Reverse-engineering some Navy (submarine?) video boards - Page 1
Forum section: electronics / projects

author: D Straney
author_rank: Frequent Contributor
timestamp: June 06, 2025, 09:43:11 pm
content: I found a few interesting boards being sold as scrap a while back, from some kind of marine video system.I'll get into the circuit details soon, but first, a little background:The CAGE code on them is 05869 (Raytheon, currently) and looking up the part numbers on the boards resulted in descriptions of "PREAMPLIFIER,DEFLECTION" and "VIDEO AMPLIFIER", and 1989 record creation dates.This doesn't tell us much alone, but an alternate listed supplier is CAGE code Z4779, for "ASC PTY LTD". ASC PTY is apparently an Australian ship manufacturer, and looking at theirWikipedia pageturned up this:QuoteLooking into theseCollins-class submarinessome more, as the date range matches these boards...QuoteQuoteQuoteSo, there's a decent chance that these boards came from the combat data system that was managed by Rockwell -> Boeing -> Raytheon. The boards would've been from the early prototyping phase most likely, judging by the 1989 NSN date and the 1986-1987 date codes on the components themselves.Let's look at the details of theVideo Amplifier Boards:These two copies are identical, except for the exact parts used for some of the resistors & diodes.The most visible feature is the hybrid module, which is a Comlinear Corp. CL103 amplifier. This is presumably very similar to theCLC103, which has a datasheet available. It's a high-current / high-slew-rate amplifier module, with a current-feedback topology, formed from an op-amp and a couple discrete transistors as output drivers.There's also no shortage of colorful resistors and metal-can transistors, along with some nice relays.With the very-non-video-amplifier-looking parts, like a bunch of digital logic in the corner, and the relative ease of tracing connections on this board, there was no way Icouldn'tfigure out the exact circuitry. After a lot of time following traces on overlaid photos of the front and back sides of the board, I ended up with the attached schematic in PDF form. We'll look through the sections one by one - it turns out there's a lot more going on here than just a video amplifier.Video amplifierLet's get the obvious part out of the way first. Two video signals enter on the backplane connector. The board selects one of these using a DPDT relay, controlled by a digital input.The selected video input then goes through two stages of discrete-transistor buffers (Q13 & Q11). The PNP-then-NPN arrangement means that the Vbe voltage drops (roughly) cancel each other, and create relatively little DC offset between input and output. The power supply connections, as I've shown them here, don't entirely make sense - it's difficult to distinguish between different copper planes and I think there's an additional supply voltage in here. But either way, Q12 forms a current sink bias (with R74 as a backup?) for Q11's buffer.After the buffers, the signal level is set by a trimmer, and a (negative) DC offset is added to it by zener diode D7 & R77/R78. From here, it's amplified by the CL103, and then sent through a 75Ω series resistor, presumably to drive a 75Ω coax cable.Another reason to suspect that the output drives a long external cable is the protection circuit, which is likely designed to absorb impulses from radar / lighting / ESD / etc. R103 biases C24 at Vcc, so that D12 & D13 will clamp the output a little above Vcc. C24 can absorb short impulses with its capacitance alone, but anything larger is handled by beefy bidirectional TVS diode D11. It's a little strange to me that this only works for positive over-voltages, and does nothing about negative ones...Speaking of protection, there's also a current-limiting circuit for the CL103's power supply, formed from Q7/Q10/Q6/Q9. The voltage drops across 2x 10Ω series resistors, in-line with positive and negative supplies to the CL103, are compared against the Vbe thresholds of Q6 & Q7. The overall effect is to limit the current draw from each power rail to roughly 60 mA: this protects the amplifier in case of a shorted output cable or too-heavy load (don't want to blow up the expensive board when someone accidentally puts a shorting connector on the output coax).Mystery analog circuit - video sync pulse generator?This is an entirely separate circuit which, as far as I can tell, seems to add some kind of synchronization pulses to a video signal. There's a digital input on the left, which gets AND'ed with a "power good" signal (we'll get to that next), so you can think of the AND gate as just a buffer during normal operation.An analog input signal enters on the backplane connector (pin B35), and passes through another 2-stage NPN-then-PNP buffer (Q3 & Q5). The output of this buffer goes through a diode (D2), another protection circuit, and to an external pin.However, this isn't the whole story. The mass of resistors on Q5's collector limits the buffer's output current (without increasing its output impedance during normal operation), allowing the output signal to be "overridden" by a lower-impedance signal source.This ability to override the output signal level without damaging the buffer is important, as we look at what the digital input does.When the digital input is low, nothing happens - the buffer functions as normal, and the output voltage is a copy of the input voltage.When the digital input goes high (rising edge), Q4 is briefly turned on by C11, and pulls the output up to a DC level in a short pulse.As the digital input stays high, Q4 turns off, and Q8 overrides the output with ~ +2V, generated by a 2.7V zener and a series diode.When the digital input goes low, Q2 is briefly turned on by C1, and pulls the output down to some negative DC level in a short pulse.This specific sequence of "positive pulse / +2V level / negative pulse" seems like some sort of synchronization indicator. My best guess is that this circuit section is used to add a synchronization pulse to a video signal, from a digital input driven by a timing generator somewhere else.Power-good indicatorA single comparator here looks at scaled combinations of +5V, a mystery negative rail, and possibly some other supply: I think this is supposed to drive its output high when all power supplies are present and at the correct levels. This "power good" signal both enables the digital input in the previous "mystery analog" circuit, and also turns on a relay (K2) which switches power to some external board.Video saturation detectorThis circuit takes a DC-coupled input from the CL103 amplifier's output, and also an AC-coupled input from the mystery sync pulse generator(?) circuit described earlier. Both these signals are compared against fixed thresholds by a fast (80 ns) LM319 comparator. Two D-flip-flops are used to latch the "threshold exceeded" state, so even a brief excursion of one signal above its threshold will be recorded. The "saturation, latched" digital outputs are sent off-board. A pair of digital inputs allows these outputs to be reset, or manually set (as a test?) under external control.My first thought was that this is supposed to indicate when either video signal goes beyond its intended limits: showing that something is wrong or there's too much gain in the system, during calibration of levels. There's probably other possibilities too, but I'm not sure what they might be.Mystery current sinkFinally, there's a stand-alone current sink that drivessomethingoff-board. The zener diode and emitter resistor set the current to a relatively constant ~2.4 mA, while a trim pot allows picking off a specific negative voltage from its collector. There's no way to know what this does in context without seeing the rest of the system.Inside the CL103 hybrid moduleI can't see a nice module without wanting to look inside, so I removed the CL103's lid on one board:The biggest die on the ceramic substrate is an op-amp: specifically, the TL072.There's a collection of other discrete transistors as well:Finally, there's a mystery device which I can't figure out:This somewhat suggests a resistor, but I'd expect to see traces,like the other silicon or thin-film resistors I've looked at under the microscope. It also could be a diode array maybe, or some kind of power transistor.Anyways, let me know if you have any insights about the mysteries contained here.

