The Tech Blog

Boat Rocker Headphone Teardown and Fault Diagnosis

Posted under DIY, Hacks, Repair, Teardown on June 19th, 2022 by Amaldev

A friend of mine dropped off a pretty old pair of wireless Bluetooth Boat Rocker headphones which were not working. The power LED turns ON but it’s unresponsive after that. Opened it up and first did a charge test with a USB current meter and found that there was no current taken from the power supply. That’s usually bad news, as that could potentially mean that the battery is bust or the main chip is blown. I opened up the battery compartment and there was no bulging of the battery. The battery was showing voltage, which was slightly low, but nothing too concerning. Then I desoldered the battery and connected a spare battery right on the PCB. Then plugged in the USB meter and voila the new battery is charging. Turned out the culprit was a faulty positive battery wire running all along the headband. It had no continuity and it was broken in between. Replacing that thin wire should get the headphones backup. The device wasn’t turning ON as the main chip couldn’t detect the battery due to the broken wire, even though it was getting external power.

Coming to the circuit analysis, these BLE headphones contain a Bluetooth chip from the Taiwanese manufacturer Airoha (AB1510). It’s a DSP chip with 48MIPS. It has all the bells and whistles for audio input, processing and outputs. It has a BLE PCB antenna. The great part of this chip is a built-in battery charge controller capable of charging at 400mA with protection. This eliminates the need for an external charging circuitry altogether. I couldn’t find a pricing for these chips though. If anyone knows please do comment. The other main IC is 24C128A, which is a 2-wire Serial EEPROM from Microchip to mostly store audio presets I suppose. The LiPo battery has a capacity of 450mAh. All in all, a reasonably well-designed headphone.

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Advanced: Semi-Additive PCB(SAP) Manufacturing

Posted under Educational, Technology on June 12th, 2022 by Amaldev

It’s a relatively new PCB manufacturing tech on the market. It is used in ultra-high density PCBs that have a very high premium on space. To understand SAP, first you need to understand the traditional PCB manufacturing process. In a simplified overview, a traditional PCB is made by taking a substrate with Copper already present on it, then you do pattern masking based on the Gerber files that your PCB software provides and then you do chemical etching to remove copper in all areas where PCB tracks and lines are not needed. It’s a subtractive process.

Now the problem with this tech is that since Copper layers are relatively thick, etching away Cu can limit the thickness of the lines. You cant usually go below 3-4mil in thickness of tracks, if you do go thinner, you have the risk of Cu tracks being totally etched away and the track can be broken at places. For very high-density PCBs, designers would want to go below the 3-4mil limit(Think about high pad count BGAs) that’s where SAP shines.

In SAP, rather than taking board with Cu already on it, they start with a substrate. They add pattern masking and do something called as deposit Cu Electroless process. That’s just a fancy way of telling that Cu is deposited on a surface chemically(Not using electricity like electroplating). The advantage of this is that you can create a very thin uniform layer of Cu. Now if you need to remove some parts of Cu so readily do that because your Cu layer is very thin and removes easily. With this tech, you can potentially go to PCB track widths of 1mil(25um) or below.

Since the conventional etching process is not there, you get straight sidewalls(Think in 3D of a PCB trace) with much finer impedance control for those PCB traces(Usual processes may create trapezoidal sidewalls due to over-etching and a has +-10% impedance variation on tracks). This tech is being used by Apple and Samsung in their designs in last 3-4years to make their circuit boards smaller and reduce the layer counts on the PCB. They use something called modified SAP (mSAP) which is a mix of traditional and the new SAP tech(It’s too big to be explained in this post)

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