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Testing/Repairing ST's

SiriusHardware

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If the lead you buy does not directly use the composite video / composite out from the ST as composite-in for the SCART interface it may instead use components to combine the Hsync and Csync outputs which are present on all variants of the ST, as the official Atari colour and Hi-Res Mono monitors both used separate syncs. If it does this it probably will not have any connection to the Composite video out / Composite sync out pin on the Atari.

I do remember a case on an Atari Forum where someone was trying very hard to use Composite video / Composite sync out as part of a SCART cable only to discover that the Composite Sync components were not fitted either, but I think that was unusual.

To be honest if any machine has the capability to output RGB to a monitor you should not hesitate to use it, RGB output is always cleaner and crisper than composite, where the various signal components are combined in one signal line, travel a metre or two along a wire and then are uncombined again. Better not to combine them in the first place, but to send them all along separate wires.
 

Nicolas 2000

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Yes, that's why I've modded my Sega's to RGB SCART. Crisp! So what I want for my Atari is a SCART cable that takes the RGB channels from the ST and the CSYNC signal, with a proper set of terminating resistors and capacitors if required. At least, that way it works on my modern flat screen. I have no experience hooking up RGB SCART to my old Philips color CRT computer monitor.

I can ask my local vintage console cable shop guy, he tends to know these details quite well for the cables he sells.
 

SiriusHardware

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Also if you want to use the Hi-Res (mono) video mode of the ST then officially you would need something like an Atari SM124 mono monitor. They run at a framerate of about 70Hz so most 'video' monitors can not work at that refresh rate, but a standard VGA monitor can - you can buy ST to VGA cables and these will allow you to use a VGA monitor as a hi-res MONO monitor, The only gotcha is whether the monitor you intend to use for that purpose has 75R termination resistors between its Vsync and Hsync input pins and GND - if it does, the separate sync outputs on the ST are not 'strong' enough to drive such a low resistance and it will not work - so measure the input resistances on your VGA monitor of choice first.

You may ask, why would anyone want to use a mono monitor - a lot of the productivity software on the ST (Desktop publishing, MIDI music authoring) ONLY runs in mono hi-res so if you have ambitions to run anything like that then a mono monitor is handy to have.
 

Nicolas 2000

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I do not own a regular old VGA CRT. Perhaps the only person on this board. :) I do have an old Philips monochrome monitor, but that one doesn't have a VGA input.

I'm not planning to use the Atari for MIDI, even though I have an extensive synthesizer studio. I don't think the popular games need hires so if it just works on my regular Philips CM8802 (or something similar) I'm happy. I prefer SCART because of the RGB support and because switches are easy to find here in thrift shops.
 

SiriusHardware

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My display of choice for the ST is the same Philips CM8254 RGB / Composite CRT monitor which I carried miles through a town centre back to where I had parked the car, after buying the monitor on impulse. I still have the STFM I bought it for as well, in 1986 or thereabouts. I do also have a 'real' Atari mono monitor, bought when VGA monitors weren't really a 'thing' yet, or if they were they certainly weren't cheap.

Actually some games (such as the famous Infocom series of text adventures, and the LucasArts games like Monkey Island) support mono mode as well as colour but you are right, 99% of games software requires / plays better / looks better in one of the colour modes.

The ST is an exceptionally good MIDI machine because it is basically a single tasking OS so the timing is not prone to being disturbed by time sharing with other tasks as it might be under Windows, Linux or MacOS. There are people who still use an ST as their main sequencer even today, myself included, but I have to admit I am not a real musician so I can afford to limp along with a Steampunk setup.
 

Nicolas 2000

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Oh I don't think the ST is too old for my studio. Rather, it is too new. :) The majority of my synths vastly predate it. I don't use MIDI in my music other than for syncing some stuff which has its own internal sequencers. I record to audiotracks directly. The Atari would be for gaming purposes only, unless it gets dethroned by the Amiga (whenever I acquire a supply for that bad boy).
 

Nicolas 2000

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I've just taken the Philips CM8802/OOG apart because its horizontal width adjustment knob was pushed inwards and I wanted to optimize the image from the Atari. Now I can use the knob again just fine. I can't turn the width all the way to the edges of the tube though. With the height, I can. I know CRT's often did not use the whole tube because of the edge distortion, but a) the more screen the better so it frustrates me a little that I can't use all of it and b) I see photos online of this monitor filled all the way to the bezel on all sides. Any ideas? is it perhaps the ST(FM in this case) that simply doesn't use all the width that the monitor has available? I was testing with Prince Of Persia.

Edit: looks like it's just the "active" screen size of the Atari ST that is smaller than the full display resolution. I see this on CRT screenshots of ST's, and I also notice that the solid background color does reach the bezel of the monitor on all sides if properly adjusted. OK! Best problem is no problem.
 
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SiriusHardware

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Yes, this was a standard 'feature' of most 1980s era home computers, the only 'display' the customer was likely to have was their TV. CRT TVs - the only sort there were in those days - typically were set up with a lot of overscan so the 'active' area of the display generated by home computers intentionally left a generous border all around. Taken to the other extreme, if they had used the whole available raster width and height to display information then most people would not have been able to see the first and last lines or the first or last few characters of every line, they would have been off the screen above and below and on either side.

