exxos's Atari, Amiga & retro forum

Need suggestions.

I have a megaSTE that was working fine, now on power all I get is a flashing keyboard light. NOTHING ELSE.

Changed psu to known good one.. same thing.

Hope you can help.

James

If the PSU is known good, (sounds like power is tripping out) you could measure on resistance the 5V to 0V on the MB and see what you get.. if its just a few ohms then something is shorting the PSU out..

Do you have an internal SCSI HDD? Possibly disconnect in case the disk is stuck and it's pulling the PSU down. Same goes for any device powered from the MSTE.

All devices were disconnected.

SO I assume it must be a bad cap. Question is.. which.. I guess I am into the schematic and try and trace the power circuit

James

I have seen the schematic for the PSU, and the board.

Should I just start following the schematic from the power input and start measuring resistance on the caps?
I know what I am looking at, but I am not sure the path to follow.

James

SO, the way I am reading this 227 and 228 are the key to the +5v line.

So is it Powergood that I am not getting right here? and thats why the PSU is not starting up? I get its a protection, but not sure what I am supposed to be checking here. I notice the reset is not in this part of the circuit, and I assume that could still be one of the issues.

James

Disconnecet the PSU and measure between +5V (red) and GND (black) on the Board PSU connector. It should be 60 Ohm or something.

Connect the PSU and maesure between +5V (red) and GND (black). It should be 5V or something. Power Good should be have 5V too.

frank.lukas wrote: 01 Feb 2021 17:02 Disconnecet the PSU and measure between +5V (red) and GND (black) on the Board PSU connector. It should be 60 Ohm or something.

Connect the PSU and maesure between +5V (red) and GND (black). It should be 5V or something. Power Good should be have 5V too.

So Ohm between 5v and ground at the psu connector is 120ohm when started voltage jumps but within the first second returns to 0 and then a cycle of power on and off continues.

Same with Power GOOD.

James

Check the PSU first. Connect a SCSI or IDE HDD to the PowerSupply and check the +5V (Red) lines ...

Measure the PowerGood Line too ...

sorry frank are you saying to check the psu independent of the MB.. putting a drive or whatever on it for a load?

If thats what you ment then yes works fine, powers up the SCSI drive and the 5v lines and PG are showing 5.21v steady.

James