GBS-8220, 23DB Connectors and Leads

[Solo761]

IMO GBS is OK for when I meddle with something, like installs, on my Amigas. But if you want to play games TV with scart is way better choice, way better.


@amigappc

I had similar problem, my TV doesn't like Amiga signals via SCART. I used SCART to HDMI adapter to get picture on it, but although it works it's not really that great and I don't want to shell out bug amounts of money on something like FrameMeister XRGB and like adapters.

In the end I bought used 22'' LCD Monitor/TV, I found it on Njuškalo (local classifieds page, for those not from Croatia ), and paid 500 kn (cca 65€) for it. It's LG, same as my main TV (LGthat doesn't work with Amiga..., I think model is LG M2262D, it has two SCARTs, one RGB and one non RGB, so far everything I connected to it works without problems, Amigas (500, 600, 1200...), Sega Mega Drive, Sega Master System, Playstation 1...

Only downside to it is that it's LG, same as my main TV, so they both react to both remotes. I had to tape over small one's IR reciever to prevent this .

[RedskullDC]

Hi Higgy, et al.

Originally Posted by Higgy

Fingers crossed speckles are a thing of the past now.

Apologies if this has already been posted somewhere here.

Ewan of http://microbeetechnology.com.au/ has come up with a fix for the white spots on the GBS boards.

His explanation:

"The SDRAM interface from the TV5725 scaler chip on the board has no damping resistors in the clock & control lines
and fails to calibrate the timing of the interface properly as a result. It is marginal and causes bad screen refresh data.
As such it took some time to track this down as the cause.

There is a track to be cut and the resistor (SMD 0603 size, or 1608 metric) gets fitted across the cut. Then the capacitor is soldered to the ground end
of a nearby bypass cap & the free end linked to the SDRAM side of the resistor that was fitted across the track cut. It is not very elegant, but it works & cures the video noise totally."

Some pics of the mod:
http://www.microbeetechnology.com.au...200Mod-pt1.JPG
http://www.microbeetechnology.com.au...200Mod-pt2.JPG
http://www.microbeetechnology.com.au...200Mod-pt3.JPG


Have done the mod to my GBS board, and the difference is noticeable.

Hope this helps,
Red

[Johan1973]

sweet, finally a complete fix

[amigappc]

Can you post HD video on Youtube where we can see how it performs? Which board exactly did you used? I see v4, v5 rev boards. I do not know which to choose?

[Solo761]

There should be no difference between v4 and v5 board. It's firmware markings and the reason for v4s is that they had a lot of these PCB made so they have v4 written although firmware in them is v5. At least that's what sellers say. My board is v4, cca one year old.

[Higgy]

Cheers for info RedskullDC.

I will have a go but will use normal components rather than surface mount ones. I think I have some reasonably small ceramic capacitors at the required value.

I wonder if Ian (aka Stedy) has spotted this as he was doing some work on the GBS?

Funny I was playing some AMIGA games on my moddied XBOX last night and said to the wife how much better AMIGA games look on emulated systems compared to running them on the actual hardware via LCD/LED TV's.

[Higgy]

Ummmm. The values shown on the picture must be more surface mount values.

Common resistor value is 47 ohms and ceramic capacitor is 10 or 22 pF if I am reading them correctly (10 and 22 as printed on the cap).

So will a 47 ohm resistor and 10pF cap be ok?

[kipper2k]

Originally Posted by Higgy

Ummmm. The values shown on the picture must be more surface mount values.

Common resistor value is 47 ohms and ceramic capacitor is 10 or 22 pF if I am reading them correctly (10 and 22 as printed on the cap).

So will a 47 ohm resistor and 10pF cap be ok?

most resistors have a +/- 5% tolerance so it would probably do, capacitors have an average 20% tolerance so a 10 should be good also

digikey have the 49.9 through hole resistors...

http://www.digikey.ca/product-search...0&pageSize=100

[Stedy]

Originally Posted by Higgy

Cheers for info RedskullDC.

I will have a go but will use normal components rather than surface mount ones. I think I have some reasonably small ceramic capacitors at the required value.

I wonder if Ian (aka Stedy) has spotted this as he was doing some work on the GBS?

Funny I was playing some AMIGA games on my moddied XBOX last night and said to the wife how much better AMIGA games look on emulated systems compared to running them on the actual hardware via LCD/LED TV's.

I've seen the post

The fix is odd. It creates a 270 MHz low pass filter for the SDRAM clock input, to smooth out high frequency ringing. Looking at the PCB, there may be a quirk, the SDRAM clock comes out of the TV5725 chip, is fed back and then goes to the SDRAM. Would need to measure signals to see what reflections are present. I'm a signal integrity engineer

I have my GBS board working with speckle free display using a derivation of my SCART cable. I have not finished my testing yet, hence no posting of the details. I will take a closer look at the SDRAM interface. I had observed some noise but not exceeding device absolute maximums of +/-2V.

