A1200 video port RGB problem

Toof · 12 February 2013, 16:06

My old 14 inch CRT tv failed yesterday whilst connected to my trusty A1200 via an RGB scart cable. There was a faint smell of burning from the tv and the tube whistled and went pop.

Long story short, the Amiga will now only output video via composite and rf, which are both perfect. If I try the scart, all I get is a dark grey/black screen with a very very faint ghost image of the boot screen. The cable has been tested on my A600 and it works fine, plus there's no obvious injury to the motherboard that I can see. Anyone know what's likely to have failed?

demolition · 12 February 2013, 16:23

Since you have a picture on composite and RF, there should be some good RGB signals in the Amiga somewhere.
I'm thinking either R232A/B/C or E258/E259/E260 are blown. Could also be the output voltages if the TV does receive RGBS but does not turn on the input if it doesn't see a voltage. So what you're seeing is just crosstalk.
Check for 5V on pin 23 and 12V on pin 22 on the Amiga RGB port.

Toof · 12 February 2013, 16:34

Thanks for that, I'll check the voltages when I get in

.

Toof · 12 February 2013, 17:47

Right, voltages are both good and the TV does switch to the correct input when the amiga is powered on.

demolition · 12 February 2013, 20:10

Next you should measure the resistance in R232A, R232B and R232C (should be 25 ohms) as well as E258R, E259R and E260R (should be low). Also check E253R which is for the sync signal (should be 47 ohms).

Hewitson · 15 February 2013, 14:41

I doubt the tube whistled and popped, it was probably a capacitor.

Toof · 16 February 2013, 03:06

Quote:

Originally Posted by Hewitson

I doubt the tube whistled and popped, it was probably a capacitor.

That was more a general statement than specific diagnosis

. The set was about 18 years old, so it had a good run. Anyway, I'll do more testing, as suggested, over the weekend and see if I can isolate the problem with the video output. Been a bit hectic this week.

Toof · 04 March 2013, 16:59

Sorry for the delay in sorting this, but anyway it turned out to be E253R. Replaced it and all is well. Thanks guys.

Off topic, but revelling in this minor victory, I completely recapped the board over the weekend, which was a good learning experience. I used the twist off method and found it very straight forward. Didn't fancy messing with hot air. The slight stability issues I had are now gone

videofx · 04 March 2013, 17:36

Nice work!

Any idea how to fix a similar problem on my 4000T? The machine appears to boot but no video on the 23pin on board video or a Picasso IV in video slot which works in my other 4000.

Any help would be greatly appreciated!

Prosonic · 11 March 2013, 02:46

i recently purchased an amiga 1200 that has ment to have working rgb only no compasite or rf out, via scart i get no output to a commodore 1084 monitor, if i remove the resister in the cable i get a faint outline of my workbench icons, should i be checking the above as well to try repair?

Mr Plow · 17 March 2013, 23:29

Hi everyone,

I've been trying to get an Amiga 1200 I bought around 10 years ago up and running but having a peculiar issue with the video display. I can get a signal out of the RF modulator without a problem, the picture and sound comes through fine but when using the composite or RGB I just get a black screen. I've tried a few things to get it working including disconnecting the floppy drive (which appears to be faulty and needs replacing anyway) and removing the RF shield in case it was shorting something on the motherboard but still no joy. I've upgraded the kickstart roms to 3.1 and these are working fine and I've had a close look at the motherboard to check for damaged caps but to my untrained eye there doesn't appear to be any bulging or dull connections.

After dragging down my old Philips CM8833 from the loft which amazingly still works the RGB output shows a diagonally rolling white line, I thought I'd check to make sure the three LCD TVs I tried were incompatible or something.

Any idea what could cause something like this? Maybe a dodgy cable but the odds of both my RGB and RF cables being faulty are pretty low I'd think.

