Mystery Of The Floppy

[Managarm]

I posted on here a while ago that both the internal and external drives on my A1200 had stopped working. They won't format and find errors on disks that aren't there. Yesterday Amiga.org member X-Ray kindly came round and had a look at it.

He swapped my internal disk drive with the one in his A500. My drive worked fine on his machine. With his drive in my machine the same problem occured. We then tried changing the floppy connector wires around, again no change. We then removed my '030 accelerator, still nothing. Finally we took the heat shield off, removed the hard drive and the keyboard connector. The same thing happened with this bare bones setup. Two things happened at this point: Alice and Paula both got warm almost straight away. After about 5/6 minutes Alice was still at the same temperature whilst Paula had become considerably hotter. Is this normal or does it suggest that there is something wrong with Paula? When this problem first started I tested the audio and it was fine. Any suggestions would be much appreciated.

[Fizzy]

It does sound like you have a board/hardware problem, going by the results of your pretty logical testing.  Especially as both internal and external floppies are effected.

Have you tried your friends psu on your amiga?  Maybe theres a problem with one of the power rails...?

The temperature of the chips is not always a sign of a problem to be honest, unless it gets to the point that you can't keep your finger on it for more than a second or two, which is usually too hot.. ;o)

However, as stated it does sound likely to be a board fault.  Not much you can diagnose/repair yourself with surface mounted stuff (unless you have the expensive gear to hand?).  Probably not worth trying to get it repaired either with so many 2nd hand ones popping up these days for so little.... (

Hope thats of some help?

[Castellen]

It's normal for those devices be be fairly warm, approx 50°C. U3 (Paula) contains a UART responsible for serial data to and from the disk drive.  The two CIAs, U7 & U8, handle the other digital I/O for the disk drive.

Depending on the exact problems you have, you can narrow it down to various hardware blocks.  E.G. if you can read anything then the RX serial data is OK, but if you can never write to a disk, it could be a problem with the TX data or write enable line.

Personally I'd just swap U3, U7 and U8 for known good devices as it only takes a couple of minutes to do.
But assuming you don't have any SMD soldering equipment handy, you can't really do a lot other than check continuity of the two serial lines and the various I/O lines between the floppy port and the relevant pins of U3, U7 & U8.
Also check for shorts to ground or +5V on those lines, as that can indicate a short circuit output logic within U7/U8.

I have A1200 schematics here if you need them:
http://amiga.serveftp.net/schematics.html

[Dr_Righteous]

I have a similar problem on a DOA board I got off ebay... With exception to the system locking up soon after it boots. It's definately a component level issue. Someday when I'm ambitious I'll gather the parts and find someone that can do the swap for me.

@Castellen
Thanks for the schematic info... I didn't know they existed for the C=1950 monitor... Mine needs a little help!  :-D

[Managarm]

Thanks for the replies about this. I tried several power supplies, all with the same result. The Paula chip is not hot to the point of burning but it is very warm to the touch. I fear the thing's knackered. It's not all bad though, everything else works and I'm networking it to my PC so I can transfer files in that way. If this problem can't be fixed it's still usable until I get another one.