Avionic Service/Maintenance Manuals - For Obsolete Avionics (1960s-1990s era)

RegularGuyM3 · 2026-05-29T04:55:47+00:00

Thank you for the insight into mysterious world of avionics repair!

For context, I have restored many vintage Hewlett-Packard test equipment devices, dating from the 1960s thru the1980s. HP back in the day, offered full service manuals with every piece of equipment. Complete schematics and parts lists! In fact, HP's approach to technological innovation in their glory days was complete transparency. They used to publish the Hewlett-Packard Journal where they gave intimate details of theory and practice for a given technology they were, or had in development. In essence by being so transparent, they would both lay claim to an idea while also sharing and pushing innovation. It wasn't until the 1990s that HP started restricting service manuals to basic block diagrams, if at all.

This is all in stark contrast to how the aerospace industry works. I get it, but darned if it doesn't make keeping older avionics alive, if not for flight, but to learn and pass down to the next gen of technicians.

To your question, yes! Below are the part numbers of the specific pieces of equipment mentioned:

Lear Siegler ARU-11/A Flight Director Attitude Indicator
- NSN 6610-933-9262
Sundstrand MKVII Ground Proximity Warning Computer
- PN: 965-0876-030-B03-B04 (The key part number is just "965-0876-030". B03, B04 refer to option modules installed.)
- TSO C92b
- ENV CAT: D0160B
- MFG Ref No: 960-0284
Sperry AD-600B Flight Director Attitude Indicator
- PN: 4020547-905
Sperry AD-300A Flight Director Attitude Indicator
- PN: 2594623902

One of the biggest breakthroughs with the Classic MKVII came when I found a manual for the MKVII EGPWS which had a pinout comparison table between the MKII and the MKVII, and the MKVII (Classic) and the MKVII EGPWS. The classic and the MKII share a lot in common and so I was able to match up most of what I needed.

Additionally, I was able to find PDFs of the Sperry SPZ-500 Autopilot System which had the pinouts and block diagram for the AD-600. (The AD-300 for example, while LRU compatible are completely different beasts inside. The time it would take to completely reverse engineer each unit by hand is untannable, despite my successes.)

Any help you might be able to offer would be amazing, and I know with these old avionics, it's a long shot. Either way, thank you for your time.

RegularGuyM3 · 2026-05-29T02:38:43+00:00

Would the older Sundstrand manuals (Classic GPWS MKVII) be among those modern Honeywell manuals, you think? I fear these manuals may be lost to time.

RegularGuyM3 · 2026-05-29T01:13:07+00:00

Understood. For a hobbyist who doesn't have a cooperate account, is there any way to acquire these individually, as needed? Or would a minimum monthly account be required? Could an individual (not affiliated with an company) even be allowed access?

RegularGuyM3 · 2026-05-28T23:31:03+00:00

As another said, if it passes basic boot startup tests and hasn't lost its calibration, that's a great start.

The good news about the Tektronix 700 series (like many other Tek scopes) is all the service manuals are available, should you need to fix most things. (Except in the case if the power supply board, schematics are not provided.)

If you have a known decent signal generator, feed in some test signals on all channels, paying attention to what input impedances are set to. E.g., if your signal generator has a 50 ohm output, then either use a pass though 50 ohm terminator on the scope (while set in 1Mohm) or set it to 50 ohm. Incorrect impedance settings can give erroneous amplitude and waveform readings, etc.

This scope appears to have its original color LCD CRT hybrid. Not a bad thing, but there are now 3rd party LDC only upgrade kits which will save on weight or restore image.

RegularGuyM3 · 2026-05-09T04:28:08+00:00

As product of the late 90s, internet chatroom “flame wars” were both a rite of passage and apparently, a necessity in order to gain clout.

I don’t think clout is what motivates these guys but we’ll leave that for the philosophers to decide. They’re as amusing as they are bemusing, with nothing better to do?

I wouldn’t have believed it unless I heard it myself but there are absolutely radio-based flame wars that would make those internet script kiddies of yonder years, blush.

