A1200 gray faint RGB but good COMP signal

Overmann · 16 March 2018, 00:25

Hi there,

I am trying to repair an old A1200 board that was dead and have gotten to the point where the only noticable problem is that the RGB signal is very faint and very gray. The composite signal is absolutely fine.

Has anyone run into this? I've attached a photo.

Jope · 16 March 2018, 08:17

Does any other motherboard work with the same video cable/tv combination?

Overmann · 16 March 2018, 14:05

Jepp, my other A1200 and my A500 work fine

solidcore · 16 March 2018, 15:45

Think this happened with my a600 on my larger Samsung tv but since my small Samsung tv amongst my Amiga shows the rgb flawlessly I didn't bother to test again on the big one so this may be tv related . Got another tv to test?
I assume you've recapped the 1200? If not probably a good place to start .

Capeview · 16 March 2018, 17:56

I had my 1200 plugged into a 1084s the other day and it only showed black and white. Couldn't work out what it was at first as was working fine before, so either the monitor is a bit iffy even though it's been fixed, or a lose connection in my 1200.

I switched the monitor off while the 1200 was still plugged in and back on again and the coloured returned??

Have you tried switching the monitor off and on while hooked up and see if it does anything different.

I had issues with both my 1200's not giving any RGB signal on my big Plasma TV but they did just show a grey screen, so there may have been something there if I turned up the brightness(Didn't think of that) but they worked fine with Composite. Could just be a signal issue with that machine?

Definitely worth trying it with an Old CRT if you can get hold of one with an RGB scart. They are the most reliable for testing out Amiga's when used them in the past.

xArtx · 17 March 2018, 02:00

For all Amigas, composite, RF, and S-Video signals
are derived from analogue RGB internally.
If any of those work, so does analogue RGB.
There’s only a few places to look if you don’t see it
working, such as cables, monitors, and the last of the
traces that lead the signals to the DB23 connector.

Overmann · 17 March 2018, 18:54

Interesting. So the cable and the monitor are working fine. Am i to understand that a caps change would not effect this then? I honestly don't know if the caps have been changed on this motherboard, but I think not.
Edit: Or are there caps right before the DB25 connection? I've ordered new caps and will be replacing them, for sure.

Overmann · 26 June 2018, 22:42

I have changed the caps now but there is no change to the machine, sadly. It appears to be working correctly but the video-port only displays a very faint grey picture while the composite out is nice and clear.

The problem is def. with the machine. The TV and cable is working perfectly with my other A1200, my C64 and my C128.

As per @xArtx suggestion I will look at the traces that leads to the DB23.

EDIT:
Well, having said that, I felt a bit stupid having taken it for granted that it's the machine that is the problem when I obviously know very little about these things, so I took the motherboard and hooked it up to my 1084s and It worked flawlessly. Clear and crisp picture on the RGB.

So why is this machine (and none of my other Amiga's) having problems with my RGB--Scart--TV setup?

idrougge · 27 June 2018, 10:27

Could it be that the 12 V or 5 V feed is not connected in the RGB port? It is used as a switching signal in the SCART cable to set the TV in RGB mode. If it is not active, the TV will try to use the sync signal as a composite signal instead. The 1084 doesn't care about the switching signal since it has a manual switch for choosing between RGB and composite.

Overmann · 27 June 2018, 14:25

Quote:

Originally Posted by idrougge

Could it be that the 12 V or 5 V feed is not connected in the RGB port? It is used as a switching signal in the SCART cable to set the TV in RGB mode. If it is not active, the TV will try to use the sync signal as a composite signal instead. The 1084 doesn't care about the switching signal since it has a manual switch for choosing between RGB and composite.

I've had a look at it now:

Pin 22 measure 12.46v
Pin 23 measure 3.00v
Also, pin 21 measure -11.29v ( i don't know if that is within range).

I've tried tracking the signal for pin 23, but at the first component (little orange resistor) has 3.0v on the side closest to the pin and .0v on the other side. Is this correct?

EDIT: Pins 11 and 12 is getting 4.96v and 4.60v. Is the little orange resistor at fault?

Daedalus · 27 June 2018, 14:47

Pin 23 is supposed to be 5V, and is wired to the RGB mode select line on the Ian Stedman type of SCART cable. This could well be your problem... It's possible the ferrite bead is damaged. That little orange resistor you mention is most likely a capacitor, in which case it should show the same voltage across it as the pin itself has over ground.

