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Osborne 1 not turning on

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pukenot

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I have an Osborne 1 that when I turn it on, a beep is heard and both red LEDs on the floppy drives turn on for half a second before turning off again, and then nothing happens. No picture on the CRT or any other activity. I can hear the faint buzz of the psu but nothing else. I replaced all the psu rifa caps before even turning it on once, so not really sure what the next move should be. Analog board and psu recap? Any ideas or suggestions are appreciated.
 

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The beep and drives turning on is very good news. Sounds like just an issue with video. If you dim the lights and peek at the neck of the CRT do you see any glow?
 
channelmaniac said:
You have a shorted tantalum cap keeping the power supply shut down. Measure resistance (with power off) from each power rail to ground.
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I tested the tantalum caps on the motherboard and I think C73 is bad. Others seemed to test fine. I'm quite new to this so I'm a bit unsure of what I'm doing lol.
 
I would think that a shorted tantalum capacitor would keep the whole computer from working, but it sounds like your machine is actually booting due to beeps and drive spins. It does sounds like a CRT power supply issue but voltages are dangerous so please be careful.
 
MicroCoreLabs said:
I would think that a shorted tantalum capacitor would keep the whole computer from working, but it sounds like your machine is actually booting due to beeps and drive spins. It does sounds like a CRT power supply issue but voltages are dangerous so please be careful.
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Yeah its trying to boot. I'll learn to properly check to see which tantalum caps have gone bad then check out the CRT board. I will be careful around the high voltages.
 
I also have another Osborne 1 I'm working on. This one is in a bit of a better state. CRT turns on and there is a picture! When this unit turns on, the speaker beeps this high pitched tone endlessly and the floppy drive LEDs stay on until its powered off . I think the problem on this one is definitely the tantalum caps from what research I did.
 

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pukenot said:
I have an Osborne 1 that when I turn it on, a beep is heard and both red LEDs on the floppy drives turn on for half a second before turning off again, and then nothing happens. No picture on the CRT or any other activity. I can hear the faint buzz of the psu but nothing else. I replaced all the psu rifa caps before even turning it on once, so not really sure what the next move should be. Analog board and psu recap? Any ideas or suggestions are appreciated.
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I had this issue once with an executive. I strongly suggest you work on the second Osborne since it's in better shape.
 
Its alive! After recapping the power supply and replacing the tantalum caps at C72 and C73 and the whole system powered on. Everything seems to work great except for video output, which causes both pictures to start rolling but whatever that's fine. Really glad I got this computer working, just in time for the new year as well.
 

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pukenot said:
Its alive! After recapping the power supply and replacing the tantalum caps at C72 and C73 and the whole system powered on. Everything seems to work great except for video output, which causes both pictures to start rolling but whatever that's fine. Really glad I got this computer working, just in time for the new year as well.
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Have you tried hooking it to a composite? Try that and see if it rolls.
 
xp0nentz said:
Have you tried hooking it to a composite? Try that and see if it rolls.
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No the video on the Osborne itself is fine. It's only when you hook it up to an external composite monitor is when both pictures start to roll. I should have phrased that better.
 
pukenot said:
No the video on the Osborne itself is fine. It's only when you hook it up to an external composite monitor is when both pictures start to roll. I should have phrased that better.
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Ah, maybe instead of returning my Executive I should've looked at the caps. I had very similar issues, and when I turned it on its side the power button's light was on but no pictures. I hit the side and got a crt turning on picture, but it was just an orange screen. I got a 5140 instead.
 
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