Re: Transwarp GS freezes

[Michael J. Mahon <mjmahon@aol.com>]

STYNX <stynx@gmx.de> wrote:
> I just made some interesting discoveries: Only one of the SMD-ICs I
> replaced was actually defective (at least one output gave a twitchy
> 3-4Volts instead of 5Volts).
> 
> I took Michael's advice to heart and used a plastic rod on the places i
> had encountered a crash while cooling the board. Only one place resulted
> in a crash: right above the CPU-Socket. I then realized, that with
> exception of the actually defective IC all ICs i replaced (actually 2)
> were located right next to the CPU. I could then recreate crashes,
> complete boot to GSOS and no message (bars on the screen) by pressing on
> the CPU-Socket or slightly "lifting" it.
> 
> Resoldering the socket didn't help. I may have a broken pin or something.
> I have to check every pin for contact with a multimeter. The CPU-socket
> is as clean as it can get (i used a glass-fiber pen even before actually
> trying to start the board for the first time). If i have to replace the
> socket ... thats some dirty work.
> 
> By the way, the TTL-Clock signal looked a bit strange. Instead of a nice
> rectangular pulse-wave it looks like this
> http://s1.directupload.net/file/d/3009/m2c2b9ye_jpg.htm
> looks like it could need a (bigger) capacitor to dampen the
> overlay-sinewave (i don't know the english word for this :-)
> 
> Since i can't compare, i dont know if this is normal.
> 
> So far, i _may_ be getting close to the error ;-)

The ringing you are seeing on the clock is very likely an artifact of your
scope probe. That amount of ringing would likely disable the card. 

High frequency signals (fast edges) must be probed very carefully--often
with expensive probes--to obtain an unperturbed waveform. 

I'd check all the traces in the vicinity of the socket (which may be buried
if it's a four-layer board) and the bypass caps near the CPU. Since ceramic
caps are extremely unlikely to fail, look for broken leads or cracked
solder joints. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon