motherboard problem

Sounds a lot like a damaged Ensonique Sound chip.
Seems somebody has been trying to attempt the chip by the portplug
and damaged the chip.

sincerely speedyG

Hello insanitor,
up to my knowledge the chip hasn´t changed between ROM 1 and ROM 3 - it´s the same...
but i´m sorry to disencourage you with a move of that chip....

such a task needs very very advanced technical experience and tools....

The Soundchip itself is still a rather simple DIP 40 Chip. But the Sound is not only dependent to that chip itself.
The Sound of the IIGS is a complex group of chips working colaborative together ( see sketch below ).

The Sound GLU ( GLU = General Logic Unit )is the chip that controls the communication between CPU and the Soundchip and it also controls partially the access between the Soundchip and the Sound RAM.

The Sound RAM is a very specific part of that process. It can be valued as a kind of temporary storage
that contains sound DATA ( digitalized sound strings ) and the Sound GLU also controls the communication
between the sound chip and it´s Sound RAM. It also can move contents from Sound RAM to regular workspace
RAM.

The Sound GLU is not a normal chip... it´s one of those big UFO´s ....
the only way to remove this chip is with special reflow tools....
and fixing it at the other board also needs very special technical tools.....
and very much experience ! It´s unfortunatly a task that can´t be performed with a soldering iron.....
even an experienced technician would think twice or three times - if he would make an attempt to such a task
- even if he has the required tools ! That traces are too thin and too fragile and the danger to harm
the mainboard and after all hard work having a totally ruined mainboard is high !

The main problem is to locate the part that really has been damaged within
the entire group of chips related to the sound.
Some of the chips may be harmed by static discharge ( Sound RAM, Sound chip, or Sound GLU )and other parts might
get damaged by temporary shortcut Output Amps complex or soundchip ) or exceeding of chiplimits of permitted
voltage ( to high voltage at port ).

The safe way is not using that chip disconnecting the speaker and inserting a replacement like a mockingboard clone...
sincerely speedyG

SpeedyG, I think you have mislabeled the sound chip.
The DIP40 next to the sound connector is the sound chip.
What you have labeled as the sound chip is the sound glu logic.

Regards
ggb

Hello ggb,
thanks a lot for the correction.
Yes your completely correct.
I corrected the picture and updated the posting also in text.
sincerely
speedyG

Hello insanitor,

NEC JAPAN
D41464C-12 = Dynamic RAM 64k X 4 Bit -120 Nanoseconds
http://pdf1.alldatasheet.com/datasheet-pdf/view/104831/NEC/UPD41464C-12.html

TMS 4464-15NLA
EHP 8745 = Dynamic RAM 64k x 4 Bit - 150 Nanoseconds
http://pdf1.alldatasheet.com/datasheet-pdf/view/103706/TI/TMS4416.html

so both are nearly same.... only differences are manufacturer and speed
the texas chips are a bit slower

---------------------------------------------------------

TMS4C1024-10N
HEP 022H9
is completely different
= 1 Meg x 1 Bit - 100 nanoseconds
http://www.datasheets360.com/pdf/-6693911820689529094

sincerely speedyG

not to get your hopes up but i may have a gs motherboard actually a complete unit--- are you still looking to get it working ... i will have to look in my storage area where i keep spare parts to make sure i do have one.
thanks
kdhill