Shaun Merrigan's Information Pages


Category: Tech


Tektronix 7854 Waveform Keyboard Rebuild

Posted by Shaun Merrigan in Electronics, Oscilloscopes, Tech. Comments Off on Tektronix 7854 Waveform Keyboard Rebuild

15th August

Tektronix 7854 Waveform Keyboard Rebuild

From the Tek Wiki:

The Tektronix 7854 Waveform Processing Oscilloscope, introduced in 1980, is a 400 MHz combined analog / digital mainframe in the 7000 series that takes two vertical and two horizontal 7000-series plug-ins. In addition to a conventional analog (real time) scope, it contains an equivalent-time sampling 10-bit digitizer and a programmable waveform processor with GPIB interface. The waveform processor can be programmed using a detachable calculator-style keyboard, using postfix operators (“reverse Polish notation” like HP calculators) that operate on entire waveforms, not just individual numbers.

Tek 7854 Mainframe #2 after cleaning

 

It is to the repair of the detachable keyboard that this post is devoted.  I purchased a keyboard for a reasonable price only to find that some keys were intermittent, and some did not work at all.

Opening up the keyboard showed that it was filled with debris:

The … Read More »


Ring Video Doorbell Cold Weather Charging

Posted by Shaun Merrigan in Ring Doorbell, Tech. Comments Off on Ring Video Doorbell Cold Weather Charging

24th February

Ring Video Doorbell Cold Weather Charging

This is a follow-up to an earlier post I made concerning the cold weather performance of the original Ring Video Doorbell. I have had the opportunity to observe the behavior of both the original Ring (i.e., the non “Pro”) and the Pro versions through several cycles of very cold (down to -30C) weather over the past two years, and I can now draw some conclusions.

Background information:

I have both the original Ring and the Ring Pro
The original Ring is hardwired to my mechanical chime doorbell
The Ring Pro is hardwired to my mechanical chime doorbell
The voltage at each doorbell is in the 19-20 VAC range (Klein CL1000 portable DVM)

Conclusions:

The Ring Pro doorbell seems unaffected by external temperature.  It operates properly even through prolonged stretches (10 days or more) of -20C to -30C outdoor temperatures.

The original Ring doorbell … Read More »


Tektronix Scope-Mobile Cart Repair Part 2

Posted by Shaun Merrigan in Electronics, Oscilloscopes, Tech. Comments Off on Tektronix Scope-Mobile Cart Repair Part 2

7th January

Tektronix Scope-Mobile Cart Repair Part 2

This post continues my repair of the Tektronix Scope-Mobile Cart and  trunnion mounts. Here is Part 1, which details the problem and my proposed solution.

The original design used 5/16″ button head bolts which screwed into the bosses and attached the aluminum box frame member to the polymer trunnion mount:

It is obvious that overtightening these bolts put the bosses into tension which caused them to fail.  The gap between the member and the boss “spring loads” the system and puts additional tensile stress on the boss.  While an aluminum casting could easily handle these stresses, the polymer obviously could not.

What I did was to glue the fractured bosses into place using a low surface energy epoxy and use them as a drilling guide (see Part 1).  Then I drilled completely through the trunnion mounts with a drill press, using … Read More »


Fallout 4 Vacuum tubes and Nixie tubes

Posted by Shaun Merrigan in Gaming, Nixie Tubes, Tech, Vacuum Tubes. Comments Off on Fallout 4 Vacuum tubes and Nixie tubes

8th February

Fallout 4 Vacuum tubes and Nixie tubes

I have been working my way through Fallout 4 and during my explorations I noticed that the labs and military installations are loaded with vintage vacuum tube equipment.  I thought I recognized the front panel of at least one piece of gear:

Front Panel render from Fallout 4 (Bethesda Softworks):

 

 Now compare this image with the front panel of the Racal RA-17:

The resemblance of the Fallout 4 render to the real Racal RA17 is striking.  This Racal-like front panel appears in nearly every lab and/or military installation that I have explored.

Another rack of equipment very frequently seen in labs and military installations is this one:

 

Fallout 4 Equipment Rack (Bethesda Softworks

This image clearly shows:

A nixie tube display (round tubes like the Burroughs 5092)
Twin green phosphor CRT displays
Several analogue meters
A row of … Read More »


NEST Thermostat Network Isolation

Posted by Shaun Merrigan in NEST Thermostat, Ring Doorbell, Tech. Comments Off on NEST Thermostat Network Isolation

6th February

NEST Thermostat Network Isolation

With the proliferation of IoT (Internet of Things) objects such as smart thermostats, sensors of all kings, video cameras, video doorbells, light bulbs, media hubs and the like it comes as no surprise that security problems are cropping up.  These IoT devices are proving to be a door through which malicious software can gain direct access to your home network behind your router.  An excellent summary of the potential security problems with IoT devices can be found here InfoSec Resources Iot Security Summary.   The takeaway is that these devices are vulnerable, and attackers can use them to penetrate your home network.  Once an attacker gains access to the network behind your router, they have the “keys to the kingdom”.  What is the solution?  As usual with home network security, there are several solutions ranging from relatively … Read More »


