Dead AKAI S1100 repair

[Yekuku]

Hi fellow VSErs,
I saved a s1100 from going into the trash bin and I would like to bring it back to life. I would like to have some support because I am not that good in troubleshooting digital circuits.


Symptoms are :
- dead mainboard, on power up nothing happens only the lcd lights up showing a blank screen, with no other activity ( no floppy seek light, no leds light). The brightness knob does not change the lcd brightness.

So far , i have replaced :
- the power supply ( the previous power pupply was not original and it could supply only 4.5V instead of 5V, so I suspect that the unit had a power supply failure)
- OS eproms
- removed all expansion cards
and still no sign of life. So the verdict is a dead mainboard.
I have a crazy theory that the previous owner might have connected the 12v line from the psu to the 5v input of the motherboard but I am hoping that I am wrong.

So the problem is that the unit does not boot up.
Here is a signal flow diagram :

I have already replaced IC10, IC11 ( system rom) , so now I am suspecting IC1 (CPU) and IC2 (data / address separator.) , or surrounding components.
I dont know how to test them.
I am thinking of checking the crystal oscillator and then checking TP1,TP2,TP3,TP4 and TP5.
Can anyone please guide me on how to check the reset line to the cpu (IC1) ?
What am I supposed to find while checking TP1,TP2,TP3,TP4 and TP5 ? If I see a pulse train does that mean that IC1 is good ?
How can check IC2 ?
I believe that there is no short on the mobo, the 5v line is not getting dragged down, I hope its just a dead component.
What other things could stop the unit from booting up ?
Any ideas would be deeply appreciated !
Here is a photo of the mainboard :

Many thanks!

Edit : I am also looking at ICs 51 & 53 that enable/disable data output (CE) on OS eprom (IC10 & IC11), if there is sth wrong there, firmware would not be loaded, right ? Should I look for a 5V reading on eproms CE pin , in order to determine if they transmit firmware data ?

[suchenderxxx]

Hi,
i have similar problems with my S 1100, do you have the schematics for the S 1100?

[Yekuku]

Hi suchenderxxx,
I am in quarantine and i dont have access to my backup right now, I ''ll be able to search for them hopefully in a few days.
This repair project burned my mind, so i put it aside for a while.
What problem are you experiencing ?

[Anarkand]

Hi there- I have the same problem atm - an akai s1100. I tried removing the PSU and using my bench PSU - I only get a blank screen - contrast does not function and there are no lights in any of the LED's of the front panel.

I could really use a schematic

[Yekuku]

Hi buddy,
you can find everything here.
this one has been the most difficult repair I have ever worked on.
If you are lucky it is just the spsu.
In my case , I have removed all logic ICs, I have found 1 dead , replaced it but it is still not working.
My thoughts are on the RAM and CPU but i havent figured it out yet.
Please feel free to share your troubleshooting.
good luck

[Anarkand]

I have tried several simple fixes - and no it is not just PSU - So I am throwing in the towel. If it was a SUPER nice synth, I'd try harder.

Thanks for sharing!

[Yekuku]

I literally burned my mind with this , so I decided to take a few months off before attempting to repair it again.
Dont throw the towel yet , I can help.
If you ever give up and decide to sell it for parts, please let me know because I am looking for some parts .
thanks

[Jar-N2]

Any updates on this project? I have the same problem and I'm wondering if you ever found a solution, that way I'd have something to work off of.

[Yekuku]

From my side there are no updates but feel free to share your troubleshooting , maybe someone can help.