Here's an interesting eBay cheap-avionics find: a used aircraft CDU from 1994, made by Teledyne Systems. (Control Display Unit: basically the main computer UI from what I understand)
From looking up the part numbers, it looks like this model was made for the US S-3 submarine hunter aircraft:
https://en.wikipedia.org/wiki/Lockheed_S-3_VikingAfter taking off the back cover, you can see a few different cards inserted into (as expected) a very nice frame for conduction-cooling the electronics:
Now, going through the cards in order...
Analog boardThis has a mixture of misc. digital logic and resistor arrays (likely as pull-ups/pull-downs), with an analog section in the middle. The part marked "PMI" (Precision Monolithics Inc., now part of Analog Devices) is an 8-bit DAC with a current output. The 8-pin DIP to the left of it is a high-speed op-amp, which likely is set up as a transconductance amp for current-to-voltage conversion, and then the large metal can is a power op-amp that can drive up to 200 mA. I don't know what external load exactly this would be driving: maybe some kind of (very very small) actuator, an unusually large analog gauge, or a reference signal to other equipment?
The resistors (presumably used as feedback for the power op-amp) are interesting too because they're encased in glass, and you can see the spiral cuts on the metal film inside that increase the length of the current path:
I could imagine that maybe these resistors are enclosed in transparent glass, rather than the normal potting with epoxy, so that they could be laser-trimmed after leads etc. are attached, for extra-tight final tolerance (as mechanical stresses from the rest of the resistor manufacturing process likely would shift the resistance somewhat). I don't really know for sure either way, though.
ICs:- JM38510/32403BRA = 54LS244: 8-bit buffer with 3-state outputs
- JM38510/37501BCA = 54ALS32: quad 2-input OR gate
- JM38510/32803BRA = 54LS245: 8-bit bidir bus transceiver with 3-state outputs
- JM38510/30903BEA = 54LS157: quad 2:1 digital mux
- JM38510/37001BCA = 54ALS00: quad 2-input NAND gate
- JM38510/30701BEA = 54LS138: 3:8-line decoder (is this doing address decoding here?)
- SNJ54ALS576AJ: octal D-FF inverted-output
- JM38510/11302BEA = DAC08: DAC 8-bit, multiplying 1 Mhz, 85 ns settling, compl. current outputs
- 5962 8962703P H0C9230 = HA7-5147/883: op-amp 100 Mhz low-offset (100µV), stable with gain ≥10
- LH0041G: 200 mA output power-op-amp
Comms boardThis board seems to be for external communications, as it has two separate explicitly-labeled MIL-STD-1553 transceivers (a common serial bus used on aircraft and in military applications). It looks like there's two separate channels, as there's two sets of...
- Pulse transformers (used for isolation of the serial bus)
- Physical-layer transceivers in metal cans
- Manchester encoder/decoder ICs specifically made for MIL-STD-1553 (the 7802901JA)
There's also a very nice, very wide ceramic DIP which turns out to be a 16-bit microcontroller, likely for offloading the communications tasks from the main processor:
There's also two mystery chips with many connections to the bus connector: wasn't able to find anything for the part number so these likely aren't off-the-shelf standard parts, but "62458" turns out to be the CAGE code for Raytheon, so these are probably some sort of custom or aerospace/military-specific parts. Best guess is that they handle backplane bus interfacing?
ICs:- M38510/21004BJA: PROM 2Kx8
- 8550201XA (large purple DIP): MCU 16-bit TTL
- (Metal can to its left is most likely 24 Mhz oscillator)
- 7802901JA: Manchester encoder/decoder & synchronizer for MIL-STD-1553
- HE1025-0-G-002: ?
- 5962-8605201 = MM54HC30: single 8-input NAND gate
- JM38510/33001BCA = 54F00: quad 2-input NAND gate
CPU boardThis is the only board which is listed as "programmed" on the label, despite the microcontroller on the comms board:
First, the non-processor items: this board has the expected EEPROM (program memory?), RAM, and misc. glue logic - both standard TTL, and programmable, as with the PAL device in the corner and the larger "SEEQ" device, where I was only able to find vague references to the part number.
The CPU itself is an MD8085, which looks like it's just the mil-spec version of the normal Intel 8085 8-bit processor: something with consumer electronics that you would've expected to see only in the 80's, but makes sense with the low processing power requirements, long design cycles, and slower qualified part availability. There's also a microcontroller though, the MD8748H: no idea what the "division of labor" is here, but best guess is that it handles low-level repetitive tasks that otherwise would steal too much time from the main processor, like keyboard scanning?