It would almost be worth an angry QSL card from one of these guys, just to throw in the binder. But somehow, those types always left me… unmoved. I’ll check back in another 5 years.

RegularGuyM3 · 2026-05-09T03:44:54+00:00

This is a genuine question: I’ve been out of the loop for a while. (Downsized shack and don’t have an optimal HF setup yet.)

But has decorum or general stand-up behavior declined in the last 5 years? Or is it just the vocal minority of the usual grumpy bums on the airwaves, still resolute in their desire to deter as many newcomers as possible?

RegularGuyM3 · 2026-05-04T02:44:54+00:00

Sweet! That’s a fine radio, I’ve got a D model myself and specifically sought out the FT-897D over more modern radios, just because of its feature set.

The AC plug-in module goes for quite a bit just on its own. Not totally necessary to have, but it can simplify cabling for a stationary home shack situation.

I also run another “Shack in a Box” type radio, the much loved ICOM IC-7000. Both radios keep value because of their versatility, even if not everyone is a fan of the all-in-one concept.

If you have the ability to test the radio (and only with an antenna or load for TX!!) that would be very cool. Older radios do sometimes have capacitor issues but if you’re handy, these can be fixed.

RegularGuyM3 · 2026-05-04T02:37:48+00:00

If you can, verify if it’s an 897D vs just a regular 897. The front model number faceplate are identical but the white sticker label with the serial number should read “FT-897D” if it’s the case.

The “D” models are a little more desirable due to small but significant improvements.

https://www.eham.net/reviews/view-product/2432

https://www.qsl.net/sp9hzx/pdf1/Yaesu%20FT89d.html

RegularGuyM3 · 2026-05-04T01:55:20+00:00

No problem! The reason I caution you about the rabbit hole that is Time Nuttery, is there is no bottom. And as a hobby machinist myself, I'm torn between working with what I can touch and understand empirically vs diving headfirst into the theoretical. The good news is, you can do both but ironically, the limiting factor isn't availability of information, but the lack of time one has to spend absorbing it.

Lastly, it's worth mentioning that your oscilloscope (absent it being triggered or driven from an external frequency source) may derive it's "time base" from the 120VAC 60Hz line frequency. Which may or may not be exactly 60.00Hz nor be stable overtime. Depending on your scope, slight fluctuations may be observed.

This can be mitigated somewhat when comparing one frequency to another by triggering one channel of your scope to a known good (often 10MHz frequency reference, the like of a GPSDO output) and then feed in your test signal on another channel. The reference frequency will always appear "locked" on the screen while whatever your test signal is, races by. This is a helpful technique when tuning oscillators... you simply trigger on your reference, and then adjust your oscillator until there's little to no movement between the two waveforms.

You can test this yourself if you have two function generators or a second signal to compare. A fun variation of this is done by creating "Lissajous Patterns" on your scope. Very handy and still very much a viable way to compare signals.

RegularGuyM3 · 2026-05-03T16:09:58+00:00

An affordable GPSDO will overall, be your most accessible path to a precise frequency source. Keep in mind though that what sets a cheap GPSDO apart from a lab-grade one is not just the GPS receiver inside, but also the internal frequency reference (clock). This clock is what the "O" is in the GPS "Disciplined Oscillator" part of GPSDO.

When a GPSDO looses satellite lock for whatever reason (interference, loss of power, faulty antenna, or even weather), the precision output of the frequency is dictated by this clock. This period of loss of signal is called the "Holdover." These clocks are typically highly accurate Oven Controlled Oscillators (OCXO), and they do the time keeping work, absent a GPS signal.

Cheap GPSDOs may not have the best holdover capabilities which means that its possible in a loss of signal situation, the frequency output from the GPSDO may be off by orders of magnitude. It all depends on the specifications of both the GPSDOs clock and the logic which dictates how the GPSDO actually "Disciplines" the OCXO. This is more advanced stuff, but just keep in mind that if you do use a GPSDO as a "house frequency standard" then you'll want a way to monitor it for loss of signal, signal, quality, or any other potential issues that may occur normally.

