A1200 flickering in screen

[amiga4001]

So I got me a "new" 1200 but while loading of disk or harddisk there is a flickering in the screen.
Looks like a loose contact antwhere on the mobo.
Tried a other psu same thing.
Tried without hd still flickering while loading of diskdrive.
Resoldered the plug on the mobo still same.
Can it be the plug on the mobo itself as when I rock it while running power falls away?
Or is the plug always that fragile?
A1200 rom 3.0 rev .10 60 MB 2.5 inch with A1200psu

[doctorq]

First of all, if you have a rev. 10 motherboard, then gongratulations. You would be the first one :-)

As for the screen flickering, is the computer connected to a TV or a monitor?

[starf81]

I'm experiencing a similar behaviour with my A1200. In particular, it shows a flickering pointer while drives work.

It seems a GND problem.

Let me know if you solve in some way and I'll do the same.

First of all check if your plug has all its three pins (the third, obviously, is for the ground...).
After, if you have a meter, try to check if the Amiga's ground contacts with the PSU's one (if you're using an external not-Amiga is more simple to test otherwise you should to screw it but... warning to your health!!! :-D ).

You said you're experiencing the problem with more than one PSU, so the problem is not on the PSU connector but it should be on the internal contacts of the Amiga connector. I'm not referring to the contacts with the motherboard (that you have resoldered) but those inside the connector itself. You'd try to move a little the plug and connector while the Amiga is turned on to see if changes something.

Last test, measure the two voltages (+5 and +12) on mobo's floppy connector and check if they are constant. Check also (when the Amiga is turned off so it's safer) if the two internal pins of the connector contacts with other Amiga's ground.

Keep me update!
Alex

[Hizoap]

Hi


Some Commodore 1200's had an missing capacitor, you would then see horizontale stripes on your screen every time your diskdrive is active. I don't know if you have this error since your screen flickers when you hd is active too.

I have alot of originale commodore service manuals but I can't seem to remember where I found this info. I just remember that the serial's of the affected 1200's were listed too.

Regards
HiZoap

[amiga4001]

Ok an update.
I wired a AT psu to the mobo with the GND +5V +12V and it booted nicely without the striping/flickering.
So I thought it must be the contraplug of the mobo.
Replaced that with one out of a A500 but same problem.
Could it be the mobo is just taking to much current out of the original psu?
As for revision no not .10 but 1D..? can't remember rest.

[Linchpin]

1D4?

[Doobrey]

amiga4001 wrote:
So I got me a "new" 1200 but while loading of disk or harddisk there is a flickering in the screen.

I had the same problem on a Rev 2B that I got a couple of years ago.
Not just horizontal lines on the screen, but noise on the audio output too.
Anyway to cut a long story short, after a couple of months the PSU packed up and when I replaced it with a spare A500 PSU I had laying about,the problem went away.

[Linchpin]

Sounds like some sort of Bad earth issue there... maybe a common fault on the a1200...

I used to get Yellow interference on the screen during IDE port use... i never really solved it, but i put it down to the PSU also.

[Doobrey]

I've just had a google about to find some more info , and came up with this on google groups
I'm just off to search through my box of bits to see if I can find a suitable cap to try it out.

edit.. wah.. no luck, all the caps I've got are way too high in capacitance  :-x