Archive for the Electronics Category

Tivoli PAL won’t run on batteries unless you plug it in first…

Posted in Electronics with tags , on August 31, 2016 by marksun


This is a seasoned Tivoli PAL AM/FM radio which I love for its retro simplicity, great sound, versatility, and clean build.  These things don’t last forever and the years take their toll. For example, when I first got it (lightly used) I had to replace the battery pack with a home build 4-pack of NiMH AA cells soldered together. I removed deteriorating tacky blue rubber finish.   Now, recently, after considerable usage, even if the battery is charged, the radio won’t turn on until the power supply is plugged in. Once it is on, I can unplug the power supply and the radio will play from the batteries.  ???


I opened it up and found I can jump start the radio without the power supply plugged in by shorting two points on the Tivoli circuit board which I found by following the 7.3 V of the battery B+ and 13.8V of the external power brick. Without a schematic or desire to trace out the circuit I decided on a hack  with a miniature momentary switch that are becoming easy to get and widely used.  Turn the radio to FM (or AM) , short press the switch, and the radio turns on.

A not pretty solution but the radio works on batteries now, and life goes on.


Soldered #28 wirewrap leads to the two contact points  to and threaded the wires out the hole used for the external power supply.  The two wires were attached to the miniature switch. I borrowed one of the recessed screw tunnels for the switch seat.  Used BONDIC to hold the switch and wires in place.   Done.

Technical note.   I don’t know the underlying cause and did not isolate the bad component.  I suspected the big 2200 uF electrolytic near the  power input jack. One of the  shorting points is connectected to the positive lead of this cap.  Later experiments to replace the cap did not fix the problem.

Below, a better shot of the two leads for jump starting the PAL.  The lead on the right is soldered directly to the + pin of the C11, the 2200 uF cap.  The other lead is soldered to a trace which carries 7.2V from the B+ battery lead.


B+ and B- connect here (below)…  That 9 pin row above it are the pins from U5 – which so far is unidentified.




Above – top view of the board.  C11 is the 2200uF cap.

Update 1/23/17 : I unsoldered the 2200 and substituted a new 5500uF low ESR cap using jumpers to the solder pads, but that did not fix the problem.  I reinserted the 2200 to get back to square one.   1/31/17 – another experimenter tried replacement of the 2200 with a new one without result.

Status: no fix yet.

Miscellaneous :  The 7.2v batter pack connects directly to U5, a mystery component.  Some circuit seems to switch in the battery pack when the power switch comes on if there is not charger or external power applied.  The PAL has a fast charging circuit, and a trickle charging circuit which switch in automatically to charge the battery pack from a 12V source.  We’ll have to think about how that circuit works.

Here is a really good site: harrysradios.  Harry did a lot of work and had a serious go at reverse engineering the radio to produce schematics.  The schematic does not include U5 which would solve the mystery of the 7.2V battery circuit.
Unfortunately, no contact information.  Harry are you out there?

Please contact me if you have an idea or solution fix this problem on this very cool radio.


Amazon Fire TV remote issues, Android Fire TV Application Problems

Posted in batteries, Electronics, technology with tags , , , on May 2, 2016 by marksun


The Amazon Fire TV remote crapped out over the weekend. I have a feeling  Duracell AAA alkaline battery corrosion did it in.  I cleaned up a bit with iso and with Corrosion Block but no dice.  AA and AAAs  leak on you especially if there is a long term low current drain. Sometimes it’s just a shiny film and hard to see if you don’t really inspect the battery and battery compartment. The remote has telltale signs of corrosion around the batteries. Hard to tell what went wrong but I suspect a leaky battery burned through a trace in the battery compartment.

This event sparked a brief effort into learning a little about FireTV and FireTV remote apps.  I’ve dug up a few random bits of information about FireTV  workings underneath the opaque black plastic packaging.

Random factoids:

  • The earlier remotes used Bluetooth.  So you don’t have to point the remote at the TV? Seems like I had to but could be wrong about that.
  • After about October 2015, new FireTV remotes use wifi-direct and not Bluetooth.
  • I suspect the broken remote I have is the “old” bluetooth model.
  • The FireTV menu system provides a means of pairing more than one remote to the FireTV unit.
  • I have seen the Wifi-direct access point belonging to my FireTV show up on my phone’s wifi access point list now and then, but not consistently.  It shows a secure connection.  I have no idea what the password is to it or whether and why one would connect to it.
  • To their credit Amazon support will replace the remote. No warranty issue at all.

I did something like this picture – an exploded view of a remote control:


Warranty? What Warranty? Six screws, not four hold the remote together. To get at the other two you have to pry off a second plastic cover piece on the back of the remote.  It’s stuck on with two sided tape and also snaps in.   There are a few clues on google images..


Here is one way to pry that second plastic back cover.  The fifth and sixth screws are under this piece.  I used a small flathead screwdriver and didn’t break any plastic.  The double sided tape however…

Did I fix the remote?


It may be possible to repair an open trace caused by corrosion, but so much easier to call Amazon for a replacement.  Losing the remote is not the end of the FireTV I found.