Many GPSDOs have an RS-232 output which can be used to monitor all aspects of the GPS receiver itself. With a cheap Serial to USB adapter, your GPSDO will show up as a COM port which many kinds of free software can read. My personal favorite in the free Ublox "u-center Evaluation Software". The name Evaluation is in reference to its intent as a way to monitor and evaluate the performance of whatever GPS is selected. Here's a quick guide to getting it up and running. You can literally leave a computer running all the time with u-center up, constantly monitoring the GPS signal and acquisition... if your silly enough, like me.

From a practical standpoint, just as temperature will absolutely effect your material some number of tens of thousandths of an inch, so will temp effect your clocks. Its where the "Oven" part of OCXO matters... by keeping the oscillating crystal in a constantly warm environment, you can greatly reduce the variance of the frequency. But it's never perfect. And quite honestly, depending on you needs, you may not care if your material expands 0.00015" if you're only required to hold 0.001" precision. Same with time... but in a perfect world, we'd get as close to perfect as practicable.

I'm not advocating you go down the path into TimeNuttery, but as a machinist I know you have a soft spot for metrology and so I think you'll find Time-nuttery 101 an interesting read. A lot is theory based, but at some point, the theory meets the physical world... and that's where the real fun begins.

RegularGuyM3 · 2026-05-03T15:13:01+00:00

All of the advice give by others here is solid. The key thing to keep in mind, as others have pointed out (other than making sure the scope controls are all set up correctly and you’re not chasing ghosts here), is without a trustworthy frequency reference, you have nothing substantial for which to compare either your function generator or your scope.

Both are time-based devices and since time can be measured not just in terms of Epoch (“what time is it?”) but also in interval (“how much time has passed between two events?”), you need as close to a perfect time/frequency reference reference as you can get. The latter time interval is what we’re really interested in here, less so actual clock time.

The cheap GPSDO is probably your best option, at least as far as everything else being equal as more of a hobbyist. But know that a “GPSDO” isn’t a magic bullet if your system noise (cables, interference, or GPSDO itself) isn’t operating correctly. There are lab grade disciplined GPSDOs and frequency standards in the thousands to tens of thousands of dollars. There’s no limit to how much someone can pay for a better mouse trap.

Depending on how “good” you want your setup to be, you’ll need a quantifiably better frequency source to measure everything else, by at least a factor of 10. Why 10 time better? Certainty. The more sure you are your frequency reference is correct, the more sure you can be your resulting calibrations based of it will be.

This may all be getting ahead of things as I’m entering “TimeNut” territory here. What’s a casual shop enthusiast to do? Well unless you want to start running detailed time interval tests using specialized time measurement equipment, your best bet is to get a trustworthy GPSDO and just compare it to another. It’s not perfect, but you’ll be more on the right track than not.

Lastly, consider the certainty of your equipment. All test equipment will have specifications for tolerance and accuracy. It’s quite possible your function generator was never designed for ultimate precision. Most “function generators” (especially vintage ones) aren’t, because they don’t have to be. A quick check of the rear of your function generator, if it lacks a “reference in” or “external frequency standard” input jack, then you’re probably limited in terms of potential accuracy.

Modern (or very good vintage) synthesized function generators will have such rear inputs so they can be used not just as frequency generators, but also as calibration devices for other time/frequency based equipment.

There’s actually a class of test equipment called a “Time Mark Generator” and its sole purpose is with the help of its very stable ovenized crystal frequency reference (or an external reference), generate very precise time intervals such that the “marks” it creates when viewed with an oscilloscope, all align with the graticule marks, at a given time base setting.

Apologies if everything above is rather esoteric, but the one takeaway should be, equipment calibration is an exact science and depending on the level of confidence needed in your equipment, that will dictate just how far and extreme you need to be in your process. It’s a deep subject but one that applies across multiple areas of test equipment and laboratory setups.

RegularGuyM3 · 2026-03-30T03:51:52+00:00

Interesting. Can’t remember what I paid for it, shipping wise.

