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Old 12 September 2019, 21:59   #1
Traindriver69
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Amiga 1200 won't tune in

hi all
I have just picked up another Amiga 1200 today the guy I brought it off said it was working but when he plugged it in the picture was rolling like it was out of tune but he blamed his modern tv.
But when I tried it on my old crt tv it will not tune in through the rf or coxal connection (yellow red and white lead) so there is a fault on the 1200.
Anyone have any ideas please.
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Old 13 September 2019, 00:25   #2
eXeler0
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Could be a number of reasons, but if it hasn't been recapped it might be some bad caps, or even damaged mobo from leaks.
But It could also be something as weird as a keyboard issue where the PAL/NTSC toggle somehow gets stuck.
My point is, you'll probably need to narrow it down a bit before you get any useful answers. (Meaning you need to open it upp ansd start disconnecting stuff and checking the mobo, caps, chips for damage)
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Old 13 September 2019, 10:52   #3
Traindriver69
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I have stripped it down today still the same board looks nice and clean.
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Old 13 September 2019, 11:49   #4
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Originally Posted by Traindriver69 View Post
I have stripped it down today still the same board looks nice and clean.
It might look 'clean' from a distance, but if you inspect it more closely, you will see that there is corrosion and the solder looks dull and corroded, especially on the caps and surrounding components. There is also seem to be some green corrosion on some of the chip pins.
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Old 13 September 2019, 13:19   #5
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That's what I call an expert eye never saw any of that what would you recommend to do next.
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Old 13 September 2019, 14:19   #6
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That's what I call an expert eye never saw any of that what would you recommend to do next.
A good start is it should have a general clean with isopropyl alcohol and a (clean) toothbrush. However, with the corrosion it will need a more abrasive method - like using a fiberglass and/or wire brush pen.

This will only perform a cleanup to get rid of and to stop corrosion spreading. There may be trace and component failure (which can also occur as a result of the cleanup), so a multimeter can be used to test continuity of the traces between components.

Here are a few invaluable resources to show the schematic and board layout to help troubleshooting issues:

https://www.amigawiki.org/doku.php?i...ice:schematics

http://www.amigapcb.org/

And the guide for the A1200 is useful - especially on how to connect the A1200 to a display:

http://www.primrosebank.net/computer...Manual-ENG.pdf

Depending on the actual issue will depend on how convoluted the whole troubleshooting, diagnosing and resolution process will be - so your mileage will vary!
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Old 14 September 2019, 03:01   #7
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The corrosion cleaned with IPA or use lemon juice? I know the latter is bizarre but it worked well for battery leak. Maybe not the same for capacitor leak?
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Old 14 September 2019, 03:26   #8
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The corrosion cleaned with IPA or use lemon juice? I know the latter is bizarre but it worked well for battery leak. Maybe not the same for capacitor leak?
Lemon juice, or white vinegar, is acidic, so it is good for neutralising the alkaline of the battery leak. But, you then still need to remove the acid with isopropyl alcohol.

Capacitor leak only needs to be cleaned up with isopropyl alcohol.

In both case it is also good to use something abrasive to help with the cleanup.
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Old 14 September 2019, 10:50   #9
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I have ordered a recap kit so as I remove the capacitors I will clean the area and hopefully get it working.
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Old 14 September 2019, 10:53   #10
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I have ordered a recap kit so as I remove the capacitors I will clean the area and hopefully get it working.
Recapping is a whole different topic in itself!

Do you have the right tools and skillset to do the recapping? If you don't, then you can do more harm than good.
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Old 14 September 2019, 14:34   #11
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I have a hot air soldering station I am a novice but I like to have a go at fixing things
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Old 14 September 2019, 14:40   #12
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Originally Posted by Traindriver69 View Post
I have a hot air soldering station I am a novice but I like to have a go at fixing things
Great! Just be mindful not to melt any plastics, especially around the keyboard connector, audio ports, floppy data/power and LED connectors, and IDE interface - mask them off with kapton tape, or something that is heat resistance.
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Old 17 September 2019, 22:05   #13
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Hi all
I have just finished doing a full recap and its exactly the same.
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Old 17 September 2019, 22:42   #14
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I'm assuming this is through composite?

I would check the pins, traces and components to/from U13 U12 (EDIT: Sorry, I meant U12 - the CXA1145 encoder).

I would also suggest you use an RGB to SCART adapter and connect using that to a SCART capable TV. Or an RGB to VGA adapter and connect to a 15khz capable monitor.

Last edited by solarmon; 24 September 2019 at 13:16.
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Old 18 September 2019, 01:44   #15
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Dumb question, have you tried another video lead?

The TV is not seeing horizontal or vertical syncs pulse reliably, hence the picture. The garish colours are due to the TV not locking on and detecting the reference black level.

I have heard of the delay lines (4 metal cans north of U12 in your photo) failing and as they provide a phase delay for PAL video, they could cause the issues you see.

Do you have a SCART cable for the Amiga?
SCART bypasses the CXA1145 video encoder that connects to the yellow plug.
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Old 18 September 2019, 12:37   #16
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I have ordered a rgb to scart will see what happens when it comes.
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Old 22 September 2019, 21:06   #17
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Quote:
Originally Posted by Traindriver69 View Post
I have a hot air soldering station I am a novice but I like to have a go at fixing things.
Relatable. Just bought one myself to do a recap.

One of my amigas also has very bad picture on composite, but at the rgb it's good. Note that your TV/Monitor has to accept the rgb signal (as scart can deliver composite, rgb and other signals). Which some TVs do and some don't.
If not (as an alternative) an A520 modulator would probably deliver a working composite signal.
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Old 22 September 2019, 21:41   #18
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This guy says the culprit is probably the external components (bandpass filter cans) to the CXA1145 chip. He replaces it (SMD) with the succeeding model CXA1645.

ikod.se does something very similar.

Both seem to have well working composite outputs now.
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Old 24 September 2019, 12:54   #19
Traindriver69
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Hi all
Rgb lead has just and through the lead the picture is perfect so it is something on the rf / coxal socket side.
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Old 24 September 2019, 13:18   #20
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Quote:
Originally Posted by Traindriver69 View Post
Hi all
Rgb lead has just and through the lead the picture is perfect so it is something on the rf / coxal socket side.
Great news that RGB video is working!

I would suggest, if you are still concerned about not having a working RF or composite video, is to investigate the CXA1145 encoder, which is U12 on the motherboard, and traces and componets around it.
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