Overmann · 27 June 2018, 15:47

Well, I'll be damned! Ok I'll have to find a replacement for this thing. Can anyone give me a nod as to what this thing is exactly? I understand that it's E263C, and that it's a filter, and cbm numer 391092-02 Chip Ferrite Bead Medium, but that still leaves me a bit clueless. :P

Is there a ferrite bead on the A600 that I can use as a replacement?

Daedalus · 27 June 2018, 16:43

A ferrite bead can be replaced with a simple wire link. Its job is the carry the signal but act as an inductor in order to suppress spikes. If you test the resistance across it, it should be more or less 0 ohms - any more and it's faulty. If it's faulty, just bridge it with some wire and see if that solves the problem, then you can look at getting a replacement from somewhere. They're easy enough to find from electronics suppliers anyway if it does turn out that you need it.

Overmann · 27 June 2018, 16:51

Quote:

Originally Posted by Daedalus

A ferrite bead can be replaced with a simple wire link. Its job is the carry the signal but act as an inductor in order to suppress spikes. If you test the resistance across it, it should be more or less 0 ohms - any more and it's faulty. If it's faulty, just bridge it with some wire and see if that solves the problem, then you can look at getting a replacement from somewhere. They're easy enough to find from electronics suppliers anyway if it does turn out that you need it.

Thanks! I don't remember If I wrote this earlier but the first fault I found on this board was that one of the traces coming from the power connector was completely fried, so this poor motherboard has probably been through a lightningstorm or something like that.:P I'm a little surprised that it's not in worse shape. Perhaps this is what killed the ferrite as well?

All in all this motherboard appears to be working pretty well. One of the solder pads had lifted, so I used a wire there (which I'm sure is stupid, but I'm not skilled enough to make a new solderpad and glue it in place), but appart from that it is closing in on fully working. I connected a hdd yesterday and It booted fine. I'm optimistic!

Daedalus · 27 June 2018, 17:37

A fried trace could easily have been the result of a short elsewhere - the 12V rail carries enough power to fry traces with a good power supply, and it's more or less unprotected on the video port so a short there could have caused such a fault. It won't directly have damaged the ferrite, I guess a short on the 5V pin might have done that, but usually ferrites are simply broken due to stress or shock, as they're quite brittle and develop hairline fractures easily.

Overmann · 28 June 2018, 00:42

Well, thank you! It works now. It's not pretty but it works! BRILLIANT!

16 March 2018, 00:25	#1
Overmann Registered User Join Date: May 2014 Location: Norway Posts: 379	A1200 gray faint RGB but good COMP signal Hi there, I am trying to repair an old A1200 board that was dead and have gotten to the point where the only noticable problem is that the RGB signal is very faint and very gray. The composite signal is absolutely fine. Has anyone run into this? I've attached a photo. Last edited by Overmann; 16 March 2018 at 00:29. Reason: image was way to large

17 March 2018, 18:54	#7
Overmann Registered User Join Date: May 2014 Location: Norway Posts: 379	Interesting. So the cable and the monitor are working fine. Am i to understand that a caps change would not effect this then? I honestly don't know if the caps have been changed on this motherboard, but I think not. Edit: Or are there caps right before the DB25 connection? I've ordered new caps and will be replacing them, for sure. Last edited by Overmann; 17 March 2018 at 19:28.

26 June 2018, 22:42	#8
Overmann Registered User Join Date: May 2014 Location: Norway Posts: 379	I have changed the caps now but there is no change to the machine, sadly. It appears to be working correctly but the video-port only displays a very faint grey picture while the composite out is nice and clear. The problem is def. with the machine. The TV and cable is working perfectly with my other A1200, my C64 and my C128. As per @xArtx suggestion I will look at the traces that leads to the DB23. EDIT: Well, having said that, I felt a bit stupid having taken it for granted that it's the machine that is the problem when I obviously know very little about these things, so I took the motherboard and hooked it up to my 1084s and It worked flawlessly. Clear and crisp picture on the RGB. So why is this machine (and none of my other Amiga's) having problems with my RGB--Scart--TV setup? Last edited by Overmann; 26 June 2018 at 23:20.

