Challenger 4P Video Problems

[dave]

Unfortunately, I do not have the means to dump any of the board.

From the photo, it looks like your board is the older rev with four 1702A EPROMS, which most modern programmers cannot recognize. I do have a 1702A programmer, and if you are willing to send me either the whole board, or just the EPROMS, I would be glad to make the copies.

An easy alternative would be to power it up and boot into the serial monitor, then enter a small program to dump the EPROM contents out the serial port.

Dave

[GenericUser]

If you have a tv with composite in I would try using that and cut out the rf modulator , one less thing to worry about

Yes! We got a little more success! The video is still scrambled, but in a WHOLE new way.

It appears to be trying to display the start-up characters, but they don't make any sense. Once BREAK is pressed the output changes just like last time, they are still scrambled, but definitely better than before. Going to test the power supplies RIGHT NOW. I will update the post when I'm finished. The pictures have also been updated to the new output.

http://s358.photobucket.com/user/xXGene ... t=9&page=1

UPDATE: Both power supplies have an output of ~5V. If i remember right one is supposed to be 5V and the other 9V. Right?

[Klyball]

That looks better,

5v is good, im gonna bet on a few bad 2114 ram chips, try pulling all the ram on the ram board leave in the first 2, then pop out the ram on the video board and swap with some of the ones you removed, if you have a tester then test them, I just bought a pile of nos 2114 and about 15% were doa

[Klyball]

one more thing

the memory board needs it own 5v supply, make sure it is powered buy one of the 2 supplies separately

Grant

[Jeff]

UPDATE: Both power supplies have an output of ~5V. If i remember right one is supposed to be 5V and the other 9V. Right?

I have nearly the same machine and got it mostly working with fantastic advice from the members here on this site.

1: Both of your power supplies should (and probably are) outputting 5V. I think the -5V you are measuring is because you have your probes backwards.
2: Garbage video screen before BREAK is normal. Its a good sign that the video board is working properly.
3: Clearing the screen (even partly) ben BREAK is pressed is a good sign that your CPU is functioning.
4: I agree with Grant, that you probably have 1 or more bad RAM chips. I would remove all but 2 of them (on your 527 board, in the lowest bank), and then add them back 2 at a time until things go sideways.
5: Reseating all the chips would be a good idea too.

The machine is definitely fixable!

/Jeff

[Jeff]

Screen Shot 2015-04-15 at 10.55.26 AM.jpg (56.7 KiB) Viewed 2227 times

Here is a simple layout of the ram chips on the 527 board. Start with the pair of RAM chips at location 1 and add them in pairs all the way to 24. if you encounter bad ram chips, remove them and continue filling the chips in order. When trying to get the computer working, you don't need all the ram installed.

The 4 'slot' backplane is divided in two groups of 2. the top 2 slots are powered by one supply, and the bottom 2 slots are powered by the other. Because the 527 board has so much RAM on it, it needs its own supply. You can install the boards in your machine in any order, as long as the 527 is fed by its own supply, so when adding the RAM, put the 540 video board on the bottom, then the 505, just above it, and finally stack the 527 on the top, so you can add ram chips easily. NOTE: When I say "top", I really mean bottom, because the machine is upside-down when open.

Let us know if the screen clears when there is only 2 RAM chips installed, or if the "garbage" on the left of the screen is still present.

Cheers
/Jeff