So don't worry about the large blank border around the active display area, that is intentional. Some of the ST demo crews managed to find ways to generate full screen width images by precisely manipulating the border colour in real time, but usually that screen area is just wasted and I can understand you wanting to enlarge the active area so it approaches closer to the edges.

My oldest synth is also not MIDIfied, at least originally, it's a Roland SH-101 monosynth, a 'Keytar' often seen being waved around , if not necessarily being played, in early1980s pop videos. I do have a MIDI-to-CV converter for it though, so it is possible for the ST to 'play' it for me.
 

SiriusHardware

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The high voltage cap is very domed but it is obviously still working to some extent otherwise the machine would not start at all. I agree it could do with changing.
 

Nicolas 2000

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The fact that I made a closeup of that cap's reactor dome with the accompanying text "I know it's Atari lore to recap and that often it's not really required. I think I'll replace this one though..." should be interpreted as me realizing -luckily- that this cap is not exactly as new and not getting any better. I will replace it and other suspicious ones in the near future, if I decide to keep the Atari.
 

SiriusHardware

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I completely agree with your scepticism about recapping, if it isn't broken, don't fix it (I am an electronics technician by trade). I have an ST and and STe and both are motoring along very nicely on all of their original capacitors.

I would make an exception for that clearly distressed high voltage cap though - it would make sense for you to fix it even if you ultimately sell it because, sod's law, that capacitor will finally blow up the day after you sell it which could create some bad feeling between you and the buyer.

There are some parts in some computers which have acquired a justifiable reputation of being change-on-sight, such as the famous exploding RIFA capacitors on the mains input side of BBC model B power supplies. Tantalum 'bead' capacitors, typically used as supply rail decoupling capacitors, are well known for their habit of failing low resistance or short circuit. Surface-mount tantalums fail as well, often burning up like match heads. But mostly, I only replace capacitors when they are actually faulty.

I have heard that recapping is justified on some later Amiga PCBs where the SMD electrolytics - not very reliable in any application - have a way of failing.

Any PCB known to have a NiMH backup battery soldered to it should be inspected regularly, and in fact it is advisable just to unsolder and remove any such battery on any item which is likely to be stored out of use for a long time - the clock battery in the Amiga 500 memory expansion 'wedge' is a notorious Amiga killer. Where I do have PCBs with backup batteries and I want that to work but I also want to protect the equipment I remove the battery, mount it somewhere well away off - board and take flying leads from it to the original pads on the PCB. Fortunately neither the ST or STe have an onboard RTC battery, but I don't know about the Mega ST / STe.
 
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Nicolas 2000

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Completely agree about the backup battery. Destroyer of worlds.

And indeed I should replace that thunderdome cap no matter whether I keep it or not. And while I'm in there, there are some other caps in the supply that appear to have a stretched jacket.
 

1ST1

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It seems like there was a mod at the RF section, tapping from the monitor out. Any idea, composite out? In that case it doesn't work.

No, that's not an RF-Mod, the STM/STFM has RF-Modulator by default.

That little board ontop of the Modulator is quite interesting, you should google for that and play with it. It is called "Autoswitch Overscan". But it mostly makes sense if you install a harddisk and use GEM software which you install on the harddisk. You will find user manual and driver.
 

Nicolas 2000

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That little board on top of the RF section is what I was refering to with the "mod at the RF section". So now I know it's an Autoswitch Overscan. But I don't know what that means or does. :) Is it of any added functional value? Especially when I plan to use an RGB to SCART cable from the monitor output?

Meanwhile, my order of console video cables should arrive towards the end of the month. Then I can test the 1040STF and the 520ST+.
 
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1ST1

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Yes, it is an added value as it makes your ST displaying higher resolutions on GEM desktop and properly programmed applications. It's about 20% more as the whole border arround the picture is used for the desktop and applications. But it has no advantages for most games as they are made for the original resolutions. Just google for the user manual and study it.
 

Nicolas 2000

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I couldn't find the actual manual, but I've found some articles on it. It talks about a software list so it knows when to switch to the high res. I assume that if something is not in the list (ie random game) it will work in the original resolution? At least in Prince Of Persia I didn't see anything extraordinary.

There is one capacitor on the Overscan board which has a leg broken or cut, so I don't know if it would work anyway. I don't need it atm as I only game.
 

1ST1

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No, vice versa... The desktop runs borderless, and it switches back to original resolution when starting programs on the list. If you want only to play color games, running that driver makes no sense. Attach a harddisk, run wordplus, calamus, pcb-edit, ... with it.

You will find everything in the neighbour forum, specialized on that series of computers... https://www.atari-forum.com/viewtopic.php?t=31954 (necessary downloads on page 3, but read all to understand...)
 

Nicolas 2000

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The conclusion indeed is that I shall leave it well alone. It's good to know that it's in the Atari, but I have no use for it so as long as it doesn't interfere with my gaming I'm happy.

That one small tantalum cap should not have a broken/cut leg though. I'm not sure how or why that came to be. Possibly it's only for filtering/decoupling the supply rail to the IC so it might work without it, but it shouldn't be that way.
 
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