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IIc - Sometimes goes dead right as drive starts to spin

dhoelzer

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I have a IIc... Works fine without the unidisk connected. Normally works fine with the unidisk connected. However, sometimes, when I power on, it will beep and begin to spin the drive and then "power off."... It looks like over-current protection, but I need some guidance about where I should direct my efforts.

The "poweroff" happens when the internal drive spins, not the unidisk.

Any pointers are welcome. Thanks!
 

Timo W.

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Either the internal or external PSU. Try a different external power brick. If the problem remains, recap the internal PSU.
 

dhoelzer

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Mm.. Pulled them all, tested (all good, one marginal) and replaced. Still has the same issue, regardless of external PSU.

Any other thoughts?
 

Timo W.

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I assumed that right from the start, but you did check the voltages already, didn't you?

Do you have a way to test the internal disk drive in any other system - or have a spare drive that you could test inside the IIc instead?

The only other issue I can think of right now, when it's not the PSU, is that the motor of the disk drive draws too much current. Either due to an internal short or because it's gunked up.
 

dhoelzer

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Yes, the voltages all look fine. The system operates completely fine most of the time. It's only sometimes that it acts in this way.

I do have an external 5.25.. I've never had it apart and it's just stored. I'll open it up and see if that drive can fit in the chassis and if the behavior is the same.

Thanks!
 

dhoelzer

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Well, I dismantled the external 5.25 unidisk. It took some doing, but I wired it in... The system behaves *identically*. As soon as the internal drive tries to spin, "powerdown" like overcurrent protection.

I'm remembering back now that I actually tried a different internal PSU in this iic a few years ago and it behaved identically. Given the different drives and recapping the internal PSU, I'm left wondering what on the board itself would do this. I'm even wondering if something in the IWM or a supporting chip is marginal.

Curiously, right before this, I was able to copy files to the internal 5.25 without an issue.. but when I try to boot from it, it dies.
 

Timo W.

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Interesting. Can't think of anything else right now. I wonder, however, what actually cuts the power. After the system "powers down", you could try to follow the voltages to the point where they are no longer present. That is, unless the external brick shuts off.

After that happened, can you turn on the system immediately again, or does it need to rest for some time to work again?
 

oldpcguy

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Two things which I am unclear on but think I know the answer to:
  1. Does this problem exist without the unidisk connected?
  2. Does this problem exist when the internal disk is not connected?
I assume you would have tried these two things but it isn't clear from the discussion if you had or not.
 

dhoelzer

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No problem when the internal disk is disconnected. Yes, this only happens with the external unidisk connected.. but without the internal drive, I can connect the unidisk and another 5.25 behind it with no problem.

I haven't tried measuring voltages when it does this, but that's a super idea. It might be tricky because sometimes it comes back to life suddenly (repowers without flipping the swtich)
 

dhoelzer

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Oh, interesting... With *anything* connected to the smartport, it can happen. It just happened with only a floppyemu connected, and that draws very little. To sum up:

* It only happens with an internal 5.25 connected
* Any 5.25 drive internally will cause it
* With the internal drive disconnected, it never happens
 

dhoelzer

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And things have gotten worse.. It will now sometimes do it with only the internal floppy installed. It does seem like it's the internal switching PSU that's cutting out because of the fault, whatever it is. I'm thinking about wiring a bench supply in to the system to see if I can follow the current.

Any thoughts about this?
 

VERAULT

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Have you tried another internal drive? The drive mechanism from any of the "plastic shell" apple 5.25" drives will connect and work as well. Doing this will determine if the fault is in the drive or the board.
 

dhoelzer

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Another question... Reviewing the schematics that AppleFritter has for the IIc, I'm noticing that sheet 5 shows that the connectors from the external PSU that I keep reading are not connected to anything, actually are... They run to the 1488 and 1489 serial lines.

Am I crazy to think that this could all be related? I have an issue on the serial ports that they only will handle 7 bit data and was preparing to replace these two chips. I've also continually wondered if this non-original external PSU that I wired according to reports that only pins 3,2 and 5,6 mattered could be the source of my problems since it is only a 1.2 amp supply. That *should* be sufficient.. but is it?

I cannot find anything definitive about what pins 1, 4, and 7 carry from the PSU.. Only that they actually are wired in. I think 4 is just a common ground, but 4 and 7 look important.

Would someone with a real iic PSU be willing to check continuity/resistance/power on these pins from the PSU?

Thanks!
 

dhoelzer

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My own question answered... I think all of this was caused by an underpowered external PSU. I switched to a 4 amp 20 volt external and all seems well.
 

Timo W.

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I run my IIc from a self-made PSU as well. Also only using pins 3,2 and 5,6.

But... 1.2 amps seems WAY to low. This could very well be your culprit. 2 amps should be minimum, the one I use is rated for 2.5 amps.
 

dhoelzer

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Nope. This is a ROM3 originally, but I have a ROM4 in it. I have to try the serial ports with the power issue addressed and see if there's a change.
 
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