exxos's Atari, Amiga & retro forum

What does 12v power anyway ? If its nothing much, pull the 12v wire out of the connector and see if there is any life ?

Exactly. That was my thought also. Pull the 12V wire and see if it comes to life.

I can only find 1 circuit in the schematics that shows the 12v on the board and I have no idea what it does.

So I will give that a go.

James

this is the only circuit I can find that uses the 12v and -12v..

Ok, so 12v and -12 goes to the 1488 U311 - which is involved in the Serial communications.. if Serial io is bad then 1488 is a possible cause.

The 1488 after looking it up is driven by 7-15 volts. SO it needs the 12 and -12. Now I am not looking at a board .. but need to see if U311 which is a 14pin DIP package is socketed (doubt it) also finding one might be difficult.

Opinions?

James

Pull the 12v wire then.. It may power parts of the audio circuit as well..

Well the board did power.. the psu started up.. fan on.. tries to initate the screen.. NO.. flashing.. black to white.. again again..

James

I doubt the 12v is the problem, even if the serial chip was dead, it'd have to be a dead short to kill it. and I don't think it would cycle like that. ST's run on just 5V so it should work with no 12V feeds at all.

I can't recall, have you checked the reset switch hasn't failed on?

Also, and again, I don't recall if you did this, but does it work without the keyboard? could there be a KBD fault causing the CTRL+ALT+DEL signal causing a reset?

No reset works fine, it does pause all this.. let it go .. starts flashing again.

No keyboard connected at the moment.

James

Bikerbob wrote: 05 Feb 2021 16:39 Well the board did power.. the psu started up.. fan on.. tries to initate the screen.. NO.. flashing.. black to white.. again again..

It may need 12V to work.. but at least you know you need to find that 12V short now to get it to power up at least..

Looks like +12 is used in a couples places beyond the rs232 chips. It powers a regulator that powers a audio device. Also supplies power to J902. I don't know if I would use a pc supply. It may deliver so much current it could burn the traces off your MSTE board.