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Osborne 1 -- internal CRT does not work/power, but external does


Experienced Member
Feb 27, 2018
totally new to Osborne and I picked up an Osborne 1 and an Osborne Vixen locally this weekend. Seller was the grandson clearing out storage and knew nothing about these machines but he did have them booting and computing. He stated that the internal monitor on the 1 was not working which I confirmed.

I've scanned the service manual and focused on the video connector from the daughter board (Screen Pac?) to the CRT. Pin 4 is supposed to be 12 VDC, but is only reading 1.2 VDC.

As you can see, the external monitor (which gets power from the motherboard connection) is working fine. So I assume the issue is with the Screen Pac or related area.

Main PCB voltages seem fine. I inspected the connector solder points and the usual bad solder joints and reflowed a couple.

Is the rainbow ribbon cable oriented properly and on the correct pin header? this is how it was when I disassembled.

Anything obvious to check from this point? Thank you!!


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made a shunt and success! I've asked the guy if he has seen this proper shunt around and he's going to check. these two machines have full documentation, original software, and tons of extras so I'd be surprised if it doesn't turn up.


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ScreenPAC, DD Adapter, but most of all, an original Osborne monitor... And a vixen to boot! It doesn't get much better than that ! :) Congrats at the haul.

Don't run them until you've replaced the RIFA caps in the power supply with new filter caps. They WILL break down and blow out jets of molten metal...

The Shunt is just a 20 way IDC connector with the cable twisted sideways at an angle so it shorts the top to the bottom and the intervening wires skip, with a little dab of black silicon on either side to cover the wire terminations so it's not so obvious... They looked kinda home-made - even the real ones.

Also be careful with the older disks as they can break apart... If they stop reading, or you get even a single one that gives a read error, you might have left some disk surface behind and it's worth pulling out the drive, cleaning the heads, then putting the original disks aside for preservation. There's a thread on using cyclomethicone to get the disk contents off.. Also, the heads need careful cleaning with an alcohol wipe if that happens as I found usualy gentle cleaning methods didn't remove the disk surface from the heads - though I don't know if it's osborne's selection of disk or just the disks I got were all like that. I don't have any problems with NOS disks in my Osborne.

There's other threads on getting a Gotek into one, and I'd love to know if some of your disks boot straight into 80 column mode - I am guessing that your monitor should show all three modes if your OS has been updated.
Thank you. first thing I did was pull the RIFA caps and they were visually cracking.

I have a greasewezel and will flux image the floppies. I assume that will work?

on the shunt, I soldered together a connector and it works as shown. that passes through all the signals power to the internal monitor? what a clunky solution.

I guess I lucked out that the shunt was not there as that made it 'non-working' and the price was right. I had a sense the monitor was unique as I couldn't find any Ebay history on it.

looking forward to finishing cleaning this up and learning about it. I'll look into the gotek connection, I have several of them.
:( How come everyone else already knows to pull the RIFA caps first... I had to smoke up two machines before I learned that.

Flux imaging floppies would work - and protect the originals, though I don't have that and just went straight to a Gotek and booted from there and made new floppies - It was also helpful when I had to make a DD adapter, but you already have one of those.

Your shunt sounds exactly like I would do it. Print up a 3D cover and glue it in place, and you're done ! :) Even better than the original.

I got a similar deal with the shunt - description was "makes a beep when powered on, monitor does not come on." - And I could see the shunt missing in the pictures, so figured it was a good risk to take.

The Gotek is a great solution. I can provide STLs for a gotek housing if you have a printer... It even has the flip up latch which hides all of the Gotek elements ( except the display ) when it's down. Fits both the original and later model.

Let me know if you're interested - I posted pictures of one in an earlier thread.
thank you! I'd love to see the STL files.

the keyboard cable on this 1 is the flat type with loom. most I see are coiled. the loom is fraying on mine.

and here's the serial # of the 1 if it is of interest.


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The flat ones are the original Osborne 1's, as is the flexible plastic structure inside that mounts everything.

The later coiled ones are the Second Generation. Same PCB, but different casing, and cable entry. That looks like a low serial, but I don't know enough to know if it's relevant. Mine is around 30,000 IIRC. My later ones are well up in the Hundreds of Thousands.

I'm pretty new to these and love them... Somehow kept buying more. Originally intended to get three - now have four and a half. ( The half is just a motherboard PCB ).
I ordered one from some feller in Kentucky, got here today. :) it looks beautiful! also got the gotek adapter which looks great. I hope to get back into this very soon.
can anyone point me to ready-to-run bootable image files for the gotek? drop the file on a usb and go. thank you!!!
I just received one of these today! Serial number 233104. My internal display works but the external display's tube doesn't power on.

The drives don't try to spin up and pressing return on the keyboard does nothing. I'll have to dig in, never messed with one of these before.

Hi Dokken, Did you have issues with the other image? It should work OK for booting. Also you have to have the cable modified or use the cable adapter since the Osborne 1 doesn't have a normal 34 way cable, but rather use one that carries power in it. Let me know what the issue was and I'll help you troubleshoot as best I can.

My first 'go to' would be to checkout the keyboard matrix with a multimeter.

The keyboards on these machines are the notorious weak points.

I've apparently got issues with my keyboard cable. the flat ribbon type. I did find that one male pin on the mobo side was broken off. I pulled the connector and patched in a pin which seems to have good continuity. but problems persist.

with the keyboard plugged in, I get a flickering screen most of the time. the enter key does not register to load the disk. flexing the connection at the mobo cases changes. sometimes it pops to a stable picture but still enter does nothing. there's a similar thread on here where someone had that issue and solved it by getting another keyboard.

furthermore, I occasionally get the smaller text on the screen. not sure if this a flaky key entry due to cable problems.

I bought a gotek adapter. it has the power lead to the gotek. still unable to read from the floppy (A) or gotek.

I'll keep trying.

thanks for the link/photo of the keys to jumper. stable picture with no keyboard, and the jumper does start the load.

from the real floppy as A, I a repeating BOOT ERROR message.

from the gotek, it seems to load the CPM system image.

fantastic! now to figure out the keyboard repair and the boot error on the floppy.


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