English Amiga Board


Go Back   English Amiga Board > Support > support.Hardware

 
 
Thread Tools
Old 13 January 2017, 20:44   #1
miribilist
 
Posts: n/a
RGB Problem? Brown Kickstart...

Hi everyone.
So, to my excitement I found my ages old A1200 under a pile of crap in the loft and keenly plugged it in.
To my joy I could hear the clicking of the HDD (which is a little faulty on the connector) and it booted up to the workbench exactly how I left it approx 15 years ago ***timewarp***

That was short lived however, as some pins on the HDD were loose and the drive seems pretty temperamental at best.

Anyway, thats not the issue Im asking about, the main problem is that the screen has a weird colour hue to it all of the time.
I cracked open the unit and noticed some grunge on a couple of capacitors, so did my research and replaced the whole lot, hoping to fix it, however this made absolutely no difference.

I will attach a picture of what Im seeing. Its as if it isn't showing any blue in the colour range. This is the same effect when using the RF aerial connector as well as the composite yellow plug into my TV.

Any ideas on what may be wrong and what I need to do to fix it?

Thanks in advance.
Attached Thumbnails
Click image for larger version

Name:	IMG_3819.jpg
Views:	145
Size:	485.1 KB
ID:	51697  
 
Old 13 January 2017, 20:52   #2
Akira
Registered User

Akira's Avatar
 
Join Date: May 2001
Location: New York
Posts: 19,265
The video encoder could have gotten damaged by the capacitor leak. This is just an idea.
Akira is offline  
Old 13 January 2017, 20:54   #3
miribilist
 
Posts: n/a
Thanks for getting back to me @Akira

Where about's is the video encoder located?
Is is replaceable (or repairable)?
 
Old 13 January 2017, 21:58   #4
Akira
Registered User

Akira's Avatar
 
Join Date: May 2001
Location: New York
Posts: 19,265
Yes to both questions.

The location is near the power port, where there's a bunch of capacitors. See if the acid has done any harm to its pins.

The encoder is a Sony CXA1145 if I am not mistaken.
http://www.amigawiki.de/doku.php?id=enarts:cxa1145

But I am not sure if you should be getting issues on RGB too if it was the encoder that was broken. Maybe it's something to do with the custom chips and acid corrosion. Give the whole board a good, microscopic look.
Akira is offline  
Old 13 January 2017, 22:05   #5
miribilist
 
Posts: n/a
thanks for that.
I'll have a closer look.
Any suggestions for deep cleaning a main board?
I'd heard a session in the dishwasher is fine (as long as any ram chips and batteries are removed first).
 
Old 13 January 2017, 22:33   #6
FOL
PSPUAE DEV

FOL's Avatar
 
Join Date: Nov 2006
Location: Barry / UK
Age: 41
Posts: 5,728
Send a message via MSN to FOL
It could also be the decoder is fine and the rgb tracks are damaged.
It looks like your missing blue.
FOL is offline  
Old 13 January 2017, 22:51   #7
paul1981
Registered User

paul1981's Avatar
 
Join Date: Oct 2013
Location: England
Posts: 178
A couple of A1200 video repair vids that you may find helpful:

[ Show youtube player ]

[ Show youtube player ]

For cleaning I'd probably get it under a tap of running warm water with a brush and some fairy liquid (being careful with the capacitors). Rinse off with more warm water and then wait a long time for it to dry, or use a hair dryer. Distilled water is supposed to be used to avoid residues, but isn't there a filter on combi boiler intakes anyway? I've not had any trouble my vinyl records with warm water so for sure motherboards will be fine.
paul1981 is offline  
Old 13 January 2017, 23:46   #8
demolition
Unregistered User
demolition's Avatar
 
Join Date: Sep 2012
Location: Copenhagen / DK
Age: 39
Posts: 3,969
You have a break in track with the blue color channel somewhere, probably caused by capacitor leaks. So you should remove all the electrolytic caps, get the MB cleaned, find the break, fix it and finally solder some new caps in there. Notice that a recap and clean by itself will not fix your problem.

I use the dishwasher for cleaning MBs but on the lowest heat setting (45 degC) and the quickest program which is 30 mins and using regular dishwasher detergent. After this, I rinse it with demineralized water to avoid any mineral deposits and then leave it in the oven on low heat (~75 degC) for several hours to dry. PCBs come out looking almost like new after this. Some people don't like to do it, but I never had any problems with it.
demolition is offline  
Old 14 January 2017, 01:45   #9
Shadowfire
Registered User
Shadowfire's Avatar
 
Join Date: Aug 2001
Location: Connecticut USA
Posts: 561
PCB's, it's whats for dinner.
Shadowfire is offline  
Old 18 January 2017, 14:57   #10
Hewitson
Registered User
Hewitson's Avatar
 
Join Date: Feb 2007
Location: Melbourne, Australia
Age: 37
Posts: 3,377
"What's cooking honey?" "Oh, just a motherboard."
Hewitson is offline  
Old 18 January 2017, 15:11   #11
jarp
Registered User

 
Join Date: Apr 2016
Location: Helsinki / Finland
Posts: 175
While PCB trace problem is more probably, you could also just have a broken cable? If you can borrow another one from somewhere, that is worth of checking. But if not it should be easy enough to check the traces using multimeter. You can find Amiga 1200 schematics from here:

http://www.amigawiki.de/doku.php?id=...ice:schematics

Since you are missing blue you should measure continuity from video port pin 5 to U30 pin 27. Unless I misread the schematics.