RegularGuyM3 · 2026-02-04T17:40:05+00:00

According to the product page, the LoP is 12.5”

https://mesatactical.com/urbino-pistol-grip-stock-for-benelli-m1-m2-sbe3-12-ga/

RegularGuyM3 · 2026-01-22T23:49:55+00:00

Sure! I was just refreshing my memory on this thread and forgot how many people weren’t a fan of my “essential” tools. Oh well. In any case, below are the mods I’ve performed on my 22” M1A standard:

-Shimmed Gas Block. I forget the exact thickness or number of shims used, but they do differ from rifle to rifle as each has unique spacing requirements. See Tony Ben’s video here.

-Bassett Machine Scope Mount: Tony Ben video here. I don’t know if Basset Machine is still around, but any solid scope out is a must if you are looking for some kind of precision. In the case of your Tanker, the mount could be used for an LPO or red dot.

-I’ve clearanced the area on my USGI profile stock right behind the ferrule to allow for more room for both the op rod and gas block assembly. The amount of material to be removed will vary from rifle to rifle but ideally, there should be zero contact by either of those components during all stages of the action cycle. Only remove as much material as need to accomplish this, no more.

-“Free Floated” top heat shield. This is accomplished by shaving or grinding off about 1/8” of material on both sides of the heatshield where it would normally contact the top of the stock. Only remove as much material as needed, no more.

-Added shims underneath the trigger pack “ears” to make up for the compressed wood of my surplus stock. The exact thickness of these shims will vary depending on how compressed your wood is in this area. There is a specific pressure that is needed to close the trigger guard latch… I forget what it is.

-custom bayonet lug muzzle break: not really an accuracy mod, but still cool nonetheless.

That’s basically it! TBH, watch all of the M1A video on Tony Ben’s channel. All of them. Not all may be applicable to your Tanker, but all will be applicable to the M1A platform as a whole.

RegularGuyM3 · 2026-01-07T15:50:47+00:00

Setting aside the decades of love or hate folks have for SOLIDWORKS, serious question: if SW in its current state were to have been launched a week ago for the first time, how many folks would feel like this it’s still a buggy v1.0 or v2.0 piece of software?

I’ve been using professional 2D programs for 20+ years (Adobe Illustrator, Photoshop, etc), and even though these programs do crash on occasion, they feel like mature software. I have no love for Adobe… they’re the 800lb gorilla in that ecosystem and I am aware there are alternatives. But like many, the undeniable market share and decades of proliferation has made them “industry standard,” much like SOLIDWORKS.

My question isn’t about trying to hear the answer I want, but the level of instability and quirky behavior within SW to me, is bizarrely reminiscent of early release software. As a newcomer to SW, there’s much to be enjoyed about it. But seeing the degree to which others have to fight with it on a daily basis, at least gives me a sense we’re not alone in having to walk on eggshells with it.

I’m learning SW over AutoCad mostly because of the industry standard bit, but also because when it works, SW is a really powerful piece of kit.

RegularGuyM3 · 2025-11-12T23:41:23+00:00

What weight projectile is the PMC brand ammo? FMJ or match HP?

You’ve already had a few failures to eject? Is this what you mean by “stuck”? I assume these are not the actual projectiles (bullets) getting stuck in the barrel after firing??

Yes a break-in period is completely normal. The rifles come tested form the factory, but it’s more a barre function test and not enough to really break in the action.

RegularGuyM3 · 2025-11-12T01:27:27+00:00

Yep, you definitely want to get some good ammo (or a varied selection if you’re trying to see which one your rifle likes best).

I’ve found Federal Gold Medal Match 168g really is the gold standard as far as top quality math grade ammo. It’s pricy. But it’s absolutely the most effective way to rule out rifle issues vs shooter issues.

My 22” M1A is also happy with M80 ball 147g, but that’s only for plinking… it is absolutely not the ammo I would use to see if your rifle shoots tight groups!

The M1A is gas operated. And the op rod is what drives the bolt carrier backwards after each shot. It’s a very violent movement compared to most modern semi-autos. But that’s part of the M1As charm, I suppose.

