Now I've done it.

[russg]

If you have a blue screen then you never get out of the ROM. Bad OS ROM, CPU or MMU. You can leave POKEY and PIA out of the computer and you'll still get through the ROM.

 

You need to swap the chips from your failing m/b into a good m/b and test them one at a time. A scope only helps when you have a pretty good idea what is happening. What you need is a logic analyzer that can trace the RESET code. And an OS listing... Not the kinds of things that most people have.

 

Bob

 

 

 

I typed the following before I 'double checked' my Antic and GTIA LSIs. I managed to kill my good 'test' mb, with just swapping Antic and GTIA.

I panicked. I finally found a good Antic and now that board is working again. So, I'm at the bottom line. I give up chip swapping, which is

all I basically do. I'm putting them all back on the shelf.

Here's what I wrote before I killed an Antic.

 

I have a 800XL mb I've been working on.

I've swapped all chips. The mb behaves differently with a

CO14803 3 versus a CO14803 12 CPU chip. The 12 goes to the

green pre-screen and doesn't boot, just sits at a dark

green screen, apparently never accessing the OS.

The #3 CO14803 will boot a disk and play all the correct

booting and program playing sounds, but has a jumping,

flashing display. I know both these CPU work fine in

a correctly working 800XL mb.

So, the #3 accesses the OS and boots a disk, but never

has a proper display.

A normal display will briefly show a color dark screen,

and then a blue screen with a cursor in the upper left.

With this blue screen, the 'pbbbbblt' sound comes with

no disk attached, and then BASIC READY comes up.

If there's a disk attached, the blue screen stays while

the disk boots, no pbbblt sound, but the disk sounds

start and go until bootup finishes.

That's a normal bootup. My bad mb makes the correct sounds

for disk or no disk, but the blue screen doesn't come.

Instead, a black screen with a few lines dancing comes

up until the pblllt sound quits and then a blue background

with stable white dots and dashes. Along with the stable

blue screen and dashes there are rapidly flashing white

inverse characters. The bottom 1/5 of the screen is

solid black.

I double checked Antic and GTIA, and now my good mb

isn't working right....... ???

[+bob1200xl]

Electronic stuff has a range of 'good' values and operating limits. What works in one board may not work in another because of minor variations in timings or voltages. Just because an ANTIC chip works in one m/b does not mean it will work in any m/b. We do not have the data or tools to tell if a chip is out of spec, so we have to swap them into a known, good board. Unfortunately, that is not a definitive test.

 

You really should do yourself a favor and swap only one chip at a time.

 

Some failures show up after the chips warm up a little. Some failures go away after the chips warm up a little.

 

There are a lot of 'gotchas'.

 

Bob