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Osborne

Not a bad idea :)

At the moment, I just have the bare membrane on the bench and it seems to be working, but not sure if it will work once reassembled.
 
Cheers, I had missed Keir's Osborne CFG page, thanks.

The way its trying to boot, sometimes getting to track 2, sometimes to track 3 makes me think its the RAM fault thats stopping the boot.
 
So using my RAM test EPROM, it was showing bit 4 chip in the range $0000 to $3FFF faulty, as CP/M uses the first few bytes of lower memory it was preventing a successful boot. Swapped out chip A23 and now it boots :)

Ran the memory tests on the diagnostic disk and all is looking good (ironic that I had to fix the memory error to run the memory test)

All the pads on the keyboard membrane are now doing what they should but now I need to try and reassemble the keyboard. The keyswitches have small springs in them and given the very light touch needed to activate the membrane, im not certain it won't just go back to having a few keys permanently pushed. Trial and error time.
 

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As I have now had to change 9 ram chips in two Osbornes, makes me wonder if the PSU startup isn't healthy for them. Might be worth investigating a mod to ensure the supplies are brought up in the right order.
 
Ah, drive B doesn't work (not tested drive A yet, not sure how to change the drive select yet)

Wanted to write a CP/M system floppy before I put it all back together as the Gotek is going to go into my other Osborne but no joy.

At first it seemed it was just the carriage being a bit stiff, but after lubrication and exercising (The diag disk has an exerciser), it still won't format. Sits at track 0 and won't go any futher.

I'm not showing an Index pulse at pin 8 so that would seem to be the fault. Its a Siemens FDD100-5 drive mech with a custom Osborne board (why did they bother, unlike Apple, its basically a full Shugart interface, just with power on the ribbon cable, cant have saved much cost) but uses the standard photo index sensor. Can't see that being easy to source, hopefully its the logic on the board, but not time to check now. Off to work.
 
No index pulses on Test point TP1/2

Think this might be the problem,
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cant work out how it happened. It looks like its been overtightened (radial stress cracks around the bush) but probably stress working its way through age.

Gluing it back together with Araldite as thats strong (and all I have), but worried it wont penetrate the cracks and it will just fail when reinstalled. Will have to take it carefully.
wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==
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agentb said:
You can boot from the 2nd drive by hitting “ instead of Enter on boot- the second drive becomes A and first is B.
Click to expand...

It worked, but I hadn't clocked that it swaps A for B logically and formatted my diag disk before I got my head around it.

That must have caused some grief back in the day.
 
There was a "Screen Pac" for the Osborne from the factory, that required some mods to the MB, and the addition of a RCA plug on the front panel.

Osborne One was my first computer, and I did the video, unfortunately don't remember all the details.
Larry
 
Yes, the screen pac isn't fitted to mine and the only one I have ever seen for sale was daft money. It plugs into the ROM and CPU sockets and changes the timings to allow the whole video port to be displayed.

Shame the circuit isn't available. Just seems to be a bit of logic and some RAM.

Anyone have a screen Pac to xray ?

Edit: just seen the ScreenPac circuit is in the service manual :)
 
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Damnit

Fixed the index sensor but it still wont format because one of the coils in the head is open circuit. Never seen it before but its the actual coil rather than the cable to the head.

So, its head swap time. I have a scrap completely different half height SSSD drive that looks to use exactly the same head and it was a simple job to pop it out of the carriage and install it instead of the original.
The cable though is twice as long and needs to be cut back, so I will need to get some unused pins to recrimp into the original connector and fingers crossed it will work.
 
Well !

Even I didn't think that was going to work !

But, new head installed, wired up and the machine is now happily formatting away :)

It was a PIG to strip down. Once the circlip on the drive helix was removed, a spring inside the stepper motor pushes the helix back against the dust cover and seizes the whole spindle. You need to prise the dust cover off to release the helix so that you can rotate it to withdraw it from the head carriage.

Then when reassembling, the stepper motor bearing protrudes from the motor and needs to engage with the hole in the chassis. Didn't notice this at first and could not work out why the circlip would not go back on.

Then the new head uses different colours and a 5 pin plug rather than the 6 pin, so needed to work out which core went to which head then put new pins on to go in the old plug housing and rebuild it all.

Just hope the second drive doesn't have the same problem as I am out of heads.

And just noticed. That was an hour and nineteen minutes to repair !
 
So (as the millennials say)

Keyboard is fully rebuilt. The gentle heating of the membrane seems to have successfully released the stuck down keypads and refitting the switches back on to the plate was a matter of melting the removed blobs back on to the stubs of the switches legs, which while time consuming was relatively easy.

The floppy head in the B drive wasn't open circuit, its just that Osborne not only used their own drive electronics, they also swapped around the pins on the head connector and I was testing between the wrong pins (doh!) but there must have been something not right with it as it worked as soon as the new head was fitted.

The A drive doesn't work either, but on this one, there is no activity at all at the head connector and looking back from the head connector, where the write gate merges with the write signal through a 3 input NOR gate, the output is always high no matter the inputs. So a few CD40025BE chips on the way (no longer manufactured in DIP format according to RS) and hopefully that will be the last fix this machine requires.

Anyone know how to convert a MFM HFE image into an FM image ? I can eventually once both machines are up and running, convert physically using floppies but as I am testing, I only have a few FM images and would like to use some of the other files I have, but they are MFM.
 
New 3 input NOR gate chip fitted and both drives now work. Aligned A by trial & error and both can boot from the same floppy but might need some fine tweaking in the future.

Its all but done and the keyboard is working great. I now have a small pile of dead I/C's from two Osborne's :)

I plan to fit the Gotek into the later unit as that has the double density card so can produce disks for both.
 
Very impressive all the debugging and fixing you did to get this Osborne sorted, wow! I can't believe one machine had so many different issues. I like my Osborne but a little bummed they can't do graphics, only text.
 
The number of failed ram chips makes
me think the Osborne psu is bringing up the -ve slightly late maybe and damaging them over time.
 
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