Edit: Oh you have problems with RF and composite also. Then you need to measure continuity from U30 pin 27 to U12 pin 4 also.
jarp is offline  
Old 18 January 2017, 15:13   #12
Pat the Cat
Banned

 
Join Date: Dec 2016
Location: Nottingham, UK
Posts: 481
Blue is typically least "intense" voltage or burst on a video system. It tends to be colour lost first in an RGB set. The human eye is a little strange, and Green colour receptors are most numerous. So green is usually last colour lost,

It's all fixable, you get this sort of issue lots if you try running genlocks using ribbon cables connected to an Amiga video port.

It does sound like modulator has bought it on the A1200, if both TV and phono are doing this. Might be fixable, not too much to replace.

What you could do is connect via 23 pin connector, see if that is same. If it is, this means maybe modulator not damaged, you can find missing blue between LISA output and video connector somewhere. Nothing really totally broken, really is just missing or damaged blue link.
Pat the Cat is offline  
Old 18 January 2017, 15:38   #13
Daedalus
Registered User

Daedalus's Avatar
 
Join Date: Jun 2009
Location: Dublin, then Glasgow
Posts: 4,285
The modulator has nothing to do with composite video output, so that's not where this fault is. It's further back in the chain, either the video encoder, video DAC or the traces connecting to them. Most likely is the video encoder just to the left of the IDE port. It's close to numerous capacitors prone to leaking, and I've repaired several A1200s and A600s with similar faults to this, all caused by traces in this area being corroded. Not a difficult job, but slow going to remove all the components in the area, clean the board and rebuild the damaged traces.
Daedalus is offline  
Old 18 January 2017, 16:05   #14
demolition
Unregistered User
demolition's Avatar
 
Join Date: Sep 2012
Location: Copenhagen / DK
Age: 39
Posts: 3,969
Quote:
Originally Posted by Pat the Cat View Post
Blue is typically least "intense" voltage or burst on a video system. It tends to be colour lost first in an RGB set. The human eye is a little strange, and Green colour receptors are most numerous. So green is usually last colour lost,
I fail to see how the eye being sensitive to green should influence which color color goes first in a video system. Yes, the eye is most sensitive to miscalibration of the green channel, but here we're talking complete loss, not just off colors like the issues people have with the GBS-82xx converters.
demolition is offline  
Old 18 January 2017, 17:29   #15
Akira
Registered User

Akira's Avatar
 
Join Date: May 2001
Location: New York
Posts: 19,265
Quote:
Originally Posted by Pat the Cat View Post
It does sound like modulator has bought it on the A1200, if both TV and phono are doing this. Might be fixable, not too much to replace.

What you could do is connect via 23 pin connector, see if that is same. If it is, this means maybe modulator not damaged, you can find missing blue between LISA output and video connector somewhere. Nothing really totally broken, really is just missing or damaged blue link.
Stop posting whatever on threads, seems like you didn't even read the original poster's text, and none of what you said makes any sense, especially saying that how the eye perceives colors has anything to do in why a computer's RGB signal would go first .

You are confusing people and not helping anyone, just making matters worse. What is your purpose?? Are you just trolling??

Quote:
Originally Posted by jarp
While PCB trace problem is more probably, you could also just have a broken cable? If you can borrow another one from somewhere, that is worth of checking. But if not it should be easy enough to check the traces using multimeter.
Yeah now here's some good advice for a first move: make sure it isn't the cable giving you issues before you go messing about with your AMiga.
Akira is offline  
Old 18 January 2017, 17:32   #16
demolition
Unregistered User
demolition's Avatar
 
Join Date: Sep 2012
Location: Copenhagen / DK
Age: 39
Posts: 3,969
Quote:
Originally Posted by Akira View Post
Yeah now here's some good advice for a first move: make sure it isn't the cable giving you issues before you go messing about with your AMiga.
Seeing as all colors are multiplexed together into a single wire in composite and RF cables, it should not be possible to get color differences like this with a broken cable. S-video can go B/W if the chrominance disappears but this is not the case here.
demolition is offline  
Old 18 January 2017, 18:09   #17
jarp
Registered User

 
Join Date: Apr 2016
Location: Helsinki / Finland
Posts: 175
Quote:
Originally Posted by demolition View Post
Seeing as all colors are multiplexed together into a single wire in composite and RF cables, it should not be possible to get color differences like this with a broken cable. S-video can go B/W if the chrominance disappears but this is not the case here.
True that. I misread the original description and made incorrect assumption that he was using RGB port.
jarp is offline  
Old 21 January 2017, 07:43   #18
xArtx
Registered User
 
Join Date: Jun 2013
Location: Australia
Posts: 679
Hi There’s a trace from pin 27 of the video DAC (BT101)
to pin 4 of the Sony video encoder with a 0.22uF capacitor between (C213 for A1200 Rev 1).

Assuiming all chips and diodes are fine, I don’t think there can be any other problem that could take out blue.
The digital blue path from Lisa to the video DAC is an 8 bit data bus just for blue.
If one of those traces was broken there would be funny business, but you’d have to cut all of them to loose blue completely.

The fact that all chips are fine is not necessarily a safe assumption.
Static damage among other things could take out a single channel for either the DAC or Sony encoder (maybe even when you did the recap).
It would be helpful to test RGB output too if you can.
xArtx is offline  
 


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
Amiga 600 rgb problem robo500 support.Hardware 3 16 April 2016 18:52
A1200 RGB problem StarEye support.Hardware 8 21 January 2012 18:50
RGB signal problem Amiten support.Hardware 7 03 September 2011 23:40
RGB to Scart Output Problem fruitlesseffort support.Hardware 5 23 February 2011 22:43
rgb cable problem stuntpup support.Hardware 25 07 October 2007 16:20

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 19:30.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
Page generated in 0.08797 seconds with 14 queries