12 September 2019, 20:59 | #1 |
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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. |
12 September 2019, 23:25 | #2 |
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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) |
13 September 2019, 09:52 | #3 |
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I have stripped it down today still the same board looks nice and clean.
Last edited by Traindriver69; 03 November 2020 at 14:06. |
13 September 2019, 10:49 | #4 |
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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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13 September 2019, 12:19 | #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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13 September 2019, 13:19 | #6 | |
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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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14 September 2019, 02:01 | #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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14 September 2019, 02:26 | #8 | |
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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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14 September 2019, 09:50 | #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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14 September 2019, 09:53 | #10 | |
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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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14 September 2019, 13:34 | #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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14 September 2019, 13:40 | #12 |
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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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17 September 2019, 21:05 | #13 |
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Hi all
I have just finished doing a full recap and its exactly the same. Last edited by Traindriver69; 03 November 2020 at 14:06. |
17 September 2019, 21:42 | #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 12:16. |
18 September 2019, 00:44 | #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. |
18 September 2019, 11:37 | #16 |
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I have ordered a rgb to scart will see what happens when it comes.
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22 September 2019, 20:06 | #17 | |
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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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22 September 2019, 20:41 | #18 |
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24 September 2019, 11:54 | #19 |
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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. |
24 September 2019, 12:18 | #20 | |
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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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