MegaSTE flashing keyboard light only

Bikerbob · Post by **Bikerbob** » Fri Jan 29, 2021 10:52 pm

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

Post by **exxos** » Fri Jan 29, 2021 11:08 pm

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..

Post by **rubber_jonnie** » Sat Jan 30, 2021 8:51 am

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.

Bikerbob · Post by **Bikerbob** » Sun Jan 31, 2021 12:09 am

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

Bikerbob · Post by **Bikerbob** » Mon Feb 01, 2021 4:13 pm

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?

: power.png (126.04 KiB) Viewed 3223 times

I know what I am looking at, but I am not sure the path to follow.

James

Bikerbob · Post by **Bikerbob** » Mon Feb 01, 2021 4:23 pm

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

frank.lukas · Post by **frank.lukas** » Mon Feb 01, 2021 5:02 pm

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.

Bikerbob · Post by **Bikerbob** » Wed Feb 03, 2021 5:59 pm

frank.lukas wrote: ↑Mon Feb 01, 2021 5:02 pm 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

frank.lukas · Post by **frank.lukas** » Wed Feb 03, 2021 7:30 pm

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

Measure the PowerGood Line too ...

Bikerbob · Post by **Bikerbob** » Wed Feb 03, 2021 9:56 pm

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

MegaSTE flashing keyboard light only

MegaSTE flashing keyboard light only

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Re: MegaSTE flashing keyboard light only

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Re: MegaSTE flashing keyboard light only