Purpose of the "back up pcb" on a Taito g-net?

[haightc]

yes, capacitors can very much be used like batteries, U2 is specially a change control ic. U1 looks to be a simple tri state ic, sometime known as a monostable multivibrator. So this is looks like this would communicate state of the board but would actually store anything. So it doesn't sound like board is instead to make sure a valid and stable current when writing saves or to ROM. I am wouldn't be surpised if the delay on start up in to make sure the conents are correctly written from the PCMCIA storage device to ROM in absense of the backup board. So the backup board them really is exaclt what is says a backup board so appear to be a separate thing.

 

[advans14]

Yeah. Triggerable prob on power-down or some event. And for a smalll Amount of time perhaps enough to write or facilitate for something.

Those three caps prob are all dried out and out of spec by now. Most systems always do score saves via actual reliable circuits such as batteries with some sort of rom or battery backed ram. Weird to rely on caps with such short available power if that is the case, kinda dumb and pointless for the home environment.

I looked at the gnet manual and it only shows it in a diagram not any written mention of it.

 

[rtw]

I would start with the connector from the BACK UP PCB to the FC PCB and tracing where the power goes.

 

[ack]

I started tracing out the 6 pin connector

PIN #	Backup PCB Side	FC PCB Side
1	PIN 7 on 74HC4538AP (U1)	PIN 92 on XILINX XC9508 (U64)
2	5V	5V
3	GND	GND
4	12V	12V
5	PIN 7 on MB3771 (U2)	PIN 1 of ADM708AR (U5)
6	PIN 8 on MB3771 (U2)	JP3 (right near 6 pin connector) IN PIN 13 and OUT PIN 11 on 74HC132 (U40) 10K Ohm resister (R38 ) Underside of FC board IN PIN 9 and OUT PIN 8 on 74HC14 (U6), Underside of FC board PIN 27 of XILINX XC9508 (U64)

Some observations from probing stuff

• At power off PIN 8 in MB3771 goes low (normally its high) for a short period of time before power is lost
• Pulling the backup PCB and measuring voltages on its 6 pin connector, showed around 5V on PIN 4 of the connector. All other pins were dead.