Milspec Teardown: AH-64A Apache Data Entry Panel

It’s time once again to see how those tax dollars are spent, this time in the form of a “Data Entry Keyboard” manufactured by Hughes Helicopters. This device was built circa 1986 or so, and was used in the AH-64A Apache. Specifically, this panel would have been located by the gunner’s left knee, and served as a general purpose input device for the Apache’s Fire Control System. Eventually the Apache was upgraded with a so-called “glass cockpit”; consolidating various vehicle functions into a handful of multi-purpose digital displays. As such, this particular device became obsolete and was pulled from the active Apache fleet.

The military vehicle aficionados out there may know that while the Apache is currently a product of Boeing, it was originally designed by Hughes Helicopter. In 1984, McDonnell Douglas purchased Hughes Helicopter and took over production of the Apache, and then McDonnell Douglas themselves were merged with Boeing in 1997.

So it’s somewhat interesting that this device bears the name of Hughes Helicopter, as of the time it was manufactured, they would have been known as McDonnell Douglas Helicopter Systems. Presumably they had to work through existing stock of components that already had Hughes branding on them, leaving some transitional examples such as this one.

But you didn’t come here for a history lesson on the American military-industrial complex, you want to know about the hardware itself. So let’s crack it open to see what we can learn about this piece of aviation history.

Due Diligence: What is This Thing?

Credit: Robert Francis via YouTube

I should mention that when I first got this particular piece, I had no idea what it was. Like most of my other military finds, this one came up on an eBay Alert I had set up for surplus electronic components, and was listed simply as “Military Surplus Data Entry Keyboard”. It looked a bit beat up, but it was cheap, and I like cheap.

When it arrived a closer look revealed the contract number stamped into the data plate on the rear of the device, and searching that online brought me to a scan of Technical Bulletin 55-1520-238-23-1, “WARRANTY PROGRAM FOR HELICOPTER, ATTACK AH-64A” from 1988. Sure enough, in Appendix A “AH-64 WARRANTED COMPONENTS”, was listed “Panel Assy, Data Entry K/B O”. So now I knew this particular piece of hardware was from the original AH-64A Apache. Unfortunately, the last AH-64A was converted to an AH-64D in 2012, so finding pictures of the cockpit was a bit harder than I’d expected.

In the end, YouTube saved the day. I found somebody who uploaded video of them sitting in what must have been one of the last remaining AH-64A Apaches in 2010, and sure enough you can see the “Data Entry Keyboard” as he pans across the panel. Mystery solved.

Keyboard Dissected

It seems reasonable to start our disassembly with the keyboard itself, which is held on to the front of the device with six bolts. With the bolts removed, you’re able to pull the keyboard away and can get to work taking out the small screws that hold the back panel on.

With the keyboard broken down to its basic components, we can see that the operation is not really that different from the cheap membrane keyboards we’re all used to playing with. The mechanism here is considerably more robust of course, as it was intended for a military aircraft, but the idea is the same. Each key on the front of the device pushes a small membrane dome, which in turn makes contact with the traces on the PCB. There are metallic contacts in each dome however, as well as a tiny spring, so the tactile feedback on the keys is very good. Important when your operator is wearing gloves and potentially in a combat situation.

Internal Construction

With the keyboard itself removed, we get our first look inside the device. I was immediately struck by the absolutely gorgeous, and no doubt incredibly expensive, connectors used throughout. Presumably to protect against vibrating lose, the connectors can’t simply be pulled out, and you need a small slotted screwdriver to unscrew and separate them. They are designed so that they will only go together one way, and prevent bending of the pins since you have no choice but to evenly loosen or tighten both sides or else it will just bind. They’re annoying to deal with, no question, but you have to admire them.

The second thing that surprised me is that there are actually two separate boards inside the device, connected together with a backplane. The backplane features a standard DB15 male port, which incidentally is the only form of external electrical connection on the entire device, and is connected to the “blades” with a larger version of the screw-down connectors.

Power Supply

The first of the “blades” we’ll take a look at is the power supply. This board is exceptionally simple, in fact it looks almost homemade. The traces on the board look like they could have been masked off with a marker, and components are minimal to the extreme. The star of the show here is the Texas Instruments LM123K, a military grade 5V regulator that can provide up to 3A and can handle input voltages as high as 20V. There’s an inductor and a handful of capacitors to help smooth things out, but that’s it.

I find it fascinating that the device has its own beefy internal voltage regulator like this. It seems the kind of thing that could have been installed in a separate module and provide 5V to all of the devices in the cockpit. Perhaps from a reliability standpoint, the designers felt it was better to provide each mission critical piece of equipment with its own dedicated power supply.

Computer Board

Now I imagined there would be some interesting electronics inside this piece of equipment, it’s the whole reason I bought the thing. But I didn’t expect there would be a compete computer inside of it.

The “Data Entry Keyboard” is powered by an Intel MD8085AH/B, the military version of the venerable Intel 8085 CPU, paired with a MD8155H/B 2048-Bit HMOS RAM module. The ROM is stored on dual MD8755A/B 2 KB EPROMs. All of these components are rated “Class V Space Level” according to their respective datasheets, so if you are planning on building a Mars rover or something, this might be a good source for some otherwise very expensive chips.

Powering Up

In the previous installment of this series I successfully revived a 70 year old “CP-142 Range Computer”, so I felt obligated to attempt a similar feat on this considerably less archaic piece of equipment. I was spurred on by the standard DB15 connector on the device, as well as the fact that it was very easy to trace out the pins for power; all I had to do was check continuity between the input leg of the LM123K regulator and the pins in the connector. Knowing the regulator can handle up to 20V from the data sheet, I provided the “Data Entry Keyboard” with 12V on the appropriate pins of the connector and hoped for the best.

I probed around the remaining pins with the oscilloscope, looking to see the telltale signs of digital communication. Eventually I found something, but it seems that either I’m making naive assumptions about how this device should work (very possible), or there’s something wrong with it. There is indeed a digital signal of some sort coming out of the device, and it changes when I hit different keys or rotate the knob, but the signal is extremely weak and very garbled.

At only around 150mV and buried in some kind of background noise, this doesn’t strike me as expected behavior. My feeling is that something is bad on the board, but the couple checks I made (CPU is getting correct voltage, clock at proper frequency) didn’t show anything obviously wrong. Though with a piece of hardware this old, it could potentially be a bad capacitor hiding on the board somewhere. It would be interesting to see if any Hackaday readers might have worked with this kind of hardware before and possibly shed some light on what I’m seeing.

Final Thoughts

I wouldn’t have expected it, but this device is actually packed with useful and valuable components. The keyboard itself can easily be interfaced with and would make an awesome PIN pad for a security system or similar projects. How many people can say they’re handling authentication with an authentic piece of hardware out of an Apache?

The computer itself, if you’re into that sort of thing, is an incredible find. As old as they are, these military grade computer components are very valuable and could be the makings of an extremely unique retrocomputer build. Dumping the existing ROM would be an interesting first step, and erasing the chips with UV and replacing the ROM with new code the next logical step.

Overall, I think this is a fantastic microcosm of military technology as a whole. The cost to build this device must have been astronomical, but once you have a look inside you can’t really deny the construction commanded the premium expense at the time. A few years later, for all the money and R&D that must have gone into this lowly keyboard, they were all chucked when the Apache was updated. No matter how much it costs to build something, you can’t stop the march of progress.

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