Challenger 4P Video Problems

GenericUser
Posts: 5
Joined: Sun Mar 08, 2015 3:27 am

Challenger 4P Video Problems

Post by GenericUser » Sun Mar 08, 2015 4:19 am

Hello!

I recently picked up a Challenger 4P that could use a little help, and unfortunately I am a noob when it comes to Ohio Scientific, or...really just all vintage computing in general.

It's in a little rough of shape, scratches, paint chipping, etc, etc, but that's not the main problem. Whenever the machine is powered on it seems pretty normal, except for the video output. It is completely scrambled, not at all like what is supposed to show up. However, the machine DOES respond to me pressing break; it changes its scrambled output to some other pattern (look at pictures of the machine and its output in the album; http://s358.photobucket.com/user/xXGene ... x/library/)

I honestly don't even know where to start. I have tried turning the knob knob on the back, which I assume is a controller, but there was no change of output on the screen. In one of the pictures I did show where it was wired to on the 505. (The grey wires; one of the last pictures if you sort it by filename)

Like I said, I'm a total noob when it comes to this stuff, and if you could help me out that would be great!

Oh, and also: ignore the blue tint on the images of the screen - that's just my cell phone being dumb

And lastly a little off-topic, At the same place I got the 4P, I found an "OSI 510 CPU" in a sad little dust covered box. I couldn't find it on the hardware list so... what it it? (It is NOT in the 4P, just got it on the side)

Thank you in advance!
Last edited by GenericUser on Sun Mar 08, 2015 12:52 pm, edited 2 times in total.

MK14HAK
Posts: 343
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

Re: Challenger 4P Help

Post by MK14HAK » Sun Mar 08, 2015 6:10 am

Try some generic trouble shooting ! You will find ccts on OSIweb.org
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator

Klyball
Posts: 195
Joined: Tue Dec 09, 2014 12:53 am

Re: Challenger 4P Help

Post by Klyball » Sun Mar 08, 2015 6:20 am

And lastly a little off-topic, At the same place I got the 4P, I found an "OSI 510 CPU" in a sad little dust covered box. I couldn't find it on the hardware list so... what it it?
i'll take it off your hands if you don't want it :D

Model 510 Triple CPU Board (6502, Z80, 6800) © 1979

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

nama
Posts: 299
Joined: Wed Mar 30, 2011 9:44 am
Location: New Zealand
Contact:

Re: Challenger 4P Help

Post by nama » Sun Mar 08, 2015 9:03 am

My first guess is that something is running, as the screen seems to clear a little after pressing BREAK. Maybe it's a problem with the video board? Other than that guess, it's hard to know where to start...

...well actually, the place to start is probably to test the voltage output from the PSU(s), and what voltages you are getting on the boards.
Next I'd test to see if you are getting any activity on the 510 CPU board. I'm not familiar with the 510 board, as it's a bit of a oddity, and I don't know how to go about trouble shooting a 3 CPU board! Maybe someone else would have more of a clue.
What CPU does it default to? the 6502 probably???

Anyway, as Mike said, download all the manuals, schematics, and whatever else, for your 4P and the boards that are installed. That's the best place to start. It may look daunting at first, but basic trouble shooting usually isn't that difficult. The fix usually goes one of two ways. Either you can get the machine running relatively quickly, or the fix gets much more difficult.

Some basic and cheap tools like a multimeter, and a logic probe are invaluable.

Phil

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono), D13 + Gotek
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON
Spares - 2 x 527, 1 x 527 [600, 610, D13 boards]

dave
Site Admin
Posts: 560
Joined: Tue Sep 09, 2008 5:24 am

Re: Challenger 4P Video Problems

Post by dave » Sun Mar 08, 2015 3:11 pm

Hi Generic User! Welcome to the site.

Congratulations on finding a really nice system! It is definitely fixable.

The knob on the back sets the baud rate (data rate) for the UART to various speeds from 300 to 9600. At those low clock speeds, that setup will probably work, but it's not good practice to route clock signals through long wires and switches like that, so eventually you'll want to replace the knob with a jumper on the board for 9600 baud. We can get to that later. In the meantime, you can ignore that knob.

From the screen image, it seems that there is actually something there, just really scrambled. Can you confirm that the scrambled white pattern disappears when you power off? You mentioned that the pattern changes when you press "break." That's really good news. Can you post pictures before power up, right after power up, and on pressing BREAK?

