Screen shadows on A600

[kipper2k]

Hi All,

A new day, a new A600 and a new problem

Heres a pic to show the problem, Workbench screen has similar shadow problems with windows, icons etc.

I've swapped out the following chips to see if that was issue,

Denise, Agnes, Gayle, CIA odd, all electrolytic caps.

shadows appear whether using Composite, or my Svideo adapter (which works great on the other ones). Doesnt matter which KS version i use, there are still shadows.

The only thing i can think of at the moment is the output from Denise somewhere downstream to affect both composite and RGB, i cant see it being one of the SMD resistors/caps feeding the RGB video output?

Once again, any ideas anyone ?




edit:... i did prove the replacement chips in other A600's so i believe the chips to be good.
edit again... there is no floppy or any ide attached, so no signs of any noise issues, other Amigas display fine in same location

[8bitbubsy]

Maybe the video decoder chip? The Sony one.
Anyways, tried the RGB port for shit and giggles? Sounds to me like a shielding problem somewhere... Not that I know this stuff, but hey..!

[Shadowfire]

Double check C237, should be 470uF (and installed in the correct direction).

Just for additional information, does it show the same symptoms in the RF modulator output, and the analog RGB output?

[kipper2k]

@shadowfire

C237 is in the right way and is a new 470uf cap. I touched up the solder joints and still no change. I cant use the RF output on the Amiga as its a PAL model and the connector that it uses is not the same as an NTSC one.

THe Amiga composite output is black & White and still has the shadows.. My Narmi Svideo adapter (plugged into the RGB output) has the same shadows using both the Svideo and composite outputs of the Narmi. (I'm using a multi system TV). All other PAL Amigas display fine

[coze]

flaky AV cable ? have any scart tv ?

[kipper2k]

Originally Posted by coze

flaky AV cable ? have any scart tv ?

there is no scart available in Canada, I'm using the same cables i use for all Amigas and its just this one that gives the shadows.

[seuden]

I have the exact same problem with my Windows machine at work. I've tried a new monitor, different resolutions and settings, can't get rid of it. I'm assuming it has to be the graphics card.

Sorry for the slight off topic I just thought it were strange.

[Muzer]

I thought everyone has that, it's just a fact of composite video (having said that, I don't have it nearly as bad as you, you can barely notice it on mine unless you look for it)

[Shadowfire]

Gah, both +VID and +VOUT can be responsible for this. It seems that one or the other is being tanked by driving strong R/G/B signals.

C460 & C459 seem to be used to generate +VREF, which appears to be used in a luminance delay line. This would actually be the first two caps I replace.

If you have a 50+Mhz oscilloscope, check +VID across C12A, compare the ripple to a known good board. A black and white checkerboard display pattern will be of immense help here! If excessive, or no reference or scope, replace C4, C408, C31, C32, C12A.

The check +VOUT across C12B, again looking at the ripple when displaying alternating black/white pixels. C12B & C409 are decoupling for this output.

Finally U12.

Edit: The Narmi unit takes its R,G,B data directly from analog R,G,B outputs at the video port. It's not surprise that both composite and svideo outputs from the Narmi show the same issue, since they're being fed the same voltages.
The fact that the A600 composite output also shows the ghosting, means that the problem isn't exclusive to one port or another.
Unfortunately, none of the IC's you mentioned at the beginning of the post, could have been the problem here. Denise (the only one which deals with video) is only outputting digital R,G,B data which is obviously not bad (a failure in the digital lines would result in RGB data being bad the entire screen).
The screenshot shows a dark trail after a high luminance output, which eventually normalizes (see to the right of the text). There is no ghosting to suggest a bad cable. Your problem is either a bad cap on the video power rails, or defective regulation. Defective regulation would most likely result in an all-white or all-black screen, so we are going to go after the capacitors on this one.

Keep in mind that these are best guesses, in the absense of a data sheet. If the luminance delay line was unutilized for the analog RGB output (which it very well may not be), I wouldn't suggest changing those caps, but I don't know for sure without the device datasheet.

[Photon]

Display problem, not Amiga output problem.

[kipper2k]

Thanks Shadowfire,

I dont have a scope here with me so i willl just swap out the suggested caps and see if that improves it

Originally Posted by Shadowfire

Gah, both +VID and +VOUT can be responsible for this. It seems that one or the other is being tanked by driving strong R/G/B signals.

C460 & C459 seem to be used to generate +VREF, which appears to be used in a luminance delay line. This would actually be the first two caps I replace.

If you have a 50+Mhz oscilloscope, check +VID across C12A, compare the ripple to a known good board. A black and white checkerboard display pattern will be of immense help here! If excessive, or no reference or scope, replace C4, C408, C31, C32, C12A.

The check +VOUT across C12B, again looking at the ripple when displaying alternating black/white pixels. C12B & C409 are decoupling for this output.

Finally U12.

