• Please review our updated Terms and Rules here

Osborne 1 troubleshooting issues

B

Bunghole102

Member
Joined
Apr 1, 2026
Messages
17
Hello,

I recently came into the possession of an Osborne 1 portable computer that I have been attempting to repair as it appears to not be working properly.

I had the machine fully disassembled, thoroughly cleaned, retrobrited, and I replaced the RIFA capacitors in the power supply which are a known point of failure but it seems to be acting the same as before I did anything to it. When I power it on, there is a brief beep from the internal speaker and the lights on the floppy drives flash when this happens and then nothing. When I power it back off, I can hear the CRT make a little whizz noise that makes me thing it is getting power but there is no image showing up. I played with the brightness and contrast and let the CRT sit for a bit as I know these old things sometimes need to warm up, but still no image from the screen.

There is also seemingly no activity coming from the floppy drives, pressing keys on the keyboard doesn't seem to register at all, and the reset button doesn't do anything. Does anyone know what the issue could be? I've heard that the power supply is prone to failure on these machines and mine may need more work (I already have more replacement caps) but I want to be certain before I proceed further.

Any help with this topic is greatly appreciated.
 
That's pretty good so far - Is the shunt in place? The one just below the right-hand floppy drive - If that is missing you will get no video.

iu


It's the one labelled "Monitor Interface". That's not a "Plug Cover" - It's a SHUNT - if it's missing, you won't see anything on the screen.
 
Have you checked the power supply?
Check the voltages, and that they are low noise with an oscilloscope.
Sometimes you have to (and probably should anyway based on age) replace the electrolytic capacitors in addition to the RIFAs.

A proper startup has a beep. Then hitting enter causes drive A to boot - you should see a steady red LED on drive A as the drive spins.

If the power supply is good, check the cables and interconnects (the video shunt mentioned earlier is one such connector).
Re-seat all of them even if they look good to the eye.
Then the logic board - first by checking for corrosion and re-seating chips.
If after all that, you still get the same problem, it's likely a chip failure on the logic board requiring more troubleshooting.

Also.. keep in mind that the Osborne keyboards are prone to failure when exposed to high humidity.
Corrosion sets in under the plastic sheeting and eats away at the metal conductors. Repair is tedious.

-J
 
Last edited:
johnx993 said:
Have you checked the power supply?
Check the voltages, and that they are low noise on a scope.
Sometimes you have to (and probably should anyway based on age) replace the electrolytic capacitors in addition to the RIFAs.

A proper startup has a beep. Then hitting enter causes drive A to boot - you should see a steady red LED on drive A as the drive spins.

If the power supply is good, check the cables and interconnects (the video shunt mentioned earlier is one such connector).
Re-seat all of them even if they look good to the eye.
Then the logic board - first by checking for corrosion and re-seating chips.
If after all that, you still get the same problem, it's likely a chip failure on the logic board requiring more troubleshooting.


-J
Click to expand...
Unfortunately I don't have a good multimeter or scope to get accurate outputs for the powers supply, although I do have a set of replacement caps. Do you know where I can find a good layout of the power supply? I'm not very experienced with recapping electronics and I only successfully replaced the RIFAs because they're not polarized.
 
One of the power lines connecting the psu to the power panel on the back of the computer snapped off and is stuck inside the connector...

Once the psu is fully recapped can I solder this thing directly to the board and keep using it or is it screwed?
 

Attachments

  • PXL_20260402_181732381.MP.jpg
    PXL_20260402_181732381.MP.jpg
    1.4 MB · Views: 9
Bunghole102 said:
Unfortunately I don't have a good multimeter or scope to get accurate outputs for the powers supply, although I do have a set of replacement caps. Do you know where I can find a good layout of the power supply? I'm not very experienced with recapping electronics and I only successfully replaced the RIFAs because they're not polarized.
Click to expand...

Vintage computing involves maintenance and repair, almost by definition. Best to invest in some good workshop equipment and tools. They will make it a much less frustrating hobby. :)
Recapping electrolytics is not difficult - just install the new with the same polarity as the old - that is positive to positive, negative to negative.
You should also get the field service manual and the Sam's charts. Both on the net these days.
=J
 
Bunghole102 said:
One of the power lines connecting the psu to the power panel on the back of the computer snapped off and is stuck inside the connector...

Once the psu is fully recapped can I solder this thing directly to the board and keep using it or is it screwed?
Click to expand...

Best to replace the connector.
-J
 
johnx993 said:
Vintage computing involves maintenance and repair, almost by definition. Best to invest in some good workshop equipment and tools. They will make it a much less frustrating hobby. :)
Recapping electrolytics is not difficult - just install the new with the same polarity as the old - that is positive to positive, negative to negative.
You should also get the field service manual and the Sam's charts. Both on the net these days
Click to expand...
I've got just the right capacitors for the job so I'll let you know when I have it recapped and if it works
 
You can get full schematics for the Osborne 1 - Look for the field service manual.

archive.org

osborne :: osborne1 :: 2F00153-01 Osborne1TechnicalManual 1982 : Free Download, Borrow, and Streaming : Internet Archive

From the bitsavers.org collection, a scanned-in computer-related document.osborne :: osborne1 :: 2F00153-01 Osborne1TechnicalManual 1982
archive.org

Osborne 1 Field Service Manual - Vintage Computer Club Malta

computersmuseum.com computersmuseum.com

The Osborne 1 PSU has two outputs. 12v and 5v. It generates the -5V on the main PCB.