If the scrambled pattern is the video output, then that gives us a starting point. First, try the horizontal and vertical controls and see if that gives you something more recognizable. I don't think it will fix it, but worth a try (and you probably already did that). BTW--just checking--are you in the US? If not, be aware that using a PAL TV could result in scrambled video if the output is configured for NTSC, and vice-versa. If you're in the US, it's probably not an issue.

What kind of test equipment can you get access to? As Nama mentioned, a multimeter and logic probe are very useful. If you can beg or borrow any kind of oscilloscope, it can sometimes be the difference between a fix and a perpetual "to do" item.

Good luck,

Dave

dave
Site Admin
Posts: 560
Joined: Tue Sep 09, 2008 5:24 am

Re: Challenger 4P Video Problems

Post by dave » Sun Mar 08, 2015 3:25 pm

GenericUser wrote: And lastly a little off-topic, At the same place I got the 4P, I found an "OSI 510 CPU" in a sad little dust covered box. I couldn't find it on the hardware list so... what it it? (It is NOT in the 4P, just got it on the side)
That's a CPU for a Challenger III. It has a 6502, 6800, and Z-80 on it. It starts up in 6502 mode, and commonly, the 6502 was used to bootstrap an OSI port of CP/M, then switched over to the Z80. It was used primarily in serial-based systems, rather than video-based systems.

It also includes a simple memory paging mechanism to support multiple time-shared work-spaces.

I don't have any docs on OSIweb.org, but Mark Spankus' site has a photo and schematics.

It's an interesting board, but will be a bit of a project to get up and running.

Good luck with it!

Dave

Klyball
Posts: 195
Joined: Tue Dec 09, 2014 12:53 am

Re: Challenger 4P Video Problems

Post by Klyball » Sun Mar 08, 2015 4:44 pm

Welcome!! it is very important to always check the power supplies in vintage computers before hand.
check ,clean and reseat all connections and boards is the next step, then dig into the schematics.
the Sams manual would be best for troubleshooting.

If you have the means, it would be very important to dump the contents of the eproms and proms on the 510 board for archiving and as back up.
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

GenericUser
Posts: 5
Joined: Sun Mar 08, 2015 3:27 am

Challenger 4P Video Problems

Post by GenericUser » Sun Mar 08, 2015 7:42 pm

dave wrote:As Nama mentioned, a multimeter and logic probe are very useful. If you can beg or borrow any kind of oscilloscope, it can sometimes be the difference between a fix and a perpetual "to do" item.
I actually DO have access to an oscilloscope. I also have a multimeter and a logic probe, so I'm pretty good in the test equipment department.

As for the baud rate knob - I did not install it, the person that had owned it last installed it.

I went ahead and added titles to both of the screen pictures, I guess I probably should have done that beforehand, but whatever. The more clear screen is the one before pressing BREAK, and the more static filled screen is after. When the machine is not turned on, it is just the standard static - no patterns whatsoever.

Yes, I am in the US and it's a NTSC TV. The TV that it is connected to is a relatively new one; it has auto-tuning so that I don't have to mess with the horizontal and vertical. I have used the same TV to work on an Atari 1200XL, so I am pretty sure it should work for the Challenger as well. I am using an RF box to connect it to the TV.
Klyball wrote:it is very important to always check the power supplies in vintage computers before hand.
As soon as I can test the power supplies I will update the post.
Klyball wrote:If you have the means, it would be very important to dump the contents of the eproms and proms on the 510 board for archiving and as back up.
Unfortunately, I do not have the means to dump any of the board. :?

Klyball
Posts: 195
Joined: Tue Dec 09, 2014 12:53 am

Re: Challenger 4P Video Problems

Post by Klyball » Sun Mar 08, 2015 9:26 pm

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

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

dave
Site Admin
Posts: 560
Joined: Tue Sep 09, 2008 5:24 am

Re: Challenger 4P Video Problems

Post by dave » Sun Mar 08, 2015 9:47 pm

Grant is right, you need to eliminate the RF modulator. That pathway can't handle the bandwidth of the 64x32 video, and could be the explanation for what you are seeing. Is there any way to find a TV or monitor with direct composite input?

Post Reply