Philips Norelco beard trimmer disassembly and battery replacement

My trusty (yet old) beard trimmer has needed to be plugged in to use for a long while now, but the batteries finally degraded so much (I suspect they were a direct short) that even plugging it into its charger failed to make it work. So, I took it apart and replaced the batteries. (They needed it, I believe they were from 2001.)

This video distills what I learned (the hard way) about the proper order of operations for disassembling this model to get to the battery to replace it.
This trimmer is from the 2001-2002 era, and I couldn’t find any model number markings on it, or photos that looked like it on the internet, so if you can identify the specific model number, please shout out in the comments…

Tektronix PWS4721 power supply teardown / diagnostics / repair

I broke my PWS4721 power supply by connecting it to a battery and driving current back into it. (I don’t remember if I reversed the polarity, or just had the output voltage lower than the battery voltage.) The end result was that the power supply had it’s output shorted internally, so that the output voltage was always near zero, and the current was right at the maximum current limit but no power was coming out of the front (or back) connections.

The broken component turned out to be Diode D408 on the main circuit board right in front of the power output header. It appears to be a reverse polarity protection diode, so it’s likely that I accidentally reversed the leads when connecting to the battery (all I remember is the spark). This diode is a 1N5408 (general purpose 1000 volt 3 amp diode) which I was able to replace for $0.40 (Although my total cost was closer to $10, as I ended up buying 10 of them just to have a few more sitting around if needed, and shipping cost me $4.33 from Digikey.) The only specialized tool I needed was a Trox-10 (t-10) screwdriver to remove the security (star) screws from the factory maintenance port so I could remove the back panel.

Of course, I had to disassemble the entire unit to get to the bottom of this circuit board to make de-soldering and diagnosis easier.  The output power rails were shorted before I removed the diode, and were NOT shorted after I removed it, and the diode had failed shorted, conducting in both directions.

In retrospect, I could have probably desoldered the diode in place from the top of the circuit board (the long lead would have been easy, and since the diode was already ruined, I could have heated up the body and pulled the whole thing out from the top and then replaced it without removing the entire circuit board. But, at the time, I wanted access to the rest of the circuit board just in case the diode wasn’t the (only) problem.

You know it’s a high quality piece of equipment because in addition to checking that it worked, they let it burn in to find out if any parts were going to fail quickly, and then calibrated it!

If you want to see how to tear down a PWS4721 and what is inside, here is the video:


And a few photos of the main board with heatsync and top logic board:


NES Classic 500 in one game console controller pinout

I had to repair the cable on one of those “500 in one classic game consoles” that look like a mini Nintendo Entertainment System (NES) but don’t actually say the “Nintendo” trademark on them anywhere.
An example can be found on Amazon here:

The order of the wires inside the controller on the PCB (NES01-JOYV1.1) is (from left to right): orange, yellow, blue, brown, white

The pinout for the wire colors at the end of the cable is as follows:

My Glowforge Lid Handle Fell off!

I went to use my Glowforge laser cutter today, and when I tried to open the lid the handle fell right off onto the floor!  This wasn’t the first failure I was expecting from this device! (I figured the laser tube would die, or something to do with the electronics would fail…but no, the glue used to attach this metal and plastic handle piece to the safety glass that makes up the lid just let go!)

Unfortunately, the lid handle has some wires running to it (for the “lid closed” sensor I assume) and now my glowforge thinks the lid is open all the time and won’t do anything. The lid handle has two wires on each side that normally plug into sockets on the end of the LED light bars on the left and right side of the lid. The one on the left nicely unplugged itself when the lid fell, but the one on the right pulled the socket off of the lightbar, and would require at a minimum some soldering to reattach the socket to the light bar PCB.

