Atari 800XL Graphics issues

[TJ76]

Good evening all

 

I've recently rediscovered my old Atari 800, and got it working again.  Power supply was dead, however after some searches for PIN out info I was able to get it working by cutting the wire and soldering the 7 PIN DIN to 5V from a USB cable that worked a treat.  Graphics output from RF modulator was poor (and far more visible connected to the 50" Panasonic plasma I am testing on that old CRTs), so sourced a 5 PIN DIN to composite cable, which improved output, however on cleaner image I am able to see hashed pixel corruption in the images.  (see attached examples).  

 

Also on the READY screen I can see some fuzzy bars horizontally across the screen and more apparent distortion on the left side.

 

Images attached.

 

I have read various pieces of info on known graphics issues, and potential fixes - replacing ANTIC chip etc.  Also read about mods such as SOPHIA to improve output, however new to tinkering with this old stuff, so unsure if this would work around the problem, or whether it would remain.  Before I look to purchase replacement parts / mods (and wanting to keep unit reasonably stock and avoid any serious soldering work),  I wondered if somebody could offer their opinion of best steps here.  Realize this likely covered elsewhere, so appreciate it if could link me to best info, would be very grateful.

 

Looks like my board is partially socketed if that helps me out re replacement chips.

 

Some images attached, and thanks in advance.

 

TJ

 

 

 

[+DrVenkman]

Well, part of what you have going on is you're displaying analog PAL signals on a modern flatscreen TV. Modern flat panel displays are much less forgiving of low-resolution vintage game and computer signals than a CRT would be. A lot of what you're seeing would be next to impossible on a tube. 

 

Having said that, there are a few different ways to sharpen things up. SOPHIA is one way - the current version is either DVI or RGB output. The upcoming SOPHIA 2 will support DVI or VGA as I understand it, though I might be mis-remembering. That will give you about as sharp an image as you can get. A UAV board will be less expensive but offer very clear, excellent quality composite and S-video output, but you'll still be dealing with whatever your TV does with vintage computer signals.

 

Finally, there's VBXE which not only adds very sharp RGB output, but actually enhances and adds additional graphics modes to the Atari, but there is relatively little software available that takes advantage of it. 

[_The Doctor__]

also most buck, switching, usb, other 5v power sources of today are very noisy and aren't all that good for an Atari at all. It pulses power, has ripples dips, and injects frequencies that the machines and their display hate... with a proper add on filter system they're not too bad... but thread after thread appears with this common scenario... just go with a linear supply... easy to buy or build... enough with the cheap usb route that ends up noisy or damaged already... this is like using a crappy battery back up with stepped approximation instead of sinusoidal wave as a power supply... it may work, people will say 'it's safe, it worked for me, power is power, just use this other things to fix it' sooner or later be it a year be it whatever... they and up talking about what they did to fix the machine, be it video or some other issue. They may even need help to figure it out and fix it...

It is what it is.........

Edited July 3, 2020 by _The Doctor__

[TJ76]

Thank you both for these responses.  I love how many people out there are still using Atari's and i'm getting very nostalgic.

 

Two great points I think here - the first I had read variations of on other threads; in that modern displays being ultimately from another age are showing up unintended effects when connected to the vintage hardware, and in my mind, the fact that projects such as SOPHIA or UAV exist is testament to that.

 

I also note the point on Power source being a potential issue, and with that being something cheap and non-invasive to replace, I'll certainly try sourcing a new PSU first, and if no effect, take that on the chin.  

 

For further info / if helps anyone else; the effects / distortions (if my memory serves correctly) may have been present already on older CRT, but have nothing around now to prove / disprove that.  I recall a very long time ago (86 / 87 perhaps) that there was a problem with the original PSU, where after a few hours of use, hard horizontal lines of distortion started appearing on screen and moving downwards, along with an audible hum.  We took it to a small computer repair shop in South Woodford, London, and they replaced the supply with an alternative that was actually from a Commodore.  This is the dead one I have here, and has P/N310200-04 which I believe was from a VIC 20 or C64.  Unsure if the PIN outs were modded for it to work or was compatible as read it had 9V and 5V output and believe I'm right saying the Atari takes +5V only.

 

So I do wonder if this was a poor fix back in the day since I also recall after some time of using after this that the lines would re-appear after several hours of use even with the replacement supply.  Not had this particular effect happen using my USB franknencable.

 

Given this additional info, if anyone thinks from this there is potential of damage to the machine due to either being connected to an inappropriate PSU before, or for some other fault that was badly worked around, i'd appreciate the input.  I'd love to get this thing working as well as possible, and awaiting an order of an SDDrive Max so I can use more software than the 7 cartridges I have, as all my tapes are long lost.

 

Thanks all and have a great weekend on your Atari's!

 

TJ

[TJ76]

Just for anyone interested since the above post I've acquired two additional 800XLs, which have cleaned up very nicely.  One fully socketted rev A version which is nice and a rev rev E which is not socketted, however interested to see the display output appears the best on this over composite out of the three.  I guess things improved with time?

 

With my original rev D, I am now using a more stable 5V supply, which makes some minor difference, however output was still quite poor with the same kind of pixel ghosting kind of effects present.

 

I have also now sourced a Sophia DVI and an Ultimate 1MB, and decided I wanted to work on my original and make it the best it could be, and leave the others stock for the moment.  Brushing up on my soldering skills, I removed the OS and MMU and added sockets, and with additional soldering, have the U1MB working great.  I have to say many many thanks to @flashjazzcat for the detailed Youtube video on the installation, which I watched several times and got me through the work successfully; after not picking up a soldering iron in years, and never having de-soldered chips previously.  Have my Sdrive Max for loading software now, however likely will grab a Side-2 to take advantage of the side-loader integration.  Or should I be waiting for Side-3?

 

Lastly, decided after deliberation to make suitable hole in case and fitted DVI header reasonably neatly for me.  Very pleased with the work, with only minor issues with the Sophia blacking out randomly at times, but far less frequent than before.  That's another post........

 

One further observation in reference to the start of my thread : in order to fit the DVI header, I had to make space and de-soldered the RF modulator.  I note now that the composite output has greatly improved and all ghosting / distortion seems to be gone.  It's a little grainier than the Sophia DVI output for sure, but closer to what I see from composite on the other two for now, so very happy with that.  Does it make sense a faulty RF modulator could influence the Composite output in this way, and so by removing it I've solved the initial issue?

 

Had lots of fun working on these when time has allowed - Not sure if will keep hold of all 3 - may see if can find good homes for them in due course, but can see myself thinking about what other upgrades I could try with them in the meantime.  On pre-order list for Sophia 2 already.  What else?  Fujinet looks interesting too.