520STm Boot Issues

[ngtwolf]

I connected to the built in modulator exactly as you described. Interestingly enough, the built in modulater showed no recognizable signal, where as the composite monitor cable to an external modulator briefly showed a dark screen, for about 4 seconds, before the static snow returned.



Yes, thanks, I would be interested in the link.



Is there a way to tell (without a working monitor) if I have TOS in ROM? I have these 6 chips in sockets.

U7,C026165-001,RP23256,0155,5M4,A0
U6,C026164-001,RP23256,0154,5M4,A0
U5,C026163-001,RP23256,0153,5M4,A0
U4,C026162-001,RP23256,0152,5M4,A1
U3,C026161-001,RP23256,0151,5M4,A0
U2,C026160-001,RP23256,0150,5L2,A6

So, one, yes those are TOS chips. So, yeah, it's built in.

second, the external composite cable doesn't connect to a modulator, it's composite and just connects to a composite connection on a tv (the yellow connection that's part of the yellow/red/white rca jacks on a tv...)...

third, here's the setup to do it with a regular monitor:

https://youtu.be/pZrTISByUb4

[1ST1]

I purchased a power supply and composite cable off ebay and now that they have arrived it is time to test. I don't have a floppy attached yet but I expected to see a "Put your Systems Disk int your Disk Drive" when turned on. Using a RF modulator plugged into a TV, I get snow, then after turning the 520STm on, get a black (or dark gray) screen for a few seconds, followed again by the snow screen. I have re-seated all of the socketed chips already.

Your troubleshooting suggestions would be appreciated.

That is very intelligent behaviour. TOS knows that it has no floppy, so it does not request to boot. Computer operating systems of that era are based on disks. If there is no disk, no use.

[Fooser]

The external composite cable doesn't connect to a modulator, it's composite and just connects to a composite connection on a tv (the yellow connection that's part of the yellow/red/white rca jacks on a tv...)...

My TV doesn't have a composite input. All of my other computers that have a composite output connect just fine to the TV though a modulator. Composite is composite, right?

I'll check out the Scart to HDMI box, thanks.

[fatwizard]

You should have gotten some kind of display with what you have. Your 520 sounds like it is the same or very similar to mine, and mine displays the green desktop with the mouse pointer and the menu items at the top, but no icons if there is no floppy drive connected. Could your machine be PAL (European) instead of NTSC (North American)? Even still, I would have expected some kind of display, even if it was garbled.

[ngtwolf]

My TV doesn't have a composite input. All of my other computers that have a composite output connect just fine to the TV though a modulator. Composite is composite, right?

I'll check out the Scart to HDMI box, thanks.

Ahh, when you mentioned modulator, I was thinking of one of these:

31LMjjvDAqL.jpg

But I'm guessing you meant one of these:

410NrfMBJsL._SX425_.jpg

So, yeah. Not sure then. If both composite directly into one of those boxes didn't work, and RF from the Atari's modulator directly into the TV itself didn't work, I'm not sure if it's worth the cost to buy the Scart/HDMI box as maybe theres another issue.

[Fooser]

You should have gotten some kind of display with what you have. Your 520 sounds like it is the same or very similar to mine, and mine displays the green desktop with the mouse pointer and the menu items at the top, but no icons if there is no floppy drive connected. Could your machine be PAL (European) instead of NTSC (North American)? Even still, I would have expected some kind of display, even if it was garbled.

My thinking also. I'm just not sure how to pursue troubleshooting from this point.

[fatwizard]

I believe the composite output depends on the RF modulator. The STs that did not have an RF modulator did not have composite video available. This, at least is true of the 1040 STf model I have, and is supported by the schematic for the machine that shows RBG signals coming to the modulator, and a composite line from the modulator to the video out port. You might pop the lid off of the modulator and have a look as a place to start.

[Fooser]

I believe the composite output depends on the RF modulator. The STs that did not have an RF modulator did not have composite video available. This, at least is true of the 1040 STf model I have, and is supported by the schematic for the machine that shows RBG signals coming to the modulator, and a composite line from the modulator to the video out port. You might pop the lid off of the modulator and have a look as a place to start.

I did pop off the lid and the trace side of the board is all that is exposed. Removing it for inspection is not trivial however. My intention was to replace any electrolytic capacitors I found but I think I'll hold off on that for the short term.

[SiriusHardware]

Without even looking in detail, those are going to be the TOS ROMs as there aren't another six unique-but-similar sized chips in the machine. The '256' portion of the 'RP' number marks them out as 32K * 8 memory devices. The C02616x-001 part is the unique Atari part number for each chip. I used 6 * 27C256 eproms as replacements when I upgraded from TOS 1.0 to TOS 1.4, decades ago. Images of pretty much all versions of the ROMs are available in one place or another online, so if you have the means to read them you could compare them against the corresponding images to determine whether the contents are OK.