A1200 Wrong Colors

[FOL]

Originally Posted by Retrofan

Sorry, not at all, as I don't have an idea about schematics, I don't understand them.

Edit: I mean... yes a cable goes here and then to there... and what? It's the same in the board. I should know what makes to have green and what doesn't, and it isn't there.

Edit: That's why I post here... I hope you can tell me what to do...

Grab the schematics, find video page, you will then understand what we are talking about, trust me.
Theres 4 lines coming from BT101, sync (which is going to green), then only 3 lines, r, g, b.
RGB go straight to 23 pin, but there are also 3 lines, going down to cxa encoder chip for Composite and RF.
Before they get to cxa there are 3 SMD caps that feed cxa with r, g, b.

Something I have come across (very rare though), is the lisa chip having bad joints, causing odd colour issues.
If the board is out of its shielding, then push on the lisa chip, see if it clears.

[Zetr0]

@RetroFan

I have just taken a few moment to go through the A1200 Schematic - Lets see if I can help explain a little bit.

Firstly we must ensure that the right voltages are correctly processed so the following list are capacitors responsible for filtering of specific voltages for the Amiga

Power Filter

Mono Ceramic

IDent.        Value        

C801        0.1uf    (+5v )
C802        .01uf    (+12v)
c803        .01uf    (-12v)
C804        .22uf    (+5v )

Electrolytic

IDent.        Value

C811        1000uf    (+5v )
C821        47uf    (+12v)
C822        47uf    (-12v)

Now once we are sure that the power is being filtered correctly we need to ensure that the Video Decoupling isn't causing a problem - this circuit creates a +/-VIO power ring that feeds a couple of chips responsible for Video Processing.

The DAC uses VIO power as part of its VREF input - so we need to ensure that nothing is causing a problem here

Video Decoupling

Mono Ceramic

IDent.        Value

C199        .22uf
C4A        .22uf
C4B        .22uf
C32        .22uf
C23        .047uf
C30B        .047uf
C30A        .22uf
C12B        .047uf
C12A        .22uf

Electrolytic

IDent.        Value

C408        1000uf
C487        10uf
C409        100uf

So lastly we have the DAC itself, this is responsible for taking 8bits of Red, 8bits of green and 8bits of blue and converting them into an analog output with a voltage intensity to denote luminosity

Video DAC - BT101 U30

Ceramic Mono

IDent.        Value

C215        .22UF VREF Pull up to +VIO (educated guess at value)
C217        .22uf VREF Pull Down to -VIO

The newly formed analog RGB signals are then fed to the Sony CXA1145 Encoder

CX1145 : U12

Mono Ceramic

IDent.        Value
C211A        .22uf
C211B        .22uf
C211C        .22uf

I dont really suspect that C211 A/B or C could be responsible for the problem you are having, however there is another area to look at -

Each Analog R.G and B component have a subtle +VIO pull ups before their output to the video port. each component of the R, G and B are Pulled up using a 1N914 Diode these are labled

D231A
D232A
D233A

of course there are VIO regulation Diodes as well for the Video Ground -VIO (again 1N914)

D231B
D232B
D233B

Thats an a lot to look at, for me I would pay most attention to the Video Decouping and the VREF pull ups C215 and C217

[FOL]

I was thinking, more along the lines of taking the cxa out of the equasion. So all your left with is the rgb lines and pullups.

Show help make it eaiser to fine issue, as you dont have to worry about that bit of the circuit.
Get the main problem sorted then, put caps back on to feed cxa.

[Zetr0]

@FOL

My friend, I was also thinking that it would be logical to remove the CXA1145 as I thought it also had a pull on the VIO, but it doesn't after writing up the list for RetroFan it turns out that it has a VVREF which is fed with a pull down and is only connected to the DAC via three ceramic capacitors.

Because of this the CXA1145 encoder is only present in the Circuit from C211A, C211B and C211C ceramic 0.22uf Capacitors... one could just remove them to isolate the CXA1145 - they would be easier to put back -

[Retrofan]

Ok Zetr0 I will start where you say:

Originally Posted by Zetr0

@RetroFan...
Thats an a lot to look at, for me I would pay most attention to the Video Decouping and the VREF pull ups C215 and C217

I appreciate a lot all yours explanations, and I hope that others, like Fol can understand them completely and argue about them. I just will try first with Fol's advice and later with yours. Edit: Or perhaps on the contrary, I will see. Thanks anyway.

[Zetr0]

@RetroFan

Theres no worries my friend, there basically the same thing, just a slightly different approach =)

[FOL]

Originally Posted by Zetr0

@FOL

Because of this the CXA1145 encoder is only present in the Circuit from C211A, C211B and C211C ceramic 0.22uf Capacitors... one could just remove them to isolate the CXA1145 - they would be easier to put back -

Thats exactly what I said or ment, lol, .
I was talking about feed caps.

Retrofans head is going to explode, .

[Retrofan]

Thanks again, Zetr0 and Fol. I just want to comment that I've readen all the threads about this same problem, and appart of the ones solved (2?) with Anemo's trick (that doesn't go to the cause), I haven't found any other fixing the problem (well, yes, one with a cold soldering -extremely rare- and another with a broken trace under a cap). What's more... Fol and Zetr0 you both have motherboards with the same problem as me and you haven't solved them.

