Cap replacement cures video artifacts?

[WhyreByter]

Just wanted to double-check if this makes sense:

I just recapped my a1200, and noticed that some video artifacts I was getting are now gone. They manifested themselves as blocks of garbage, about 1 character block high by 3-4 character block wide, and 2-3 of them on the screen at a time. They would show up when the computer was first turned on, and then go away after a minute or two. This would happen whether it was running through my indivison, my a520, or composite.

Now, after recapping, my audio sounds better, and my video artifacts are gone.

Question: does this symptom going away make sense as a result of recapping? I'm happy that it did, but I was thinking that it was more like a marginal video ram that was funky while cool, and then warmed up. Or, some solder joint, etc.

Thanks!
WhyreByter

---------- Post added at 23:04 ---------- Previous post was at 22:23 ----------

Meh. Looks like I was wrong. The artifacts are still there. They're also slightly different. They're horizontal lines, about 20 pixels wide by 3-4 pixels high, and seem to "crawl" with different colors.

Seem to pop up when the computer is cold, and a few windows are open. Almost always get one/two at the top of the screen, where the memory displays are.

Any thoughts on culprits? The video does look better (sharper) after the recap, though.

Cheers!
WhyreByter

 

[Elerion]

Maybe there is a cure for this. Can you answer these questions:

What's the revision of the board?
Commodore or Escom?
Do you have some accelerator card inserted?
Do artifacts disappear after removing accelerator card?

 

[merlinkv]

Hi

Added to Elerion questions..

Do you use FlickerFixer?
Monitor works good with other Amiga/PC?

Best wishes

 

[WhyreByter]

Thanks!

Its a 1d1, commodore
I have a GVP Jaws with 16mb
Repros with or without accelerator
Happens on multiple tvs/monitors
Happens with or without my indivision installed (want to doublecheck that)
Happens through a520, vga, composite

Thanks!
WhyteByter

 

[rkauer]

Short the ferrite bead E127 on the under side of the motherboard.

If this don't cure the problem you may have to solder a 2.2uF x 16V capacitor on the transistor pad very near the Lisa chip (upper side of the board).

 

[WhyreByter]

Well, shoot! Looks like I fed you guys some bad info. Tonight, I tore the computer down to the components, and redid my troubleshooting:

- Removing the accelerator doesn't make a difference (other than a much slower computer!)
- It actually only comes out over the Indivision AGA connection (I swore that it used to come out over every connection type, but can't repro that now)
- Spraying the mounting socket area of the Indivision with a "can of cold" will cause the artifacts to come back immediately
- Pressing on the mount in just the right place (which seems to vary) will result in a reduction/cessation of the artifacts

I pulled the Indivision, and checked the socket, and all the pins look in place/aligned, and the socket doesn't look cracked, etc. It has been sanded down on the face, and does "snap" into place when installing.

So, now, o wise ones, thoughts? :huh: The next step I can think of is to *gently* bend out the pins so that they make better contact while the chip is warming up. But, I'm in no hurry, so give me your input!

Thanks, all!
WhyreByter

 

[rkauer]

Short ferrite bead E127 on the under side of the mobo.

 

[WhyreByter]

Short ferrite bead E127 on the under side of the mobo.

Ok, I'll bite, but it'll have to wait until tomorrow night. But, I gotta ask: what's the theory behind this as a fix for the symptoms? Looking at the schematics, E127 is on the CCK line on the Alice, which does handle chip-RAM interfacing. But, ferrite beads are used to filter high-frequency noise, which, in this case, seems like a good thing, so...

I'm not arguing, I just like to understand the "why", along with the "what".

Thanks!
WhyreByter

 

[merlinkv]

@WhyreByter

Is a common issue with fat Lisa's (Alice), marked HP, and many Indivisions 1200.

Try fixing the Indivision with a little amount of hot glue in the socket. This prevent bad contacts and Indy "jumps".

