hueyjones70

This is excellent info. I am thinking about purchasing a 1040.

I have swapped every IC on the board.

I tried the syscheck and it told me that the RAM chips U9 ands U15 were bad. Sometimes it would give different readings but that was the most consistent. I resocketed the RAM and now U9 and U12 are the only chips that are not bad. I have tested every IC in a working computer and they all check our OK. I can only surmise that there is a bad trace somewhere or maybe an IC pin is not making contact.

I have an 800XL that has a similar issue. Mine is vertically scrolling continuously and I have tested every IC in another computer and I cannot isolate the problem. I have a logic probe but I don't know how to use it.

I just received my syscheck last week. I used it on a nonworking computer and it indicated that all of the RAM chips were bad but when I replaced the RAM it still showed bad and the supposedly bad ram checked out on another computer. Where should I go next.

That is what I would expect also. I sold an 800XL on eBay and the buyer messaged me that he couldn't get a stable video and then he said he was using a commodore power supply. I looked up the pinouts and I replied that he shouldn't use the commodore supply.

What would happen if someone tried to power an Atari XL with a C64 power supply.

I noted a reference to a "syscheck" board. Is it still possible to get one? What does it do? Where can I find info?

Working on an 800XL and get a very bad video on boot. The computer never does a proper boot. Sometimes I get this screen and sometimes I get no video at all. I have tested every IC on the board with a working board and I cannot find one that is faulty. Any ideas of where I should look. My diagnostic tools consist of a multimeter and a logic probe.

Sometimes the mylar gets a slight indentation that makes the key contact points to be permanently touching each other. If you haven't fixed the problem yet, I have found that you can get some of those stick-on paper rings that are used as reinforcers for pages in a notebook and place it over the appropriate key contact on the mylar. This creates a space between the and that takes care of the problem.

You can piggyback the UAV onto the 4050 and keep the modulator function but why would you want to?

I know that it has to be broken that is why I have it connected to the switch but when the modulator is removed, there is no voltage on any of the switch posts.

I have been installing a dual OS EPROM in the OS socket and running a wire from pin 27 to the middle post of the channel select switch. The switch then changes the OS when the switch position is changed. One post of the channel switch shows 5 volts when the modulater is present. With the modulator removed there is no voltage on any post and the switch doesn't change the OS.

I removed the RF modulator from an 800XL and I need to restore voltage to the channel select switch. What is the best way or easiest way to do this?

The problem was with the monitor DIN.