Help with Atari STf - RGB - Cannot get video/sync

[czietz]

I just tried one of my other ataris with the same cable, and while I *do* get a good picture of the desktop initially, if for example I select "about" the desktop, when the info screen pops up it starts rolling....

If this other Atari was a STfm, then it has composite video on pin 2 and this scrolling might be a completely different problem; one that affects some STfms when the screen content is (mostly) white. But lets solve one problem at a time...

- My STF should have Sync on pin 2 anyway, but I would need to add a 330 ohm resistor on the cable to pin 20 of the SCART to bring it to acceptable level (although in your case you didn't need it) and that should work when connecting to my PVM.

Correct. To my knowledge, every 1040STF has composite sync on pin 2, only early 520ST don't. I don't know why the Retro Computer Shack claimed otherwise, because on their eBay page the 1040STF is listed as compatible: www.ebay.com/itm/250978089310

- Another option could be to modify and make my own cable where I combine the H-Sync + V-Sync signals (with a couple of resistors I saw here: http://atariage.com/forums/topic/91644- ... try1583158 ) and feed that result to pin 20 of the scart connector.
Does that sound about right?

I have no experience with that mod. But of course if all the sync signals (including H and V) have failed on your 1040STF, this won't work either.

Do you have any original Atari monitor (be it color or mono) to test with?

[walterg74]

I just tried one of my other ataris with the same cable, and while I *do* get a good picture of the desktop initially, if for example I select "about" the desktop, when the info screen pops up it starts rolling....

If this other Atari was a STfm, then it has composite video on pin 2 and this scrolling might be a completely different problem; one that affects some STfms when the screen content is (mostly) white. But lets solve one problem at a time...

- My STF should have Sync on pin 2 anyway, but I would need to add a 330 ohm resistor on the cable to pin 20 of the SCART to bring it to acceptable level (although in your case you didn't need it) and that should work when connecting to my PVM.

Correct. To my knowledge, every 1040STF has composite sync on pin 2, only early 520ST don't. I don't know why the Retro Computer Shack claimed otherwise, because on their eBay page the 1040STF is listed as compatible: http://www.ebay.com/itm/250978089310

- Another option could be to modify and make my own cable where I combine the H-Sync + V-Sync signals (with a couple of resistors I saw here: http://atariage.com/forums/topic/91644- ... try1583158 ) and feed that result to pin 20 of the scart connector.
Does that sound about right?

I have no experience with that mod. But of course if all the sync signals (including H and V) have failed on your 1040STF, this won't work either.

Do you have any original Atari monitor (be it color or mono) to test with?

Unfortunately no, I had recently purchased an Atari SC-1435, but it died shortly after buying it (just give a high pitch noise when powered).

The Atari I tested yesterday was not an STFM, it was a 520 STE

I do see what you say about his article, and it does seem very strange, as it does in fact state the STF as compatible! I will e-mail him again asking specifically about this, although I did see the cable of his I have has the RGB resistors but nothin on the sync pin.

This is what said on two different e-mails:

"Your Atari STF won't work with a Composite video lead, or RGB Scart lead,
as it doesn't have Composite video out."

"Your STF doesn't have Composite Video out, which is used for Sync on an RGB lead,
this is why it won't work with you PVM."

So that puzzles me...

Just for the record, while I will be selling 2 and keeping 3, at the moment I have the following Ataris on hand:

1040 STFM - PAL
520 STE w/4MB - PAL
1040 STF - NTSC
520 STFM - PAL
520 STE - PAL

[czietz]

Yes, please ask the owner of the Retro Computer Shack. I'm interested what he knows that I don't. As previously said as far as I know every 1040STF has composite sync. The components for it are in the schematic and they are also present on the different board revisions of 1040STFs shown on http://www.atari-wiki.com/index.php/Ata ... _revisions

Anyway: Back to your original problem, because your monitor with separate H- and VSYNC inputs has to work even without composite sync. Based on your voltage measurements I still suspect at least one of the sync signals has failed, although it's hard to be sure without a scope trace. HSYNC and VSYNC come directly from the GLUE IC. You could try tracing them back, maybe it's just a bad solder joint or contact.

