A3000 HDD LED driven by external source (Example: ZuluSCSI)

[StompinSteve]

Hello,

This is a short tutorial on how to make the A3000 HDD LED work with something else than the internal SCSI Controller. For example, a ZuluSCSI attached to a WarpEngine or separate Zorro SCSI-Controller, that sort of thing.

Such an "adapter" is **only** needed when the Amiga 3000 HDD-LED, which requires 4 Volt to operate, cannot be powered by a component that delivers less. If the component that is controlling your 3000's HDD LED, outputs 5V for example, you are fine. Just insert a resistor inline to bring it down to 4V and you are done.
But a ZuluSCSI for example, outputs 3V on its LED Header. So a "step-up transformer to bring it up to 4V is then needed". This is what the adapter I'm explaining here effectively does.

The original thread, where various ideas, approaches and solutions were discussed at great length is here: https://eab.abime.net/showthread.php?t=114333

This artice merely describes the solution that I chose for myself and how to implement it. I would like to keep this thread clean. Please use the before mentioned thread to discuss technicals details, others ways of reaching the goal etc. etc. Thank you for understanding.

Creating the "HDD LED external source Adapter":

Step 1.
Disconnect the HDD-LED from the +5V line on the 3000D LED Board. I simply cut the traces of the + and - to make the HDD LED fully "stand alone".

Step 2.
Solder wires to the HDD-LED's + and - solder-points on the LED-Board (which are still there) and route them through the chassis.

Step 3.
Make a connector of some kind so that you can easily disconnect the HDD LED later on. I'll call this the "LED Connector A" from now on.
"LED Connector B" will be the connector that plugs into the "LED Connector A".
It is "LED Connector B" that goes towards the NPN Resistor and the ZuluSCSI or SCSI-Controller etc.
In my case, I used a 3-Pin Case-fan connector (male and female) and used 2 of the 3 wires. This connector makes it impossible to plug them together incorrectly, reversing the polarity.
You will find a white version of such a (female) connector that connects the LED-Board to the Motherboard's 3-pin header.

Step 4.
Solder the 50K Ohm Resistor (R1 in the schematic) to the Base (middle) pin and isolate it with heat-shrink tubing (HST).

Step 5.
Find a +5V Source. I used a Molex (Harddisk) connector, snipping of the yellow wire (+12V) and it's black ground wire so that only the red wire (+5V) and it's ground wire remained.
As wire-colours can vary, use your multi-meter to identify what is 12V and 5V !

Step 6.
Solder the 460 Ohm resistor (R2 in the schematic) to the + wire coming from your +5V source (in my case the red wire coming from the molex connector).

Step 7.
Solder the same 460 Ohm resistor (R2) to the LED's Anode (+) side of the wire that goes to "LED Connector B". Make sure you choose the right pin on that connector !!

Step 8.
Take the ground wire that comes out of that same "LED Connector B" which comes from the Kathode (-) side of the HDD-LED, and solder it to the "Collector Pin" of the transistor.

Step 9.
Take the ground wire from the power source (Molex connector in my case) and solder it to the "Emitter Pin" of the transistor.

Step 10.
Take the ground wire from the LED Header on your ZuluSCSI or SCSI-Controller etc. and also solder it to the "Emitter Pin" of the transistor.

Step 11.
Solder the other end of the 50K Ohm Resistor R1 from Step 4 (connected to the Base Pin of the transistor) and solder it to the + wire coming from the LED Header on your ZuluSCSI or SCSI-Controller etc.

Time to test it.
Connect the +5V Source and hook up a standard modern 5V 20mA LED to "LED Connector B". We will use this "sacrificial" temporary LED to test the concept and protect the real HDD-LED from destruction if anything goes wrong (polarity reversed, over-voltage etc.).

Power on the Amiga. The temporary LED should blink during HDD activity. As this LED is a 20mA LED, it will not be very bright as it needs R2 to be 200 Ohm to light up normally. But R2 is 460 Ohm (needed for the real HDD-LED) which makes the temporary LED shine not as bright. This is ok. The most important thing is that this temporary LED flickers during activity.

Kicking in open doors: throughout the build, use heat-shrink tubing to properly isolate things from another. In the end, the entire adapter is heat-shrink tube'd to make a nice little package.

When this works, power-off the Amiga and hook up "LED Connector B" (coming from your "adapter") to "LED Connector A" (coming from the A3000's HDD-LED). Then power on the Amiga and enjoy the original LED flicker happily when there is HDD Disk I/O.