The video circuit is independent of the memory - you'll generally get some display if everything is working.

A multimeter can confirm the 12v and 5v sources. If you need, you can replace the PSU with a different PSU to provide those voltages - it doesn't take a lot of power on either.

An oscilloscope can allow you to follow the signals at the shunt that go to the monitor to see if the video is coming out, as is the sync signals.

That's the first steps you want to follow.

Outside of the RIFA caps in the PSU, any OTHER faults, including ANY of the other capacitors, is likely indicative of more serious problems. RECAPPING is NOT repairing a computer - it's generally not even required for the Osborne 1 PSUs which still work well even after all these years - I did fix ONE by recapping, but only because a blown RIFA had burned a hole in several nearby capacitor and this had caused them to fail. Otherwise, it's generally not a good repair technique and I wouldn't recommend it.

Blindly changing components is expensive, often unnecessary and rarely fixes Osbornes. ( Though some computers such as the c64 are so notorious for the problem it's still important. )

Note the most common capacitor failings on the Osborne 1 outside the RIFA caps is the tantalums on the main PCB. These can short out crippling one of the voltage rails - hence why it's important to check the voltage rails are stable and correct under operation with a multimeter.

You can disassemble an osborne 1 and run in on the bench. Be careful of the high voltages present on some of the wires. They can kill.
 
As cj7hawk mentions, trial and error replacements are expensive (and time consuming).
As I said earlier - invest in some good bench equipment to aid troubleshooting.
Approach it logically and methodically.
Though recapping has some value for preventive maintenance.

I have a total of 6 Osbornes. 2 required recapping electrolytics on the PSU, if that's any indication.

-J
 
johnx993 said:
As cj7hawk mentions, trial and error replacements are expensive (and time consuming).
As I said earlier - invest in some good bench equipment to aid troubleshooting.
Approach it logically and methodically.
Though recapping has some value for preventive maintenance.

I have a total of 6 Osbornes. 2 required recapping electrolytics on the PSU, if that's any indication.

-J
Click to expand...

You said it better than I did - Logically and methodically :)

I just re-read the "Snapped Off" bit - THOSE connectors will last forever. THEY don't break... So I'm wondering if you have dry joints - that DOES happen VERY often and is something to check. I assume you've already soldered the pin back into place and straightened it, but check the others... There are no redundant lines on the power supply connector - even for the same rails. So resoldering them will make sure there's good contact.

Also, as noted, the beep and other activity is a VERY good sign - suggests the main board is working.

There's a thread about an external monitor adapter that allows you to connect an external monitor to an Osborne 1 also - they are easy enough to make on some prototyping board. Maybe make one up and see if it's the monitor or the computer.

C

Thread 'Osborne 1 Video Adapter.'

Hi All,

It's not my schematic - just a repackaging of one of the original Osborne1A's video adapter, but modified to fit in the very tight slot of the Osborne1Bs video/reset/battery bay.

It's a low-profile design and comes out roughly flush with the top of the face, so will pack away nicely. I wil make up a nice case for it so it looks good, and can be easily installed and removed. Due to the design, it only fits properly one way, so should also avoid those incidents of people plugging them in upside down. All of the components sit below are are pretty much touching the O1's surface, so...
  • Like
  • Love

Finally, You don't need an expensive oscilloscope to fix something like an Osborne 1... The cheap ( Often around $50 and sometimes lower ) scopes are often suitable... You only need a few MHz of bandwidth for a 4MHz computer.

Let us know what you find as you progress @Bunghole102 :)

David
 
It sounds like I have a lot of shopping I need to do 😂 but once I get everything sorted I will be providing updates. I will definitely look into finding an adapter for the video output. As for the broken plug, I haven't had the chance yet to solder it back in place and the pin itself is actually stuck inside the connector so I have to attempt to pull it out, but with any luck I'll get it back in place
 
You have received some good advice here. If I can help you, let me know. I know a thing or two about the Osborne, and have no idea how many I have.
 
kc4bqk said:
You have received some good advice here. If I can help you, let me know. I know a thing or two about the Osborne, and have no idea how many I have.
Click to expand...
So I was fixing the broken pin on the power supply and the pad lifted off of the PCB... Am I screwed at this point?
 
Bunghole102 said:
So I was fixing the broken pin on the power supply and the pad lifted off of the PCB... Am I screwed at this point?
Click to expand...

Not screwed - If it's the PSU it should be possible to locate where it went to and run a suitably thick jumper wire. But it's not ideal.

Might not have been your fault either - if a dry joint was there, it might have gotten hot enough to delaminate.
 
If it is a through hole pad you are talking about you can insert a hollow Copper Rivet and
flare it. That will help you by allowing the part to be soldered back in place, and you can
add a jumper wire as needed.

You just need to specify the proper hole size by fitting a small drill bit into the missing pad's
hole to find the proper size rivet. There are many sizes.

Use a numbered drill index to properly size the hole.

A Photo of that are would be nice.

Larry
 
ldkraemer said:
If it is a through hole pad you are talking about you can insert a hollow Copper Rivet and
flare it. That will help you by allowing the part to be soldered back in place, and you can
add a jumper wire as needed.

You just need to specify the proper hole size by fitting a small drill bit into the missing pad's
hole to find the proper size rivet. There are many sizes.

Use a numbered drill index to properly size the hole.

A Photo of that are would be nice.

Larry
Click to expand...

That is a very serious sounding solution - and would make a very professional looking repair.
 
You must log in or register to reply here.
Back
Top