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Osborne 1 screen flash

N

nelgin

Member
Joined
Dec 11, 2023
Messages
20
Hi all,

I just picked up an Osborne 1 and it's a lot different from most that I've seen on the internet. It seems to have an early serial number but on the screen it says OZROM 1E #00187 (c) 1984 Micro Management.

I assume this is because it appears to have the 80 column upgrade. It also has the double density upgrade. The keyboard is connected with a ribbon cable rather than the coiled cable.

Turn I turn it on, both drives flash briefly and the screen constantly flickers "Slip disk in drive and press RETURN" as if a key is being held down and it keeps refreshing until enter is pressed. I took the keyboard apart by removing a screen on either side next to the clamp location, then removed 4 screws that hold the keyboard onto the riser.

All the internal cables look secure and I pressed all the keys several times to make sure none of them were stuck. If I turn the computer on, then the image is static and not flickering and the graphics change periodically while waiting for return.

So first question: Any idea what I can do to fix this issue?


Next, taking it apart, I removed 2 screws either side of the handle, maybe 5-6 around the power supply. There were 7 on the front bezel, one at the bottom, two at the top and 2 on each side. Inside I had to remove 4 (well 3, one was missing) that held the internal chassis to the internal frame then I had to slide the whole thing forward. I probably should have done it upside down side the weight of the CRT started to bend the motherboard.

At this point, since I'm going to eventually add the gotek, I removed the motherboard which and did a RIFA check on the power supply. The two large caps next to each other look a little bulged so I'll probably remove those and replace the RIFAs too. You never forget your first RIFA :)

Second question: Any recommendation for replacement caps? I know modern components are much better than 80's so should I use that same voltage and capacitance?


Since I'm going to put the gotek into the B drive slot, I'll remove it and keep it safe. The A drive I'll remove and lube and clean the heads while it's out.

Third Question: is there anything else I should look at before putting it all back together?

I did find a service manual and it seems I have an original style bezel, looking at the disassembly instructions.

I'm hopeful that some knowledgable Osborne 1 people are here who can assist.

Thanks,
 
Welcome! Keep us posted on your progress! I also acquired an Osborne 1 recently and plan on restoring it over the winter break
 
Thanks all. Unless I can get the keyboard sorted, there will be no progress, I fear. That said, I've ordered a gotek from Amazon since it's free delivery so I just need the adapter. I'm still hopeful that someone will have a spare so I don't have to get a minimum amount from OSHPark.
 
The keyboard is ony a matrix - You can check with a multimeter for the stuck key. Some have suggested a heat gun can fix the issue. Also, there is a keyboard kit going for a reasonable price in one of the thread.

Gotek is not too difficult to get going.

You can make an adapting cable with some 34 way ribbon, and a couple of pin header and edge connector IDCs. There's another thread with someone who wants to get some adapters so maybe go halves with them?

You also need to consider the ESR for the capacitors.
 
cj7hawk said:
The keyboard is ony a matrix - You can check with a multimeter for the stuck key. Some have suggested a heat gun can fix the issue. Also, there is a keyboard kit going for a reasonable price in one of the thread.
Click to expand...

Good to know. I'll check it out tonight.

cj7hawk said:
Gotek is not too difficult to get going.
Click to expand...

Nope. Seems not.

cj7hawk said:
You can make an adapting cable with some 34 way ribbon, and a couple of pin header and edge connector IDCs. There's another thread with someone who wants to get some adapters so maybe go halves with them?

You also need to consider the ESR for the capacitors.
Click to expand...

Yeah that was me. I don't want to go halves with myself :)
 
I pulled the ribbon cable off the keyboard and started testing each pin and got quite a few that had continuity. Are there any that should or it is expected that all pin connections are open. If they're all supposed to be open then I'll hit it with my hot air gun. I really don't see an option to get to the circuit board, though I'm sure it's possible.
 
nelgin said:
Hi all,
placement caps? I know modern components are much better than 80's so should I use that same voltage and capacitance?


Thanks,
Click to expand...

That is not necessarily true for electrolytic capacitors.

Modern ones are significantly physically smaller than the older ones for the same uF ratings and voltage rating & temperature & ESR rating. But otherwise they don't significantly out-spec the vintage types. In fact there is an advantage for the larger sized ones of yesteryear , especially in switching supplies where they heat because of the ripple currents and the capacitor's ESR, the physically larger capacitor heats less because as a physical object, it has a lower thermal resistance.

Since the modern capacitors are smaller for the three basic ratings, you can therefore step up the rating of the replacement parts, to attain a capacitor of a similar physical size (see why this is important below).

So, for example if the original part was 85 deg C rated , you can move up the a 105 deg C part or a 120/125 deg C part etc. High temp rated caps last longer. Nichicon & Panasonic make very good ones. And with each step up its a bigger sized part.