[veegee]

Just to confirm what Christian is saying - I have just checked with my scope and both my 1040STf and my Mega 4 have a TTL composite sync signal on pin 2 of the monitor socket. They both read about 3.6v peak to peak.

Again backing up what Christian has said I think your monitors and cables are good and you have a fault on the motherboard with one or both of the sync lines - I would go back to basics and check that the continuity from the GLUE to the socket is all good.

[Kubik]

TL;DR - however, I had sync problems with one ST few months ago, and the problem was dead 74xx (I think it was 7404) chip in the sync chain.

[walterg74]

Yes, please ask the owner of the Retro Computer Shack. I'm interested what he knows that I don't. As previously said as far as I know every 1040STF has composite sync. The components for it are in the schematic and they are also present on the different board revisions of 1040STFs shown on http://www.atari-wiki.com/index.php/Ata ... _revisions

Anyway: Back to your original problem, because your monitor with separate H- and VSYNC inputs has to work even without composite sync. Based on your voltage measurements I still suspect at least one of the sync signals has failed, although it's hard to be sure without a scope trace. HSYNC and VSYNC come directly from the GLUE IC. You could try tracing them back, maybe it's just a bad solder joint or contact.

Wow.. so didn't expect that.. .asked him and the rpely was that it seems the guy is in the hospital due to leukemia...

[walterg74]

Just to confirm what Christian is saying - I have just checked with my scope and both my 1040STf and my Mega 4 have a TTL composite sync signal on pin 2 of the monitor socket. They both read about 3.6v peak to peak.

Again backing up what Christian has said I think your monitors and cables are good and you have a fault on the motherboard with one or both of the sync lines - I would go back to basics and check that the continuity from the GLUE to the socket is all good.

So before checking that, you think I should try the 300ohm resistor on pin 2? Or should it work without that?

[walterg74]

TL;DR - however, I had sync problems with one ST few months ago, and the problem was dead 74xx (I think it was 7404) chip in the sync chain.

Thanks for the update. I guess my delay is because I don-t really know how to check/test all this stuff properly internally

[walterg74]

Hey guys. I finally got my components to arrive.

I purchased:

TWO DIN 13 connectors
One SCART male plug
ONe DB-9 connector.

I figure I can try to build one of each, one straight SCART and the other for the commodore monitors.

Given all the anove in this thread, can ypu please recommend a final design for each (with any resistors or whatever I may need that the cables,I have tried so far do not have?

I figure I will only have one shot at each (and that's even considering I don't screw up the soldering )

Thanks!

[walterg74]

Just to confirm what Christian is saying - I have just checked with my scope and both my 1040STf and my Mega 4 have a TTL composite sync signal on pin 2 of the monitor socket. They both read about 3.6v peak to peak.

Again backing up what Christian has said I think your monitors and cables are good and you have a fault on the motherboard with one or both of the sync lines - I would go back to basics and check that the continuity from the GLUE to the socket is all good.

Yes, please ask the owner of the Retro Computer Shack. I'm interested what he knows that I don't. As previously said as far as I know every 1040STF has composite sync. The components for it are in the schematic and they are also present on the different board revisions of 1040STFs shown on http://www.atari-wiki.com/index.php/Ata ... _revisions

Anyway: Back to your original problem, because your monitor with separate H- and VSYNC inputs has to work even without composite sync. Based on your voltage measurements I still suspect at least one of the sync signals has failed, although it's hard to be sure without a scope trace. HSYNC and VSYNC come directly from the GLUE IC. You could try tracing them back, maybe it's just a bad solder joint or contact.

Hey guys,

By an incredible stroke of luck, I found an SM124 last week on our "local ebay". I went to pick it up today and tested the STf with it and the picture came up fine! So I don't think there's anything wrong with the Atari itself. (Even if mono uses a different pin, sync is still the same, right?)

So if all's right, can you recommend a cable build/schematic that should work with this Atari on a commodore and/or pvm monitor then?

[walterg74]

Bumpity?

