Challenger 4P Video Problems

dave
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Re: Challenger 4P Video Problems

Post by dave » Sun Mar 08, 2015 10:02 pm

GenericUser wrote:
dave wrote:
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
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Challenger 4P Video Problems

Post by GenericUser » Sun Mar 08, 2015 10:38 pm

Klyball wrote: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
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Re: Challenger 4P Video Problems

Post by Klyball » Mon Mar 09, 2015 2:39 am

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
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Klyball
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Re: Challenger 4P Video Problems

Post by Klyball » Mon Mar 09, 2015 4:37 pm

one more thing

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

Grant
Replica 600 Rev D:8K,CEGMON
Replica 610 Rev B: 24k,MPI B-51 with Custom Data separator D-13
510 on the bench/replica 582 backplane/replica 470a /replica 555/original 570B/2 x Shugart 851
Ongoing : 630 ,620 ,510,542c,custom 590,SA1200,592,594,596,598

Jeff
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Re: Challenger 4P Video Problems

Post by Jeff » Wed Apr 15, 2015 5:37 pm

GenericUser wrote: 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
Image

Jeff
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Re: Challenger 4P Video Problems

Post by Jeff » Wed Apr 15, 2015 6:00 pm

Screen Shot 2015-04-15 at 10.55.26 AM.jpg
Screen Shot 2015-04-15 at 10.55.26 AM.jpg (56.7 KiB) Viewed 3905 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
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Re: Challenger 4P Video Problems

Post by GenericUser » Thu Aug 15, 2019 9:31 pm

Okay, after a 4.5 year break, I can proudly announce that I'm done being an ignorant middle schooler. Thank you guys for being so patient with 15 y/o me :oops:
The "-5v" from having my probes backwards absolutely kills me.

I was getting ready to sell the poor thing as-is on ebay, but started looking through all of the documentation I got with it and decided it was far too interesting and important to get rid of. So I'm back at trying to fix it again.

The current status of the machine is that it displays nothing upon first startup, but a quick flick of the power switch off and on again gets it to display garbage characters (some of which slowly morph over time). I have removed all but one pair of the RAM, and the video is still corrupt. As suggested by Klyball, I swapped the RAM on the video board with the same result. Unfortunately I have no way to tell what RAM chips are good and which are bad; any suggestions on a tester? Thankfully the break key still changes the output. Where do I go from here?

Also, the video board seems to be hurt in other ways. The output starts off strong and clear, but gets more and more dim as it heats up. Or perhaps its a power supply issue?

Thanks again

Mark
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Re: Challenger 4P Video Problems

Post by Mark » Fri Aug 16, 2019 8:15 am

Hi,
It sounds to me like the voltage is changing on the supply powering the 540 board.
Even without any CPU or additional memory boards in an OSI, a 540 board should display a non-changing pattern of characters once powered up, (depending on what the on-board RAM has randomly powered up with). If the display changes or fades out, then there are either bad ICs/semiconductors or bad power. Flicking the power off & on can cause the RAM chips to initialize with other data changing the pattern on the screen. Check for warm chips, use cold spray (or an inverted can of air duster) to probe for thermal failures. Measure the voltages again when things change. There may be very noisy (high ripple) 5v if the filter capacitors have failed in the power supply. The displayed characters should not change or morph, but I have seen that when the voltages were too high or too low. (It could also indicate bad ROM or logic on the 540 board). Also the displayed characters should look like something from the OSI character set.
OSI-CHARGEN.gif
OSI-CHARGEN.gif (5.14 KiB) Viewed 431 times
With a complete system, upon RESET the CPU will access the program in the boot ROM to fill the 540 video RAM with $20 characters. The system depends on working RAM from $0 to at least $200 to get that far. If it doesn't work correctly, how the screen fails can give you indications of data line buffer failures, addressing failures etc. I used to use a simple portable AM radio to pick up RF from the OSI to monitor what it was doing. You could hear the screen clears, keyboard polling and program execution. You can hear when the CPU crashes as the noise changes to a single tone or when it got stuck in a loop - repeating noise. Generally random "white" noise indicated things were working correctly.

Much of my C4PMF system instability was finally cured by replacing the 2 old linear OSI supplies, with a modern multi-voltage switching supply. Reseating chips and replacing suspect sockets with gold machined-pin sockets has helped too.

Good Luck!
-Mark

GenericUser
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Re: Challenger 4P Video Problems

Post by GenericUser » Sun Aug 18, 2019 11:09 pm

Okay, just to eliminate any power supply issues, I have a 5v, 100W one on order. Hopefully that will clear some issues up. I will get back once it is installed.

Thanks!

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