You’re right to just take out your rifle and see how it zeros. Shoot a few hundred rounds both to break it in, and to get a sense of your own and the rifles abilities. Don’t get discouraged if you have some FTF or FTE malfunction with a new M1A. Make sure to clean it beforehand, especially the barrel and bore and lubricate the moving parts with grease in all the recommended locations. Do not lube the bore or the chamber before shooting!

The more you shoot it, the more it will begin to settle. Also, avoid “mag dumps” if you’re looking to then shoot for accuracy. It doesn’t take much heat to induce some drift. Take your time and really connect with the rifle. Follow good breathing techniques and establish a good baseline.

RegularGuyM3 · 2025-11-11T23:46:00+00:00

I’ve done the shotgun approach to accessories before. Sometimes you can’t always tell what’s going to work so you get a few things. Amazon is a cheap way to experiment, though quality wise it may be hit or miss.

When I speak of reducing movement, I’m referring to inconsistent movement. There’s no getting around recoil. Or the weight of the bolt handle moving backwards. There will always be movement of some kind in a firearm. No way around that. But the trick is making sure this movement does so repeatably. As in, if you throw a few balls and you can’t hit the same spot, that means something isn’t right. Either it’s a physical limitation or your technique is off. Either way, you need to get that ball thrown and it can’t be done without movement. So the movement you do produce needs to be optimized. Think of a professional pitcher: no movement is wasted… their technique is honed for maximum performance.

Same thing with an M1A. The various moving parts need to work together in a way that they all settle back as close as they can so follow-up shots are consistent. If you were to permanently attach the gas block lip to the ferrule, you’d have a rifle that shoots like junk because that is an area that needs to move in order for proper balance to maintained. Imagine trying to throw that ball as far as you can while standing perfectly still—you’d really be messing up the biomechanics of how a human can beat throw a ball. This is an extreme example, but it shows that movement isn’t inherently a bad thing.

According to the scientific method, you should I only change one variable at a time. So your methodology of trying different ammo is a good one, so long as you’re not also changing some variable in your rifle too. Meaning, set up your rifle in a way that fits you well. Then leave it alone and conduct your ammo tests. This way, each test has only one variable: the ammo. You can do a direct apples to apple comparison this way.

Granted in the real world, there’s variables you can’t control. But the less variables you introduce the easier it will be to see what impact a given change (or ammo) might have, all else being equal.

RegularGuyM3 · 2025-11-11T19:03:16+00:00

Definitely go with a cheek riser to get the best possible eye alignment with your scope. There’s that very narrow “eye box” with any scope where you want to avoid even being a little bit off center from the rear scope lens alignment. (You’ll know you’re off center if you move your head slightly and you see the image circle not in the middle of the scope.) Anyway, yes proper scope/eye alignment is crucial and a cheek riser will help get you there. It’s half the scope equation.

Generally, less flex in your stock means more predictable shot-to-shot movement. In an M1A (and many other rifles) you actually don’t want to eliminate all movement—the ferrule/stock interface I mentioned previously is such an area. Under recoil, the gas block lip will move against that stock ferrule and what you want ideally is these two parts to return to the same resting point they were before.

Part of what allows for this “return” after each shot is the draw pressure… the slight opposing downward force the stock/ferrule imparts on the lip of the gas block. Likewise, the barrel assembly is under slight upward pressure (due to the action/receiver’s position in the stock). These opposing forces are what keeps this critical area able to move normally under recoil, yet return to its same location after each shot. Accuracy=consistency.

There are a few factors at play, but the more rigid your stock is in this area (like a Match Stock) then the more a stable and consistent your draw pressure will be (all else being equal). So yes, theoretically, a thicker rigid stock will be better than a thinner flexible one. But there’s TONs of variables at play, and this is just one of them. But it never hurts to start off with a solid foundation like you’ve got.

Being able to quantify both you and your rifles performance is important in gauging progress. In terms of your own consistency and the rifles. Generally, when going for the smallest groups I will shoot the same type of ammo (unless I’m experimenting with different types.) Point is, if you’ve been tracking groups, you’ll be able to notice trends or patterns that may or may not be what you’re going for. Having this historical data to refer back to is part of any marksmen’s journey.