Loedown · 18 March 2013, 06:09

Quote:

Originally Posted by Mr Plow

Hi everyone,

I've been trying to get an Amiga 1200 I bought around 10 years ago up and running but having a peculiar issue with the video display. I can get a signal out of the RF modulator without a problem, the picture and sound comes through fine but when using the composite or RGB I just get a black screen. I've tried a few things to get it working including disconnecting the floppy drive (which appears to be faulty and needs replacing anyway) and removing the RF shield in case it was shorting something on the motherboard but still no joy. I've upgraded the kickstart roms to 3.1 and these are working fine and I've had a close look at the motherboard to check for damaged caps but to my untrained eye there doesn't appear to be any bulging or dull connections.

After dragging down my old Philips CM8833 from the loft which amazingly still works the RGB output shows a diagonally rolling white line, I thought I'd check to make sure the three LCD TVs I tried were incompatible or something.

Any idea what could cause something like this? Maybe a dodgy cable but the odds of both my RGB and RF cables being faulty are pretty low I'd think.

Most likely you have a horizontal sync issue with the monitor, older sets and monitors used to have the horizontal adjustment on the back but I would dare say that it's internal on that monitor.

Leaking caps give a smell like well matured urine or dead fish and there's often like a fluff type substance near the leaks, especially the 10uF and 22uF caps in the cluster near the video section.

john1979 · 18 March 2013, 06:27

Quote:

Originally Posted by Loedown

Most likely you have a horizontal sync issue with the monitor, older sets and monitors used to have the horizontal adjustment on the back but I would dare say that it's internal on that monitor.

That would imply his LCD TVs that he tried are incompatible with the Amiga, which they aren't.

It's a fault on the Amiga side.

Loedown · 18 March 2013, 14:00

Quote:

Originally Posted by john1979

That would imply his LCD TVs that he tried are incompatible with the Amiga, which they aren't.

It's a fault on the Amiga side.

Maybe not but it still sounds like a sync problem.

Mr Plow · 18 March 2013, 17:20

I'll try and get hold of a multimeter and check out the resistors as suggested for Toof's problem. Regarding the Philips monitor, it works fine with my other consoles via Scart so I don't think the problem lies there but thanks for the suggestion.

Loedown · 19 March 2013, 05:27

Horizontal tearing is caused by a lack of sync and you're talking about antiquated hardware that does fail due to even things like resistor drift, crystals drift as well with time.

On the DB 23 you have Vsync and Hsync and if those signals aren't getting through it's certainly not going to synch and by rotating the Hsync on the monitor you may have gotten a clear picture and been able to ascertain that the fault lies with the Amiga where it's just out of frequency or close to the border.

We can only do our best by solving these problems but without the unit in front of us it does make it difficult.

12 February 2013, 16:06	#1
Toof Registered User Join Date: Mar 2011 Location: UK Age: 51 Posts: 22	A1200 video port RGB problem My old 14 inch CRT tv failed yesterday whilst connected to my trusty A1200 via an RGB scart cable. There was a faint smell of burning from the tv and the tube whistled and went pop. Long story short, the Amiga will now only output video via composite and rf, which are both perfect. If I try the scart, all I get is a dark grey/black screen with a very very faint ghost image of the boot screen. The cable has been tested on my A600 and it works fine, plus there's no obvious injury to the motherboard that I can see. Anyone know what's likely to have failed?

17 March 2013, 23:29	#11
Mr Plow Registered User Join Date: Mar 2013 Location: United Kingdom Posts: 12	A1200 - Video Problem Hi everyone, I've been trying to get an Amiga 1200 I bought around 10 years ago up and running but having a peculiar issue with the video display. I can get a signal out of the RF modulator without a problem, the picture and sound comes through fine but when using the composite or RGB I just get a black screen. I've tried a few things to get it working including disconnecting the floppy drive (which appears to be faulty and needs replacing anyway) and removing the RF shield in case it was shorting something on the motherboard but still no joy. I've upgraded the kickstart roms to 3.1 and these are working fine and I've had a close look at the motherboard to check for damaged caps but to my untrained eye there doesn't appear to be any bulging or dull connections. After dragging down my old Philips CM8833 from the loft which amazingly still works the RGB output shows a diagonally rolling white line, I thought I'd check to make sure the three LCD TVs I tried were incompatible or something. Any idea what could cause something like this? Maybe a dodgy cable but the odds of both my RGB and RF cables being faulty are pretty low I'd think.