Also, (while leaving the uF value alone) you can also move up a step or two in the voltage rating to attain a larger part.

By doing those things, you then can have a superior replacement part, of the same uF value, that closely matches the original physical size.

When replacing a typical radial pcb mount capacitor, ideally the the lead pitch matches the holes in the pcb. When this is the case, the capacitor can be fitted with its rubber base flush against the pcb. The reason this helps is mechanical stability and if the capacitor gets bumped it doesn't cause forces on the pcb pads. If a smaller part is fitted and the base of the capacitor sits above the pcb surface, the pads are more vulnerable.

There are a few areas where other improvements can be made. When it comes to replacing electrolytics in the range of 1uF with ratings of 63V and below, better longevity is to replace these with MKT film capacitors, because then they will never require future replacements, provided of course they are a good physical fit for the holes/spacing on the pcb.
 
I haven't tried the hot air gun method - so I can't advise on appropriate cautions sorry.

Yes, they are supposed to be open for the most part.

You can also use a dupont connector to bridge the "enter" key to manually kick off a boot. Beware the 12v lines - they will destroy any digital logic level inputs they come in contact with.

David.
 
Hugo, thanks for all that. I actually went and ordered the recap kit from Console5 as suggested by mbliss11. I hope I did the right thing.
 
So I wanted to strip this keyboard down, suspecting the membrane. Not sure sure where to go. I can pop they keycaps off and then there's a black cover that appears stuck down. I had a peek but don't see any screws. Are the back of the keys really melted to the board? There must be an intermediate step ? I checked youtube but nobody seems to go that far into deconstructing the keyboard. This is the keyboard with the ribbon cable not the curled one.
 
nelgin said:
So I wanted to strip this keyboard down, suspecting the membrane. Not sure sure where to go. I can pop they keycaps off and then there's a black cover that appears stuck down. I had a peek but don't see any screws. Are the back of the keys really melted to the board? There must be an intermediate step ? I checked youtube but nobody seems to go that far into deconstructing the keyboard. This is the keyboard with the ribbon cable not the curled one.
Click to expand...
We discuss the keyboard here: https://forum.vcfed.org/index.php?threads/osborne-keyboard-identification.1245068/ and here: https://forum.vcfed.org/index.php?threads/has-anyone-seen-an-osborne-keyboard-like-this.1244898/

It's a TEC keyboard likely, and can be taken apart but I haven't needed to.
 
I would like to have a copy of the ROM.
nelgin said:
Thanks all. Unless I can get the keyboard sorted, there will be no progress, I fear. That said, I've ordered a gotek from Amazon since it's free delivery so I just need the adapter. I'm still hopeful that someone will have a spare so I don't have to get a minimum amount from OSHPark.
Click to expand...
There are some adapters on Ebay ready to use with the Gotek
 
Hi @nelgin ,

I hope you get the keyboard sorted.
Actually I think you have an even more extraordinary Osborne than you think.
The message "OZROM 1E #00187 (c) 1984 Micro Management." Refers to a third party rom made available for the Osborne 1 so not related to a 80 character mod.
The most interesting part of this rom is the build in memory test, this test was removed from the Osborne stock rom after version 1.2.

I am searching for an Osborne rom with an in build memory test, but rom version 1.2 (nor ozrom) image is not to be found, so your post triggered my attention.

Details of this ozrom rom can be found in this document; https://bitsavers.org/bits/Osborne/Osborne1/OZROM_1E.pdf
 
gemini said:
Hi @nelgin ,

I hope you get the keyboard sorted.
Actually I think you have an even more extraordinary Osborne than you think.
The message "OZROM 1E #00187 (c) 1984 Micro Management." Refers to a third party rom made available for the Osborne 1 so not related to a 80 character mod.
The most interesting part of this rom is the build in memory test, this test was removed from the Osborne stock rom after version 1.2.

I am searching for an Osborne rom with an in build memory test, but rom version 1.2 (nor ozrom) image is not to be found, so your post triggered my attention.

Details of this ozrom rom can be found in this document; https://bitsavers.org/bits/Osborne/Osborne1/OZROM_1E.pdf
Click to expand...
@nelgin Do you have the means to dump that OZROM EPROM?
 
Yes, the keys really are melted into place. They can easily be removed using a stanley blade to cut off the melted ends, then the bits left off can be melted back into place. I did this with both of my keyboards but it is quite time consuming.

Mine had stuck keys and no amount of pressing would release them.

The membrane looks impossible to separate. I tried to use my heat gun to separate them but they remained stuck. However, as I ran the gun over the cells of the membrane I could see that the stuck ones 'popped up' and the membrane started to work again.

Since then, others have had luck heating the metal plate side without having to remove the keys.

Both my machines have not had any repeat problems with the keyboard.
 
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