Problem with A1200 composite output

damiraga · 13 October 2011, 00:15

One of two A1200s I picked up recently has some issues with its composite video output, so I hope some of EAB´s hardware gurus will help me get it fixed.
This A1200 is an NTSC model and is hooked up to a Samsung SyncMaster 940MW (Multisystem) LCD TV. When connected to TV´s composite video input, the display is distorted and color is missing (see photos 1 and 2). When connected using RGB to SCART cable (Stedy´s design), the display is much better (photo 3). The other A1200 is PAL and its composite output is OK. TV has no problems accepting either PAL or NTSC and was tested with NTSC DVD player.

Any ideas, what to check first? Please keep in mind that I don´t have access to an oscilloscope, so I am limited in terms of how much diagnostics I am able to do. Any help is greatly appreciated!!!

FOL · 13 October 2011, 01:51

Check the schematics.

Could be the DAC.
BT101 should be alright as you have RGB fine.

damiraga · 13 October 2011, 09:09

Isn´t BT101 video DAC? How about CXA1145 encoder?
How do I test these?
Does service manual for A1200 exist? All I could find were schematics.

Quote:

Originally Posted by FOL

Check the schematics.

Could be the DAC.
BT101 should be alright as you have RGB fine.

FOL · 13 October 2011, 10:58

Quote:

Originally Posted by damiraga

Isn´t BT101 video DAC? How about CXA1145 encoder?
How do I test these?
Does service manual for A1200 exist? All I could find were schematics.

Service manual is schematics.

Yeh, thats what I ment, DAC should be ok as your getting RGB fine.
I would assume the inputs are fine to the encoder, so it could be;
Encoder,
Delay line,
or maybe caps associated with the encoder circuit.

This is all guess work, just by looking at the manual.
Not really the same as working on it yourself.

damiraga · 13 October 2011, 16:04

I was hoping there was more detailed service manual with troubleshooting steps/flowchart or some test points information.
Anyway, I will start with caps, as this seems to be the simplest route.

Thanks!

voyager · 13 October 2011, 18:53

And your PSU..

damiraga · 13 October 2011, 23:06

The PSU I am using is a modified ATX power supply. I also tested it with standard A500 (heavy) PSU and the problem remains.

FOL · 14 October 2011, 00:43

Quote:

Originally Posted by damiraga

The PSU I am using is a modified ATX power supply. I also tested it with standard A500 (heavy) PSU and the problem remains.

If it were a PSU issue, then all colour would be lost including RGB.
We have already narrowed it down, as 23pin RGB is working.

damiraga · 15 October 2011, 02:01

I think I am onto something. At some point this A1200 was equipped with Indivision AGA. In order to reduce tearing in high-res modes, previous owner did try to do E127R hack (short the resistor). Unfortunately, he lifted one of the traces of the E127R (the inner one, next to E129R). He told me he thought he repaired this.
By looking at the schematics, E127 is the CCK line (colour clock) which would explain my missing color issue.
Any suggestions how to fix this? Where is this pad/trace connecting to? I have a hard time following the schematics on my laptop display. I should really get them printed (A3 size).

damiraga · 15 October 2011, 23:26

Short update: I repaired the damaged trace and have replaced the resistor that was removed. Unfortunately, the problem remains, so I am back to square one.
My next step is to replace the caps, which are the most likely culprit, considering this specific A1200 was sitting in a storage since 2008.

FOL · 16 October 2011, 01:23

Could also be the delay line.
This wouldnt effect RGB, but would effect both RF and Composite.

rkauer · 20 October 2011, 04:14

Are you trying a NTSC Amiga into a PAL TV via composite? Will never work correctly this way.

Use SCART or other RGB solution and all will be good on earth again.

damiraga · 20 October 2011, 08:35

No! I have two multisystem LCD TVs both of which officially support PAL and NTSC (via all analog inputs - RF, Composite, S-Video). There is definitely something wrong with composite and RF output (look at the second photo and pay attention to window borders). If I use RGB output, either directly to C1084s or via Scart to LCD, everything looks perfect.

rkauer · 31 October 2011, 20:44

Then the problem is your TV trying to identify a mode that is not compatible. Chances are you have a PAL Amiga running in NTSC mode.

