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TRS-80 Start-up Zaps Disks

H

Holmes

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I just heard about TRS-80s zapping disks when turning on with a disk in the drive. I think it applies to the model III or 4. I tried an internet search on this, but couldn't find anything.

Does anyone have more info on this? Do we know why this happens? Is there a fix?

Thanks.
 
Yes, it happens sometimes. It also applies to the Model 1. You also want to remove the Floppy(s) before
turning power ON/OFF. There is no FIX as far as I know.

I always turned on the Floppy Drives, EI, Keyboard (CPU) with the Break Key Held DOWN, and when the
system was up, I'd type ?MEM

That gave me a quick look at the available memory. Then I would insert Floppy(s) and Reset to boot the floppy.

Power Down was in Reverse order.

Larry
 
Ok, thanks.

What does holding break do when turning on?

I'm surprised we don't know why this disk zapping happens yet. I wonder if this was a problem back when the computer was current? Maybe it has to do with an aging component in the computer or floppy circuits. Maybe a leaky capacitor?

I'm just worried about forgetting this step, and zapping a disk. And these disks are hard to find!
 
Holding the BREAK Key Down while Powering Up (M1, MIII, M4) will get you to the Basic that is in ROM.
The ?MEM command will show the available memory of the machine.

The problem is a Spike from the Power being turned on that Writes on the floppy, but not every time (only
once in a while) and that clobbers the Media.

It has been a problem from Day One with the Model 1. Just get used to keeping the Floppy(s) out of the Drive
until you are ready to depress RESET. (Same for Model III & M4).

You may be lucky and get away with leaving the floppy in the drive, but over time it will get clobbered.


Larry
 
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It happened to me this week on a Model I. Of course, it was an accidental powering off of the entire rig by bumping the switch on the power strip.

Early drives claimed to have protection against this, but with internal drives it was never as bad because they lost power as well as everything else. External drives it can get you because for whatever reason noise hits them on the bus. Later drives were much less prone to it.
 
I was thinking a couple years ago that it site would be nice to have a comprehensive list of machines that are known to do this.
 
Model IIs were also notorious for this issue, especially the earlier ones with the single channel floppy controller.
 
I'll make it easy for ya, Anything made before 1985. Heh.

I am pretty sure Commodores suffered this as well. They had logic inside though. I've been aligning and calibrating several drives today using my Model I as the actuator. Wiped out my diagnostics disk track 24 today just bumping into the that blasted power switch. Only takes a few minutes to fix it, I've got the master that I built on MIRE. Has a really early version of TDC so it works great for me. Its interesting that MIRE did this though, it emulates the EI too good. Of course, it may not even be the EI, might be the old Tandon TM-50s.

I'm going to have to be more careful before I wipe out my only Dysan alignment disk. I think I'm going to reroute the power to that station so I can't bump it.
 
I never encountered this on any Disk ][, 1540, 1541, or any drive in a PC or XT. So I don't think it's just anything made before 1985. If I ever heard back then that it was an issue, I sure don't remember it.

I never encountered it at all until I got a 4040 a few years ago. And even then I didn't realise what was happening until I got a Kaypro II.
 
On my Model 4D I've always followed the practice of inserting the disk first but not closing the door until after I turn on the power. At that point it should start booting up without any user intervention, at least on a Model 4. On a Model III or earlier you may need to press the reset button.
 
OK, thanks all!

It does seem like keeping the drive door open will keep the head off the disk itself, so it should be safe.

I guess I'll just have to discipline myself to keep the drive door open on turn on/off. I was at my TRS-80 the other day, and my 5-year-old was talking to me about something, and I flipped the switch! Aargh! Luckily it looks like no damage was done this time, but it seems it's a roll of the dice.
 
What I found through experimentation is that it at least almost always does write garbage. But sometimes it writes it somewhere that you don't catch it right away.

I thought some time ago about having a latching circuit so that every time the computer is turned on, the user has to press a button one time before the drive can write for the rest of the power-on duration.
 
Also true of many other systems. It's supposed to never happen with PCs, but I always eject disks first. With an old system using external drives, like a S-100 box or Ohio Scientific system, you're almost guaranteed to wreck a disk if you habitually leave them in when powering up or powering down.
 
I was reading some of the tech docs for various drives, and I think the TEAC talks about how it has circuitry to prevent this. I still don't trust it, been burned too many times.
 
Same with the power supervisor circuits on my Ferroelectric RAM board(s)...I designed them, they work, but I still halt the machine and hold it in reset if I care about the contents of memory :)
 
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