Amiga Capacitors placed wrong from factory

[arjanv]

Hi,


Question, i've about to replace some capacitors on a A1200 and A4000.
Now i've read something about some are placed wrong polarity from the factory.


A4000 C433 and C443? A4000 rev B or D


Have other amigas placed some capacitors wrong?



thougt i've read somewhere also a A3640?


Anyone have more info or a list?


Thanks

[arttu80]

Never heard of A4000 audio caps mispolarity (but maybe some A1200 mobos), but sure enough you must follow this guide;

http://amiga.serveftp.net/A3640_capacitor.html

[Munchkin]

Never heard about that on any Amiga but I remember that at least one cap was mounted the wrong way on some C64 boards.

[Castellen]

A4000 C433 and C443? A4000 rev B or D

Have other amigas placed some capacitors wrong?

The polarity of those two capacitors aren't really a problem.  Though the resulting output of the op-amp puts about -1V on the + side of the capacitors, so technically they are reversed biased by 1V, but that's not what causes issues.  Despite the many internet myths, the capacitors leak because the liquid electrolyte inside degrades over time and becomes unstable.


As mentioned already, the A3640 has three capacitors that are placed with the incorrect polarity.  They all leak just the same, the correct polarity and reverse polarity ones.

And as I recall, C171 in the A3000T (on the -12V rail) might have incorrect silkscreen on the main board?  It's correct on the schematic.  I struck the problem once, but not sure if it was a wide spread manufacturing issue, or a one-off.

[Chucky]

yes they have the wrong polarity..  attach a oscilloscope and you see that minus is connected to groud..  and that is normally ok!.  BUT!  plus swings between 0 and -2.4V

so they shoould be reveresed

[som99]

On the Amiga CD32 C408 and C811 are soldered with reverse polarity. I have noticed that NTSC machined have this corrected (on all NTSC machines I've recapped/repaired) just check when replacing