A1200 no video - worst repair ever? - please help.

chris.magson

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Hi Peeps,

I'm in one of the far reaches of the world, Namibia, and after quite a bit of deliberation, I finally got to ordering a replacement board for my (un)trusty A1200 with no sound (not a cap problem).

Well I ended up getting it from EBay, from a popular seller, and unfortunately it looks like I ended up with another lemon (a rev 1D1 one)...

Let me explain exactly what transpired - I'm sure someone here will know what it is:

Unpacked, connected keyboard, cf, and ps to board and then to telly via video out. Immediately wb screen looked wonky, with wavey lines running down. Moving the mouse also caused ripples on the screen. Screen was jumping intermittently. I could see enough, sort of, to navigate and open a tune - audio was working!
In about 90 seconds, TV (Sony Bravia) started losing signal (like a faulty rca cable).
I was still troubleshooting, then signal went completely. Total time about 3 minutes.

I lifted the top shield (it was shipped complete with top and bottom shield) and stepped back in shock and awe at the spider's nest under there... OMW! This is the worst cap job I've ever seen (I'm not an electrician - I'm talking about images on the web)

Here it is... please revel in its awesomeness:
11016497_10204929647673705_401128552_n.jpg
The cap on the yellow stalks is only soldered successfully(!) on one side. The other actually has melted plastic shielding holding it on, the wires brushing against the cap terminal.
Is there a record book for the worst 'fixes' ever? This one is surely up there, isn't it?

Anyway, I cleaned it off best I could. Underneath is perhaps the reason for the stalks... 2 1/2 solder pads were missing. In fact, there are gouge marks next to the pads and it looks like someone removed the old caps with a screwdriver, lifting them and the pads.

11015329_10204941105320139_1047694223_n.jpg

Unfortunately, it's the worst pads to go... there are no tracks ontop of the board I can bridge them to.

Best I could make out from the remaining via's, I've taken one terminal each of the two the caps to the back of the board as such:
C409 -ve terminal onto C804 (looks like ground side?)
C263 -ve terminal onto R235 (via comes out on the 3 of R235)
(I don't know if it was the right thing to do, but I epoxied those two smd's - on the padless ends - to the board)

11022928_10204949066919174_1372282099_n.jpg 11005584_10204944346721172_147948781_n.jpg 11015121_10204944392082306_1652046332_n.jpg
Are my modifications Ok or did I gimp it?

I still don't have any video.
I've probed (with 22uF cap inline to telly input) pin 20, and the telly almost wants to show something (no signal goes away), but it's just blankness.
(If I do this on my old, audioless board, I get a picture)

Is it possible U12 is damaged?

I don't have a scope and the telly has a sort of autosensing on the video in, so doesn't show anything making it very hard to troubleshoot.
The board is still working... Cannon Fodder booting off stiffy sounds awesome, but naught to see.

Thank you kindly for any help or advice.
 
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TheCorfiot

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If you can get an A520 modulator, i think you may find it works through the RGB port.

:)
 
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bebek

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As I remember If you fit C237 (470uF) you should have composite out too. These 100uF caps are not required if there is no modulator.
 
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chris.magson

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As I remember If you fit C237 (470uF) you should have composite out too. These 100uF caps are not required if there is no modulator.

You are 100% right. Seems like only C237 is required for the composite (It is there - middle pic is before I put it back). I can remove all the 100uF's (C239 and C236 and C235).
I don't know what C409 is for... that's the other 100uF cap I 'patched' with the green wire.


Ok... found C409 on the video decoupling.
And I have it connected to the ground side of C804 which is drawn on the power input circuit. So that looks ok.

What about all of these ferrite beads in the schematic? Loads of them. Can they go pop?
 
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chris.magson

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If you can get an A520 modulator, i think you may find it works through the RGB port.

:)

I've just ordered one for £5...
Hoping that it works... and it should if it's U12 that's bust, right?

But I'd still like to fix her... she deserves the dignity of not needing pokey modulator bits hanging out just to work. ;)
 

roy_bates

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the part you are referring to is a cxa1145 video encoder its made by sony,but i suppose you already know that.
 

chris.magson

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Why do you need modulator? The picture is horrible ...

I did read that too... but some picture is better than none. And at least I'll know it's just the encoder then...
If the A520 works, I'll work on getting something better out of the RGB...

Would something like this work? Can it handle the 15khz RGB?

RGB / CGA/ EGA/ YUV to VGA Arcade HD Video Converter Board abb
http://www.ebay.co.uk/itm/RGB-CGA-EGA-YUV-to-VGA-Arcade-HD-Video-Converter-Board-abb-/201248455872?pt=LH_DefaultDomain_3&hash=item2edb57bcc0

 

roy_bates

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yeah itll work...but its not the best.

to be honest,all you need though is a rgb to scart lead and your set.

but your best off finding out if the video is working through the rgb port first...
 
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chris.magson

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roy_bates

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yes,we do have to wait and see...


if you dont know what it is,it will be very difficult for anyone here to say what it is.

have you looked at the schematics for this machine?
 
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chris.magson

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have you looked at the schematics for this machine?

Yes, I have the schematics. And with the forums help yesterday, it's much clearer what's what.
There isn't really much in between pin20 of u12 and the video-out jack. Just the 470uF cap... which I replaced.
Maybe I should put back the modulator, and see if I can get an RF signal... I'd need an older telly for that (somewhere in the garage - have to find and dig it out).

I also read a bit on a mod for s-video output: The mod pulls C and Y from u12 for S-Video out. I have s-video on my LCD... would this be a better option?
http://eab.abime.net/showthread.php?t=40249
 

roy_bates

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if you up for it give it a go.

but,you still need to fix the video problem
 

chris.magson

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if you up for it give it a go.

Hey guys, here's some feedback. The A520 is still about 2 weeks out, but I decided to give the s-video mod a stab.
It took me a few days to scavenge all the parts from old circuit boards (luckily I have quite a few). So, with zero cost, (except the project board) here's what I ended up with:
.11040151_10204989863699068_711550598_n.jpg
Which I soldered directly onto pins 15,16, 19 and 24 of U12.
And that gave me this...
11040812_10204990628038176_868740560_n.jpg

and plenty happiness.

So I think it's safe to say problem found... U12 is kaput. I'll be ordering a new CXA1145 as soon as I find one with delivery cost less than US$41 !!!

The picture is so much better than composite. I'll def be looking at soldering this circuit onto some veroboard and putting it permanently with a s-video out socket into where the rf modulator was.

PS... when I first switched on, I could not get signal. I checked and double-checked and was just about to tear everything apart and pack it in, when I had a brain fart to swap the wires on the s-video out. Bam! Picture. The pinouts on a socket are of course mirrored! Doh.
 
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RichyV

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chris.magson

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Here's where I am with the veroboard version. Not necessarily going in this spot - it's just for scale. I'll prolly remove those compos(h)ite video and rf capacitors (oops, composite one's already gone)... and I think this might well be a permanent fix that I'll leave.

The s-video jack is also not yet mounted. Just there for scale.
The veroboard is finished, but not yet tested... bedtime now. :)
10997243_10204992626408134_2066700572_n.jpg
 
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