conformal coating – Experimental Engineering

Posted on February 9, 2017February 9, 2017 by The Engineer — 3 Comments

Anker PowerPort Speed 5 USB Rapid Charger Teardown

Here’s a piece of tech that is growing all the more important in recent times, with devices with huge battery capacities, a quick charger. This unit supports Qualcomm’s Quick Charge 3 standard, where the device being charged can negotiate with the charger for a higher-power link, by increasing the bus voltage past the usual 5v.

The casing feels rather nice on this unit, sturdy & well designed. All the legends on the case are laser marked, apart from the front side logo which is part of the injection moulding.

The power capacity of this charger is pretty impressive, with outputs for QC3 from 3.6-6.5v at 3A, up to 12v 1.5A. Standard USB charging is limited at 4.8A for the other 3 ports.

The two of the 5 USB ports are colour coded blue on the QC3 ports. The other 3 are standard 5v ports, the only thing that doesn’t make sense in the ratings is the overall current rating of the 5v supply (4.8A), and the rated current of each of the ports (2.4A) – this is 7.2A total rather than 4.8A.

The casing is glued together at the seam, but it gave in to some percussive attack with a screwdriver handle. The inside of this supply is mostly hidden by the large heatspreader on the top.

This is a nicely designed board, the creepage distances are at least 8mm between the primary & secondary sides, the bottom also has a conformal coating, with extra silicone around the primary-side switching transistor pins, presumably to decrease the chances of the board flashing over between the close pins.
On the lower 3 USB ports can be seen the 3 SOT-23 USB charge control ICs. These are probably similar to the Texas Instruments TPS2514 controllers, which I’ve experimented with before, however I can’t read the numbers due to the conformal coating. The other semiconductors on this side of the board are part of the voltage feedback circuits for the SMPS. The 5v supply optocoupler is in the centre bottom of the board.

Desoldering the pair of primary side transistors allowed me to easily remove the heatspreader from the supply. There’s thermal pads & grease over everything to get rid of the heat. Here can be seen there are two transformers, forming completely separate supplies for the standard USB side of things & the QC3 side. Measuring the voltages on the main filter capacitors showed me the difference – the QC3 supply is held at 14.2v, and is managed through other circuits further on in the power chain. There’s plenty of mains filtering on the input, as well as common-mode chokes on the DC outputs before they reach the USB ports.

Here’s where the QC3 magic happens, a small DC-DC buck converter for each of the two ports. The data lines are also connected to these modules, so all the control logic is located on these too. The TO-220 device to the left is the main rectifier.

Posted on November 16, 2016 by The Engineer — Leave a comment

Mercedes Benz Temic Central Locking / Immobilizer Module Teardown

The other day I was given a random pile of car electronic parts from the scrap bin at the local garage, so I decided to do a few teardowns. This first one is a Temic Central Locking / Immobiliser module from a Mercedes van. Judging by the 125kHz stamped on the label, this also has RFID capability.

The casing just unclips, revealing the PCB. Surprisingly for an automotive module, there is no conformal coating on this (they’re usually heavily coated in protective lacquer to prevent moisture ingress).

The large IC from Motorola I’m assuming to be a microcontroller, but I didn’t manage to find anything from the markings. There’s not much else in here apart from some glue logic, and what I think is the 125Khz toroidal antenna in the top left corner.

Posted on July 2, 2016 by The Engineer — 2 Comments

Eberspacher D5W ECU Constant Overheat Error

Here’s another Eberspacher control unit, this time from an ancient D5W 5kW water heater. The system in this case is just flaky – sometimes the heater will start without fault & run perfectly, then suddenly will stop working entirely.
The error codes are read on these very old units via an indicator lamp connected to a test terminal. In this case the code was the one for Overheat Shutdown.

Considering this fault occurs when the heater is stone cold, I figured it was either a fault with the sensor itself or the ECU.

The temperature sensor is located on the heat exchanger, right next to the hot water outlet fitting. I’m not sure what the spec is, but it reads exactly 1KΩ at room temperature.

The PCB is held into the aluminium can by means of crimps around the edge that lock into the plastic terminal cover. Inserting a screwdriver & expanding the crimps allows the PCB to be slid out.

The factory date stamp on the microcontroller dates this unit to March 1989 – considerably older than I expected!
Unlike the newer versions that use transistors, this ECU has a bunch of PCB relays to do the high current switching of the water pump motor, fan motor & glowplug.
Overall the board looks to be solidly constructed, with silicone around all the larger components.

Here’s the solder side of the PCB, which has a generous coating of sealant to keep moisture out.

Looking at the solder joints for the row of relays on the top side of the PCB, it looks like that there’s some dry joints here.
I suspect that years of vibration has taken it’s toll, as the relays are otherwise unsupported. It wouldn’t be possible to use silicone to secure these devices as they are completely open – any sealant would likely stop them from operating.

Using a very hot soldering iron I managed to get the joints to reflow properly, using lots of flux to make sure the conformal coating didn’t interfere with the reflow.