Scandoubler problem - hardware fault?

[Amiwin]

Hi, I have an internal Power Computing ScanMagic for my A1200.

I think the scandoubler has a slight fault. It doubles the scan of 15khz modes no problem and displays them very clearly - but there is a problem with "passing through" the higher rate modes (like multiscan/DBLPal).

At first (in a 30khz modes) it seems fine - it works as it should and the picture is very clear. After about 10 mins, as I'm moving my mouse around and opening/dragging windows, the screen starts flickering and "rolling". This flickering and distortion continues until about 20mins later, the screen goes entirely distorted off its own accord and the monitor cant hold its sync (ie. it switches itself off saying No Signal).

I've tried 3 different monitors and the same problem occurs. I've tried switching the Amiga on and off. It seems to work properly again if I leave it for about half an hour... maybe to cool down? (the board gets very hot).

It is positioned correctly, I've tried replacing it and cleaning the contacts, checked the cable, checked the connectors... I don't know what's wrong.

Its strange as, at first, it only starts flickering when I move stuff around or when things change on-screen. But it gets worse by itself anyway.

Apart from that it is doubling the rates of 15khz modes perfectly.

Do you have any suggestions?

Thanks.

[Damion]

Is the Power Computing version made by DCE? If
so, the picture should reamain stable in the
pass-through modes. I've used DBLNTSC before
for hours with no problems.

[Amiwin]

Yes I think so.

[z5]

@Amiwin:

I have the same problem with my scandoubler and A1200. I seem to recall that this is a fault of a certain revision of the A1200 motherboard, but i'm not sure.

[Damion]

What motherboard revision do you guys have?
I actually had to return the first SD I bought
because white colors would tear away and "bleed"
through the display. The second one I got has
been working flawless.

[Amiwin]

I think it's a 1D. I'll check properly soon.

Thanks for helping!  :-)

[Damion]

@Amiwin

Thanks for helping!:-)

No prob!

On further thought, here is a good way to determine
the cause of your video problem:

1. If you don't already have one, pick up a 23 to
15-pin video adapter so you can hook your VGA
monitor directly to the amiga video port
(about 15 Euro/USD on ebay or from any amiga
dealer).

2. Select the offending "30khz" video mode and save.

3. Turn off the machine, and connect the monitor
directly to the amiga 23-pin video port via the
adapter.

3. Fire up the machine and let it run. If the display
remains stable, you can be reasonably sure the fault
is with the scandoubler. If the display begins
to distort ala before, you probably need to have
the motherboard "timing" repairs made.

If you do end up needing the "timing" fixes,
there are a few people on this board who
have done them before and can help, or
I'm sure someone can recommend a shop
capable of making the repairs. Apparently
all but some Commodore revisions and the
last of the Escom machines may need "the fix".

Hope this helps!

[Amiwin]

I happen to have the said adaptor and I bought the scandoubler to replace it.

Of course, it works fine with the regular adaptor. :-(

Do you reckon the timing fix may help anyway? If so can you give me more info? :-)

Thanks again

[Damion]

Here're some threads about A1200 video problems:

http://www.amiga.org/forums/showthread.php?t=1455

http://www.amiga.org/forums/showthread.php?t=1549

Here's a site about the "timing" problems and
their relation to some "Apollo" cards:

http://www.haigh1.freeserve.co.uk/Apollo_crashing.htm

My bet would be on the SD itself being the
problem, as it works fine without it. It's
entirely possible though that a "timing"
fault could somehow affect the display only
when "passed through" the SD, but it seems very
unlikely.

[KennyR]

Ok, this is a problem with certain revisions of the A1200 motherboard, and isn't anything to do with the ID4 timing problems.

From the Eyetech website:

Changes to the A1200's video circuitry to meet new EC interference emission standards means that some monitors exhibit horizontal 'tearing' of the screen image when using the PC-compatible screen modes of DBLPAL, DBLNTSC, Super72, Productivity etc. (Standard 15 kHz screen modes work fine).

Eyetech also do a fix for it. Check the link.

[Damion]

Not exactly, that's a different problem related
to video problems mainly with RF output on later
motherboards.

There were early NTSC US C= boards that exhibited
this tearing problem (obviously nothing to do
with "EC" regulations) and not just the 1D4
revisions.

The confusing issue is whether or not the
"timing fixes" involving Alice and Budgie
have anything to to with video problems, or
only affect accelerators/controllers/etc.
The fix involves removing capacitors under
Alice, so I'd say it's likely. It would be
nice if there was a single resource somewhere
that gave some more detailed specifics.

[Amiwin]

You're all being very helpful, thankyou!

I can now confirm the motherboard's revision.
It's 1B. Sorry about that, I couldn't remember - I just opened the machine now to check.

I really hope it's not the scandoubler as I picked it up from eBay for £13.50 (not bad) and I really can't afford a brand new one.

I am handy with a soldering iron so, if I must try and apply this motherboard patch I can do so no problem.

It's strange because during the first 5 minutes (while the display still looks ok) the tearing and monitor distortion only happens when things on-screen change, like when I'm dragging windows or opening menus... or moving my mouse around rapidly.

It's really strange... it feels like there's something wrong with the amiga - as if it's losing sync?

But everything is perfect with the standard VGA adaptor bar the fact I can't use 15kHz. :-(

Any suggestions as to what I should do? Any bugs with my 1B motherboard that could affect it?

I have emailed the eBay  seller - maybe he knows anything/i can can get a refund?  :-? Either way I don't lose much.

[Amiwin]

Got a reply from the seller:

I think I'd only used it extensively with the 15khz mode - but from memory,
when I had used it with other modes, I think I'd tried different monitor
drivers, such as the vga ones.  I think it's an issue with the timing
signals (which come from the rgb port, hence the passthrough) in some modes,
but is really only fixable with the fully internal scandoublers that tend to
be more expensive. I think they connect internally across two chips.

Like you say, it could be due to the heat generated by the higher modes -
but I don't think I'd ever used it at the high modes for very long.

Now I am even more confused. I thought Multiscan WAS the VGA driver ... I have the VGAOnly patch installed and I am sure I've done everything right.

[zipper]

So, it clips onto the Lisa chip? With a socket, hole in the middle? The first thing is to try a fan to eliminate overheating. Or test with a cool spray on Lisa (and maybe the SD chips,too). My external SD/FliFi crawls because of warming up, needing trim pot use if I want a good picture as  cold as well as warm, too. :-?

[Amiwin]

Yes, it clips onto Lisa, but has no hole. It is a PCB with a chip socket underneath, with a cable that goes outside the amiga case to another PCB which has a VGA connector and a connector that goes into the Amiga RGB port.

"My external SD/FliFi crawls because of warming up, needing trim pot use if I want a good picture as cold as well as warm, too. "

What do you mean by the above?

Thanks.