Best wishes

 

[Zetr0]

Short ferrite bead E127 on the under side of the mobo.

Ok, I'll bite, but it'll have to wait until tomorrow night. But, I gotta ask: what's the theory behind this as a fix for the symptoms? Looking at the schematics, E127 is on the CCK line on the Alice, which does handle chip-RAM interfacing. But, ferrite beads are used to filter high-frequency noise, which, in this case, seems like a good thing, so...

I'm not arguing, I just like to understand the "why", along with the "what".

Thanks!
WhyreByter

Its about the Colour (color) Clock signal, the ferrite bead is enough to skew the signal when in conjunction with the Indivision on some HP Lisa's

you see the CCK is a very dirty signal compared to other Clocks within the Amiga, and some chips infact reflect an echo or a small portion of it. My theory is that this doppler pulse gets picked as as another partial pulse via the Indivision - thus causing the artifacts on the screen as the adapter attempts to update in time with the pulse.

removing and bridging the ferrite bead in this instance smooths this problem, I postulate this is because removes (or drastically reduces) the echo of the CCK signal.


Simple as really =)


If you are still getting this issue without the Indivision AGA, then its like one of three possible things

1. Lisa Failure
2. Video DAC failure
3. Cross bleed from the Composite circuit
(possibly damage from an old cap leak)

3. Cross Bleed
Personally I would rule out this as this would be a persistent problem and not just appear / disappear.

2. Video Dac
This would most likely present itself as a lot more trouble on the screen, but wouldn't effect the output from the Inidivision.

3. Lisa Failure
Its quite likely this chip might have a micro-fracture in one or more solder pads, I would suggest if bridging the E127 doesn't fix the problem, perhaps laying down some fresh solder on the pads of the LISA.


Good luck and remember - take pics... it will not only commemorate a repair, but also act as inspiration to others with similar problems...

Oh... and we love our Hardware Pr0n =)

 

[WhyreByter]

It's a1200 night, so I'm looking at this now... Pulled the board, and looking for E127. I find an E127R and E127C.

Neither look like ferrite beads I'm used to. Looking at the schematic, you could be referring to either...?

Thanks!
WhyreByter

 

[rkauer]

Which revision is this board? The E127 is a resistor or a ferrite bead pending on revision. Short the resistor without mercy. Don't mess with the capacitor.

 

[WhyreByter]

I'm... speechless...

I'm... speechless...

@Zetr0 and rkauer:

So, I admit that I was skeptical of the fix of removing a ferrite bead, designed to limit noise, from a line that was theoretically noisy. It just doesn't make sense in my mind.

But, failing other options, I broke out my SMD tweezers and pulled E127R (I have a rev. 1D1 motherboard), and tacked in a bit of component lead. Took her inside, hooked her up to the indivision/accelerator/LCD, and fired her up.

To my surprise, the picture is flawless, even on the highest resolutions (which is where the artifacting was worst, which supports the CCK as the culprit).

You were right, and thanks, again for your help. I'm not happy with the bit of lead, so I need to find a SMD 0-ohm resistor locally (yeah, right), but it's pretty much 100% now, functionally!

Now, I've got this world peace issue; think you can help with that...?

Cheers, and thanks again!
WhyreByter

 

[rkauer]

No need to thanks, mate.

Pictures are a great "thank you" way to demonstrate your happiness. (Right, everything for a bit of hardware pr0n...)

 

[WhyreByter]

No need to thanks, mate.

Pictures are a great "thank you" way to demonstrate your happiness. (Right, everything for a bit of hardware pr0n...)

I knew someone was going to mention that... I tried to take a pic of the removal/replacement, but my macro just wasn't getting a good pic of that small of an area. Not much to see, either. <shrug>

But, I promise to make up for it with a photo-trip through my a4k power supply rebuild experience, hopefully tonight, but maybe tomorrow. :nod:

Cheers!
WhyreByter