Help identifying IC:s in SB Extigy!

[SONiQ]

Hello.

I'm new to this forum, but I do think I post in the right section.....

I have a used SoundBlaster Extigy USB sound "card", which has started behaving oddly. It stopped working at all, and after a lot of extensive errorsearching I narrowed the error down to two possible IC:s on the PCB.

The most likely candidat is a DIP6 SMD IC, only marked "658" and with an underlined "L". Nothing more. This one runs hot as hell and actually melts the plastic of a pen when touching it's surface.

The second one, sitting right next to the above, is a DIP8 SMD IC, marked "LTKD" and the manufacturerlogo "LT", nothing more.

Touching these chips with your bare finger can make the unit reset, hang or even turn off randomly.

Do *ANYONE* know what those IC:s are???

Quick recap: One DIP6 SMD IC marked "658" and an underlined "L". And one DIP8 SMD IC maked "LTKD" and logo "LT".

Help, please, anyone who can shed some light!!

Regards.

//
SONiQ

[Chris Jennings]

Found the linear technology one

http://www.linear.com/pc/downloadDoc...63,P1906,D1453

HTH

Chris

[Chris Jennings]

The other one could be the following as the LT chip needs a low on resistance MOSFET. Looks like something is shorting out the power converter.

http://www.fairchildsemi.com/ds/FD/FDC658P.pdf

Chris

[SONiQ]

Thanks.

The first one, though not resembling the chip in name, certainly looks the bit for the LTKD chip.

The other one is spot on.

Since it's the 658/MOSFET that runs the most extreme hot, and seem most sensitive to touch, I suspect it has been avalanched and short out somehow.

The Extigy do work, as far as I've noticed, on the Phones output, and the mic- and line input, with level controls. I've not been able to test the Dobly decoder or linelevel outputs, but when the ICs) have problems, the hum is subtle on the headphones at static level, regardless of set volume, input lines or even the soft ON/OFF switch. Though, not at full volume, it seems, but rather somewhere around 50%. Physical detah/reattach/detach....etc.... can solve ot temporarily, but it always come back......... so, it seems likely that it is the MOSFET that has virtually burnt through to shortcircuit.....

It seem to control on/bootup chip power and also, somehow punch through to the amplifier stages without going through volume controls.........

Could I possibly exchange the 658 for a non-SMD low-power P-channel MOSFET?

Suggestions?

And very big thanks, Chris, for the quick replies. =)

[SONiQ]

....or, possibly there is a shorted resistor on the biased input of the power converter..... hmmmm.... this calls for a areasweep with the DVM around the mentioned IC:s............ even if it seems odd a short would still let the unit power up.......... will get back with results. Interesting indeed. =)

[Chris Jennings]

Originally posted by SONiQ

The first one, though not resembling the chip in name, certainly looks the bit for the LTKD chip.

The package marking on page 2 of the datasheet identifies its marking as LTKD.

Glad to help, but I know little about the soundblaster cards, maybe someone else can help trace the fault.

Good luck

Chris

[SONiQ]

Originally posted by Chris Jennings


The package marking on page 2 of the datasheet identifies its marking as LTKD.

Glad to help, but I know little about the soundblaster cards, maybe someone else can help trace the fault.

Good luck

Chris

Been measuring the surrounding components, but so far without luck.
Perhaps the step-down converter is faulty in itself....... now I just need to figure out a way to replace it.

Thanks for the help!