Next- did you know that you can plug a USB keyboard into the Amazon Fire?   By chance I found I could control all the functions of the Fire TV this way ( I have the model that came with the remote and external brick power supply, not the “stick”).  So while I’m waiting for the remote, this will keep us connected to the big screen TV for Netflix.  Hint. You use the TV screen as the monitor see and set the TV input to the AmazonFire HDMI port.  There is some mumbo jumbo about the USB port being for developers.  That’s a bit further than I want to go with this.

Next – The Amazon FireTV app… …  the obvious alternative to the Amazon TV remote control is to use the Android device with the FireTV app.  This normally worked well,  I’ve used it on and off for a while,  and only recently on my phone, but today I managed to kill the app somehow.   The symptom … the app begins with the “elect a Device to Connect and Searching for Fire TV devices,  but cannot “find” the FireTV device.  The “Troubleshooting” link suggests rebooting android device, rebooting the FireTV (restart), deleting all data from the FireTV app,unistalling and reinstalling the app, multiple power cycles of the FireTV.  No dice.  ( I did not do a factory reset of the FireTV – it can be done with the USB keyboard for example if you don’t have a remote.)

Several hours later …

The app is working again.  Why?  I don’t know.  I decided to try it, then for the sake of form,  power-cycled the FireTV.  Suddenly the device showed up on the app and we’re in business.  There is still an issue with the app finding the FireTV device.  Or having found it, it Cannot Connect. The app is unreliable now.

But what is the cause of the app failure? What changed?

I wonder if this is a software problem in the FireTV …  gotta be.  The user can do nothing.  There don’t seem to be any easy ways to pry open the software like you can the remote control case.


Amazon’s Fire TV Remote Control

Broadband Modem – Motorolla Arris SB6141

Posted in Computers, Electronics, Networks with tags , , on August 16, 2015 by marksun

Costco Item 774054 Modem SB6141  $74.99
Specs:  DOCSIS 3.0 cable modem, 8 download and 4 upload channels , IPV6 (who cares) compatible, Download speed 343 mbps, 2 year limited warranty

After, lets face it, decades of renting broadband modems from Oceanic Cable, I bought a broadband cable modem today from Costco to replace the stock DOCSIS 3.0 cable modem with my own.  The rental charge is about $8 per month from Oceanic and I’ll get that back as soon as I return the old modem.

The physical installation is very simple but you must be willing to get on your hands and knees  and mess with the cables and plastic boxes under a desk. It is somewhat necessary that you are able to identify your modem, the modem power brick (aka wall wart), the broadband cable (tv cable),  your router, nand the router to modem ethernet cable.   You can do this.


  • Disconnect the coax cable and router RG45 cable from the old modem and connect these to the new one.
  • Power up.
  • Have the modem Manufacture and MAC address handy for the new modem
  • Call Oceanic – on Oahu that would be 643-2100 – tolerate their menu system —
  • Talk to the nice tech on the on the other end who is happy to help out ( this is for real – Oceanic in Hawaii has superb technical support. Of course your mileage may vary)
  • Provide the info she needs
  • It took two power cycles of modem and direct connect PC for the network to come up.
    • there are five lights – when everything is working from top to bottom  –
      1. power (green solid),
      2. Receive (blue solid),
      3. Send (blue solid),
      4. Online – internet connection (green solid) ,
      5. link (flashing blue – GigE connection)
    • When things weren’t working  2 and 3 were flashing green – probably indicating the computer (or router) was not responsive/working.  After rebooting computer, all came up.  All three 2,3,4 must be solid or there is a problem.
  • Pack up the old modem for return to Oceanic


The unit is white plastic, stands upright, and has an unimpressive cheap feel to it. In this case appearances have no relevance having nothing to do with function.  The white chassis is said to be the color of the retail release, while the black case is supposed to be only for cable operators.  The indicator lights are bright and may be distracting to sensitive persons.  Performance: normal.  I measured download 55mbp +-  upload 6 mbps – this is what my plan is supposed to provide, so no issues.  I expect this device to last three to five years and be a trouble-free, out of sight out of mind device.  There is a small liability to having my own modem.   For example, if I make Oceanic come to my house to troubleshoot it, they will charge $58 per hour since it’s my modem and my problem.  However that’s only if they send someone out, at my request, which won’t happen. If the modem is dead we can figure that out and it’s time to buy a new one.

Reviews- there are many reviews of this device,  google “modem sb6141 review” for device specs and reviews.  Basically all good.  For what it’s worth Dave Murray of “The Wirecutter” rates the SB6141 “the best cable modem”.  This article is worth reading for some background on the device.


Linksys SRX200 down, enter the WRT1900AC

Posted in Computers, Electronics, Uncategorized with tags , , , on May 18, 2014 by marksun

The SRX200 stopped working last night after being flaky for some time.  It was put in service April 3, 2011 for a service life of just over 3 years.  This seems to be about how it goes with these routers.  Being on continuously for days, weeks, months, and years, it is a short, hot life on the shelf dealing packets.