There's two similar-looking Raytheon(?) chips here too, with different part numbers but again maybe for bus interfacing? The fact that these appear on both the CPU board and the comms board convinced me that the two copies on the comms board didn't correspond to the two MIL-STD-1553 channels, and that they weren't related directly to the serial connections.
ICs:- MD8748H: MCU 8-bit MOS
- 7136799-1 / DM2817A-250: programmable logic?
- PAL...: programmable logic, erasable
- (Metal can is likely 12 Mhz oscillator)
- CY7C186A-45: SRAM 8Kx8
- 7901001QA / MD8085AH: CPU 8-bit 3 Mhz 8085 https://www.cpu-world.com/CPUs/8085/Intel-MD8085AH-B%20(7901001QA).html
- JM38510/22402BYA: EEPROM?
- HE0904-0-G-002: ?
- JM38510/34001BCA: quad 2-input AND gate, "F" family
- JM38510/33002BCA = 54F04: hex inverter
- JM38510/32403BRA = 54LS244: 8-bit buffer with 3-state outputs
- JM38510/32401BRA = 54LS240: 8-bit inverter with 3-state outputs
- JM38510/32803BRA = 54LS245: 8-bit bidir bus transceiver with 3-state outputs
Power supplyThis (shielded) power supply most likely steps down the aircraft power to run the 5V supply that drives all the old power-hungry digital logic. There's a UC1845-equivalent PWM controller, a single MOSFET (helpfully marked "G D S"), then two dual-diode(?) packages and two transformers or inductors. With the single MOSFET, my guess is that it's a forward converter driving a transformer (left-most magnetics) with the 2x dual diodes used as a full-wave rectifier, feeding a buck inductor (right-most magnetics). The additional diodes could be for snubbers, or there could be an additional voltage rail that it produces.
The arrangement of 4 individual diodes though does look suspiciously like a (lower-current) full-wave rectifier:
...and some of the metal cans could be transistors used as linear regulators (couldn't find what the larger can is, the smaller one with the Linear Technology logo seems to be a voltage reference):
The passives "standing on their head" against the metal I'm guessing are small inductors used for output filtering.
The DIP-14s are just LM139 equivalents, quad comparators, probably used to do UVLO/OVP/"power good" indication or sequencing of multiple power rails.
Power supply / EMI filterThis one's the chunkiest one by far, and responsible for most of the weight.
When I looked up the part number of the big metal box on this board, it was listed as an EMI filter, however I don't think that's the full story. From the weight of this assembly I originally thought it was a transformer, and the only power supply onboard. Unless it had some really, really serious low-frequency-suppressing chokes or had to deal with massive currents I would never expect an EMI filter to be this heavy; plus, it lists output voltages that don't appear on the input (70VAC and 18VAC). The 28VDC inputs and outputs are unconnected, but the 115VAC input and 5VAC input/output are used: so it looks like it gets 115VAC & 5VAC externally - I've heard (but don't remember where from) that 5VAC is a common aircraft lighting thing? So maybe that provides the backlights for the keypad?
There's a bridge rectifier and bulk capacitor hidden at the corner, but otherwise that's it for this board:
There are some unused footprints, which may be for inrush control or something like that:
This board also acts as a pass-through for a bunch of external I/O from the circular connector(s) directly to the backplane. I do like the aesthetics of multi-layer boards where you can see traces buried at different levels inside, like mountain ranges slowly fading into the distance:
Powering up?As everything looks intact, I was hoping I could turn it on and check that the display works at a minimum, maybe overwrite the internal program (if the CPU situation was nice and simple...which it's not) or figure out the display/keypad connections to swap out the CPU card as wall art and hook up something of my own to use the whole thing as a UI for something else.
Would've been very helpful if the "EMI filter" was really only an EMI filter, as in that case I could provide a DC supply directly to the output of the bridge rectifier on that board, and power up the system that way: however, because of the step-down action implied by the labeling, and the fact I couldn't find continuity from the 115VAC input terminals to any of the output terminals, it looks like that part really is a transformer. So that means that further installments are going to have to wait until I can put together some kind of simple 400 Hz AC source to actually drive the input power connections properly.