Ring Video Doorbell Cold Weather Charging Problem and Solution

Posted by Shaun Merrigan in Ring Doorbell, Tech. Comments Off on Ring Video Doorbell Cold Weather Charging Problem and Solution

23rd January

Ring Video Doorbell Cold Weather Charging Problem and Solution

I installed a Ring Video Doorbell (RVD) last spring (2015) and overall, I am quite happy with the utility and performance of the unit. Like any new IoT (Internet of Things) device there will be issues, growing pains and problems to be solved.  This post concerns the cold weather performance of the Ring Video Doorbell.

There are several relevant background points:

The Ring Video Doorbell is installed hardwired
The Ring Video Doorbell charges from the wiring above about -19C (-2F)
The Ring Video Doorbell is installed in a single family residence with the camera facing the street
The Ring Video Doorbell wireless signal has to penetrate wire mesh stucco and several walls to get to my router

Initially, I had my RVD motion settings to maximum sensitivity (30 ft radius) and “Standard” Alert frequency.  This meant I was … Read More »


Numitron Clock Project

Posted by Shaun Merrigan in Tech, Time and Frequency, Vacuum Tubes. Comments Off on Numitron Clock Project

21st February

Numitron Clock Project

Numitrons are low voltage incandescent display devices perfected and marketed by RCA (see RCA advert above) in the early 1970’s.  I would call this a bridge technology as the display is incandescent, but can be driven by integrated circuits.   They were quickly displaced by solid state LED (light emitting diode) devices from the mid 1970’s onward.

This is a Numitron:

The look and feel of a Numitron display appeals to me and I wanted to reboot my building and soldering skills , so I decided to build a Numitron clock.  I based my clock on the RCA DR2000 which has a beautiful 15mm display height and a board and parts kit (no longer available) from Richard White.  Here are some images of the construction process:

  

And here is an image series of the finished clock just before, at, and … Read More »


Sonos: Music library not found fix

Posted by Shaun Merrigan in Tech. Comments Off on Sonos: Music library not found fix

2nd January

Sonos: Music library not found fix

I have a wired Sonos system and a central media server (WHS 2011) which hosts all my media content .  Prior to  the latest Sonos update (v5.2), I had no problems accessing my music which is hosted on the server via any connected Sonos controller on either PC’s or iPads.  Post v5.2, however I lost access to the music library.  I tried:

Deleting the shared music folder and re-adding it from different controllers
Modifying the shared music folder permissions on the server
Confirming that SONOS was added as a user on the server
Installing the Sonos controller on the server (!!) and adding the shared directly from the server

All of the above attempts failed with the same error:  The computer “server123” cannot be found.  What is important here is that all my other music sharing services (iTunes, Windows Media Player, … Read More »


HP/Symmetricom Z3805A GPS Disciplined Oscillator

Posted by Shaun Merrigan in Tech, Time and Frequency. Comments Off on HP/Symmetricom Z3805A GPS Disciplined Oscillator

22nd November

I recently acquired two HP/Symmetricom Z3805A GPS Disciplined Oscillator receiver/clocks.  These units seem to have several different configurations both inside the box and of the box itself, but all appear to have:

Two 10Mhz outputs
Two 1PPS outputs
24v DC power requirement

Inside the box, I have seen reports of:

HP 10811 DOXCO (10Mhz)
Symmetricom  DOXCO (5Mhz with a doubler)
MTI 260 DOXCO
16 channel GPS receiver (newer builds)
6 channel GPS receiver (older builds)

The box itself can be Samsung rack mount or HP benchtop.   My particular units were older  Samsung rackmount builds, but do have the desirable HP 10811 DOXCO.   Both units had older 6 channel GPS receivers that exhibited the 1024 week GPS rollover bug.  (That is, they displayed a date that was 1024 weeks in the past due to nature of the 10 bit week counter used in the receiver.)  I simply swapped the GPS … Read More »


Lucent KS-24361 HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system

Posted by Shaun Merrigan in Tech, Time and Frequency. Comments Off on Lucent KS-24361 HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system

9th November

Lucent KS-24361 HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system

I have updated my Time and Frequency GPSCon pages to show my recently powered on Lucent KS-24361 HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system.

The GPSCon page can be found here: Lucent GPS

Here is a photo of the unit:

In a nutshell, these two units each contain a Double Oven Controlled Quartz Crystal Oscillator (DOCXO) made by Milliren (MTI).  Both of these oscillators are GPS disciplined using an onboard GPS timing receiver located in the REF 1 box. 

These are NOS (new old stock) surplus units which were manufactured around 2000.  The useful outputs are 10 and 15Mhz and 1PPS.  It will be very interesting to see how this unit performs over the long term.

 

Shaun Merrigan