Osborne 1a - Works but still flakey

[tezza]

After the RAM chip transplant a few months ago my beloved Ozzie now works.

However... like most old curmudgeons (human or computer) things seem to fall apart sometimes. I can't seem to leave it on for more than 4 hours at a stretch without it crashing. It's random, and generally in spectacular fashion. By the latter I mean the screen goes to garbage, drives may switch on (and stay on!) and sometimes even the internal beeper is beeping!

However, if I switch it off, wait some seconds, then on again..it's fine! At least until the next time it throws a fit. This could be in 15 mins or 4 hours. It's random, and not that common, but it usually can't go more than 4 hours of continual use.

Now, I guess the cause here could be a zillion things. But given that the symtoms when crashed are somewhat similar to the symptoms that occured with my bad RAM, I'm wondering if it's not RAM related? Or maybe the power suppy? Could it be that the power supply is a bit flakey, fluctuates out of tolerance range and trips some (possibly also flakey) RAM chips?

Any ideas?

Tez

 

[Sharkonwheels]

Ozzies are known to be a problem when hot. try getting a small fan to blow into the vent on the top (you ARE opening it, right) to see if that is it.

If so, you can mod some kind of fan inside the case, either drawing 12V from the PSU, or straight off the AC input of the PSU.

My primary O1a has one of the Exec handle-fans in it from a dead Exec, and I wired it into the PSU.


T

 

[tezza]

Ozzies are known to be a problem when hot. try getting a small fan to blow into the vent on the top (you ARE opening it, right) to see if that is it.

Yes, I noticed that little covered vent when I first got the machine and always open it up.

Heat *could* be a possiblity. The "computer room" above the garage can get quite hot in summer (which we've just had) although I don't think the times I've left it running up there have been particularly hot days.

Do they crash as described if they overheat? Hopefully it is as simple as this but I have my doubts.

Days are cooler now., and I haven't had the Ozzie out for a while. Maybe I'll give it another endurance test.

Tez

 

[Sharkonwheels]

Once it's on and running, just remember, just because it's cool outside, has nothing to do with the temp inside the case. There is absolutely ZERO airflow because there are no fans, so if you can rig up a fan to suck the air out, like laying it on the vent, that would allow you to test and see if it solves anything.


T

 

[Druid6900]

While you're in there, reseat all the socketted chips and what-not as, over time, they have a tendency to "walk" out of their sockets from the same heat/cool type of cycle that heaves concrete sidewalks.

 

[modem7]

From the Osbourne 1 Technical Manual (1982):

"Maximum operating ambient air temperature 85 degrees F
Humidity - 95% relative, non-condensing
Minimum operating ambient air temperature 32 degrees F"

That max. temp line doesn't include time periods or duty cycles, and therefore the "85 degrees F" (30 degrees C) is for continual operation.
However, considering the present age of the Osbourne 1's, one has to account for deterioration of some of the components.

Does it get above 30 degrees C in New Zealand ?

So I guess you need to determine if your 1a is significantly more heat sensitive than the average 1a, and if it is, hunt for the problem component.
That is of course if heat is the trigger.
Your "However, if I switch it off, wait some seconds, then on again..it's fine!" doesn't suggest heat to me. If the problem was heat related, I would expect that you would have to wait a few minutes at least, not seconds.

But I think I've found the cause of your problem. I've always known that my 1a is sensitive to short power interruptions, and a screen full of garbage is the typical result of such an interruption. The short power interruptions were due to some of my power cords not sitting tight enough in the 1a's power supply socket.
I've just experimented on my 1a by pulling out the power plug then reinserting it quickly. That mostly results in a screen full of garbage but every so often, guess what, the drives activate (and stay on) and the speaker beeps.

1. Bad power supply ??
2. Unreliable 240Vac in your area ??
3. Bad power cable (contacts in plug not mating properly with contacts in 1a power socket)

 

[tezza]

Does it get above 30 degrees C in New Zealand ?

LOL! It doesn't reach into the 40s like Melbourne sometimes, but mid-summer it can certainly get to 32 or so where I live. In the room above the garage though, it can get way higher.

At the times I was running the Ozzie up there, the temp would have been about 25-30....not that hot but close to it's maximum it would seem.