@photon,

all other amigas work great, no display issues except for this amiga.

[Shadowfire]

After studying the schematic a bit more, if you want native NTSC composite output (with color) from this machine, without the Narmi, it should be quite simple.

1. Move R245 (pal video clock) to R246 (ntsc video clock)
2. Move R203 to R202 (or vice-versa, the schematic isn't 100% clear on which position is PAL and which one is NTSC) (CXA1145 pal/ntsc select)

[Zetr0]

@Kipps

man.... you love getting into trouble.... COOL!

okay... the following points

1. you recieve this Blaring of signal with strong colours contrasts,
2. this is prevailent even when using the RGB->Svideo Encoder

Point 1. (can happend if- )

A crappy cheap cable / shielding fault
Poor Cleaning cap(s)
CXA1145 needs replacing (very rarely this!)

BUT because of point 2

The AD724/5 completey decouples the amiga from the video output, as you know my friend, this sucks in a nice RGB source to output to either SVideo or Composite. with banding on this then it strikes home of a shielding fault inside the monitor / tv

to be fair, rkauer / stedy and TheCorfiot would really know more on how to help you in the latter =)

[kipper2k]

Thanks for the input Zetr0,

I have 3 more A600s in the "to be fixed" pile and after that i should be good. I'm thinking (hoping) that mabbe one or more of the caps are bad, it is possible my soldering was bad (Haha... did i just say that ),

This board is pretty manky so i'll give it a good clean, i'll probably do it tomorrow, tonight was sit back and do diddly squat night

[kipper2k]

Originally Posted by Shadowfire

After studying the schematic a bit more, if you want native NTSC composite output (with color) from this machine, without the Narmi, it should be quite simple.

1. Move R245 (pal video clock) to R246 (ntsc video clock)
2. Move R203 to R202 (or vice-versa, the schematic isn't 100% clear on which position is PAL and which one is NTSC) (CXA1145 pal/ntsc select)

Thanks Shadowfire. R203 is populated on the Pal board. Gonna be busy tonight


edit... been doing some thinking, if this works then there should be no reason why i cant add the Svideo circuit from the Amiga CD32 to get a nice Svideo output. so its added to the list for tonite

[Zetr0]

I thought the CD32 already had SVideo ?

the board has points for RGB too, althought I would then disable the Svideo and add an video amp to the red / blue and green out =D

[kipper2k]

Ok, here we go,

Originally Posted by Shadowfire
After studying the schematic a bit more, if you want native NTSC composite output (with color) from this machine, without the Narmi, it should be quite simple.

1. Move R245 (pal video clock) to R246 (ntsc video clock)
2. Move R203 to R202 (or vice-versa, the schematic isn't 100% clear on which position is PAL and which one is NTSC) (CXA1145 pal/ntsc select)
_________________________________________________________---

I moved the above components, Still no colour on NTSC, only on PAL.

I removed all caps in the power input area, i removed the Sony encoder chip, removed the RF module, cleaned up the area, checked all traces and they were all good. Replaced the Sony encoder with a spare, replaced all the electrolytics i removed with new ones.

Booted it up with my Narmi adapter using Svideo (default Pal mode on PAL input to my TV)... No shadows!! , picture is in colour, stable and focused fine. Tried composite output from the Narmi and same as the Svideo except picture quality not so good.


@Zetro

I was thinking if i can persuade the Sony decoder to put out NTSC colour then i can build the svideo cct that the CD32 uses and put the Svideo connector on the back of the Amiga where the RF module was (it will fit quite nicely)

@Shadowfire

I rechecked R202 and it is a 0ohm resistor that is supposed to send 5v to pin 7 of the encoder chip to enable NTSC but i am reading less than 1volt so i am going to do a little more checking. I checked my NTSC board and the "Pal goodies" portion of the circuit is not even included on the board, so there may be a few more differences.
Also according to the schematics R245/r246 should be 2.7K but the board has a 1k resistor on it. (The NTSC Amiga also has a 1K too so i am not sure what is going on there.

[Zetr0]

@Kipps

just drag the Y/C off the CXA and boost it with some 2n3904 transistors ala-so =)



as you know building a circuit like this you will need to keep it tight or signal lengths may pickup interference.

[kipper2k]

Thanks Zetr0,

I'll give it a go, Will it output NTSC colour even though its originating from a PAL signal... I still haven't got my head wrapped around all these different frequencies, formats etc, makes my head wanna explode

[kipper2k]

Hers a pinout of the CXA1145 (actually its equivalent

http://members.optusnet.com.au/evilt...rt/es71145.pdf

from what i see i should be able to apply 5v to pin 7, remove the clock signal from pin 6 and apply an external 3.579MHz crystal to pin 6 which should be correct frequency for NTSC, however i am unsure if the colour carrier frequency would be correct to either output composite or tie in to pins 15 and 16 for YC output for SVideo