Troubleshooting Notes: Tektronix 7A26

Blown R829

Blown R829, Tektronix 7A26

Tektronix 7A26 Manual

I am working to repair this 7A26, Serial Number: BXXXX.  First observed symptoms is that it drags down the power supply of the scope.  So far I have noticed R829, a 422 ohm resistor has been vaporized.

A New Project

After all this time, I’m going to start blogging again, and try to put some more useful information out there.  My latest project is  I am working on a set of tutorials and reviews to begin populating that site, feel free to contribute if you like.

A Rant… and an Update!

Looking East
Looking east from the tent…

The Rant:  Laptop manufacturers, please stop trying to claim that the video device in your laptop is any different than the others, allow us to use reference drivers from the chip vendor.  Really you guys aren’t prepared to offer updates or do anything to help us, the consumers, anyway as long as we already bought the laptop.  If you can’t see fit to do that, at least update the drivers for longer than the six months after product launch(I’m looking at you HP).

The Update:  Really, where does time go?  I am finishing a few weeks in the field, training for my next trip to the sand.  I expect that within the next 6 months, however I will not provide anything closer to an exact date in this location.  Work has kept me very busy, but I am preparing to release some updates on the projects that I am currently working on.

Converting a Cisco 7960g IP Phone to SIP

Cisco Systems manufactures some of the most common IP phones used in a business environment, but as delivered they depend on Cisco Call Manager servers. The servers and software licensing involved are prohibitively expensive for a non-enterprise. Far easier for a small business or individual is to use a SIP-based VOIP system. There are several considerations to keep in mind here.

-These phones are built to work with Power Over Ethernet(PoE), but by some accounts are not standards-compliant with 802.3af. I would appreciate someone confirming that for me with a Cisco phone and a non-Cisco PoE switch. All Cisco PoE switches should power it just fine, but for smaller cheaper deployments there are AC adaptors and single-line power injectors.

-Cisco produces a SIP firmware for these phones. However it is somewhat difficult to obtain. The only legal way to do so is to have a account, with a paid support subscription(about 15 dollars per year). However the firmware is available in other places but these are grey area or worse. I won’t link it, but it is out there. The usual disclaimers about illegal software apply.

-Cisco sells two versions of the same hardware, one includes a license for CCM, one does not. If one is going to use SIP, a license is not required. The unlicensed phones, often sold as “spares” are much cheaper.

-The instructions on the Cisco website for loading the SIP firmware include a wealth of information, but still appear to be incomplete. The software version currently on the phone has a large impact on how to proceed loading new firmware.

-As the phone boots up it expects to receive an IP address and the address of a TFTP server from DHCP. The TFTP server address needs to be pushed as DHCP option 66. These can also be configured manually(static IP and TFTP) from the on-screen menus.

-The phone will request a series of configuration files from the server, and if they are formatted correctly it will pull and install the new firmware from the server. Once the SIP firmware is loaded, the TFTP server is not required. All SIP settings can be entered from on-screen menus.

-The phone will request several files in order, and depending on which files exist on the server will configure the phone for different protocols.

-The firmware will contain 5 files in a zip. Extract to the TFTP root directory.

The phone I obtained(thrift store for $10), was loaded with SCCP(Skinny) firmware version 7.2(3.0). The current version of SIP firmware version is 8.12. The Cisco website indicates that the phone will read the OS79XX.TXT file and read the correct version of firmware from that file. Reviewing TFTP server logs, the phone never requested that file. Apparently the version of firmware on the phone was newer than the tutorial was written for. Piecing together information from around the web, I discovered that two additional files are needed to force the phone to load the SIP firmware. The two files are named SIPDefault.cnf and SIP(MAC ADDRESS).cnf. The MAC is read from the back of the phone and typed as all numbers/caps and no separators. The contents of my files is posted below. There are many options that can be set with these configuration files, but right now these are just focused on loading the correct firmware.


You will need to change “Image Version” to the firmware you wish to load if different from SIP 8.12.  References to may need to be changed to your TFTP server address.

image_version: "P0S3-8-12-00"

proxy1_address: ""
# proxy2_address: ""
# proxy3_address: ""
# proxy4_address: ""
# Proxy Server Port
# proxy1_port:"5060"
# proxy2_port:"5060"
# proxy3_port:"5060"
# proxy4_port:"5060"

proxy_emergency: ""
proxy_emergency_port: "5060"
proxy_backup: ""
proxy_backup_port: "5060"
outbound_proxy: ""
outbound_proxy_port: "5060"
nat_enable: "0"
nat_address: ""
voip_control_port: "5060"
start_media_port: "16348"
end_media_port:  "20134"
nat_received_processing: "1"
dyn_dns_addr_1: ""
dyn_dns_addr_2: ""
dyn_tftp_addr: ""
tftp_cfg_dir: "./"

proxy_register: "1"
timer_register_expires: "120"
preferred_codec: "none"
tos_media: "5"
enable_vad: "0"
dial_template: "dialplan"
network_media_type: "auto"
autocomplete: "1"
telnet_level: "2"