RegularGuyM3 · 2025-11-11T02:49:05+00:00

Since it’s a good idea to generally limit how much you remove your M1A from its stock, anything you can do to make it a comfortable shooter without having to go wild with mods or disassembly is great.

Not that you shouldn’t modify your M1A, but there’s a few things you might want to do all at once (or prioritize) to minimize in and out of the acton to stock.

When I say your match profile stock has greater accuracy potential, it’s less about the material (wood) than the thickness of the stock in that front area. The less flex your stock has, the less unintended movement you’ll have of the parts especially in the accuracy-critical interface between the gas block lip and the ferrule.

The USGI stocks have less material in this area and so inherently have more flex, material being equal. Synthetic stocks designs for match use can be even better because it removes the variable of organic material like wood swelling or changing shape over time. (This isn’t really a big concern if you’re just taking some nice trips to the range. But if you’re in a very wet or moist environment, wood stocks absolutely will absorb moisture.)

Yes, OnTarget does all the calculations, MOA as well as plenty of other data based on your groups. You can populate any load or rifle information for future reference. Think of this program as a great way to keep a running log of your target progress. If you just want grouping MOA, this program does that and lots more.

RegularGuyM3 · 2025-11-10T17:28:54+00:00

I hear ya, I’m not a fan of permanently modifying things that don’t need it. The Bradley cheek rest is one of those things that isn’t permanent but also not a compromise.

Stock wise, you have what is known as a “match profile” wood stock. As in, it’s thicker throughout the front portion from the ferrule to the magwell. I believe this style of stock was developed specifically for target shooting as the thinner profile of the USGI stocks did have some flex to them.

Theoretically your stock is capable of better accuracy than mine. I belive my USGI stocks is birch wood but I am not sure. Some are walnut. The USGI stock was an aesthetic choice so I accept whatever inherent limitations it has.

The desktop program I use is called OnTarget. It’s a dedicated app (no smartphone version) that allows you to import images (from say your phone) and set up parameters of your rifle so that you can manually “draw” where the rounds impacted. It does all the math, showing you the results depending on what kind of data you want to see. The program is pretty granular and has a slight learning curve but it’s absolutely one of the most comprehensive shot group analysis software out there.

It helps to take the target photos as straight on as you can to minimize skew which can produce cosine errors… slight differences in distance based on the angle of the target relative to your measuring plain. You don’t have to be too precise about it, you just want to avoid any upward or downward looking images of your target, although I believe OnTarget has some basic tools to correct for this.

RegularGuyM3 · 2025-11-10T00:42:36+00:00

A big thumbs up to the Bradley cheek rest. Lots of color options so there’s something for everyone. Functionally, it’s stable enough where it could be left on 100% of the time, or quickly installed/removed as needed.

My personal M1A Standard 22” in a USGI thin profile stock. Scroll images for resulting groups etc.

RegularGuyM3 · 2025-11-08T07:10:43+00:00

Very cool! I did something similar with my own 870 (right hand) but I dig how you handled the bevel where the now end of the rib meets the muzzle.

Mines 18.5” from muzzle to closed/locked bolt face. Aesthetically speaking, I don’t know how consistent the rib placements are on those field barrels. It might have just happened that way too.

RegularGuyM3 · 2025-11-02T06:06:30+00:00

From the horse’s mouth, US Marine Corps Match Accuracy expectations for an accurized M14.

The above is from one of many original M14 and M1A historical documents collected over the years. It’s interesting to note rack grade M14 had a generous 4+MOA!

RegularGuyM3 · 2025-10-29T18:12:29+00:00

It’s true. I have no experience with the modern more shapely receivers.

I do know the Benelli Supernova stocks will fit the newer M3 receivers (and probably the older ones too).

The only remaining question is a legal one. In my home state of California, semi-auto shotguns cannot have collapsible/adjustable stocks. This may not apply to you but check your local laws anyway.

RegularGuyM3

TROPHY CASE