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.

[Amiwin]

Yes I think so.

[Amiwin]

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

Thanks for helping!  :-)

[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

[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.

[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.

[Amiwin]

IT'S FIXED!!! IT'S WORKING FINE!!!!!!!

I want to worship Zipper.

How I fixed it? 4 pieces of blu-tack, and a nice large brand new CPU fan.

I've tacked the fan onto the scandoubler and it's been running for at least an hour and a half with NO PROBLEMS!!!!

It's a miracle... I am SOOOO chuffed.

A little active cooling goes a long way...

Still, i wonder why its overheating in the first place. Maybe my power supply? I have just finished my towered amiga so it's using the PC power supply.

I don't know. Anyway its working great now and I'm over the moon.

Many thanks for all your help - everyone. :-)

I love this site.

[Amiwin]

Thx v. much zipper, that explains a lot of things now :-)

That was some very informative info and I'm just so pleased that its all working again.

The fan is quite big... it seems to be cooling some of the other custom chips down :-) That can't hurt!

I'm now tidying up my lovely new tower A1200! Now complete with scandoubler :-D

I'll post some pics if you want! :-)

[Amiwin]

So, should this present any long-term effects... will the noise on the power line affect anything?

Is the overheating a design fault or my use of a PC power supply?

Sorry, I'm no electronics expert and I'm afraid the first part of your post; I couldn't understand it.

Thanks :-)

[Amiwin]

I'm certainly interested! :-)

Keep me informed on this project :-D