Teardown – Experimental Engineering

Posted on April 3, 2020February 1, 2020 by The Engineer — 1 Comment

NEC LT-25 DLP Projector Autopsy

Time for another projector! This one was brought to me with a fault, described as a shadow in the middle of the image, shortly after the lamp was replaced after exploding. This is an older DLP projector, with a UHP mercury lamp. I’ve already removed the top cover of the projector here, showing the internals. The light engine is along the front of the unit, with the lamp on the right. The main control board on top contains all the image processing logic & control functions.

The other side of the mainboard holds the processing chipset. This is probably one of the biggest flip-chip BGA packages I’ve ever seen, the DDP2000. Along with the DAD1000 on the right, these format & send the image data to the DLP chip, via the large white header.

After the mains PCB is removed from the chassis, the rest of the light engine is visible. The DLP is hidden on the left, behind the large heatsink & interface PCB. The light engine is spread out a lot more on this projector, across the entire front of the unit.

A closeup of the light engine shows the back of the phase sensor for the colourwheel, and the mounting brackets for the optics.

The dichroic colourwheel is tucked into the gap between the lamphouse & the first optic.

Hiding at the back of the projector is the alloy frame holding the power supplies & cooling ducts.

After removing the brackets, the DC power supply & the lamp ballast are visible. Since this projector uses a UHP arc lamp, the DC power supply which has the usual low voltage outputs for the logic board, has an auxiliary output from the +340v rail after the PFC circuit that supplies power to the lamp ballast.

The lamp ballast is a pretty standard design, using an Osram control board.

After removing the top cover with the colourwheel, the main optic chain is visible. The usual mirror tunnel homogenizer at the start, with a convex & aspheric lens on the left.

The lamphouse has a last-resort thermal cutout to shut the ballast down if the cooling fans fail. These lamps output some serious heat, and likely wouldn’t last longer than a couple of minutes without cooling.

The final turning optics before the DLP chip are hidden in the Mg casting of the light engine.

The DLP is the older type, with the large ceramic LGA package.

After the DLP, the light is routed through the objective lens, to the screen. This is the back of the lens inside the light engine.

And here is the main problem with the projector – the last lens in the optical chain before the DLP chip has been roasted by the intense light flux from the lamp. Unfortunately NEC cheaped out on this one – it’s the only optic in the machine that isn’t made of glass. This was likely caused by some contamination on the lens, which starts the process of absorbing light on the surface. The resulting heat then causes discolouring of the lens, which absorbs more heat. A chain reaction ensues, ending in the lens completely destroying itself.

The projection lens has a couple of sensors, for the focus & zoom, along with a focus motor. This is driven by feedback from a distance sensor in the base so no manual focusing is required.

Posted on February 25, 2020December 21, 2019 by The Engineer — Leave a comment

Oil/Fuel Transfer Pump Teardown

Yet another wonder of Chinese mass-production, this is a cheap (£10 shipped) oil/fuel transfer pump from eBay. Primarily intended for removing oil from engines through the dipstick tube, these are usually sold for all kinds of pumping uses. As will become clear, pumping highly flammable liquids with these might just be a bad plan. Power is supplied through a pair of croc clips, from a 12v battery. Power consumption is quoted at 5A, with a max runtime of 30 minutes.

The coiled cable runs into the back of the plastic housing, where a power switch is also mounted. There’s some ventilation holes, but nowhere for air to flow in at the other end. Smart.

Removing the 4 screws on the front cover allows the pump unit to slide out, this is just held in place by the clamped halves of the housing on the rubber grommets on the pump ports. This is definitely a positive-displacement pump, as would be required to be self-priming.

The pump is driven through a gear reduction from the motor.

The motor itself is a bog-standard brushed type – and the reason why flammable liquids such as Petrol should not be pumped with this unit. It’s not ignition protected by any stretch of the imagination, and my guess is the shaft seal isn’t brilliant. So any combustible vapour around the motor is going to be ignited quickly by the sparking brushes on the commutator.

Removing the front cover reveals the pump’s innards. It’s a sliding vane pump! The vanes themselves are made from copper-plated steel, the rotor looks to be metal injection moulded from iron or steel. As the housing is a soft alloy – probably Zinc or Aluminium – I would predict that the steel vanes will make relatively short work of the housing, rather rapidly wearing away the inner surface. Only time will tell on this one.

The rotor is only slipped onto the shaft splines, and comes out easily. The shaft itself does have a seal.

Posted on February 15, 2020October 20, 2019 by The Engineer — Leave a comment

Chinese LED Projector Teardown

Another Chinese eBay teardown! This is a “720p” LED projector, available from nearly everywhere for very little cash. But they are very little cash for a reason – they’re total shit. The resolution as stated is a blantant lie – the LCD panel used in these is usually around 320×240, nowhere near the 1280×720 as stated. Being small & portable, there’s very little lighting power available, and they barely work to a level watchable without eye strain even in a completely dark room. You literally get what you pay for! Above is the projector with the top removed, showing the main board, which is fairly densely populated.

The main processor appears to be an MST3M182VGC-LF-Z1, a SoC designed specifically for LCD TV applications. This runs the internal firmware from a serial flash, a PN25F32 32Mbit (4MB). As this projector has the capability to play files from USB & SD Card, as well as from A/V inputs, there’s an Alcor Micro AU6438BS USB 2.0 Single LUN Flash controller on the right to deal with the MicroSD slot interfacing. The left top corner of the board is completely dedicated to power control, with various switching converters & transistors.

The bottom of the board is also dedicated to the remaining portion of power control – more switching regulators here generate the voltage rails required for the SoC, along with LED drive.

Removing the board allows access to the optical components of the projector.

Here the LED module has been removed from the casing, better showing the optical arrangement. There’s a Fresnel lens, then a polariser, the LCD panel itself, another lens, then the final turning mirror to the objective lens.

Here the rest of the optical components have been removed, showing the objective with it’s helical focusing track, which moves the lens, and the turning mirror. Behind the mirror is the pitiful speaker.

Here the main components are laid out, with lenses either side of the LCD & polariser.

Now onto the light source of the projector – the LED module. This is buried inside the module with a conical reflector, and a small heatsink on the back.

Removing the reflector shows the LED itself, with a thermal fuse in series for protection. The LED is screwed to the aluminium heatsink for cooling – my guess is this is roughly a 6W LED, with 3 series pairs of dies in parallel.