solder the capacitors and inductor (where do I get that? What value?) parallell to each other, on to the power connector (5V + GND) on the GBS-8220 board. I would appreciate it if I could get a photo, to confirm this.

Thanks a lot in advance!

/MacDknife

Thanks for the info, Johan. I will try to do this without burning the house down.

: P
/MacD

[Johan1973]

Let me know if you need any help.

Thanks Johan, I'm taking you up on that.

OK, I'm planning to do this:
1 ) looping the 5V cable a couple of times through a ferrite block (Elfa ArtikleNr: 58-550-36)

2 ) Solder two inductors (Elfa: 58-609-33) and two 1mF capacitors (Elfa: 67-257-52) in parallell, behind the power contact on the GBS-8220 board. I will of course cover the inductors in shrink tubing or something and tape them together.

Is this correct or have I misunderstood the whole thing completely?



/MacDknife

[Johan1973]

Ok. you can not just loop it a few times. You need the many many wirings around a center metal block like you have in a transformer to make an effective inductor. And it is not 1 mF capacitors, it is 1000 mF (uF = micro farad) capacitors.

If you just wrap the wires around a single ferrite core, your inductor will be to weak to do much good. I have some spare coils from transformers around, I could solder something for you and send you if you pay for the shipping.

The second schematic you attached is wrong. It will cause a short.

Just noticed that when you look att the larger image, the transparent background was shown in black, so here's the same image again with a white background.

BTW, 1mF (milli) = 1000µF (micro), right?

The Ferrite block for the 5v cable (58-550-36), has nothing to do with transformers. It is just to help suppress noise: http://www.ce-mag.com/archive/02/11/may.html.

Theses inductors (58-609-33) only have 10 µH. At least how much do I need then? Do they need to manage 2A as well?


/MacD

[Johan1973]

Originally Posted by MacDknife

Just noticed that when you look att the largere image, the transparent background was shown in black, so here's the same image again with a white background.


/MacD

DO NOT wire it this way. The inductors there is wired as shorts between + and ground.

[Johan1973]

The both coils for + and - needs to wrapped around the same core, that is what makes the voltage spikes even out. Thats why a transformer is better to use.
Do not risk damage to your electronics by wiring things you are not sure about.
I will try to make a schematic for you.

[Johan1973]

I made a quick schematic that explains how it should be wired up. Please ask questions if there is something you do not understand about it

Thank you very much Johan! That makes it very much clearer. Of course I can't have the inductors between 5V and ground! DOH!
If I have understood your schematics correctly, it does mean though that I have to create a new power input, which I was hoping to avoid.

Maybe I should just try the (58-550-36) ferrite block to start off with and see upp much "noise" it suppresses? Then if that is not enough, I could try the circuit, but, how about the inductance? Do I need more Henry or not?

I wouldn't mind if you made the circuit for me and I would pay you for it and the work, but I would like to try myself first. One learns a lot by doing it oneself, even if there are times...



/MacD

[Johan1973]

The more the better up to a certain point, I did not measure it. I just used a transformer because I knew it would be more than enough, and the design was already perfect for the job. AND I have some laying around Thats why I offered to solder this for you and send you if you are interested

OK Johan, I give up trying to do this myself! I cannot seem to find what is needed, at home or the net. The worst part is that I have now learnt that almost all new power adapters are switching adapters (to save power) and not all have enough noise suppression for the switching circuits in them. This makes one think: is there a market out there for noise suppressors?

On Elfa I could only find 1 AC/DC adapter for 2A and it says nothing about ripple or noise suppresion, only that it is a switching power adapter (Elfa: 69-975-84). It was the one I bought.

Anyhoo... Tell me what you need and how much I need to pay.
I really appreciate all the help with this.

/Errol

[Johan1973]

I will solder this thing tomorrow, then I will check what it cost to ship and get back to you. Please send me a private message here with your name, address, etc

[attle]

Johan1973: Very nice that you provided a schematic

I'm planning to maybe use the internal PSU (molex adaptor) in my A4000 to power the GBS board, so I can mount it internally. Do you guys think that could pose a problem with power draw etc? It's just a standard A4000/030 with CF drive, no CDROM etc.

[Johan1973]

2 amps are no more than a harddrive. I dont think it will be a problem. What you do need to know is that the GBS 8220 runs hot, so if you install it inside the A4000, you need to have some airflow over it.

[Johan1973]

Today I made a 23 Pin to Scart + VGA cable so I could have my TV hooked up at the same time as the GBS 8220. I just wanted to share it with anyone who finds this thread and is looking for information on how to use these boards with an amiga;

REMOVED FOR NOW. REVISION OF SCHEMATIC COMING UP ASAP.

I highly recommend using like an old twisted pair cat5 network cable, and use the twisted pairs for red, green, blue, with their respective ground twisted around them (16-red ground, 17-green ground, 18-blue ground).

UPDATE: You should NEVER hook this cable up to a real VGA monitor, as you need a 74HCT14 to buffer the vertical sync + Horizontal sync in such a case.

[Johan1973]

Well, I have finally made a complete cable for hooking up the Amiga to the GBS 8220 through the VGA connector for input. It adds a schmitt-trigger inverter buffer. With this I have no single white random dots in the image.
It is as close to perfect as I can get it at the moment, with crisp clear picture quality. I recommend using a 74HCT14 or 74AHCT14 and not the 74HC14.

REMOVED FOR NOW. REVISION OF SCHEMATIC COMING UP ASAP.

[Johan1973]

Improved circuit with interference filter, and simplified (since CBS 8220 do not really need vertical sync).

REMOVED FOR NOW. REVISION OF SCHEMATIC COMING UP ASAP.

[cpiac64]

you lost vcc to pin 23 in this schematic

thanks, now is correct

[Johan1973]

Thanks for reminding me. Missed that...