cnf_join_enable: "1"
semi_attended_transfer: "0"
call_waiting: "1"
anonymous_call_block: "0"
callerid_blocking: "0"
dnd_control: "0"

dtmf_inband: "1"
dtmf_outofband: "avt"
dtmf_db_level: "3"
dtmf_avt_payload: "101�
timer_t1: "500"
timer_t2: "4000"
sip_retx: "10"
sip_invite_retx: "6"
timer_invite_expires: "180"
sntp_mode: "directedbroadcast"
sntp_server: ""
time_zone: "CST"
time_format_24hr: "1"
dst_offset: "1"
dst_start_month: "April"
dst_start_day: ""
dst_start_day_of_week: "Sun"
dst_start_week_of_month: "1"
dst_start_time: "2"
dst_stop_month: "Nov"
dst_stop_day: "1"
dst_stop_day_of_week: "Sunday"
dst_stop_week_of_month: ""
dst_stop_time: "2"
dst_auto_adjust: "1"
messages_uri: "*99"
services_url: "http://example.domain.ext/services/menu.xml"
directory_url: "http://example.domain.ext/services/directory.php"               
logo_url: "http://example.domain.ext/imagename.bmp"

http_proxy_addr: ""
http_proxy_port: 80
remote_party_id: 0


File will need to be named with MAC address of your phone.  May need to have version edited the same as SIPDefault.cnf

image_version: "P0S3-8-12-00"


So Here We Are… Part 2

I have arrived down in Florida now. Settled in in a small town called Niceville near the coast. Now that I am here, I am starting to work on more electronics. I just finished fighting with firmware upgrades on a Cisco 7960g IP phone, and I will post instructions and lessons learned from that experience. The TI Launchpad continues to provide education in embedded C. I used a random piece of perfboard and added an LED to each I/O pin, and am using that to learn. I sampled some 74HC595 shift registers from TI and I hope to use one to allow me to drive an LCD. I have many projects in the works, but a lack of dollars means that they only proceed so quickly…

So Here We Are…

It has been way too long since I have posted a single thing here.  Here is trying again.


My Life:

I am now back in the US, resuming normal work schedule.  I am now preparing to pack up and move to Florida.  Sometime in the next month or so I will be loading up my truck and driving down.  Updates will follow.


Most are somewhat on hold right now, but will resume shortly.  I am finally getting into microcontrollers in a big way, courtesy of the MSP430 Launchpad from Texas Instruments.  This should open up a whole new world of projects that weren’t possible before.  The store that was previously planned for this site is on hold.  The plan is now to sell products on an established site such as eBay.  I don’t want to be in the position of maintaining ANY customer information in this day when data breaches are normal.  I simply cannot afford the potential liability.  The site continues to be updated when any new versions are available.  Currently the site runs on a VPS from Slicehost with an Nginx backend, although I feel I have reached the limits of Nginx and will soon be moving to Apache, mainly for non-public projects stored on the same server.

Store Status

Preparations are almost complete for the launch of the store. All PCB products that are un-assembled are sold at cost. Assembled products include a nominal charge for the costs of solder and assembly. With the first series of products, there is no goal of profit, merely hoping to assist fellow hobbyists. Other, more advanced products will follow in the May/June timeframe that will hopefully turn into a second source of income.

Saturday Project/Product Updates – Jan 29 2011

I’m just going to start doing a weekly recap of all products and projects.  It will certainly help my inbox.

MicroSD Breakout – The parts are all waiting in North Carolina except for the PCBs which should be back from fabrication any day now.  Pre-Orders will open on 15 Feb, and shipping will begin as soon as I return to the US, 1-3 weeks after.

Rackmount Xbox 360

  • USB Header PCB is out to fabricate.  Parts are on order.
  • CAD for the case is nearing completion.
  • Major issue so far is the bluetooth/ring-of-light PCB.  It is too tall for a 1u case, and going to 2u is extremely wasteful.  I am currently considering different methods of mounting it at this time.  I am trying to document what protocols are used to communicate with the wireless module(READ: Can I extend it on several feet of cable into a box to mount under the TV?)

New Project – I will be integrating a Motorola Surfboard cable modem and a high power wireless router into a 1u rackmount case to better fit the layout of my apartment.  This is unlikely to be for sale due to its limited application, but all CAD files will be posted here.

MicroSD Breakout

Prototype PCB

MicroSD Breakout Prototype

Planning an upgrade for your WRT54G?  Other Router?  Interfacing with an Arduino or other microcontroller?  This is the board for you.  Its small size allows for a variety of mounting options.

*Note that the picture is currently of the prototype.  Production boards are identical except for added silkscreen labels.

**Board color may vary.  Current batch is blue.  Every effort will be made to update this listing as new batches arrive.

Rackmount XBOX 360 Part 1

In the course of my travels, I have learned that rackmount kit survives much better than any other.  Therefore I will be working on a casemod to install an XBOX 360 in a 1u rackmount case.  One challenge is that the USB header for the front USB is too tall and must be removed from the board.   I could reuse the existing header, but it is mounted inside a little metal box with too much plastic.  Going out to fab today is my replacement.  Nothing special.

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