Goldstar FC-200 missing 5V

Supporter (3)

22-01-2021, 18:50

Hi everyone!

im try to repair goldstar msx FC-200
first i was check all voltages and bingo, i have 12V and -12V but 5V is missing.

So i check transformer and this is ok, im suspecting 5V regulator is broken but i dont understand how this regulator work, is a str9005 with 5 pins, according from left to to right:

1 pin output
2 pin is output fine adjustment (is not connected on board)
3 pin is output ON / OFF control
4 pin is input
5 pin is GND

Pin 3 is mystery for me because in datasheet if i good understand, while this pin have 2V or above the regulator is on OFF state and dont give 5V on motherboard. This is stupid because on PSU board this pin is connected via resistor to +12V ! and next is connected via wires to motherboard connector P2. I dont know what motherboard doing with this signal because i cant find this in schematics.

So maybe someone in this forum can help me ?

Thanks a lot!

By Pentarou

Champion (316)

23-01-2021, 06:51

Maybe this thread could help?
Talent DPC-200 Power Supply Failure

Motherboard connector P2, could be cartridge slot protection switch?

By kataklysm

Supporter (3)

23-01-2021, 13:57

Yep ! you have a right, this connector is connected to cartridge slot protection and it short 12v via resistor 4.7k to GND. So on my board 5V is working but i have only black screen. Using termovision i was find one warming more than others ram chip and this is my suspect now

By kataklysm

Supporter (3)

23-01-2021, 16:29

Hmm im replaced U15 from hm4864p-2 to hm4864ap-15 i think its probably good replacment. For now all ram chips warming equal so i think all of tham are ok but still i have only black screen...

i think about change ROM chip but schematics form service manual is low quality - which chip is the rom chip on pcb ?

By Pentarou

Champion (316)

23-01-2021, 18:48

Page 31 of service manual:
U5A,B == ROM,M-ROM BASIC