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Old 05 March 2010, 00:07   #1
elmasta
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Repairing an a1200 with green display

Hello all,

I bought an A1200 with a video problem. I knew of the video problem beforehand but the price was ok and I thought it could be easily repairable. Also, I always wanted an a1200 . However the problem seemed a little more complicated than I thought initially. I researched into the problem and concluded its was the DAC.

What I did was to check the input signals R0-R7, G0-G7, B0-B7 and the output from the dac IOR,IOG,IOB with different colour screens. The result was always the same, IOR and IOB stayed low no matter what color screen. Conclusion, the DAC is dead.

So am I starting to think on getting a DAC and replacing it myself, but being and old component it looks difficult to find one.

My questions are, ¿has anybody here replaced the dac? ¿where did you get it? ¿how much should I expect its cost to be?

thanks
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Old 05 March 2010, 03:12   #2
Zetr0
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@elmasta

I changed one on mine

I used a hot-air rework station -

removed the DAC from a dead A1200 motherboard
removed the dead DAC from the working motherboard
Soldered up the DAC with some nice Silver Bearing solder 0.015 and a soldering irion

About 20 minutes work.
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Old 05 March 2010, 03:57   #3
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>removed the DAC from a dead A1200 motherboard
>removed the dead DAC from the working motherboard

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Old 05 March 2010, 04:11   #4
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*hehe*

reads a little crazy indeed!!

but thats the sum of it.

you could also then say

Soldered good DAC from dead motherboard onto the good motherboard with the dead DAC removed.

.... phewww... dont have a drink before that sentence!!!
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Old 05 March 2010, 05:01   #5
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just had 4 beers.. had to read that twice!

lost
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Old 05 March 2010, 13:29   #6
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I removed both DAC's from two A1200 motherboards, one of which was dead.

On the working motheroard I then replaced the DAC with the working one...


(alcohol friendly version)
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Old 05 March 2010, 22:42   #7
elmasta
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haha! It's was clear to me, no alcohol here . yet...

Thing is, I don't have another a1200 mb. Does anyone know of any respectable company that sells them?

About the soldering part, I was planning to remove it by cutting the pins with a knife following the techniques posted in eab's soldering hints post and this page i found on the net. I plan on being very careful

By the time being I'll investigate on getting the IC.

Last edited by elmasta; 05 March 2010 at 23:11.
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Old 06 March 2010, 04:03   #8
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The CXA1145 can be a pain in the back to locate.

I don't know if its successors (CXA1645 is the latest one) are a drop-in replacement (read the datasheets from both parts!).

BTW: welcome to EAB, it is nice to see another fellow south-american here.
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Old 06 March 2010, 04:40   #9
elmasta
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Quote:
Originally Posted by rkauer View Post
The CXA1145 can be a pain in the back to locate.
Actually, it's the DAC which is VP101.

Quote:
Originally Posted by rkauer View Post
BTW: welcome to EAB, it is nice to see another fellow south-american here.
Obrigado!

--

This is how it looks on composite out. It's the pallete from digipaint 3.


Last edited by elmasta; 06 March 2010 at 04:49.
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Old 06 March 2010, 21:16   #10
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elmasta,

yo can purchase a RGB to SVHS /composite adapter for your amiga here
http://www.amigamaniac.com/
the adapter comes with own DAC and will not use anymore the sony CXA1145 chip
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Old 06 March 2010, 22:05   #11
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Quote:
Originally Posted by Fabie View Post
elmasta,

yo can purchase a RGB to SVHS /composite adapter for your amiga here
http://www.amigamaniac.com/
the adapter comes with own DAC and will not use anymore the sony CXA1145 chip
Thanks for the info, but the CXA1145 is not the DAC. It's a video encoder. It takes the RGB analog signal generated from the VP101 DAC and generates a PAL/NTSC signal.

In my case, the VP101 is at fault, AFAIK the CXA1145 is fine.

Last edited by elmasta; 06 March 2010 at 22:07. Reason: misspelled VP101
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Old 06 March 2010, 22:09   #12
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there is an irony, I have an A1200 mobo here that blasts only red out LOL!!! blue and greed are deceased....

alas I dont have a spare either VP101 DAC either.
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Old 06 March 2010, 23:57   #13
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Quote:
Originally Posted by elmasta View Post
Thanks for the info, but the CXA1145 is not the DAC. It's a video encoder. It takes the RGB analog signal generated from the VP101 DAC and generates a PAL/NTSC signal.

In my case, the VP101 is at fault, AFAIK the CXA1145 is fine.
if you think that the damage is in VP101 chip the only solution is to get a scandoubler....it will take the video directly from the Amiga Chips
Depends of the model of the scandoubler but for example flicker magic by DCE take video from lisa or alice....
Will work...I guarante...I had an A1200 with damage in blue.....red and green worked ok
Purchased flicker Magic scandoubler and everything was fine
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Old 07 March 2010, 01:05   #14
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Found one A1200 MB for replace, is cheaper than scadoubler and from all..
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Old 07 March 2010, 02:01   #15
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for those of you that are interested -


You can still get the "VP101 3BA" DAC that you find installed on the Rev 2B A1200

heres some info on the unit including a spec sheet and here is a order-request form thats from DigiKey .

I have no doubt that they would require a Minimum Order Quantity or now these days its a Minimum Order Cost, but theres no harm in asking for handfull of samples.

please make sure that you check the finer points, like the compatbility of this component to others in other revisions of A1200's

I have PM'd this infos to elmasta
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Old 07 March 2010, 02:27   #16
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Quote:
Originally Posted by Anemos View Post
Found one A1200 MB for replace, is cheaper than scadoubler and from all..
fot the money of a scandoubler you get a full A1200 with VGA output...
otherwise you get a new A1200 mobo for idem price but not VGA
so...which is the best choice?

SCANDOUBLER
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Old 07 March 2010, 15:35   #17
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more info for those interested:

I've been researching how to sustitute the chip, what I found is that there were two types of DACs used by Commodore. The VP101 and the ADV101. I guess depending on the motherboard revision (mine is 1D).

Both, VP101 and ADV101 are obsolete, but you can still get them, as Zethr0 said before. I don't know at what price yet.

Also I found that Analog Devices, the maker of ADV101 has a replacement part called ADV7120 which is pin compatible with ADV101, thus also compatible with VP101. Datasheets looks copy and pasted, so I guess it's compatible

Hope this info helps.

As for the scandoubler, I'm sure its a fine piece of hardware. But there's a limit to what I want to spend in this.
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Old 07 March 2010, 15:48   #18
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have you checked for any leaked caps ? It might be that IOR and IOB are shorted somewhere on the board with GND so changing the DAC might be unncessary ... I think it's more likely than DAC dying on you for no reason.
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Old 07 March 2010, 17:54   #19
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Quote:
Originally Posted by coze View Post
have you checked for any leaked caps ? It might be that IOR and IOB are shorted somewhere on the board with GND so changing the DAC might be unncessary ... I think it's more likely than DAC dying on you for no reason.
Thanks. Yes I checked that, and IOR, IOG and IOB measure 50ohm to ground, so no short there.

I didn't mention earlier, but the DAC gets hot almost inmediately. That was one of the reasons I suspected it was broken.
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