[exxos]

This is a known Video sync fault..

http://www.exxoshost.co.uk/atari/last/S ... /index.htm

[czietz]

This is a known Video sync fault..

http://www.exxoshost.co.uk/atari/last/S ... /index.htm

Wait, wasn't this fault only present on STfm machines, and caused by the composite video signal of the modulator? Walter's problem -- if I recall this thread correctly -- was with an STF without modulator. So no composite video there -- so I think the problem you mention does not apply.

@walterg74: The SM124 uses separate H and V sync, SCART cables don't. Unfortunately, though, I can't help with a cable that will work with your Commodore and/or PVM, because I don't own any of these.

[walterg74]

This is a known Video sync fault..

http://www.exxoshost.co.uk/atari/last/S ... /index.htm

Wait, wasn't this fault only present on STfm machines, and caused by the composite video signal of the modulator? Walter's problem -- if I recall this thread correctly -- was with an STF without modulator. So no composite video there -- so I think the problem you mention does not apply.

@walterg74: The SM124 uses separate H and V sync, SCART cables don't. Unfortunately, though, I can't help with a cable that will work with your Commodore and/or PVM, because I don't own any of these.

Thanks cziet. While you may not have these, if that's the case with the SM124 (I couldn't find a pinout of it and it's cable) at least this means the H & V sync limes of my atari are fine for sure. right..? And if that's the case I could try to make my own cable with separate H&V for the commodore monitor (which all pinouts I found say it does use those signals?) or combine them, to get Csync and make a "normal" SCART cable?

Like this one that is supposed to work with ALL Ataris..?

http://www.atari-forum.com/viewtopic.ph ... 67#p304567

[czietz]

Yes, the SM124 works with separate sync lines, see for example page 9 in the service manual http://dev-docs.atariforge.org/files/SM ... _MT-21.pdf. So the H and V sync lines are fine. (One could of course think of very exotic faults in the GLUE chip that cause H and V sync only to fail in color mode, but that's highly unlikely.)

Composite sync could still be broken on your Atari, though. So Ian's SCART cable -- the one you posted the link to -- may not work for you, if indeed there's an issue with the composite sync on your STF.

[walterg74]

Yes, the SM124 works with separate sync lines, see for example page 9 in the service manual http://dev-docs.atariforge.org/files/SM ... _MT-21.pdf. So the H and V sync lines are fine. (One could of course think of very exotic faults in the GLUE chip that cause H and V sync only to fail in color mode, but that's highly unlikely.)

Composite sync could still be broken on your Atari, though. So Ian's SCART cable -- the one you posted the link to -- may not work for you, if indeed there's an issue with the composite sync on your STF.

Ok, thanks. I think I will try that cable first, since it will work anyway for my other ataris too and see what happens, and if it doesn't work I will go ahead and to the one with H+V which *should* work,with the 1084S-D2...

Thanks again.

[walterg74]

Yes, the SM124 works with separate sync lines, see for example page 9 in the service manual http://dev-docs.atariforge.org/files/SM ... _MT-21.pdf. So the H and V sync lines are fine. (One could of course think of very exotic faults in the GLUE chip that cause H and V sync only to fail in color mode, but that's highly unlikely.)

Composite sync could still be broken on your Atari, though. So Ian's SCART cable -- the one you posted the link to -- may not work for you, if indeed there's an issue with the composite sync on your STF.

Ok, so finally had time to revisit this...

Recap: Atari STf. Does not work with "normal" ST SCART cables. Works fine with Atari SM124 mono monitor.

Today I tried the modification of Ian's cable, adding the 330 resistor to the cable coming from pin 2, as indicated for ataris with no comp video (the cable had no resistors on that cable/pin).

It did not work...

What I get is what you see in the picture attached. Same cable with another atari works fine.

Does this mean that the signal on pin 2 of my atari is non existant or is broken? Does this seem like a "typical" sync issue?

I found yet another article talking about combining the separate H and V sync signals (this was for connecting to a sony rgb monitor), and it was basically adding a diode and resistor to each output, and combining the 2 resistor ends, with that going to pin 20/sync of the SCART connector.