27 June 2018, 15:47	#12
Overmann Registered User Join Date: May 2014 Location: Norway Posts: 379	Well, I'll be damned! Ok I'll have to find a replacement for this thing. Can anyone give me a nod as to what this thing is exactly? I understand that it's E263C, and that it's a filter, and cbm numer 391092-02 Chip Ferrite Bead Medium, but that still leaves me a bit clueless. :P Is there a ferrite bead on the A600 that I can use as a replacement? Last edited by Overmann; 27 June 2018 at 16:46. Reason: The ferrite bead was E263C. not E263R

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16 March 2018, 08:17	#2
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	Does any other motherboard work with the same video cable/tv combination?

16 March 2018, 14:05	#3
Overmann Registered User Join Date: May 2014 Location: Norway Posts: 379	Jepp, my other A1200 and my A500 work fine

16 March 2018, 15:45	#4
solidcore Registered User Join Date: Sep 2017 Location: birmingham, uk Posts: 548	Think this happened with my a600 on my larger Samsung tv but since my small Samsung tv amongst my Amiga shows the rgb flawlessly I didn't bother to test again on the big one so this may be tv related . Got another tv to test? I assume you've recapped the 1200? If not probably a good place to start .

16 March 2018, 17:56	#5
Capeview Registered User Join Date: Mar 2018 Location: London/UK Posts: 46	I had my 1200 plugged into a 1084s the other day and it only showed black and white. Couldn't work out what it was at first as was working fine before, so either the monitor is a bit iffy even though it's been fixed, or a lose connection in my 1200. I switched the monitor off while the 1200 was still plugged in and back on again and the coloured returned?? Have you tried switching the monitor off and on while hooked up and see if it does anything different. I had issues with both my 1200's not giving any RGB signal on my big Plasma TV but they did just show a grey screen, so there may have been something there if I turned up the brightness(Didn't think of that) but they worked fine with Composite. Could just be a signal issue with that machine? Definitely worth trying it with an Old CRT if you can get hold of one with an RGB scart. They are the most reliable for testing out Amiga's when used them in the past.

17 March 2018, 02:00	#6
xArtx Registered User Join Date: Jun 2013 Location: Australia Posts: 685	For all Amigas, composite, RF, and S-Video signals are derived from analogue RGB internally. If any of those work, so does analogue RGB. There’s only a few places to look if you don’t see it working, such as cables, monitors, and the last of the traces that lead the signals to the DB23 connector.

27 June 2018, 10:27	#9
idrougge Registered User Join Date: Sep 2007 Location: Stockholm Posts: 4,332	Could it be that the 12 V or 5 V feed is not connected in the RGB port? It is used as a switching signal in the SCART cable to set the TV in RGB mode. If it is not active, the TV will try to use the sync signal as a composite signal instead. The 1084 doesn't care about the switching signal since it has a manual switch for choosing between RGB and composite.

27 June 2018, 14:47	#11
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	Pin 23 is supposed to be 5V, and is wired to the RGB mode select line on the Ian Stedman type of SCART cable. This could well be your problem... It's possible the ferrite bead is damaged. That little orange resistor you mention is most likely a capacitor, in which case it should show the same voltage across it as the pin itself has over ground.

27 June 2018, 16:43	#13
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	A ferrite bead can be replaced with a simple wire link. Its job is the carry the signal but act as an inductor in order to suppress spikes. If you test the resistance across it, it should be more or less 0 ohms - any more and it's faulty. If it's faulty, just bridge it with some wire and see if that solves the problem, then you can look at getting a replacement from somewhere. They're easy enough to find from electronics suppliers anyway if it does turn out that you need it.

27 June 2018, 17:37	#15
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	A fried trace could easily have been the result of a short elsewhere - the 12V rail carries enough power to fry traces with a good power supply, and it's more or less unprotected on the video port so a short there could have caused such a fault. It won't directly have damaged the ferrite, I guess a short on the 5V pin might have done that, but usually ferrites are simply broken due to stress or shock, as they're quite brittle and develop hairline fractures easily.

28 June 2018, 00:42	#16
Overmann Registered User Join Date: May 2014 Location: Norway Posts: 379	Well, thank you! It works now. It's not pretty but it works! BRILLIANT!

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