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12 February 2013, 16:23	#2
demolition Unregistered User Join Date: Sep 2012 Location: Copenhagen / DK Age: 44 Posts: 4,190	Since you have a picture on composite and RF, there should be some good RGB signals in the Amiga somewhere. I'm thinking either R232A/B/C or E258/E259/E260 are blown. Could also be the output voltages if the TV does receive RGBS but does not turn on the input if it doesn't see a voltage. So what you're seeing is just crosstalk. Check for 5V on pin 23 and 12V on pin 22 on the Amiga RGB port.

12 February 2013, 16:34	#3
Toof Registered User Join Date: Mar 2011 Location: UK Age: 51 Posts: 22	Thanks for that, I'll check the voltages when I get in .

12 February 2013, 17:47	#4
Toof Registered User Join Date: Mar 2011 Location: UK Age: 51 Posts: 22	Right, voltages are both good and the TV does switch to the correct input when the amiga is powered on.

12 February 2013, 20:10	#5
demolition Unregistered User Join Date: Sep 2012 Location: Copenhagen / DK Age: 44 Posts: 4,190	Next you should measure the resistance in R232A, R232B and R232C (should be 25 ohms) as well as E258R, E259R and E260R (should be low). Also check E253R which is for the sync signal (should be 47 ohms).

15 February 2013, 14:41	#6
Hewitson Registered User Join Date: Feb 2007 Location: Melbourne, Australia Age: 41 Posts: 3,773	I doubt the tube whistled and popped, it was probably a capacitor.

04 March 2013, 16:59	#8
Toof Registered User Join Date: Mar 2011 Location: UK Age: 51 Posts: 22	Sorry for the delay in sorting this, but anyway it turned out to be E253R. Replaced it and all is well. Thanks guys. Off topic, but revelling in this minor victory, I completely recapped the board over the weekend, which was a good learning experience. I used the twist off method and found it very straight forward. Didn't fancy messing with hot air. The slight stability issues I had are now gone

04 March 2013, 17:36	#9
videofx Registered User Join Date: Jan 2013 Location: Chicago, IL USA Posts: 585	Nice work! Any idea how to fix a similar problem on my 4000T? The machine appears to boot but no video on the 23pin on board video or a Picasso IV in video slot which works in my other 4000. Any help would be greatly appreciated!

11 March 2013, 02:46	#10
Prosonic Registered User Join Date: Mar 2013 Location: Morwell Victoria Australia Age: 49 Posts: 113	i recently purchased an amiga 1200 that has ment to have working rgb only no compasite or rf out, via scart i get no output to a commodore 1084 monitor, if i remove the resister in the cable i get a faint outline of my workbench icons, should i be checking the above as well to try repair?

18 March 2013, 17:20	#15
Mr Plow Registered User Join Date: Mar 2013 Location: United Kingdom Posts: 12	I'll try and get hold of a multimeter and check out the resistors as suggested for Toof's problem. Regarding the Philips monitor, it works fine with my other consoles via Scart so I don't think the problem lies there but thanks for the suggestion.

19 March 2013, 05:27	#16
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	Horizontal tearing is caused by a lack of sync and you're talking about antiquated hardware that does fail due to even things like resistor drift, crystals drift as well with time. On the DB 23 you have Vsync and Hsync and if those signals aren't getting through it's certainly not going to synch and by rotating the Hsync on the monitor you may have gotten a clear picture and been able to ascertain that the fault lies with the Amiga where it's just out of frequency or close to the border. We can only do our best by solving these problems but without the unit in front of us it does make it difficult.

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