Thoughts?

[czietz]

I still think the most probable cause is that there is something wrong with the composite sync signal. Sorry, but after all this time I don't fully remember what you already did to locate the problem. If I recall correctly, the SCART cable and TV work with another ST, so they are confirmed to be good. Right?

Do you maybe know someone with an oscilloscope? (Even one of these sub-100$ "toy" scopes will do.) A scope trace of the signal at pin 2 of the Atari's monitor connector might help diagnose the issue.

[walterg74]

I still think the most probable cause is that there is something wrong with the composite sync signal. Sorry, but after all this time I don't fully remember what you already did to locate the problem. If I recall correctly, the SCART cable and TV work with another ST, so they are confirmed to be good. Right?

Do you maybe know someone with an oscilloscope? (Even one of these sub-100$ "toy" scopes will do.) A scope trace of the signal at pin 2 of the Atari's monitor connector might help diagnose the issue.

Yes, correct, it's basically what I entered above as "recap". The same cable works fine with other ataris. And also this same machine works just fine w oth the atari sm124 monitor, so I know the hsync and vsync are ok (also while I didn't buy it, the seller had it hooked up to an atari color monitor, so color lines should be ok as well).

If I can get someone with a scope, what should I tell them to measure/look for on pin 2?

[czietz]

If I can get someone with a scope, what should I tell them to measure/look for on pin 2?

Voltages and timings, basically. Also whether there is any ripple or over-shoot/under-shoot in the signal. The composite sync signal should be high most of the time, with a regular sequence of short low pulses (HSYNC pulses). 60 or 50 times per second (depending on whether you have a US or European STf) there should be a longer low pulse (VSYNC pulse). If required, I can measure the composite sync signal at my STf as a reference.

[walterg74]

If I can get someone with a scope, what should I tell them to measure/look for on pin 2?

Voltages and timings, basically. Also whether there is any ripple or over-shoot/under-shoot in the signal. The composite sync signal should be high most of the time, with a regular sequence of short low pulses (HSYNC pulses). 60 or 50 times per second (depending on whether you have a US or European STf) there should be a longer low pulse (VSYNC pulse). If required, I can measure the composite sync signal at my STf as a reference.

Ok, thanks. That would be awesome. I'll as my coworker on monday if we can look at it with his scope.

[czietz]

OK, measurement done on my European 1040STf, directly at the monitor connector, pin 2.

This is the horizontal timing -- an entire line (including HSYNC) takes 64 µs, the HSYNC pulse itself is about 5 µs long:

NewFile26.png

Note: Horizontal timing will vary slightly with an US model.

This the the VSYNC pulse with a duration of about 192 µs. You should see one every 16,66 ms (US model, 60 Hz) or every 20 ms (European model, 50 Hz):

NewFile25.png

[walterg74]

OK, measurement done on my European 1040STf, directly at the monitor connector, pin 2.

This is the horizontal timing -- an entire line (including HSYNC) takes 64 µs, the HSYNC pulse itself is about 5 µs long:
NewFile26.png

Note: Horizontal timing will vary slightly with an US model.

This the the VSYNC pulse with a duration of about 192 µs. You should see one every 16,66 ms (US model, 60 Hz) or every 20 ms (European model, 50 Hz):
NewFile25.png

Thanks!! I will print this out and take it with the computer to contrast. I assume if he has and uses the scope he will know what settings are needed to get each graph? Or are there any special indications?

[czietz]

For the VSYNC pulse it's best to use pulse triggering, i.e. letting the scope only trigger to pulses of a certain duration. Other than that there's nothing challenging in measuring the composite sync signal.

[walterg74]

For the VSYNC pulse it's best to use pulse triggering, i.e. letting the scope only trigger to pulses of a certain duration. Other than that there's nothing challenging in measuring the composite sync signal.

Ok, sounds good! Crossing fingers I'll be able to find something...

As a curiosity (since I would still like to make a cable using hsync and vsync), take a look at this forum post, and the small pdf attached to the last post:

http://forums.parallax.com/discussion/1 ... osite-sync