520ST displays row of bombs at power up

[thgill]

Picked up a bunch of free Atari ST items off Craigslist and having problems with the 520ST. When you power it up it displays either some garbled graphics or just a row of 20 bombs.

 

The machine on the inside has several mods done to it. Extra memory, something plugged into the underside of the keyboards that has 2 AA batteries plugged into it (real time clock?) and what looks like some kind of video mod with a switch beside it. Perhaps composite?

 

 

Here are some photos of the 520ST:

 

 

 

 

 

 

 

 

 

 

Any ideas on where to begin trouble shooting this?

 

 

 

Also received:

 

SM124 monitor

Two SF354 floppy drives with power supplies. One has been modded with a double sided drive (works) and the other is still stock with a single sided drive. But it doesn't appear to function correctly. Powers up and just spins and makes a god awful sound.

Couple floppy drive cables

Joysticks

Bunch of disks. Probably 70 or 80 disks

[Rybags]

I'd suspect that RAM upgrade probably has a dodgy connection or two somewhere.

 

The monitor port - doubt it's composite, if so there should be an RGB to S-Video/Composite chip somewhere, such as an MC1377. More likely it just allows the ST to run monochrome hires mode on an EGA type monitor.

 

No idea what that mod to the keyboard processor is - maybe some sort of key-based powerup system?

 

Maybe try taking the batteries out, could be that they preserve some sort of settings that are causing the powerup crash - although this is a very big stab in the dark.

[thgill]

Probably is the ram upgrade. I looked over it and everything looks in place. I didn't see any wires hanging loose.

 

I tried powering the machine up with the keyboard disconnected, same bootup problems. Rules out some keyboard issues.

[Rybags]

All I can suggest is get out the multimeter and check every single connection between the RAM modules and where they attach to the motherboard.

 

And possibly a step further, follow the traces to the next point on the motherboard and check those too.

[Nesbroslash]

I checked the Wikipedia article on ST errors and this is all it said

16–23 bombs: [unassigned, reserved]

I'd say there might be an internal error. You might want to take this to someone who can repair and inspect old computers.

[Rybags]

Since it's been modded so much, I'd give such a "generic" person a miss.

 

Someone who knows the ST well and has performed such mods and diagnosed the machine before would be the way to go.

[thgill]

I am really interested in knowing about the keyboard and video mods.

 

Will hopefully have some time this weekend to look the ram over closer and inspect it's connections.

[tjlazer]

Looks like it has a TOS switcher and a VGA mono output? And a 4MB upgrade via 1MB Simms? Cool. Reseat all the chips and make sure there is no corrosion. You might also pull the TOS chips and install a regular set as there might be a bad connection there as well. I also got a couple 520STs and got a few of them working, retrobrited the cases, etc. Its fun and rewarding.

[thgill]

Ahhh a TOS switcher...that makes sense.

 

Any idea about that board and battery combo attached to the keyboard? Some type of real time clock?

[atarian1]

To me, the obvious ones are the:

RAM upgrade (the stuff in front)

TOS switcher (the left side stuff connected to a switch in back)

 

I don't know what the 9-pin port is connected to. It could be a CGA/EGA/VGA output port? It looks like it since it looks like the wires are connected to the monitor connector pins.

 

The RCA jack is audio out since it's connected to pin 1 of the monitor port which is audio out.

[thgill]

Ok, got it open in front of me again.

 

I agree that the single rca jack is for audio out. The DB9 appears to just be soldered straight to the points on the pcb right behind the 13pin monitor connector. I am going to guess its just another RGB out port. Perhaps who ever modded this didn't 13 pin connectors available to make an RGB lead for a different monitor (like a commodore 1084) and decided to just add an easier to supply DB9 connector.

 

Looking into the ram upgrade now to see if anything appears to have disconnected.

[thgill]

So it seems the row of bombs at power up have went away.

 

Now I just have a blank white screen with these short vertical grey bars

 

Each once is maybe a half inch long and a pixel or two wide.

 

Looks kinda like this:

 

| | | | | | | | |
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| | | | | | | | |
| | | | | | | |

 

I have looked over the ram upgrade and I can't identify anything that looks incorrect, broken or otherwise.

[thgill]

Think I found the problem.

 

Measured the PSU tonight to see if possibly it wasn't working correctly.

 

The 12v and -12v measured fine.

 

However the 5v rail measured 15 volts!!

 

 

Any ideas if it might have done some permanent damage to any chips in the machine?

 

 

I am going to try hook the 520st up to a PC power supply and see if it springs to life. Hopefully nothing is burned up inside!

[+rdemming]

 

 

Any idea about that board and battery combo attached to the keyboard? Some type of real time clock?

 

The processor in the keyboard is also responsible for keeping track of time. But if you switch the power off, the time is gone too. So this mod makes sure the keyboard processor keeps power when the Atari is turned off. So the keyboard processor keeps updating the time even when the power is off.

 

Robert

[walter_J64bit]

WOW, That's just an awesome 520ST , I hope you can get up and running!