As my warranty has expired, Glowforge offered to charge me $200 for round trip shipping of the unit to and from their repair location, and after they receive the unit they will tell me how much a repair would cost (if a repair is possible.) The customer service email said that they couldn’t repair the part in the field as some of the parts that would need to be replaced require calibration which they can’t do in the field. (I assume they were speaking about the camera mounted on the underside of the lid. They may have mistakenly thought that the lid had separated from the hinge in the back, but I guess if they replace the lid entirely instead of just attaching the handle again they would need to re-calibrate that camera to the rest of the laser cutter.)

Since a brand new cheap Chinese K40 laser cutter only costs $400-500, I decided to attempt this repair on my own. After laying out a moving blanket to protect the laser tube from errant solder drops, I was able to solder the socket back in place with only a few scorch marks on the shiny white PCB.


I plugged the lid closed sensors back into the sockets, held the handle onto the lid while closing it (the weight of the lid keeps the handle in place when closed) and my Glowforge operated as normal!  The only thing remaining is to determine the right type of adhesive to permanently re-attach the handle to the lid. Glowforge support understandably didn’t want to go on record with a specific recommendation for this unauthorized DIY repair, so I went with JB Weld (Clear) 2 part 5 minute epoxy. So far, the handle remains attached to the underside of the glass lid.


Mechatronic system for an art project

A local artist asked me if I could build a mechatronic system that would cause “something” to emerge from a piece of art “every so often”. (I’m being vague as it’s not my idea to share.)

I suggested the addition of an PIR (passive infrared)  motion sensor so that the “something” could also react to the approach of people.

I am using a SparkFun Arduino compatible Micro-Pro board, due to its small size and built in USB port which can be used for both programming and power.  In the video and photos, I’m using a small 9g hobby servo, but I have also tested the same circuit with a standard 3003 size servo.  I am powering the SERVO directly from the RAW (red) and GND (black) pins on the MicroPro board (so basically, right from the USB power), and the control line (white) is wired to pin 3 on the board.

The PIR module has three pins. +5V, ground and signal. You provide it with power, and when it detects motion it raises the signal line (it even has a built in pull down resistor on the signal line).  I connected it’s (yellow) signal line to pin 5, and ran it’s black line to GND and red line to the VCC connection on the Micro-pro. (Which is actually tied directly to the USB power supply and doesn’t make use of the onboard regulator when the pro-micro is powered via the USB port.)

The code is a small arduino sketch that will sweep the servo when it detects motion, or every X seconds if it doesn’t detect motion, with a configurable “cool down” period after activating. You can download it here:

The entire circuit can be powered by a USB cell phone charger. I wanted to be able to make it battery powered simply by plugging in a USB powerbank, but unfortunately, the circuit doesn’t draw enough current when not moving the servo to keep most USB Powerbanks from shutting down due to their “low current auto power off” features.
There are a few USB powerbanks on the market which have an “always on” feature for use with low current devices such as webcams, but you can’t just power it with any USB powerbank.


Running our 240 volt Well Pump in a power outage

The last hurricane knocked out our electricity for 3.5 days. (Other people in our neighborhood were without power for 6+ days). I have a 120 volt inverter that I used to power our fridge, microwave and internet, but our well pump requires 240 volts.  It was really annoying to have to transfer water from our tub to the toilet tank to flush, and not be able to wash our hands at the sink or get water from the tap when we wanted to.

My wife has given me a $1,000 budget to expand our backup system so that we can run the well pump in power outages, and the first step is to figure out the actual power draw of the well pump.

The pump is powered off of a 20 amp circuit, so the maximum draw is 240v * 20A = 4,800 watts. I measured the actual continuous draw when the pump is running at just under 10 amps, or 10 * 240 = 2,400 watts continuous.  I will probably need to purchase an inverter with a surge rating of twice that to support the inductive surge the pump motor is likely to draw when it first turns on.

I hooked up an energy monitor to the pump circuit and monitored it for a few weeks. The energy monitor estimates that the well pump uses between 6-8 kWh of power over the course of a month, so I will only need 1-2 kWh of battery capacity to be able to run it for several days.

