Glitch with Lucasfilm games

[ApolloBoy]

I have a 256K 800XL, and whenever I run a Lucasfilm game on it, the Lucasfilm Games logo is wavy and distorted (it's kind of hard to describe), and it even does this for the intros on Ballblazer on Rescue on Fractalus. The actual games run perfectly fine, so I'm wondering if the 256K mod is causing this problem. For the record, my 800XL has the 256K Rambo mod.

[Rybags]

Sounds plausible.

 

Just tried my carts of RoF and BB and it doesn't do that... although my Rambo capability comes via VBXE.

 

At least that all but eliminates the software itself as having the problem.

 

Does it do the same with anything else? How about try some stuff that's heavy on the GTIA modes such as Numen or the Asskicker demo.

[Rybags]

Just had a look at these games in the emu to see where it puts those screens.

 

Does the Lucasfilm logo screen get the problem in RoF? This particular part doesn't put the screen in the bankable area.

 

For the space station part, and all of the Ballblazer load screen, the bankable area is used for screen RAM ($4000 onwards).

 

You could try some stuff in BASIC to see if you can reproduce the artifacts:

 

10 POKE 106,96

20 GR. 9

30 FOR X=0 to 79

40 C. X:PL. X,0:DR. X,159

50 NEXT X

999 G. 999

[ApolloBoy]

IIRC, Numen requires 320K so I can't try that out. I might try the Asskicker demo but I'm not sure if it runs on an NTSC Atari or not.

 

Anyway, the Lucasfilm logo distortion occurs on every Lucasfilm game I've tried. Both my Ballblazer and Rescue on Fractalus carts have the problem, and it also extends to The Eidolon and Koronis Rift. Even the disk versions of Ballblazer and RoF had the same issue (for the record I'm using a SIO2PC). I'll go ahead and give the BASIC command a shot when I get home.

 

Also, I tested the RAM in my 800XL (all 256K of it) to make sure my RAM wasn't bad, and all of the RAM checks out.

[ApolloBoy]

I ran the BASIC command and the distortion shows up. Now I'm not sure if my GTIA is bad or if the GTIA doesn't agree with the expanded RAM.

[Rybags]

Probably something amiss with the upgrade then.

 

Maybe try the Basic program a few more times, with variations on line 10.

 

Try values of 64, 128, 160 and 192 as the second value in the POKE statement.

 

You'll probably need to do it without loading DOS though.

[thorfdbg]

I ran the BASIC command and the distortion shows up. Now I'm not sure if my GTIA is bad or if the GTIA doesn't agree with the expanded RAM.

The GTIA itself doesn't have an interface to the RAM; it gets its data through ANTIC. You have probably a faulty GTIA, or

damaged it when installing the RAM upgrade?

 

So long,

Thomas

[ApolloBoy]

I ran the BASIC command and the distortion shows up. Now I'm not sure if my GTIA is bad or if the GTIA doesn't agree with the expanded RAM.

The GTIA itself doesn't have an interface to the RAM; it gets its data through ANTIC. You have probably a faulty GTIA, or

damaged it when installing the RAM upgrade?

I didn't do the upgrade myself (it was done by the original owner over 20 years ago), so I have no idea if the GTIA was damaged or not. I don't see how it could've been damaged since the Rambo mod has wires going to the PIA and a resistor.

[Rybags]

Can you try that Basic program again? This time with the other values in the POKE statement.

[SuperSparky]

Here are some possible causes:

 

• Not enough power from the power supply. Lack of sufficient current can cause the analog circuitry to get "upset".
  
• RAM interface wiring possibly crossing the video circuitry and causing interference.
  
• Poorly done RAM expansion. Perhaps missing the 33 ohm resistors?
  
• The monitor is perhaps the one with the problem, not the XL. This sort of problem is also a poor power supply, but this time in the monitor. Try it on a modern TV (if not already).
  

[ApolloBoy]

Not enough power from the power supply. Lack of sufficient current can cause the analog circuitry to get "upset".

I'll pull out my multimeter and see if the PSU could be the problem. Unfortunately I have the "ingot" PSU so there's a good chance it could be faulty.

 

RAM interface wiring possibly crossing the video circuitry and causing interference.

I'm not sure if that's the case since it's only connected to the PIA, R32, and it's plugged into U27. Maybe I'll put some foil around the wires connecting the mod to the PIA and see if that reduces the interference.

 

Poorly done RAM expansion. Perhaps missing the 33 ohm resistors?

I looked at both the mod and the Atari and didn't notice any missing parts.

 

The monitor is perhaps the one with the problem, not the XL. This sort of problem is also a poor power supply, but this time in the monitor. Try it on a modern TV (if not already).

I'm using the 800XL on a 6-year old Philips CRT. I do have a Commodore 1702, but I really don't want to lug it out of the garage just for this.

 

Rybags, I tried out the same command with the variations, and they still give me the same result.

[ApolloBoy]

I just got some humming in the audio when I booted up my 800XL today, and I think the culprit is the PSU. At this point I think I can rule out the GTIA and the Rambo mod as the source of the problem.

[Rybags]

Best to get another PSU before that one fries the system.

 

It mightn't necessarily be causing these graphical glitches, but a dead system will make that problem seem trivial.