Author Topic: Help request with 6128 sync - solved  (Read 293 times)

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Offline auberwn

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Help request with 6128 sync - solved
« on: 10:52, 27 April 20 »

EDIT: It turned out the Extron 202 Rxi I was using doesn't like the CPC. Connecting it directly to the monitor works fine.
EDIT2: After connecting it directly on the BVM monitor I found it to be too bright. After some test using variable resistors I put 500 Ohm resistors between the RGB lines and ground (not in line - that didn't seem to work for me). The result looks good enough for me but you could do better.

ORIGINAL POST:I would appreciate any help with the following issue.
I 'm trying to use my 6128 with my BVM monitor. In between I use an Extron rxi 202.
It start's up fine but when a game starts the Extron (and of course the monitor) loses sync. Not on all screens but on most of them - always on the main game.
This issue doesn't appear when using the green monitor - although there is a little horizontal shaking there two but that's always been the case.
So this is an interfacing issue (it seems).
I've tried everything I can think of:
 - straight csync (pin 4) and straight luma (pin 6).
 - both csync and luma through 470ohm
 - both csync and luma through variable resistor - 1K, 4.7K, 25K
 - both csync and luma through 220uf capacitor
 - both csync and luma through 470ohm (or variable resistor - 1K, 4.7K, 25K) and then 220uf capacitor - both csync and luma through lm1881 stripper and combinations with the above on input and output
By both I mean tried once with csync and once with luma.
I've cried on some occasions between all this.
Some things I noticed:
 - the luma signal and less noticeably the csync has some horizontal distortion about 1/3 of the screen from the top. It's very noticeable when I tapped the luma signal straight from the 40010 (before the onboard resistor)
 - the syncing gets a little better when I add some resistance on the output and some of the screens get more stable, with some horizontal distortions, but sync is still lost on the main game.
 - when the disk drive is working I notice the screen is slightly affected - is there a way to filter this out?


The 202 rxi and my BVM (early model 2016p) are very particular with the sync.
But on all other occasions I've been able to  get them to work.
When all else fails the lm1881 has always pulled through in the past. The Extron seems to like it.


For a power supply I'm using two switching adapters (5V and 12V) with at least 2A. I've tried using another 5V 2A power supply as well - no difference.
I'm making my tests directly on the pcb behind the video port - I've cut the csync line between two test points.
I'm using 5V from the location on the pcb that the power cable for the disk drive is attached.


Again I'd appreciate your help.
« Last Edit: 19:24, 29 April 20 by auberwn »

Offline Bryce

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Re: Help request with 6120 sync
« Reply #1 on: 12:32, 27 April 20 »
Your problem may be the switched mode power supplies. To get a good sync you need to be sure that both devices (CPC and monitor) have exactly the same ground level. This can be difficult to achieve with a switched mode power supply.

Bryce.

Offline auberwn

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Re: Help request with 6128 sync
« Reply #2 on: 17:13, 27 April 20 »

To test this I used the power from my green AMSTRAD monitor and got the same exact result.

Thanks for the reply.

Offline Bryce

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Re: Help request with 6128 sync
« Reply #3 on: 20:36, 27 April 20 »
Ok, but does the CPC GND and the monitor GND have a good connection?

Bryce.

Offline auberwn

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Re: Help request with 6128 sync
« Reply #4 on: 12:26, 28 April 20 »
I checked again and yes GND from the CPC is connected from the console to the 202rxi.

I've removed everything from the sync line and it looks to be more stable than everything else I've tried.
I'm using Robocop as the test and there is a screen which comes up first (pre-loading), then a menu (which alternates with a hi-score screen), then the "robocop directives" screen and finally the game proper.
With my mods at best I could see the first screen (pre-loading) but with horizontal tearing. after than sync was lost.
Now the first robocop screen is fine, the menu occasionally loses sync, the "robocop directives" screen loses sync a few times and the game proper loses sync always.

Are there any capacitors which might affect this? I haven't replaced any of them.

Addition:
I've checked and the 40010 VCC pin reads 5.05V. I'm saying this because I thing that at least power supply wise the chips are well fed (not considering the noise ofcourse).
« Last Edit: 12:46, 28 April 20 by auberwn »

Offline Bryce

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Re: Help request with 6128 sync
« Reply #5 on: 12:37, 28 April 20 »
No, capacitor changes won't make a difference. Can you send me a link to the exact monitor you are using?

Bryce.

Offline auberwn

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Re: Help request with 6128 sync
« Reply #6 on: 14:56, 28 April 20 »
It's an old one. Sony BVM 2016p.
Right now I'm connecting to the 202 rxi and that to the monitor.
I can see the rxi is losing sync on it's display so I'm thinking I should try to connect the CPC directly to the monitor and see what will happen. I'll have to make an adapter for that. I'll post results.

Offline Bryce

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Re: Help request with 6128 sync
« Reply #7 on: 15:27, 28 April 20 »
Ah, I've just found out what a 202 RXI is. This is most likely where the problem lies. These devices sample the sync signal as soon as a connection is made and continue sampling the sync at exactly that frequency. If a game changes the sync rate later to achieve some effect such as smoothing the scrolling, the rxi will loose the sync because it's not where it expected it to be.

Bryce.

Offline auberwn

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Re: Help request with 6128 sync
« Reply #8 on: 22:48, 28 April 20 »
And at the same time I tested connecting the CPC directly to the monitor and it works fine. :-[


Thank you Bryce and apologies for wasting your time.
I've never had the Extron do this and I've thrown quite a few stuff at it. It's a little picky - it requires clean composite sync and not composite video but if the device didn't provide that then I just used an lm1881.
I'll update the original post in case any poor soul ends up here in the future.
« Last Edit: 22:50, 28 April 20 by auberwn »