The WRT1900AC is huge by comparison and comes at a hefty price of $267.77 or so at Best Buy.  It’s a dual band 2.4 and 5 GHZ ,  has USB 3.0 and a SATA USB 2.0 Port enabling it to function as a NAS, 4  Gig  ethernet ports, a Dual core 1.2GHz CPU, and most interesting of all is an OpenSource ready device meaning it will be able to take firmware uploads that will make possible advanced controls for this router, perhaps at the expense of a reasonably good interface.




C-NET gave this router very high marks.

The command interface is accessible using it’s default IP of

The NAS feature is extremely interesting and we’ll be checking that out soon enough.

Setup.  The router comes with minimalist instructions and a DVD.  You do need to go through these steps to activate the router for Internet connectivity.


Printer: MP640R

WIFI: Configured using “Wifi Push Button protected setup”.  The standard select device/passcode approach did not work.


This router produces  10M interference at 28.121581 MHZ.
So far, don’t know how to get rid of this except to turn off the router.  May 18 2014
(Try lowering the data rate which may move the “birdie” somewhere else.)


House FM Transmitter

Posted in Electronics, house tech, technology with tags on February 20, 2011 by marksun

To get some sound around the house,  I bought   a HLLY CZH-05A FM transmitter  that seemed to have a practical and workable design with power to cover the whole house.  In fact at 500 mw power output, I was a little concerned about too much power… more on that later.   After a delay for Chinese New Years, it arrived.  No instructions. No matter.  I hooked it up and it worked great and did indeed cover the whole house.   I took the radio outside  and still crystal clear.  Then I walked out to the mailbox about 200 feet away and still had great sound.  I took a walk around the neighborhood and could still hear my radio station. So far so good as far as being able to hear it around the house.  However there are other considerations, like legality.

With a power rating of 500 mw (1/2 watt) the transmitter is not a high power blowtorch but not exactly a low power device either.  The FCC Part 15 regulation for low power FM band transmitters sets a field strength limit of 250 uV/m @ 3 meters.   Approximately 7 billion people, including myself,  don’t own field strength meters. Fortunately,  there seems to be a consensus on the Internet that this field strength corresponds to  a  range of about 200 feet.  From the standpoint of power,  FM transmitters  with 10-20 mw output are touted as FCC Part 15 compliant.

With my IPOD hooked up and the antenna extended about 30″, I did a range check using an FM frequency well removed from commercial statements to avoid interference.   I tuned the car radio  to the transmitter and drove up the hill in my neighborhood.  I could hear my radio transmitter at the top of the hill a mile from home.   I drove down the hill where the road crosses the freeway a mile away and still had a strong signal.  I kept on going and while there were places where the signal faded or became noisy,  it was still strong in some areas a couple of miles from home.   In the car over a mile  from home, the radio sounded pretty good,  comparable in quality and strength to  commercial FM stations, and louder than some of the weaker stations.

Next,  I range tested the system with the antenna collapsed to about 7″.   In this test, the short antenna effectively limited the range to less than 100 meters or an area of  maybe four football fields around the house.  Still, I would guess that this configuration is still of borderline legality.  Trouble is the transmitter gets hot.

What about not using an antenna?  Here the problem is that the antenna is part of the transmitter circuit.  Without one, there is no load to dissipate the transmitter power and the components of the transmitter overheat, possibly cooking the transmitter.

As far as legality in the US is concerned for an unlicensed FM transmitter, the antenna combined with the transmitter is the key.  To get low power output and minimal range from a radio transmitter, the requirement for an antenna  is to minimize radiation but still provide an electrical load for the transmitter output circuit.  How about  dummy loads,  used to test transmitters, and attach one to the antenna output connector in place of the real antenna.   It seemed like the place to start.  Dummy loads are very simple, especially for a low power transmitter.  In practice there is some radiation from a dummy load.  One could expect short range  without the transmitter overheating.   I went to Radio Shack, bought a packet of 100 ohm 1/2 watt carbon resisters and a connector (BNC) to construct a dummy load.  Two 100 ohm 1/2 watt  resistors in parallel equal 50 ohms and can dissipate 1 watt of power.  I soldered these across the leads of connector to make the load and attached the BNC connector to the antenna jack of the transmitter.

I’ve been using the transmitter like this for a few days and the dummy load does what it is supposed to do. The signal is clear only around the house and immediate vicinity.  Outside the house, the signal fades to noise within 100 feet or so.

The resistors get warm to the touch.  To help keep the temperature down, I glued on a small aluminum heat sink I had laying around, which soaks the heat from the resistors.

The transmitter itself is  a 500 mw HLLY CZH-05A.  The radio seems to be nicely made.  Sound is great.  HLLY manufactures FM transmitters with power output from 500 mw to 20 watts. The higher power (e.g. 5 watt)  HLLY transmitters have some notoriety on the internet as electromagnetic interference (EMI) emitters.

In the end, we have a super short range whole house FM radio station.  The sound is great and I’ve found a new use for FM radios.