Challenger 3 OEM Restoration

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glitch
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Re: Challenger 3 OEM Restoration

Post by glitch » Mon Jul 29, 2019 1:16 am

RAM test seems to be effective, apparently something in the GW-OSI-RAM1 design is marginal. Standby on that.

I spent several hours diagnosing an OSI 470 floppy controller I've had for years that never worked correctly. A way into debugging it, I switched in my usual 470 board to find out that it no longer boots! After another hour or two of debugging, I found out I had some intermittent contact in the A12 board. Some of the solder tails on the Molex female sockets had fatigued and cracked, and were only sometimes making contact. So, I'd check out your A12 board/cable and make sure it's in good shape, since B drive works but A doesn't.
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OSI Challenger 3, 510 CPU, 8" floppies, 74 MB hard disk system in need of restore
Parts bin Challenger 3 board set, never had a chassis in its time

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glitch
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Re: Challenger 3 OEM Restoration

Post by glitch » Mon Jul 29, 2019 7:09 pm

Nevermind about the GW-OSI-RAM1 maybe having a timing issue, it seems I have a backplane fault!
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OSI Challenger 3, 510 CPU, 8" floppies, 74 MB hard disk system in need of restore
Parts bin Challenger 3 board set, never had a chassis in its time

CrawfordG
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Joined: Sat Jun 22, 2019 7:38 pm

Re: Challenger 3 OEM Restoration

Post by CrawfordG » Sat Aug 03, 2019 1:28 pm

Folks,

Spent yesterday working on the C3. Flaky memory seems to be one issue, and I solved that with a cooling fan. I used the mem test from a SSJ reprint, serial loaded.

I have 2 8”floppies, the top one (Drive A) an index error, and the bottom one (B) partially works. I ended up swapping the disk controller boards between the 2 floppies, and the Drive B mechanism with the drive A board works with C3DUMP. Drive A mech with Drive B PCB’s = no index. So, I conclude that the index error must be in the Drive A mechanism. No boot from the new transplant, though.

One thing I noticed,was that previously the head on Drive A stepped back to track 0 on startup. Now, the drive will not retract. I can’t recall if this happened when the power came on or when I try disk boot H/D/M? D . So I can dump sectors with C3DUMP, but have to retract the head by spinning the stepper back.

Some questions...

How is head retract supposed to work?

I have some similar 8” drives, would they work with OSI? (Last attached to an IMSAI)

Does the OSI-RAM card need to have memory management configured for the C3 to work?

How much RAM do the OSI disk OSes need to boot?

Thoughts on replacements for the index LED?

Thanks,
Crawford

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glitch
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Re: Challenger 3 OEM Restoration

Post by glitch » Sat Aug 03, 2019 2:52 pm

The A drive should home to track 0 when you hit D at the H/D/M? prompt.

You can use other 8" drives as long as they have an onboard data separator, which is fairly common for 8" drives. I use a Shugart SA800 with my test Ohio Scientific setup. You will probably have to rejumper the drive options to make it work with the OSI 470.

Can't say I've ever tried to boot OS-65D with less than 48K of RAM. I suspect it'll work with less, but I'm sure someone else here knows for sure.
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OSI Challenger 3, 510 CPU, 8" floppies, 74 MB hard disk system in need of restore
Parts bin Challenger 3 board set, never had a chassis in its time

CrawfordG
Posts: 11
Joined: Sat Jun 22, 2019 7:38 pm

Re: Challenger 3 OEM Restoration

Post by CrawfordG » Sat Aug 03, 2019 8:12 pm

Folks,

Well, things I learned today:

My Shugart fd800-2 drives do not have data separators onboard...rats! My Shugart Drive did reset to track 0 when I selected disk boot, but no boot yet. When I ran C3DUMP on this drive I got a lot of zeroes, because no data separator.

Mark’s memory test works great and gives a lot more feedback while it works.

Still need to check my index LED.

-Crawford

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glitch
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Re: Challenger 3 OEM Restoration

Post by glitch » Sat Aug 03, 2019 8:35 pm

Are you sure it doesn't have data separation on board? There's a jumper to enable it. Being a SA800-2 it should be one of the LSI chip drives (big 40 pin DIP near the middle of the PC board), AFAIK all of the LSI drives have it built in.
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OSI Challenger 3, 510 CPU, 8" floppies, 74 MB hard disk system in need of restore
Parts bin Challenger 3 board set, never had a chassis in its time

CrawfordG
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Re: Challenger 3 OEM Restoration

Post by CrawfordG » Sat Aug 03, 2019 10:34 pm

Jonathan,

Well I’m grasping at straws here..

Well, the disk has a plate that says model 800-2, but it has no LSI, jus MSI TTl. I’m going by the info on the SA-800 OM manual page 6, from Mark’s site. There’s no TS jumper so that’s the conclusion I made.

No output from the seimens Drive with the index issue. I did find some IR LEDs in the supplies.

-Crawford

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glitch
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Re: Challenger 3 OEM Restoration

Post by glitch » Sun Aug 04, 2019 1:29 am

Huh, OK, well, if it's the TTL board (bunch of 14 and 16 pin chips, discrete power transistors) then the data separator is an optional thing.

IIRC, on the Siemens drives, I had a dead receiver in the source-sensor pair. I was able to drill it out and glue in a different phototransistor, but had to change values in resistors on the comparator used to detect the index hole to get it to reliably detect index. No big deal as long as you have a scope or logic probe to watch the index line. Of course, if you can find the original part number, all the better.
Check out The Glitch Works
OSI Challenger 3, 510 CPU, 8" floppies, 74 MB hard disk system in need of restore
Parts bin Challenger 3 board set, never had a chassis in its time

CrawfordG
Posts: 11
Joined: Sat Jun 22, 2019 7:38 pm

Re: Challenger 3 OEM Restoration

Post by CrawfordG » Sat Aug 17, 2019 6:18 pm

Folks,

A little progress on the disk front. I found an IR diode from MicroCenter (NTE 3028) that is a perfect fit mechanically for the index hole LED. This diode seems to be working correctly as-is.

I also re-soldered the molex connector on the disk ribbon cable, just in case.

After all this, the disk attempts to home to track zero. When it reaches track zero it judders near the home mark, but does not stop. So, it does not boot of course.

Next I will rewire the secondary drive to act as primary.

As a side note, I bought a dual l 8" drive at a hamfest. The drives are very clean, but are Shugart drives without the data separator circuit. I have some FDC9216 data separator chips that should work.

-Crawford

CrawfordG
Posts: 11
Joined: Sat Jun 22, 2019 7:38 pm

Re: Challenger 3 OEM Restoration

Post by CrawfordG » Sat Aug 17, 2019 7:43 pm

Folks,

Well, the juddering whilst seeking track zero also affects two other drives, so it’s not likely to be drive-related.

So, I guess I need to look at the home signal getting back to the disk controller.

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