Your "However, if I switch it off, wait some seconds, then on again..it's fine!" doesn't suggest heat to me. If the problem was heat related, I would expect that you would have to wait a few minutes at least, not seconds.

Yea, in the three times this has happened, it was always ok after flicking the switch back on.

But I think I've found the cause of your problem. I've always known that my 1a is sensitive to short power interruptions, and a screen full of garbage is the typical result of such an interruption. The short power interruptions were due to some of my power cords not sitting tight enough in the 1a's power supply socket.
I've just experimented on my 1a by pulling out the power plug then reinserting it quickly. That mostly results in a screen full of garbage but every so often, guess what, the drives activate (and stay on) and the speaker beeps.

1. Bad power supply ??
2. Unreliable 240Vac in your area ??
3. Bad power cable (contacts in plug not mating properly with contacts in 1a power socket)

It's good you've duplicated the symptom. You're also a brave man! I wouldn't have done that kind of experiment one of my vintage systems. You have my thanks for exploring the problem though. I may need to buy you a beer next time I'm in Melbourne for taking a risk like that.

Yes, my initial theory was that it was power-related. I wouldn't be surprised. Not only because we are dealing with a vintage computer, but also it was the first one I pulled apart. The capacitors blew in the power supply and I replaced them. It was my first attempt at vintage repair. I wasn't very skilled with a soldering iron and I didn't have a manual to show me how to assemble/disassemble the thing. There may be some loose connections or dry solder joints in there I've disturbed.

Alternatively it is the supply. It should be steady but if the Ozzie is very sensitive to fluctuations, maybe not steady enough.

One of these evenings, I'll open it again and have a good visual inspection.

Tez

 

[modem7]

You're also a brave man! I wouldn't have done that kind of experiment one of my vintage systems.

Not even for a fellow ANZAC ? Only joking. To me, a computer is simply a bunch of metal, plastic, semiconductor and ceramic that has been arranged in such a way as to be useful. Right now I'm hearing many cries of, "heresy".
My 1a is the least desirable computer in my collection and so if it were damaged and I couldn't repair it, so be it. My risk increased the collective knowledge of the 1a (well, at least within these forums).

And don't rule out the drives and motherboard. There could be a component in them that is temporarily overloading the power supply.

 

[chuckcmagee]

I am close to 100% certain that the little fan blowing on it will solve the problem. Sounds like an overheating thing to me.

 

[Sharkonwheels]

I am close to 100% certain that the little fan blowing on it will solve the problem. Sounds like an overheating thing to me.

Heh - I'm not THAT certain

I know heat is a HUGE problem with 01's, and always has beed, but Druid and M7 have made excellent suggestions, as well.

I guess that's what's good about a forum such as this: We can draw on each other's collective knowledge, and experience, and if you think about it, no matter what problem we run into, more than likely someone has a solution!


T

 

[billdeg]

Yes it could be the power supply. Check with a volt meter every half hour to see what's happending, but I have a hunch - I don't think it's RAM or heat. Based on your symptoms and my own experience it sounds like you have a PLA or similar support chip issue. If it were RAM overheating it would happen much sooner.

Question - if you're using the system for an hour, and then turn on and off the system will it boot properly or do you have to wait a little while? Are there any chips on the board that are unusually hot?

I happen to have a similar system on one of my work benches (to replace the disk drive), but otherwise the system seems OK. While I am in there I will take a look to see if I can identify the specific chip ID to target. You don't really have much to lose if you can find a spare.

Of course the schematics and an oscilloscope would be useful for before and after testing.

I had a similar problem almost exactly as you described with a PET 2001-16N

Bill

 

[tezza]

Question - if you're using the system for an hour, and then turn on and off the system will it boot properly or do you have to wait a little while?

Hi Bill,

No, I don't have to wait. Switch it off, wait 15 seconds or so (like I do with any computer when switching off and on) and then on again and it boots just fine? Some kind of loose connection or voltage spike is the most likely problem I think. I should try physically moving the machine while it's on. That might help with the "loose connection" theory

I haven't had much time lately to play around with my old vintage machines lately, including working through some of the suggestions here. There are a number of things happening in my life at the moment which has put the ole vintage gear on the back burner. These new activities will go on for a few months. They are good things, but I find spare time is pretty limited just at the moment.

Oh well, only 15 years to go until retirement