Disc drive led: what drives it?

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DutchAcorn
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Disc drive led: what drives it?

Post by DutchAcorn » Sat Jun 16, 2018 10:42 am

Fixing an A5000 I have gotten as far as the desktop and the disc drive is now recognised. But it does not work yet. The led is constantly on and I get a “drive empty” error. From the circuit diagram I can’t find a specific signal that drives the drive led:
5A148226-A798-4895-A339-C93BDE686B7F.jpeg
Or is it the Sel2 line that does this?

Thanks!
Paul

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danielj
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Re: Disc drive led: what drives it?

Post by danielj » Sat Jun 16, 2018 10:50 am

You'll get "drive empty" if the disc controller's not receiving regular index pulses :) - I'd check that line!

d.

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Re: Disc drive led: what drives it?

Post by DutchAcorn » Sat Jun 16, 2018 11:07 am

danielj wrote:
Sat Jun 16, 2018 10:50 am
You'll get "drive empty" if the disc controller's not receiving regular index pulses :) - I'd check that line!

d.
Thanks Daniel, the index lines seem ok... I am suspecting IC42 as that is in the (rather large) area affected by corrosion. But it would be good to know if the symptoms match the lines running through IC42.
Paul

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Re: Disc drive led: what drives it?

Post by 1024MAK » Sat Jun 16, 2018 12:53 pm

DutchAcorn wrote:
Sat Jun 16, 2018 10:42 am
Fixing an A5000 I have gotten as far as the desktop and the disc drive is now recognised. But it does not work yet. The led is constantly on and I get a “drive empty” error. From the circuit diagram I can’t find a specific signal that drives the drive led:

Or is it the Sel2 line that does this?

Thanks!
I can't say for definite with original A5000 drives, as I've not had one in bits. But have tinkered with other drives.

What actually controls the LED on the front of a floppy drive varies between manufacturers and different designs of drive.
Most often, it's a combination of the drive/device select (DSx) line (that the drive is configured to respond to), the motor on (MO) control line and the drives internal "I'm okay" status.

Not all drives have/use all of the above logic. Some only use one or two controls. 5.25" floppy drives often had a link/jumper shunt to select the configuration of the LED. Some drives even have an input line so that the computer can control the LED.

Mark
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DutchAcorn
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Re: Disc drive led: what drives it?

Post by DutchAcorn » Sun Jun 17, 2018 6:53 am

1024MAK wrote:
Sat Jun 16, 2018 12:53 pm
DutchAcorn wrote:
Sat Jun 16, 2018 10:42 am
Fixing an A5000 I have gotten as far as the desktop and the disc drive is now recognised. But it does not work yet. The led is constantly on and I get a “drive empty” error. From the circuit diagram I can’t find a specific signal that drives the drive led:

Or is it the Sel2 line that does this?

Thanks!
I can't say for definite with original A5000 drives, as I've not had one in bits. But have tinkered with other drives.

What actually controls the LED on the front of a floppy drive varies between manufacturers and different designs of drive.
Most often, it's a combination of the drive/device select (DSx) line (that the drive is configured to respond to), the motor on (MO) control line and the drives internal "I'm okay" status.

Not all drives have/use all of the above logic. Some only use one or two controls. 5.25" floppy drives often had a link/jumper shunt to select the configuration of the LED. Some drives even have an input line so that the computer can control the LED.

Mark
That confirms my suspicion of IC42.
5664FC7C-4CB5-4DE6-9A2C-F6F98AA5C935.jpeg

With a logic probe I found that inputs as well as outputs are low on IC42. Which is not what you’d expect from an inverter (7406). So I'll order, replace and see where it gets me.

I thought I'd try the IDE again and this time it worked! Not only were a few tracks broken on the PCB, the cable I was using was also faulty :roll:

So now it is only the floppy drive. Oh, and somehow the power led and HD leds don't work so I'll need to look into those as well.
Paul

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Re: Disc drive led: what drives it?

Post by steve3000 » Sun Jun 17, 2018 7:22 am

Well done on identifying IC42, I've had to replace this on a battery damaged A5000 in the past too. Other two ICs I've had problems with are the buffers for the IDE HDD data lines, so keep an eye on these if you HDD doesn't function in future.

For the HDD LED, there's a track which runs across the width of the pcb right at the front (as you look at it with battery on the right) - I've had to repair this in the past to get the LED working.

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Re: Disc drive led: what drives it?

Post by daveejhitchins » Sun Jun 17, 2018 9:03 am

If it's of any help (?), here's how we did it on our IDE interface:
LED Drive.png
Which gives Power-on and Drive-activity in one LED (I still have some of these!).

Dave H :D
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Re: Disc drive led: what drives it?

Post by 1024MAK » Sun Jun 17, 2018 9:51 am

It is indeed likely that the 7406 inverter has failed. But before changing it, keep in mind that this chip has open-collector outputs. That is, it can only drive the output lines low. External pull-up resistors are needed to pull the outputs high.

So it is worthwhile confirming that the pull-up resistors are present and test okay, and have a +5V supply.

As with any suspect chip, carefully use your multimeter to confirm that it does have a supply by testing between it's Vcc and GND pins. Loss of either the +5V supply or the GND connection can and does cause weird logic chip behaviour...

Good luck :wink:

Mark
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Re: Disc drive led: what drives it?

Post by 1024MAK » Sun Jun 17, 2018 9:57 am

daveejhitchins wrote:
Sun Jun 17, 2018 9:03 am
If it's of any help (?), here's how we did it on our IDE interface:
Which gives Power-on and Drive-activity in one LED (I still have some of these!).
Ahh yes, your cunning design to use a bi-colour two pin LED :D

Mark
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Re: Disc drive led: what drives it?

Post by DutchAcorn » Thu Jun 21, 2018 9:16 pm

Replaced IC42 and the A5000 has a working disc drive! \:D/
Paul

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Re: Disc drive led: what drives it?

Post by DutchAcorn » Fri Jul 20, 2018 7:43 am

steve3000 wrote:
Sun Jun 17, 2018 7:22 am
... For the HDD LED, there's a track which runs across the width of the pcb right at the front (as you look at it with battery on the right) - I've had to repair this in the past to get the LED working.
The tracks were fine / fixed but the LEDs were not:
9CF3A510-0F22-419C-9993-B19C1F92D497.jpeg
I just got new ones and installed them, all working now. I just need to think what to do with the remaining 198 LEDs from the batch I bought... :lol:
Paul

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