author: rsjsouza
author_rank: Super Contributor
timestamp: June 06, 2025, 09:59:48 pm
content: Incredible photographs, teardown and analysis - thank you!Regrettably I don't have much idea about the mystery device. Odd that all five terminals connect to the same pad, suggesting some sort of capacitor (?) bank that could be connected to three other parts on the other side (two transistors and one bridged connection to another part). Perhaps each of the five wires could be added during manufacturing to trim the part? The remaining two unconnected pads could suggest these capacitors (?) were not necessary. I can only speculate, though.

author: D Straney
author_rank: Frequent Contributor
timestamp: June 06, 2025, 10:41:36 pm
content: Thanks - and ooh, good point about it being a capacitor. Hadn't even considered that at first, but it makes a whole lot of sense now as a tunable capacitor, seeing the binary increments in pad areas. Going counter-clockwise from the tiny pad at middle-left: you have very roughly x1, x2, x4, x8, x16, x32 (unused), ignoring the tiny unused one in the top-right corner. I wonder if this is used in the feedback compensation, and they selectively added wirebonds during test, to tweak the overshoot & stability for the particular transistor batch.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 07, 2025, 12:59:46 am
content: Do you know you can import your photographs into KiCad with:PCB Editor / Place / Add Reference Image? The images can be scaled and scaled to match the PCB size. This is a quite nice Reverse-engineering aid.Photographs often have (barrel) distortion, uneven lighting, shadows parallax errors and such. It helps a lot if you first try to keep distortion down (make photographs perpendicular from the center of the PCB. Make the photo's from far away and at maximum zoom level to reduce barrel distortion. You can make corrections with an image manipulation program such as Gimp or Krita. You can also mirror the backside to make it match the front, and use transparency and on/off of the pictures to work on different parts.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 07, 2025, 06:59:36 am
content: Thanks, great pics!It was all so much more colorful.