Although via RGB the colour will be present, most TVs doesn't "like" a PAL-60 signal.

13 October 2011, 00:15	#1
damiraga Registered User Join Date: Mar 2011 Location: Sarajevo, Bosnia-Herzegovina Posts: 53	Problem with A1200 composite output One of two A1200s I picked up recently has some issues with its composite video output, so I hope some of EAB´s hardware gurus will help me get it fixed. This A1200 is an NTSC model and is hooked up to a Samsung SyncMaster 940MW (Multisystem) LCD TV. When connected to TV´s composite video input, the display is distorted and color is missing (see photos 1 and 2). When connected using RGB to SCART cable (Stedy´s design), the display is much better (photo 3). The other A1200 is PAL and its composite output is OK. TV has no problems accepting either PAL or NTSC and was tested with NTSC DVD player. Any ideas, what to check first? Please keep in mind that I don´t have access to an oscilloscope, so I am limited in terms of how much diagnostics I am able to do. Any help is greatly appreciated!!!

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13 October 2011, 01:51	#2
FOL PSPUAE DEV Join Date: Nov 2006 Location: Wales / UK Age: 45 Posts: 6,047	Check the schematics. Could be the DAC. BT101 should be alright as you have RGB fine.

13 October 2011, 16:04	#5
damiraga Registered User Join Date: Mar 2011 Location: Sarajevo, Bosnia-Herzegovina Posts: 53	I was hoping there was more detailed service manual with troubleshooting steps/flowchart or some test points information. Anyway, I will start with caps, as this seems to be the simplest route. Thanks!

13 October 2011, 18:53	#6
voyager The show must go on. Join Date: Dec 2010 Location: Alkmaar Nederland Posts: 269	And your PSU..

13 October 2011, 23:06	#7
damiraga Registered User Join Date: Mar 2011 Location: Sarajevo, Bosnia-Herzegovina Posts: 53	The PSU I am using is a modified ATX power supply. I also tested it with standard A500 (heavy) PSU and the problem remains.

15 October 2011, 02:01	#9
damiraga Registered User Join Date: Mar 2011 Location: Sarajevo, Bosnia-Herzegovina Posts: 53	I think I am onto something. At some point this A1200 was equipped with Indivision AGA. In order to reduce tearing in high-res modes, previous owner did try to do E127R hack (short the resistor). Unfortunately, he lifted one of the traces of the E127R (the inner one, next to E129R). He told me he thought he repaired this. By looking at the schematics, E127 is the CCK line (colour clock) which would explain my missing color issue. Any suggestions how to fix this? Where is this pad/trace connecting to? I have a hard time following the schematics on my laptop display. I should really get them printed (A3 size).

15 October 2011, 23:26	#10
damiraga Registered User Join Date: Mar 2011 Location: Sarajevo, Bosnia-Herzegovina Posts: 53	Short update: I repaired the damaged trace and have replaced the resistor that was removed. Unfortunately, the problem remains, so I am back to square one. My next step is to replace the caps, which are the most likely culprit, considering this specific A1200 was sitting in a storage since 2008.

16 October 2011, 01:23	#11
FOL PSPUAE DEV Join Date: Nov 2006 Location: Wales / UK Age: 45 Posts: 6,047	Could also be the delay line. This wouldnt effect RGB, but would effect both RF and Composite.

20 October 2011, 04:14	#12
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	Are you trying a NTSC Amiga into a PAL TV via composite? Will never work correctly this way. Use SCART or other RGB solution and all will be good on earth again.

20 October 2011, 08:35	#13
damiraga Registered User Join Date: Mar 2011 Location: Sarajevo, Bosnia-Herzegovina Posts: 53	No! I have two multisystem LCD TVs both of which officially support PAL and NTSC (via all analog inputs - RF, Composite, S-Video). There is definitely something wrong with composite and RF output (look at the second photo and pay attention to window borders). If I use RGB output, either directly to C1084s or via Scart to LCD, everything looks perfect.

31 October 2011, 20:44	#14
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	Then the problem is your TV trying to identify a mode that is not compatible. Chances are you have a PAL Amiga running in NTSC mode. Although via RGB the colour will be present, most TVs doesn't "like" a PAL-60 signal.

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