@kipper2k

A 47 ohm or 56 ohm resistor should suffice. If you use AC termination, you want the terminating resistor, Rt to be less than z0, which is the PCB characteristic impedance. Common PCB impedances are 50 or 60 ohms, hence th 49.9 ohm standard value. You can tolerate upto 20% variation in value, 10% is preferred though.

My 'guide book' on high speed issues http://www.amazon.co.uk/Digital-Desi...h+speed+design very expensive now!!!!!

Ian

[amigappc]

If you gurus find a way to fine-tune it, we all could have great cheap solution for old machines this way. Please, keep up good work!

[Higgy]

Nice work and info.
Well I will hold off cutting any tracks and soldering on any components this weekend.

[Stedy]

Hi,

Can someone with a GBS board try a test for me?

If you connect it to the Amiga using the cable supplied, which has RGB video + sync, can you connect the sync signal via a 560 ohm to 1K (whatever value you have) resistor?

Use my SCART cable diagram as a guide, http://www.ianstedman.co.uk/Amiga/am...CART_cable.pngthe connection from pin 10, is shown with a 330 ohm resistor, change this as detailed above.

On my setup, this removed the white speckles. I want to know if I've been lucky or it genuinely helps.

Ian

P.S.

I have the datasheets on the video chips now

[Higgy]

I have adjusted the resistors on my spare scart.
My video grounds are joined.
I also noticed it did not have a logic ground so I added an additional wire.

I will try later with Amiga and GBS, but first got to try and finish wiring Raspberry Pi with wires for a MAME cocktail table me and a friend are building!

[Higgy]

Evening.
Well I tried the cable and I still have speckles. I have been watching 'Enjoy the Silents' demo and when there are colourful things moving on screen - lots of speckles.

I also tried another cable and it looks the same.

From memory when adjusting the R G B pots on the GBS motherboard that had an effect. I have not touched mine as it took ages trying to get a decent white (still grey looking).

[amigappc]

Is this low quality board issue, or Amiga RGB port has some specifics which need to be processed? Does artefacts show when you connect other consoles or computers using GBS?

[Johan1973]

I have connected ZX +2 and Amiga 500, Amiga 1200. It shows no matter what the RGB source is. The fault is at the GBS8220 end.

[amigappc]

Hmm, maybe a silly question, but can this be reported to the board manufacturer somehow? Maybe they can correct it in some new revision?

[Anemos]

I have 2 different revisions, same sh@it.
If i remember good is ver.4 and ver.5

[jbenam]

Originally Posted by Stedy

I have the datasheets on the video chips now

Exciting stuff, I should totally get that GBS-8220 now... Are there any real differences between the 8220 and the 8200?

[Stedy]

Hi,

@Higgy

What board revision do you have?

@thread

This is the list of tests I'm working through on the GBS82XX:


* Measure the +5V current using current probe and DMM
* Measure the on-board 3.3V supply ripple, FFT DC to 200 MHz.
* Feed in 3.3V LVTTL sync signal, see what happens, does noise go away?
* AC couple video, 220uF capacitors before termination/potentiometers.
* Test LM1881 see what happens.
* Try CGA from the Amiga.
* Feed in composite PAL video signal to Y of YPbPR input, is the image stable?
* Feed CVBS into Sync input.
* Use VGA input feed Amiga video but set ID pins.
* Feed in composite NTSC video signal to Y input. Use NVidia card + drivers to set this
* Measure Nintendo Wii YPbPr signal, then feed it into the GBS-8200 or hack NVidia card to output YpBPr.
* Locate the LLC or Genlock clock, see what frequency it is with video fed in.
* Check SDRAM scan conversion signals
* Buy and try a LMH1980 http://www.ti.com/product/lmh1980
* Build a RGB + Sync to YPbPr circuit, http://www.linear.com/solutions/1311
* Prototype SCUTA CPLD for sync maybe required.
* Add scanline generator?

Quite a list, when I'm done, which won't be soon, I'll publish the list either on my website or Wordpress blog.

I have changed one component on the board, as the 1.8V power supply was borderline stable. The sync signal
does affect, the Amigas 5V CMOS is not compatible with 3.3V LVTTL!
Now I have the software manual, I'll be able to play. The last video chip I worked with, took about 150 hours to understand,
the GBS boards have a lot in common with what I am familiar
with, so I know where to tweak first.

Have not done much testing with games yet, static video test patterns are good for colour/focus/flickering.