OSI 2C4P fix

[nama]

Hi everyone,
This is my first post here. Some of you may know me as that annoying guy trying to track down an OSI machine...well, I finally got one, but it's a real 'fixer-upper' for sure.

The machine arrived yesterday and smelt bad like mouse poop. I decided the first thing was to take it apart and wash it. Now I have the boards out of the machine and on my workbench and powered by a switching power supply. After a bit of fiddling around I was able to get a screen of random characters.

I have started a repair log, and was hoping to get help and advice from the knowledgable peeps here to get it working. You can see the start of the log here:

http://web.me.com/lord_philip/other_com ... P_Fix.html

My next step is to remove all the socketed IC's and clean the legs. Maybe this will help.

Back soon...

Philip

[nama]

Well, I've made a lot of progress in one day. I now have the prompt, and even ran a very small program from the monitor.

I'm not getting reset on the CPU, so I have to force it by briefly grounding pin 40 of the 6502. Can anyone point me in the right direction on where (and how) to look for the faulty component in the reset circuit on the 505 board.

Thanks in advance.

Phil

[nama]

Thanks to Mark Csele for pointing out the error of my ways. I was assuming that the machine had reset on power up, but like many machines of that era it was manually triggered. It's been soooooo long since Ive used a OSI machine I have forgotten all this stuff.I'm 42 now, and was maybe 10 when I used to use them at my Dad's University. Too long.

There was a button that someone had installed in the case, but the connector was loose on the other end. so I didn't know where it went. I installed the button assembly to J3, and now with a quick push I get reset. there are two wires coming off the keyboard that are snipped and are the same color as the wires now going to this button, so my guess is that these wires once hooked up to the keyboard and reset was triggered somehow from there. I'll look into that.

[nama]

After a bit of searching it seems that the two wires that come off the keyboard do connect to the reset circuit which are triggered by the 'Break' key. Please let know if I'm mistaken.

[Steve Gray]

welcome,

Yes, the break key resets the machine. I actually removed the break key on my original machine and installed a switch, since I was forever hitting break by mistake

It's great you have things working! I'm interested in how you are powering the machine via switching supply. It's something I might have to do as well with my second machine.

Steve

[nama]

Firstly, apologies. Seems I posted this thread in completely the wrong place. Hopefully Dave can move it somewhere more appropriate.

Hi Steve, yes the switcher seems to work quite well. The one I have does get quite hot. Hopefully once the case is all fixed up and everything is back inside, the fan will keep things a little cooler. Thanks for the confirmation on the 'Break' Key. I think I'll eventually wire that up to it's original state.

So I'm trying to figure out how to get the machine working with a serial connection so I can transfer some programs from a PC using Monitor. When I got it it didn't have a DB25 installed and therefor no connection to the 505b board. I have been told that it's simple by adding a few jumper wires, but I have not been able to find out exactly where to add them, and it seems my board has already been jumpered.

I'm not sure if it's jumpered for serial, or something completely different. Does anyone know where I can find a definitive answer on how to wire it up?

Cheers

[nama]

SUCCESS!

I decided to wire up a serial connection on the off chance the board was already jumpered for it...well, what do you know, it worked!

http://web.mac.com/lord_philip/other_co ... ix.html#19

Now that the main machine is fixed (although I'm still having issues with the other 24k board) I'm going to concentrate on the cosmetic issues. First I have to get the case sandblasted, then I'm going to patch all the holes with HTS 2000 (amazing stuff)

http://www.youtube.com/watch?v=N-cv3R4fWZc

and then get the entire case powder coated again.

Finally I need to track down an authentic fuse holder, and get a new nameplate made.

Big thanks to Mark Csele for all his help.

Phil

[dave]

Thread moved to Discussion & Projects.

That's great Phil! I remember that auction! I also bought a couple of boards from the same seller. You got a nice machine there. Fixing the other RAM board should be pretty straightforward.

Have you checked the power rails on the second 527 board? If not, then it is also possible that your second board is wired for a separate power supply, and not powerd from the bus. Since each 2114 can draw up to 100 mA (70 mA for a -L part), a fully populated 527 will soak up about 3.5 to 4.8 amps, up to 25W! These machines came stock with 5V, 4.5A power supplies which could not handle at most one RAM board. To add the second 527 card, one had to add another power supply just for that 527. The 527 power rails are connected to a 4-pin Molex on the side of the board, but can be jumpered to the 48-line bus power (photo from Mark's Lab board catalog attached, with extra power port circled.)

OSI527.jpg (78.49 KiB) Viewed 8862 times

If your switcher can handle the power, you should be able to jumper to the bus.

You also might want to check out the Sept and Dec 1986 volumes of Peek(65), which describe hooking up a 5.25" or 3.5" standard DS/HD drive.

Best of luck! Keep us posted.

Dave

[dave]

Now that the main machine is fixed (although I'm still having issues with the other 24k board) I'm going to concentrate on the cosmetic issues. First I have to get the case sandblasted, then I'm going to patch all the holes with HTS 2000 (amazing stuff)

http://www.youtube.com/watch?v=N-cv3R4fWZc

and then get the entire case powder coated again.
...
Phil

That does look pretty amazing. I will have to pick some up. I've used JB weld to repair a chunk missing from a HP-9825 case--also great stuff, but takes longer due to the drying time. I'm very interested to see the results of the powder coating. Definitely keep us updated!

Best regards,

Dave

[nama]

Thanks for moving the thread, and thanks for the info on both the drives and the RAM boards.

Regarding the RAM boards: My present switcher supplies 5V @ 5A. so it may not be enough to power the second card. I have already ordered another switcher from ebay (cheap $25). This is the switcher I was going to install in the machine it is rated at 5V 6A. Hopefully this will be enough for both cards.
One of my cards does indeed have the molex connector installed, but when the machine arrived it was not connected to anything.
I also discovered that I don't need the -9 volts for my setup. removing the -9V adaptor board does not seem to effect anything.

Re disk drive. thanks for pointing me to the peek65 article. seems very interesting. I can possibly get hold of a Tandon TM-100 drive. Do you think I would be able use this drive? I did come across one reference on the web to a C1P user having a TM-100 drive for his setup, so I think it's possible.

Will keep you posted on the case fix too.

Thanks again.
Phil