520STm Boot Issues

[Fooser]

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.

 

[vwestlife]

Except for the very earliest version, the Atari 520ST has its operating system (TOS) in ROM, so if you don't have any floppy drives (either built-in or external), the GEM Desktop should appear within a few seconds after turning it on. If you do have a floppy drive, it will take a while longer as it checks for a disk with startup/configuration files on it, but the Desktop should eventually appear after 15-20 seconds or so.

Even if you do have the earliest version without TOS in ROM, it should show a boot screen that mimics the appearance of the GEM Desktop:

And if I understand your setup correctly, you bought a cable that connects to the Atari's large round DIN video output port and provides a composite video output, and you're connecting it to an external RF modulator and then to a TV set. But if you need an RF output rather than composite video, why not just use the RF modulator that is built in to the computer? Have you tried it instead?

 

[ngtwolf]

And if I understand your setup correctly, you bought a cable that connects to the Atari's large round DIN video output port and provides a composite video output, and you're connecting it to an external RF modulator and then to a TV set. But if you need an RF output rather than composite video, why not just use the RF modulator that is built in to the computer? Have you tried it instead?

Nothing to add to what vwestlife said as far as the boot process/timing/etc.

A quick addendum to the RF piece. If you have a composite cable for the ST (the one that connects to the large din connector on the ST), then that needs to be connected to a composite connection (yellow) on the TV and the TV has to be set to composite video. In order to use RF, there's likely a piece missing. First, as vwestlife said, you can use a regular RCA cable to plug into the modulator on the ST, however the other end will likely need to be connected to a 'RCA to Type F' connector which then connects to the coax connector on a modern TV (modern being anything in the last 20 or so years). Also, the TV needs to support antenna and not just digital cable.

 

[g4ugm]

Whilst TOS is in ROM doesn't it get confused if no floppy at all...

 

[fatwizard]

I have a 520 ST currently setup. The original form factor with TOS in ROM, an external power supply, and no internal floppy drive. I just tried booting it up with the floppy drive disconnected, and after a few seconds it comes to a blank GEM desktop.

 

[Fooser]

Frankly I don't know if I have the earliest model with TOS in rom or not. I was hoping to be able to tell by what showed on the screen after boot.

Due to storage limitations, rather then have a plethora of monitors hanging around, I use a tried and true RF modulator / TV configuration on all my vintage computers. I've thus far been successful at fixing them all... knock on wood. This is the last one not yet working.

I tried the Television port. I'm a little confused by the L / H switch and what channel to put the TV on, but I tried all combinations and could not get a signal. Maybe a bad cap?

I also was concerned that, if I had the early model, the boot process might just fail if it couldn't see a floppy drive to load TOS from. I've found a Samsung SFD-321B and modded it for DS0. I also built a external drive cable based on this discussion: http://www.atari-forum.com/viewtopic.php?t=26656. This introduces another point of failure risk since I might have screwed up the cable but at this point is sounds like I need to follow though and give it a whirl. What's the worst that can happen? <grin>

 

[Fooser]

I've also considered replacing the 6 ROM TOS. I've read (conflicting) posts that I can simply replace the roms with TOS 1.02 or 1.04 if they are still available. Since the floppy loaded TOS takes up valuable 512K memory, this sounds like the way to go anyway. It would also eliminate the question of if it needs a working floppy connected. Of course, I may already have a ROM based TOS so it may be a waste of money.

If I had some ham, I'd have some ham and eggs... if I had some eggs!

 

[vwestlife]

I tried the Television port. I'm a little confused by the L / H switch and what channel to put the TV on, but I tried all combinations and could not get a signal.

That's the channel selector switch. I know the older 8-bit Atari computers output on either channel 2 or 3, but I don't recall if that's also true for the ST series or if they use channels 3 and 4 like most other 1980s systems.

Try connecting the audio output of your composite video cable to an audio amplifier and speaker. Even if the video signal isn't working for some reason, if the computer is running you should hear key clicks coming from the speaker as you press keys on the keyboard.

 

[ngtwolf]

I've also considered replacing the 6 ROM TOS. I've read (conflicting) posts that I can simply replace the roms with TOS 1.02 or 1.04 if they are still available.

If you have TOS Rom chips, then you're good. You shouldn't need to boot to a TOS floppy at all, so that isn't your problem... The machine should come up to a screen after about 20 seconds. Even without TOS in rom, you should be at least getting a solid screen, so if you're getting static still, theres another issue. As an aside, if you have an Eprom burner, you can burn 1.04 roms pretty easily or they are also available on ebay.

One thing to note on early STs, the composite cable only works if the RF modulator works. It's why (and getting into a slight tangent) that ST's without a modulator don't work with composite cable either. There are other ways to get video on the ST with a regular LCD, but it requires about $60 in parts (a specific SCART HDMI box and a SCART ST cable). i can link that or i've linked it in other threads.

As for the modulator, I believe the H/L switch on there is Channel 3/4... Just wanted to confirm that you are using a cable directly from the ST into the back of a TV? You don't need any RF modulator box, because the ST is doing that directly with its built in box. You should connect a standard RCA cable from the back of the computer into a "RCA to type F converter" and then screw that connector onto the Antenna port on your tv. Set the tv to 3/4 (maybe 2, can't recall) and flip the switch accordingly.

 

[Fooser]

One thing to note on early STs, the composite cable only works if the RF modulator works. It's why (and getting into a slight tangent) that ST's without a modulator don't work with composite cable either.

As for the modulator, I believe the H/L switch on there is Channel 3/4... Just wanted to confirm that you are using a cable directly from the ST into the back of a TV? You don't need any RF modulator box, because the ST is doing that directly with its built in box. You should connect a standard RCA cable from the back of the computer into a "RCA to type F converter" and then screw that connector onto the Antenna port on your tv. Set the tv to 3/4 (maybe 2, can't recall) and flip the switch accordingly.

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.

There are other ways to get video on the ST with a regular LCD, but it requires about $60 in parts (a specific SCART HDMI box and a SCART ST cable). I can link that or i've linked it in other threads.

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

If you have TOS Rom chips, then you're good.

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

 

[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:



But I'm guessing you meant one of these:



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.