author: iMo
author_rank: Super Contributor
timestamp: June 07, 2025, 08:42:51 am
content: I like the metal passive cooling frames on the PCB, where the chips, transistors and some of the resistors and diodes are coupled to via the grey thermal paste.. Something people at the metrology section my start to apply as well..

author: RoGeorge
author_rank: Super Contributor
timestamp: June 07, 2025, 09:27:01 am
content: Those white ceramic thermal slabs might be Beryllium Oxide.Don't grind them!

author: D Straney
author_rank: Frequent Contributor
timestamp: June 07, 2025, 04:50:58 pm
content: Quote from: Doctorandus_P on June 07, 2025, 12:59:46 amDidn't know about that feature in KiCAD - that's useful, thanks. My current process (which works great actually, highly recommend) is taking flat-ish photos of the front & back, importing into Gimp as semi-transparent layers, mirroring the back side, and using the Perspective tool on one of the layers to account for distortion, matching up the mounting holes or other distinctive features between the two. For example, here's part of the video amp board:Quote from: RoGeorge on June 07, 2025, 06:59:36 amGlad you like them - and yes, half my reason for picking up old boards is the great color variety.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 05:49:35 pm
content: Quote from: Doctorandus_P on June 07, 2025, 12:59:46 amTo remove “convergence” distortion from a photograph caused by the object plane not being parallel to the image plane (film or sensor), I find it useful to photograph flat circuit boards on a vinyl “self healing” cutting pad that has a 0.5 inch grid pattern. I then process the image through Paintshop using the perspective correction tool, anchoring the reference quadrilateral to four grid points on the background, before cropping and scaling as required. Other photo processing software has analogous perspective tools.

