Author Topic: GX4000 Controller and Video Issues  (Read 244 times)

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Offline siccoyote

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GX4000 Controller and Video Issues
« on: 03:06, 11 November 19 »
I have two GX4000s, one is fine and good and dandy.

The other looks like it's had a bit more of a hard live, nothing much but a couple of scuffs.

This one when I start it up with Burning Rubber it just jump straight into the game, even if no joypad is plugged in.If I put my C4CPC cart in, it zooms through the menu loads up Switchblade and the attack meter goes up and won't release, but all other controls work if I plug a pad in.

Any idea where the problem might be?
« Last Edit: 10:41, 13 November 19 by siccoyote »

Offline Bryce

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #1 on: 09:26, 11 November 19 »
Hi,
     the most likely culprit is the sound chip (AY-3-8912). It needs to be replaced.

Bryce.

Offline siccoyote

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #2 on: 23:26, 11 November 19 »
Hi,
     the most likely culprit is the sound chip (AY-3-8912). It needs to be replaced.

Bryce.


Offline Urusergi

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #3 on: 23:37, 11 November 19 »
@siccoyote the sound chip (and asic) also controls the keyboard and joystick matrix
« Last Edit: 23:41, 11 November 19 by Urusergi »

Offline Bryce

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #4 on: 09:42, 12 November 19 »


No really, that was serious. The sound chip has an 8-bit digital input that the CPC and GX uses to read keyboard/joystick inputs. As Urusergi also mentioned there also the other side ie: the chip that creates the output signals for the scan, however, on a GX4000 this is done by the ASIC and that's not a part that's available, so hope that it is the AY.

Bryce.

Offline siccoyote

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #5 on: 11:40, 12 November 19 »
Thanks for the response, I'll think about buying and fitting a new AY chip, shame they didn't socket it like the CPU.

I'm afraid you'll have to forgive me I had about a 8 month Electronics eduction before they buldosed where I was studying (literally). Then I moved to the software side. So I can just about follow guides, do a bit of soldering etc. But as far are chips go it all sounds like star trek and magic 50% of the time.


I'm trying to have my GX4000 be the best it can be.

Also rather than starting another topic I have been having a hard time reading stuff sometimes in games due to streaking.

I read in the dirty video thread about this being due to them taking capacitors out or something? (the original example picture is gone)

Just wondering what the simplest solution is to this without risking wrecking my consoles.

At the moment got it connected with a good scart cable connected to the scart socket on the back (checked a DVD player with it and the signal didn't have streaks) almost bought a Monitor port to scart cable but sounds lke that wouldn't help.

Offline Bryce

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #6 on: 12:26, 12 November 19 »
Yes, saving the last pennies by removing the output caps is what causes some of that streaking.

Removing the AY in one piece can be difficult, I'd advise you use this method to avoid tearing the PCB apart: http://www.cpcwiki.eu/index.php/IC_Repair

As for chips being all Star Trek and Magic, yup, that's my opinion too and I'm meant to be an expert on this stuff :D

Bryce.
 

Offline siccoyote

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #7 on: 16:13, 12 November 19 »
Leaving the AY part aside for the moment. Would the fix you propose for the video make the scart clear?

I can't find anywhere that says what pins are actually connected on the scart socket. Whether it has RGB through the scart or just composite?

I can't make head nor tail of the circuit diagrams in the other thread

Can't work out where the capacitors would go on this: https://commons.wikimedia.org/wiki/File:Amstrad-GX4000-Motherboard-Flat-Top.jpg

I might use the dodgy one with the duff controls to try out the video fix on.

Would need a guide though :)

Offline Bryce

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #8 on: 16:37, 12 November 19 »
It might. there are many things that can make the SCART signal fuzzy. You would need to know exactly what your current setup is.
I posted somewhere in the forum about where the caps need to go, but that was for a CPC+, not a GX and they are on the monitor socket, not the SCART socket, so if you are using the SCART output they wouldn't change anything.

Bryce.

Offline siccoyote

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #9 on: 17:15, 12 November 19 »
Well tried two different Scart cables on two different CRTs (one Philips, one Panasonic) using two different GXs, and tried a dvd player connected via the same scart cables.

Both GXs have that ghosting to the right, which is more prominant the higher contrast it is, white on black and black on white (like the game over in picrocs) is worst. While DVD player doesn't seem to have that issue.

Does anyone else have that issue? I'm going to sleep. Stay frosty.

Offline gerald

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #10 on: 18:30, 12 November 19 »
It might. there are many things that can make the SCART signal fuzzy. You would need to know exactly what your current setup is.
I posted somewhere in the forum about where the caps need to go, but that was for a CPC+, not a GX and they are on the monitor socket, not the SCART socket, so if you are using the SCART output they wouldn't change anything.

Bryce.
There a also 2 different GX4000 model : with and without RF modulator.
- On the version without the RF modulator, RGB signals are buffered version of the DIN ones.
- On the version with the RF modulator, the scart RGB signals are buffered by the CXA1145 that create the composite signal used by the modulator and also passed to the SCART.
So either the buffered RGB is low pass filtered by the CXA1145 or what your are seeing is the composite signal.
Can you force the RGB input on your TV ?
Also, are your scart cable fully wired, ie with RGB ?

« Last Edit: 18:33, 12 November 19 by gerald »

Offline siccoyote

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Re: GX4000 Button 1 on Controller 1 (port) always on
« Reply #11 on: 10:15, 13 November 19 »
Both my machines are UK ones with an RF box inside. Well checked my wire and assumed it was fully wired since seemed a good one and very thick cable, but when I checked it with a multimeter the red doesn't seem to be connected, I grabed an old dusty cable and it was connected so used that. I think it does show a slight difference. I can't force my TV to use RGB as far as I can see the only option there is an SVHS option but the colours are everywhere and wrong on that.
It looks a bit better but the shadow on the right is still there.



Edit: Ah well I guess I have an answer of wether it's using the RGB signal from the scart. I moved it to another TV, the scart I was using to test is a bit iffy. I plugged it in turned it on, and it showed only red, then I wiggled it a bit and then only red and green, so it's definitely the RGB source. but the shadow was still there even with just red. So seems it's distorted  going to the RGB on the scart.

Edit Edit: Just plugged it into my LCD TV and it's very clear on there. I just wish I knew what to do to fix it, I'm guessing it's a problem in all GX4000, well at least this kind with the RF box.
« Last Edit: 12:00, 14 November 19 by siccoyote »