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First 5 months report & payback calculations – Grid Tie Solar System

Five months ago we turned on our new grid tie solar system and started to produce power.

Component Failures & Warranty Service
In the first five months, we have had two components replaced under warranty. The first was one of the 36 SolarEdge DC optimizer units (A $75 component with a 25 year warranty) that are mounted under each of the solar panels. The Solar Edge monitoring system had flagged that one of the optimizers was not reporting (and presumably also not producing power) and sent a message to our installer (3Guys Solar). They called me (before I even knew anything was wrong) and let me know they would be sending a crew out to climb up on the roof to replace it the next day, so that particular panel was only down for only 2 days. The other 35 panels continued to produce power.  The crew said that they sometimes have to replace several optimizers on a house, and some houses never have any fail.

The second component to fail was the system’s main DC->AC inverter, a 10kW Solar Edge grid tie inverter (a $2,000 component with a 12 year warranty). On October 23rd I noticed on the phone monitoring app that we had no power produced, so that night I went out and rebooted the inverter.  The next day, 3Guys solar called me to report that they had received a fault code from the Inverter via the Solar Edge monitoring system and were working with Solar Edge to try and resolve the fault. The following day they called again to tell me that they would need to replace the inverter under warranty. Unfortunately, it took close to two weeks to receive the replacement unit from Solar Edge, so we were not producing solar power again until the 7th of November.

It was concerning to have the inverter  fail within the first three months, but it is covered by a 12 year warranty, was replaced within two weeks and we haven’t had any problems since. 3 Guys Solar also sent us a check for $95 to cover the cost of the energy generation lost during this period. This is a limited time program, and was not part of their original install contract, so the check was not expected but appreciated. (By my estimates they overpaid us by 20-30$ for the energy the system wasn’t producing while the inverter was down.) The warranty coverage by 3Guys Solar (the installer) and Solar Edge (equipment manufacturer) left nothing to be desired.  My expectation is that with solid state electrical equipment like this, most of the failures that are going to happen will happen early in the life-cycle (or very late in the lifecycle), and I hope the equipment will be stable now that we’ve gotten the early failures out of the way.

Power Generated & Usage

In this 5 month period, we generated 5096 kWh of solar power, and used 7405 kWh of electricity (paying for 2309 kWh from Duke, at a cost of $337.44 (-$95 credit from 3GS lowers this to $242.44)).


In the same 5 month period last year, we used and paid for 7378 kWh of electricity from Duke, (costing $977.81) so our usage appears to be closely correlated to before we had the solar system.

By averaging production between the week before and the week after, I estimate that in the 15 day period our inverter was down we should have produced an additional 540 kWh of power ( $70 of electricity at 13 cents per kWh). So without the inverter failure, we would have produced around 5636 of the 7405 kWh we used, or 76% of our total electricity usage via solar. [With the inverter failure, we were only at 69% of our power from the sun.] Our goal was to produce 80% of our electricity from the sun, so these numbers are close to our goal, and I hope that the sunny spring (and no more inverter failures) will raise our percentage.

From a cost perspective, because Duke Energy has a fixed customer charge, our solar cost savings is lower than percentage of power generated, and was a savings of between 65% to 75% off our electric bill.

Seasonal Effects on Future Predictions

Estimates made with less than a full year of solar data are going to be wildly inaccurate. The Aug->January time period is cooler than other months, so our AC usage will be lower, but there is also less solar production in the winter, meaning that our generation will be lower as well.  The following numbers are a guess, and are much less accurate than those I hope to calculate after the system has been working for a full year.

Over the same 5 month period last year, the solar system has saved us between $640 and $735 (depending upon if you add in the non-contractually obligated 95$ check that 3Guys Solar sent us).  This equates to an estimated payback period of  11 to 12.75 years.  (The 1.75 years, or 14% difference in payback time is driven by the 13% difference in cost savings that $95 check equates to over the 5 month period.)