author: D Straney
author_rank: Frequent Contributor
timestamp: June 07, 2025, 05:54:15 pm
content: Ok, here's the other one, theDeflection Pre-amp Board:There's quite a variety of things going on here:...including some pulse transformers:...some nice glass capacitors:...and a whole row of testpoints along the top, that are easy to clip leads to:There's a shielded metal can:When opened, it has auA733 differential "video amplifier", and some of those very nice square Vishay precision resistors.This looks much more analog than the other board, but there's still the question of what the couple digital logic ICs and pulse transformers are for. After following the traces, I ended up with the attached PDF. Just like before, I'll walk through the circuit sections one by one.Power SuppliesLet's introduce this one early since the analog parts will be easier to understand afterwards. The power supply situation is complicated here: it seems like there's 3 sets of bipolar supplies...Vcc & Vee: used for small-signal stuff, like the front-end amplifier & comparators (±12V-15V?)Vcc2 & Vee2: used for the discrete-transistor differential amplifiers; likely a higher voltage (maybe ±20-30V?)Vcc3 & Vee3: these are regulated by D21 & D13 to be 7.5V above (and below) Vcc2 & Vee2; probably used for providing "beyond-the-rails" biasing of the Vcc2/Vee2 amplifiers.+5V for the digital logic is regulated on-board from Vcc. There's also a mystery PNP-switch circuit, unconnected to anything else here, which is used by something(?) off-board.Analog AmplifierThis is probably the "deflection pre-amp" that the name refers to. At the left-hand side (differential amplifier stage 1), there's a variety of differential inputs that can get mixed together at different ratios: I'm not sure whether this is meant for actually mixing different signal sources, or for selecting a different gain depending on how things are connected. I don't know what the gain of the uA733 is; the datasheet didn't have an easy formula and I didn't feel like putting in the time to figure it out from the internal schematic.After the uA733, the differential amplification continues, but all-discrete. The outputs of the uA733 feed two differential pairs of transistors: one PNP, and one NPN. These two transistors are in a co-packaged matched pair. The differential pairs are biased pretty simply with emitter resistors (R86, R91), and one of the transistors in each pair does nothing with its collector current (Q13A, Q14B). The "output transistor" in each pair (Q13B, Q14A) has a cascode connection (Q15 & Q16).The outputs to this section have an interesting current-source bias, fed from the higher Vcc3 & Vee3. Looking at the high-side one for example: it looks like D22 is supposed to (roughly) compensate for the Vbe of Q19, and R104/R106 together with Q19 & Q20 create a current mirror with a cascode output. With the 10V zener (D23) connected to the output, on the input of the current mirror, it seems like the current source's output is supposed to scale with the output voltage. As output voltage decreases (more current through Q15), the current from this bias current source also increases. This acts to decrease the gain somewhat; I would've expected the opposite (stronger bias as Q15 drive decreases) to save dissipation, but guess that wasn't the goal here.There's also some feedback through R83 & R84 (plus the tiny-value glass capacitors in parallel), which actually looks positive when I map out the directions - maybe I got something wrong on the circuit tracing. The ratio of R83+R84 to R80 sets the feedback ratio, and R81+C14 seem to tweak the frequency response (although not by much, as 4.7KΩ >> 510Ω).These amplified differential outputs then move on to the 3rd stage, at the right-hand side. These two outputs are set a fixed voltage apart by a string of diodes (D18/D19/D20/D97), to set the bias to the two common-emitter output transistors (Q10/Q12) set up for push-pull on a single-ended output. The two collectors are set a fixed voltage apart by two zeners (D4/D5), and the "final" output signal is taken from the middle of that. There's local negative feedback here added, not just by the emitter resistors (R56/R44), but by some resistors & a diode string (D6-D8/R30/R49) from the output back to the NPN emitter.This final output is sent to two pins on the connector; this is likely the amplified deflection(?) signal.Pulse GeneratorThat amplified deflection(?) signal from the previous stage enters at the left here. Besides going to the external connected, it also gets scaled down and compared against two different thresholds (one negative, one positive) by an LM119 dual (fast 80ns) comparator. Each output (at TP30, TP33) is low when the signal is within these -14V to +16V bounds. The AND gate (U2C) provides an external digital indicator that the deflection signal is inside this range.The rest is a little more complicated, with two one-shots and some more AND gates. Darlington pairs are used to alternately drive either side of the center-tapped pulse transformers.Here's what I think it does:When the deflection signal is within the -14V to +16V, nothing happens.When the signal goes < -14V, the top pulse transformer's output goes positive (arbitrarily-assigned polarities). When the signal re-enters the -14V to +16V range, both pulse transformers give a negative pulse (3 µs, set by U1B).When the signal goes > +16V, the bottom pulse transformer's output goes positive. When the signal re-enters the -14V to +16V range, again, both pulse transformers give a negative pulse.The purpose of U1A seems to be to guarantee that the negative pulse happens, even if the deflection signal goes outside these bounds very briefly.Now, why? I don't know. I don't know if the deflection signal is a raster signal (like on broadcast TV: nice predictable sawtooth), or if it's a vector display (so constantly changing and less predictable). This circuit section seems like it might detect either (1) an embedded synchronization pulse for timing of some other display circuitry, or (2) some inherent feature of the deflection, like a re-trace pulse, to again synchronize with some other part of the display system.

