Challenger C4P estate sale find project

[Dokken]

keyboard echo works!

also, it seems the original 6502 was good. these solder joints were likely the cause of my original flakiness. only bad chips I've found were 2x ram on the video board which originally caused half the screen to be garbage..

Screen Shot 2022-07-16 at 5.08.58 AM.png (4.69 MiB) Viewed 30112 times

[Dokken]

floppy drive.

pressing D does not clear the screen. drive led comes on and says on when powered. if I slide the head in, power the drive, it will step back to home/outer track and spin with the led on. no further stepping or activity. I'm testing with the CUSTOMER DEMO disk that came with it.

can you verify this this is/was connected correctly?

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head connector is keyed to 123x5 with white wire to the left (from front) and on the left most pin of the connector. it looks like this is the correct location, but there are other connector pins. just want to verify.

Screen Shot 2022-07-16 at 4.22.28 PM.png (2.46 MiB) Viewed 30098 times

34 pin ribbon orientation is the way it was mounted with the cable crimped in the back of the case. connector is not keyed, and no marking for pin 1 (which I believe would be the right-most contact when looking from the front). on the PC side, the red IDE cable is attached to a DIP-type header mounted to a pcb that connects to the top side (when upright) of the processor board. no other components inline. where's the floppy controller?

and can I test with a standard PC IDE drive? On my TRS-80s with similar Tandon drives, I can easily substitute a PC IDE floppy or a gotek.

I have a variety of old full height and modern IDE drives along with goteks if they can be used.

[Mark]

I no longer have original OSI MPI drives, so I can't verify connection orientation.
However according to the product manual I think it looks correct (Head 0 is J3 pin 6-10? )
The OSI floppy drive is similar to a standard PC 360K floppy except the OSI uses a simple FM encoding scheme that requires disk Read Data be converted into separate clock and data streams. The MPI-51 drives have a small daughter board on the front left(?) that does this. The OSI disk controller consists of a 6821 PIA, some interface buffers, and a 6850 ACIA. Very basic. Long ago I modified my OSI with an inline data separator, allowing me to use standard 1/2 height PC drives or Gotek etc.

The fact that the drive steps to Track 0 when pressing 'D' after reset indicates the interface connectors are oriented correctly and the OSI can send and receive control signals from the drive. (The OSI screen clears upon RESET but nothing visible happens until the floppy reads data & executes programs after pressing 'D' )

The first thing I would do is clean the disk head even if it doesn't look dirty. Most of my drive problems start there.

If that doesn't help, there is a great OSI disk diagnostics program that was created a couple years ago by David Gesswein that can help you diagnose problems. However you will need a serial connection to load it in your OSI.
David's disk test can be destructive, so don't use an original disk when testing! See David's full page here. There are alternate data separator projects you can find on OSIWEB if you search for them & want to go that route.

Good Luck!

[Dokken]

thanks. I do see the daughter board on the floppy logic board where you described. front left attached with a pin header and a zip tie.

I found my USB to serial converter. has a male d-sub on it. I'll have to figure out the cabling to the OSI.

[Dokken]

Serial connection:

I found a DB9 to DB25 (?) cable. Connections looks like this:

Screen Shot 2022-07-17 at 2.55.12 PM connections cables.png (2.41 MiB) Viewed 30078 times

The Keyspan USB to serial adapter seems to be configured properly in windows 10 with drivers. I used this keyspan for a couple of years a while back and it worked fine. LED on keyspan blinks when I type into putty.

Screen Shot 2022-07-17 at 2.53.45 PM keyspan usb.png (2.42 MiB) Viewed 30078 times

I configured putty as follows: Serial, COM3, 300 baud.

Screen Shot 2022-07-17 at 2.54.17 PM puty config.png (2.69 MiB) Viewed 30078 times

I typed in the serial test program Mark referenced.
You can test for proper serial I/O using a 21 byte program found here https://osiweb.org/osiforum/viewtopic.p ... rial#p4186 on a different thread.

here's what I see on the challenger screen:

Screen Shot 2022-07-17 at 3.02.32 PM challenger output.png (2.8 MiB) Viewed 30078 times

the challenger screen continuously 'jiggles' like it is doing something. the keyspan led lights when I type into putty. but nothing else, no visible data.

am I doing something obviously wrong? suggestions? fat finger of the serial test?

thank you

[Mark]

Hi,
It's been so long since I've used an unmodified C4P, that I may have left out an important step. According to the A15 pinout guide from the manual (attached) , it looks like the "Printer" port may be active by default, which may only have serial out. The "modem" port is bidirectional, but requires a control bit to be set active in order to get it working. Entering .F703/34 should activate the modem port. (This confused me years ago and I hard wired the default port to be bidirectional) So before the program you entered, add A9 34 8D 03 F7

Also I think the 1st serial program you typed in had an extra character. The screen shake seems to be a side effect of an endless loop accessing video memory. Try the version below.

