Atari 800XL power issue - Atari NEWBIE

[JoeG]

I'm new to Atari computers, and the 800XL I purchased off of ebay is my first. It was sold, and shown in the listing, as working. Unfortunately, it doesn't now. My intention was to learn about the Atari 800XL before I started to attempt to repair one. Well, I advanced ahead to the learning how to repair one now.

Here's the issue:
- When I plug the male power plug into the Atari 800XL female power port while their is power to the plug, the voltages drop from +5v to zero. Even with the separate power switch off or on.
- The power plug has been checked to ensure that pins 1 and 4 are +5v, and that pins 3 and 5 have a good ground. The other pins are not used. Everything looks good.
- When I connect the male power plug (without power to the plug) to the female power port on the Atari 800XL and check for continuity from the plug pins (by using a small hook clip wire lead between the plug and the power port) and the corresponding power port legs that connect to the PCB, they all have continuity as they should. To restate this, there is continuity from plug pins, the power port female connectors on the Atari, and to the power port legs that connect to the PCB. All good.
- As an aside, I have no video signal as well as a result (not a surprise with no power).

It appears that I have ground short? Not sure. I've never seen anything like this before when I've been repairing Commodore PC's. If it is a ground short, where's a good place to start checking for the short? All the chips are in sockets, so I could pull those if needed.

I'm at a loss on my next step. Any help is appreciated!

Thank you!

Joe

[teenix]

I don't know much about this item, but from what I can see there are 17 or so capacitors across the 5V power supply input after the power switch, plus many in other parts of the circuit. Any one of these could be a problem if one has a short. It may be obvious by looking for swelling, discoloration etc.

The 5V rail looks like it splits into 4 sections, and any one of these could be powering a faulty component. I cannot see links for the power supply main rails, so isolating these for testing might be difficult.

If there is a high load dragging the 5V supply down, something on a circuit board is probably getting warm or hot, so this may help find the issue.

It may also be a problem the power supply. You might like to put a load on that and see if it holds steady at 5V. I don't know what current it can typically source.

cheers

Tony

[JoeG]

SOLVED!

The problem was that Pin 2 (shield) was making contact with Pin 4 (+5v) in the Power Cube. I happened to find it by checking for continuity on pins where there shouldn't be any. Given the confined space within the cube, having things touch when they shouldn't after surrounding components in a small protective case is easy to do. The fix was to cut Pin 2. The 800XL booted up to a yellow screen. Then I powered off, pressed down on the chips (all of them are in sockets), and powered the system back on. It booted straight to a "READY" prompt. Time to clean the chips and sockets!

I communicated and worked with the Power Cube provider during the entire process, and he was very helpful. He's sending me a new unit at no cost even though I said he didn't have to do that since it's working now. Great customer service!

Thank you Tony for the recommendations, even though I was dreading going down that route. I'm glad I avoided it by finding the problem outside of the Atari 800XL.

Joe

[TychoBrahe4736]

I envy you Joe. When I was a kid, the Atari 400 (membrane keyboard) was the first computer I ever had (thanks mom and dad!). But I always wished I could have the 800 (mostly for a real keyboard).

Have fun!

[ctrclckws]

In Fall of 1982 I entered college at one of the first schools to require home computers for some of their students.

The computer of choice in the pilot program was the Atari 800, big brother to the membrane key 400.

I stayed with the Atari ecosystem for years, until after college when I got a 286 PC compatible.

They were quite advanced for the time.

Enjoy.

[TychoBrahe4736]

(06-18-2024 02:32 PM)ctrclckws Wrote:  They were quite advanced for the time.

They sure were. I had the BASIC cartridge, but eventually (and I don't remember where - perhaps I typed the whole thing in and saved to my cassette) I was following along with a book on 6502 assembler and learning assembly. It was very empowering to just be able to understand that, thanks to the book. I also liked how easy the designers made it to access the hardware (peek and poke and accessing the blitter - all that stuff I barely remember). And of course, it played some great games compared to my Atari 2600 :-)

These are some of the books I can remember having:

- Your Atari Computer: A Guide to Atari 400/800 Computers
- Compute!s First Book of Atari
- Machine Language For Beginners by Richard Mansfield

That last one, I still have. I used to take that thing on vacations with me. I'm sure mom and dad thought I was nuts.

Okay, toning it down a little. I get excited and nostalgic thinking about how I used to love computers. And depressed that, though I use them at my job daily, they are no longer magic.

[Steve Simpkin]

My first computer was an Ohio Scientific Challenger 1P that I bought in 1979 while in High School. I used it to learn BASIC/6502 assembly programing and to play games. My second computer was an Atari 800XL in 1984. We used that computer for games, word processing, spreadsheets, BASIC/6502 assembly programing and to log onto BBS sites. It was a lot of fun back in the day. We did not get a "PC" until around 1992 (a 286 compatible). It was... less fun.

[TychoBrahe4736]

I promise I'll stop monopolizing this soon! Just remembered two more books that for nostalgic sake I recommend.

- Racing the Beam by Nick Montfort and Ian Bogost (Atari stuff)
- The Future Was Here by Jimmy Maher (Commodore Amiga stuff)

[JoeG]

All great replies!

My first was a Commodore VIC-20. I couldn't afford anything else until much later, and it was also a 80286 PC, monochrome with Hercules Graphics Adapter.

Joe

[ctrclckws]

(06-24-2024 10:41 PM)JoeG Wrote:  All great replies!

My first was a Commodore VIC-20. I couldn't afford anything else until much later, and it was also a 80286 PC, monochrome with Hercules Graphics Adapter.

Joe

Hercules Green or Yellow Screen?

During college I used my Atari 800 to machine language program a Commodore 64 or VIC-20 for my roommates physics project.
fun times

[JoeG]

Gold/Yellow screen. It was easier on the eyes, in my opinion.

That's sounds like fun!

Joe

[ctrclckws]

(06-25-2024 05:42 PM)JoeG Wrote:  Gold/Yellow screen. It was easier on the eyes, in my opinion.

That's sounds like fun!

Joe

My first jobs 286 also had a yellow screen.

[Craig Bladow]

(06-18-2024 04:33 PM)Steve Simpkin Wrote:  My first computer was an Ohio Scientific Challenger 1P that I bought in 1979 while in High School. I used it to learn BASIC/6502 assembly programing and to play games. ..

Same here, I wrote a screen text editor for the 1P, entering the machine op codes using the built in monitor. The 1P was followed by a Commodore 64, an Amiga 500 and PC's in the 90's.

[Dol]

(05-19-2024 10:04 PM)JoeG Wrote:  SOLVED!

Thank you Tony for the recommendations, even though I was dreading going down that route. I'm glad I avoided it by finding the problem outside of the Atari 800XL.

Joe

If you have a decent SuperVideo Monitor there is a display out mod to greatly enhance the video output clarity somewhere.

http://ftp.pigwa.net/stuff/collections/a...ervid.html
https://web.archive.org/web/201410010000...%201.0.pdf