what's going on with this 520st?

[y-bot]

 

Even without a disk drive hooked up it should display something different than this, correct? Any suggestions? I have a disk drive but I believe the power supply is dead. I don't want to put any time/money in to it if the computer has issues.

Thanks!

[oky2000]

Try removing and reseating all the removable chips. My original ST did this sometimes and was cured with the old 4 inch drop onto the desk pretty quickly too.

[GadgetUK]

RAM, or Glu IMO. But a chap on atari forum thinks it could be MMU or video shifter, both possible.

[y-bot]

Reseated all the chips and no change.

[GadgetUK]

So it looks like you need to start swapping chips. I take it the PSU voltages are OK?

[y-bot]

Ha, I didn't realize the square chips were socketed. Pulled the both, reseated and now it works! I need a mouse and I need to figure out what's up with the disk drive power supply.

[GadgetUK]

Awesome!!! Any idea which it was that solved it? At least you didnt need to get any replacement bits.

[TheNameOfTheGame]

You might wanna put some clips over those chips...it *will* happen again and it gets to be a pain to open up and reseat those chips....unless you wanna do the *desk drop* hehe.

[y-bot]

There was already a clip on one of the chips. I had a 520STfm apart to start swapping stuff and it has a large PCB plugged in to one of those square sockets. That's when I realized they were socketed. Never seen anything like those before. I pulled the two, one clipped and one not, reseated and it worked. Not sure which one was the problem.

[GadgetUK]

Ah, the PCB plugged into one of the sockets, is it a Marpet Xtra RAM by chance? Or some other RAM upgrade? Those have a tendancy to make the MMU loose as they creep out.

[y-bot]

I don't know what that upgrade thing is but that is in an Atari 520STfm that I was going to rob parts from. The one I fixed is a 520ST without an internal floppy. Now trying to figure out what's going on with this external floppy. I think the power supply is dead. Searching for the pinout now. Anyone have that? Atari part no. C0700091-014 power supply model 1103.

Edited September 11, 2013 by y-bot

[y-bot]

I figured out the pinout myself. Here it is for future reference:

 

looking at the power supply connector female end clockwise. First number is my number, last number is the number marked on the back of the plug where ther wires are connected. I think the power supply is functioning correctly but the plug may be worn or there is a wire broken.

 

1 white wire +5V marked "1"

2 red +12V marked "4"

3 black 12V ground marked "2"

4 not used marked "5"

5 blue 5V ground marked "3"