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Author Topic: New, old A1200  (Read 2357 times)

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Offline espenboTopic starter

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New, old A1200
« on: November 27, 2011, 10:59:45 PM »
Hello

I just bogth a "new" A1200 board.
It did work grate the first day. But now I getting bad image. I can see det workbech but it's red and green and going up.
And somtimes I get 9/10 of the screen red and a small green stripe on the left...

I have tride swithing with other roms roms,

Please help...

Espen
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Offline bbond007

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Re: New, old A1200
« Reply #1 on: November 27, 2011, 11:31:28 PM »
Quote from: espenbo;669281
Hello

I just bogth a "new" A1200 board.
It did work grate the first day. But now I getting bad image. I can see det workbech but it's red and green and going up.
And somtimes I get 9/10 of the screen red and a small green stripe on the left...

I have tride swithing with other roms roms,

Please help...

Espen


Red I think is ROM chips. Try and reset those.

good luck
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Offline espenboTopic starter

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Re: New, old A1200
« Reply #2 on: November 28, 2011, 09:08:55 PM »
Quote from: bbond007;669288
Red I think is ROM chips. Try and reset those.


Have tride....

Give you a picture of what I see....

Espen
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Offline Ancalimon

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Re: New, old A1200
« Reply #3 on: November 28, 2011, 09:30:01 PM »
maybe the capacitors need changing? or there's a problem with the monitor cable?
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Offline espenboTopic starter

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Re: New, old A1200
« Reply #4 on: November 28, 2011, 10:02:27 PM »
I tried the monitor cabel (S-video) on A other Amiga. All OK
Tried to use that Amigas 3.1 Roms, same problem.
Tried a other TV-card, same problem.
Tried to ohm betewen the leggs of the ROM and the back side of the Amiga PCD board. OK

I have not tride the capacitors. They look ok.
Is there som way to messure if they are ok? Can I just messure Volt betwen the 2 leggs/pins?

Any other ideas?

Tanks in advance
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Offline espenboTopic starter

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Re: New, old A1200
« Reply #5 on: November 28, 2011, 10:54:38 PM »
I tride a bit of messuring. On thise board and other on not working. Havent tride a working board.

Is the Volt OK?
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Offline Daedalus

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Re: New, old A1200
« Reply #6 on: November 28, 2011, 11:22:22 PM »
Okay, this is almost certainly *not* a ROM, CPU or memory issue. It's most likely to be a bad connection in the video circuits, but could also be bad capacitors in the video area too I guess. When you say you're using S-Video, how exactly are you connecting to the Amiga? Have you checked all the connections between the video connector and the PCB? Examine them very carefully for cracks or bad looking solder. Try gently wiggling the connector to see if the problem flickers or anything...
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Offline espenboTopic starter

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Re: New, old A1200
« Reply #7 on: November 28, 2011, 11:46:15 PM »
I'm connected with the yellow plugg in the amiga to my TV-card in the computer.
I have on computer with XP and TV-card. And one with linux and TV-card.

My working Amiga gives a good screen output on both TV-cards.
With the same cabel my other Amiga gives the red output on both TV-cards. And sometimes a red screen, with green on the rigth side.

I do think it's bad capacitors. But I would like to test it first. Befor sending it away to replace them. Incase that not the problem.

:)
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Offline Daedalus

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Re: New, old A1200
« Reply #8 on: November 29, 2011, 12:07:12 AM »
Hmmm... Fair enough, if you're using the yellow composite connector, then it's not the connector causing that issue. It might be hard to find a bad cap in the video circuits without an oscilloscope (have you access to one?), but the only ones it could really be are C212 and C213, both near U12 (the video encoder). Pins 2, 3 and 4 of U12 are connected to pins 26, 25 and 27 of U30 (the video DAC) and carry the red, green and blue signals respectively. From your picture it appears that the green and blue signals are missing (25->3 and 27->4) whereas red is working (26->2). These signals are also used for the video out/monitor port on the A1200, and there are a couple of other components involved at that stage as well which might need to be checked.

But check for obvious things first: Look for short circuits around U30, U12 and the monitor connector, also around capacitors C211-213, diodes D231A-233B, and resistors R231A-232C... If it's not something obvious, you'll need to trace those signals with a scope to get a better idea of the problem...
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Offline espenboTopic starter

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Re: New, old A1200
« Reply #9 on: November 29, 2011, 09:21:07 PM »
Quote from: Daedalus;669433
Hmmm... Fair enough, if you're using the yellow composite connector, then it's not the connector causing that issue. It might be hard to find a bad cap in the video circuits without an oscilloscope (have you access to one?), but the only ones it could really be are C212 and C213, both near U12 (the video encoder). Pins 2, 3 and 4 of U12 are connected to pins 26, 25 and 27 of U30 (the video DAC) and carry the red, green and blue signals respectively. From your picture it appears that the green and blue signals are missing (25->3 and 27->4) whereas red is working (26->2). These signals are also used for the video out/monitor port on the A1200, and there are a couple of other components involved at that stage as well which might need to be checked.

But check for obvious things first: Look for short circuits around U30, U12 and the monitor connector, also around capacitors C211-213, diodes D231A-233B, and resistors R231A-232C... If it's not something obvious, you'll need to trace those signals with a scope to get a better idea of the problem...


I think I give up.
Thanks for the help

It's boot but with a red picture:(

So ho should I send my two not working A1200 board to for a repair? And a replacemant of capacitors?
I live in Norway. So maby sombody in Europe?
And does not cost to much ;)


I don't have a oscilloscope.
But would somthing like thise work?
http://www.bestoscilloscope.com/virtual/hantek-dso-2090.html
Maby I should begin saving money for one.
I havent just a oscilloscope since my school days, som 10 years agoe.
I have a certificate of apprenticeship as an electrician.
But now I work as a automation technician. So it's not the same as working with electronics. But I do understand som of it :)

Espen
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