[FOL]

Originally Posted by Retrofan

Thanks again, Zetr0 and Fol. I just want to comment that I've readen all the threads about this same problem, and appart of the ones solved (2?) with Anemo's trick (that doesn't go to the cause), I hadn't find any other fixing the problem. What's more... Fol and Zetr0 you both have motherboards with the same problem as me and you haven't solve them.

Lack of time on my part. I really dont have time to look deep into it.
Plus, I never tend to repair anything at home, lack of room.

[Retrofan]

Originally Posted by FOL

Grab the schematics, ... blah, blah, blah... sorry, you understand me, Fol...

Something I have come across (very rare though), is the lisa chip having bad joints, causing odd colour issues.
If the board is out of its shielding, then push on the lisa chip, see if it clears.

Ejem... I swear it was the same than before, but I was reading your posts full of info (of what I only get a part of it), but... It seems I get the part that matters. I've just pressed Lisa and ... I have this (the photo is right):



Well, it can be that my U30 isn't well soldered or that it's the "very rare, though" case of Fol.

Will see tomorrow resoldering Lisa...

Edit: No, it wasn't Lisa, it was I had to resolder U30. Now it is like always. I will start trying caps.

[Zetr0]

@RetroFan

its quite possible you have

1. a Dry solder joint or joints on your motherboard.
2. possibly a damaged pad from a previous / past capacitor leak

Since I have the kit here, I would run the hot-air and remove LISA to inspect the board underneath -I would then solder her back in.

However I don't know if you have that type of tool, so I would suggest re-soldering LISA - pay close attention as not to hold the iron too long on those legs.

[Retrofan]

Thanks. No, I don't have but the hot air gun used to remove paint and so, that I don't like to use for this (it's got a temp regulator and so). I don't know if it's ok to use it.

In fact I've resoldered Lisa thinking that my last image was caused by "her" (I pressed Lisa before booting, so I wasn't sure what it was).
No difference.

I've desoldered and tried with some caps too, C24, the one beside E231, C21 and C459.

I believe I'm doing nothing desoldering a cap to solder the same again later.

I've sent a message to Amigakit to see if they can sell me a kit of caps, as mines have to be tired with so much problems, so I think I should start changing them all. I've got to try to contact Cosmos, but on Ebay I don't see anything either.

The truth is that I'm a little tired of changing things without result. I think I should change the caps and then send it to Amigakit, but they have a lot of work at the moment, so it could take some time.

Btw: What's for the cable in this photo soldered to the pins of the DAC? http://amiga.resource.cx/photos/phot...res=hi&lang=en

[Zetr0]

Originally Posted by Retrofan

...
Btw: What's for the cable in this photo soldered to the pins of the DAC? http://amiga.resource.cx/photos/phot...res=hi&lang=en

That my friend is a motherboard routing fix, I would need to tripple check the schematic but I believe this pertains to the VREF input (not VIO).

[FOL]

Originally Posted by Zetr0

That my friend is a motherboard routing fix, I would need to tripple check the schematic but I believe this pertains to the VREF input (not VIO).

Zetr0 is right, but its not board specific. Nothing to do with rev either, if I recall.
If yours had it originally, then you should re add it.

[Retrofan]

No, it hadn't it. I think I'll try to contact Cosmos and get and change the caps and later I will send it to Amigakit.

Edit: Cosmos is already sending me a kit now .

Edit: If any other wants to try to fix it, I could pay him with an spare DAC I've got around here (the original).

[Jope]

I'll just type in my experiences, even though this will repeat what others said.

The Sony CXA1145 chip is a composite/s-video encoder, not an amplifier. The RGB signals go to it (but not through it) because otherwise you couldn't make composite video.

I have had broken CXA1145s cause missing/weak colours on the RGB port. An easy workaround in this case is to just remove the three caps before the encoder, then it will be isolated from the RGB signals. Who needs composite anyway, when you can have glorious RGB.

Also the BT101 DAC has been the source of these problems in a few I've repaired with one of the colour components either missing or weakened.

In the end it can also be one of the discrete components on the RGB signal path after the DAC. A scope helps in troubleshooting..

[Retrofan]

Thanks Jope. Well, in fact, as I can't test components, I'm changing them, and I've already changed CXA1145 and BT101 DAC. Next step is changing all the caps. I've already ordered a pack from Cosmos, and as he said: "For your blue screen, install my new capacitors and see !".

I mean, it can be also a faulty cap, can't it? And better to change them.

[rampartsagain]

seeing this thread some times my amiga when entering workbench flickers colors like crazy when reading hd or floppy i don´t no if this is something related to this topic , i am lazy on reading today

[FOL]

Originally Posted by Retrofan

I mean, it can be also a faulty cap, can't it? And better to change them.

Not always true, it could be a cap has leaked and caused damage in the layers of the board. Then it becomes more fun to find issue.

[Retrofan]

This is the Never Ending Story. Well, I've changed the caps, but now I can't boot and I've got this:



Edit: I'm using for C303, C304 and C459 that originally have 22uF, 25v others with 22uF, 16v , but Cosmos told me it isn't a problem.
Apart of that some are originally 100, 6A, 2NA and I'm using 100, 6b, 16v, and others originally are 10, 35A, 25B and I'm using 543, 10,16E. No idea about it, just using the kit of Cosmos.

I was thinking in a short, but I don't find any.