My system has been changed from the the way it was shipped from factory, but you may just need to swap pins 2 & 3 (NULL modem) to get it to talk. You only need pins 2,3 & 7 on the DB-25 end (I can't remember if you need to jumper hardware flow control signals 6=8=20 too.)

Code: Select all

.0300/A9
34
8D
03
F7
AD
00
FC
4A
90
FA
AC
01
FC
AD
00
FC
4A
4A
90
F9
8C
01
FC
B0
EB
.0300G

A15 I/O panel pinout

A15-pinout.gif (96.39 KiB) Viewed 30074 times

[bxdanny]

Dokken,

Has there been any further progress, either with the disk drive or the serial communication with a PC? For a while this thread was so active, with you and Mark exchanging messages sometimes twice a day. Now it's been almost a month with no word.

As Mark pointed out, you should try both 300 and 1200 bps for the serial communication, and both pins 2 and 3 (on J9) for the incoming serial connection. Actually, I expect that pin 2 of the connector with the incoming signal would be the correct one to use. The best way might be to connect pin 2 on J8 (shown as normally left unconnected) to pin 3 on J9, and then use J8 (the "printer" port) to connect the serial cable from the PC. (Since the PC acts like a terminal, it will be wired as DTE, Data Terminal Equipment, the opposite way from a modem, which would be DCE, or Data Communications Equipment. A simple mnemonic I thought of when reading this thread last month would be TTT, or Terminal Transmits on Two. It is obviously the SOUND of "T" that matters here, since "three" also starts with the letter T, but not with its usual sound.)

I don't think you ever posted a list of all the disks you got with the system. You said there were 13? It would be interesting to see what they are. If there are any that haven't already been posted here or on Mark's site, perhaps you could send those to him for imaging if you can't get the drive working.

[Dokken]

Hi, I'm still here but had to take a break from the OSI. I'll get back on it soon and will get a listing of the floppies. there's probably 25 or so.

[Dokken]

six months later and I pulled the OSI Challenger 4P out again. I feel like I'm starting over. I believe the computer is working fine and the floppy drive wants to work but does not.

Current status: shift lock pressed/down, powers on to garbage, drive spins up with red led on and CUSTOMER DEMO disk in. press break key screen displays H/D/M. pressing D will return drive head to outside track. at times, the H/D/M will clear from the screen and the disk acts like it is trying to load something but eventually just spins.

I'm wondering if there's possibly a physical connection or cable issue since this seems intermittent ?

is the head connector oriented properly and in the right place?

osi floppy head conn.png (1.25 MiB) Viewed 28846 times

this little doo-dad board seems very unstable with its pin connector. what is it's function?

osi floppy add on board.png (2.12 MiB) Viewed 28846 times

when I first pulled the drive apart, I notice the head stepper was working but the drive motor wasn't. I looked under at the belt, and there was a broken piece of plastic wedged in the belt. cleared that and motor works.


thought on getting the drive to work? I have a few similar Tandon SS drives from TRS-80 Model 1s if that would be of help to substitute. from brief reading it looks like a special interface is required to use most other drives, including gotek.

[bxdanny]

>>> drive spins up with red led on and CUSTOMER DEMO disk in

As I was recently reminded, OSI warned consistently about powering either the computer or drive on or off with a disk in the drive, since that can cause transients that can damage the information on a disk. OSI 5.25" drives were especially susceptible to that, since the head always remained loaded against the diskette. I hope your disk has not been damaged. You could try booting some of the others you say you have, taking care that they are only in the drive while the computer and drive are both powered on.

That "doo-dad board" is the FM data separator. It is definitely needed by OSI systems, although most other computers didn't need it. However, I understand that user Klyball on this forum sells an interface (replacing the standard "paddleboard" and cable) that includes a data separator external to the drive, eliminating the need for the internal one.

That the H/D/M? "sometimes" clears from the screen says that sometimes, enough of track 0 loads correctly enough for the screen-clear routine on it to be able to execute, so the cables are presumably connected correctly. Try cleaning the heads and, If you can, run the drive speed test (from Mark's site). Perhaps the belt being stretched by having that piece of plastic wedged under it is causing the speed to be off?