author: jwet
author_rank: Frequent Contributor
timestamp: June 09, 2025, 07:16:37 pm
content: I designed US Sub stuff during this ERA (mid 80's to mid 90's). Here maybe is a bit of background.The two mother spec's for all this equipment was MIL-C-23200 for serious stuff, reactor controls etc and MIL-C-16400 for environmental and rad monitoring type stuff. I think 16400 was the spec for Diesel boats or what was left of them of that ERA. These were good specs, things were built really solid and were pretty easy to work on. 23200 stuff had led's on every power rail on a board by board basis, had remoted test points that came out to a panel, etc- nice to work on. 16400 was tamed down and emphasized COTS and simplicity. A lot of the equipment specs had a short MTTR (mean time to repair) that was demonstrated in first article testing. This created a systems had a bunch of BIT or BITE (built in test) to detect and isolate error with simple flow charts in the tech manuals. BIT was kind of a mixed blessing- it added complexity and could give false warnings, etc. What the Navy was trying to do was a good idea but difficult. They wanted to minimize removing equipment to send to a depot level repair. All this modular equipment could be fixed on board or at worst alongside a tender. Stuff is really jammed into a sub and removing stuff is a mess.The module format you show is some kind of what was called a "SEM", standard electronic module. These had a standardardized size and connector and backplane- ironically, they're were about 4 different families as electronics was advancing fast in the 80's. The AN-BSY-1 Sonar was built with thousands of these and Navsea was trying to standardize on them to simplify logistics. We built an APD, air particulate radiation monitoring system (IM-239) that used them- about the size of a dishwasher- subs had 3 aboard in different area. Our processor was cigar box sized made up of a back plane and SEM modules. The small ones were about 2 x 2" and had a few MSI TTL IC's on them- conformal coated with a nice connector and a card puller rail. Our system used a dozen of these and then had one double wide double height module that contained an 8 bit microcontroller (8048) and some memory, etc. This was "our" SEM- the idea was you'd use 90% standard stuff and have one custom SEM. The back plane on ours was COTS and wire wrapped originally but converted to a PCB after the first 100 units. The rest of the system was built with large modules that could be replaced easily. (LRU's- line replaceable units.) I think there were 8 LRU's, a detector, high voltage preamp, paper feed, vaccum pump, control box, etc. All could be replaced easily.The whole methodology was sort of flawed. The highest failure rate item in a system are always mechanical and especially connectors. This system had tons of connectors, many more than would be otherwise required. Even though they were really nice connectors, they were a bad design choice. When you add in that salty, diesel, musty air of a sub, connectors were the bane of these systems. Our techs used drums of deoxit and cleaning sticks.What I imagine that this system's functions as the input for a periscope camera system. Its likely that were two two cameras in the main retractable mast for redundancy. That circuitry with comparators and MSI logic are sync detection (BIT) to detect camera failures. Something like a National LM1881 would have been nice but this wasn't made in a military version. Some of the other stuff looks like switchover stuff and a system to generate just a blank screen on loss of signal instead of snow. This would be called a blue screen generator in modern color parlance. The mystery component is likely an adjustment to boost or cut high frequencies on the final output to compensate for coax loss at high F. This is called Tilt I think. Equipment of this era completely banned pots or any analog type adjustments. There had been some study that showed the life cycle cost of a field adjustable pot as some astronomical number between training and test procedures. Equipment sometimes included pots as a factory only adjustment as a last resort. We had some places where resistors were paralleled and install at final cal and test to avoid any pots.Interesting task and great work on the pics and schematics.

author: D Straney
author_rank: Frequent Contributor
timestamp: June 10, 2025, 04:48:11 pm
content: Wow, that's great context, and interesting hearing about your own experiences with this stuff. On the subject of corrosion, I once opened up a friend's not-very-old salt lamp (just a hollowed-out salt crystal sitting around a standard lamp base) to add an inline switch, and was surprised to see that the steel parts had corroded almost to oblivion, and the copper in the lamp cord was green all the way up to the plug - I guess ambient humidity was enough to spread around the salt and do some serious damage. Obviously there wasn't any gold/nickel plating or conformal coating to help out there, but still, can only imagine the state of those connectors.I think I've seen some modules like you describe in various scrap auctions, not very large and with the same connectors, sometimes a little bit of circuitry and sometimes only one large IC...good to know what they are now. Deciding on level of modularity and built-in-test seem like the big philosophical hard-to-nail-down questions for a design, that I've definitely struggled with. Have seen things which err on the too-little side of testability much more often, so it's more of a unique experience seeing things which err on the too-much side, where the amount of board area for test circuitry starts approaching 40% (once you include all the resistors sitting in series with the many testpoint connections). I did once see a co-worker build a piece of custom test equipment though which had a whole ARM-based MCU board just for monitoring the (few) voltage rails in the system and display the voltage & current readings on some internal displays - thought that was pretty excessive.