If it turns out that our solar system produces a much higher percentage of our usage in the sunny spring months, or if Duke Energy raises their rates, this payback period could drop.  If we use too much AC in the summer, or Duke lowers their rates (?!?!) the payback period could increase. I’ll feel much more confident about the estimate after collecting a full year of usage and generation data. (And even then, solar generation and electrical usage can still vary year to year with the weather.)

Megatree Ball Topper

For Christmas 2017, I built a computer controlled RGB Pixel LED megatree around a pine tree in my yard. For Christmas 2018, I built a 48″ outside diameter “ball” topper for the tree. (It looks better when it’s pulled 20′ up the tree, and lit up at night…)

This was the first “large scale” project that made use of my Maslow CNC router to cut out a large number of parts (which took many hours) that bolt together in such a way that each individual part can fit into a 27 gallon tote for storage.

I think it actually took longer to cut out all of the parts than to paint them, but painting them with exterior house paint for some weather protection also took a bit of effort.

If you want my OpenSCAD files to make your own version, you can find it in this zip file:

And here is a video that shows off some of the animations I sequenced for 2018:

Orlando OTA Channels – 2018

A list of the digital over the air (OTA) channels I can pick up from the west side of Orlando.

  • 2_1 – WESH-DT (NBC)
    • 2_2 – Me TV
  • 18_1 – WKCF-DT (CW)
    • 18_2 – Justice
    • 18_3 – estrell
  • 35_1 – WOFL-DT (FOX)
    • 35_2 – Light
  • 24_1 – WUCF-DT (PBS)
    • 24_2 – Create
    • 24_3 – Kids
    • 24_4 – NHK
    • 24_5 – World
  • 45_1 – WTGL-DT (IND?)
  • 6_1 – WKMD-DT (CBS)
    • 6_2 – Cozi TV
    • 6_3 – Decades
  • 27_1 – WRDQ-DT (IND?)
    • 27_2 – Antenna
    • 27_4 – GRIT TV
  • 31_2 – WTMO-SD (Telemundo)
  • 68_1 – WEFS-HD (  far away station?)
    • 68_2 WEFS-CL
    • 68_3 WEFS-NS
    • 68_4 WEFS-FL
  • 15_1 – WDSC-HD (far away station?)
    • 15_2 – WDSC-ED
    • 15_3 – WDSC-WV
  • 9_1 – WFTV-HD ( ABC )
    • 9_2 – Laff
    • 9_3 – Escape
  • 55_1 – WACX-D1 (REL IND?)
    • 55_2 – D2
    • 55_3 – D3
    • 55_4 – D4
    • 55_5 – D5
    • 55_6 – D6
    • 55_7 – D7
    • 55_8 – D8
    • 55_9 – D9
    • 55_10 – D10
    • 55_11 – D11
  • 65_1 – WRBW-DT ( My TV)
    • 65_2 – Movies!
    • 65_3 – H&I
    • 65_4 – BUZZR
  • 52_1 – TBN HD
    • 52_2 – HILLSNG
    • 52_3 – COMBO
    • 52_4 – Enlace
    • 52_5 – Salsa

Optimizing Pokemon Go Gift Exchanges / XP from Friendship levels

The addition of Trading / Friends / Gifts to Pokemon Go has added an extra level of play (work?) to the game. These are my thoughts on how to optimize friendship and gift sending and opening.

My starting assumptions:

  1. The goal of exchanging gifts is to build up friendship levels as quickly as possible so that Pokemon trades cost less stardust. [I am explicitly rejecting the idea that the primary reason to open gifts is to restock items.]
  2. You have not yet reached level 40 (or still care about building up your XP) and are willing to use Lucky Eggs to increase the XP you receive from friendship level increases.  [If you don’t care about XP, optimizing Pokemon gift exchanges becomes much easier.]


The Simple System (for Level 40 Players)

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