Shaun Merrigan's Information Pages


Category: Electronics


Tektronix TM500 Module Holder

Posted by Shaun Merrigan in 3D Printing, Electronics, Restoration, Tech. Comments Off on Tektronix TM500 Module Holder

28th June

I have previously written about the substantial number of different modules available for the Tektronix TM500 and TM5000 module plug-in systems. Since the equipment is now anywhere from 20 – 40 years old it needs to be refreshed and/or repaired before going back into service. This often means working on the modules while they are not installed in the power frame:

TM500 Extender Overview: Connects between module and power frame.

TM500 Extender Overview: Connects between module and power frame.

Dan Meeks Extender Closeup. This extender allows monitoring of all supply voltages and currents. It also has LED indicators for each voltage rail.

Extender Plugged into Power Frame

Extender Plugged into module. This allows working on the module outside of the power frame.

From the image above, the extender board projects beyond the edges of the plug-in. This means that the plug in … Read More »


Tektronix TM500 Power Frame Tester

Posted by Shaun Merrigan in Electronics, Test Equipment. Comments Off on Tektronix TM500 Power Frame Tester

25th June

The Tektronix TM50n is an “n”bay (where n = 1 to 6, the number of bays) power frame which can host and power TM500 plug-ins. It was available in 1 through 6 bay versions and was the predecessor to the TM5000 power frame: See my post here about the TM5000 power frames. Tektronix themselves had dozens of plug-ins available which comprised power supplies, signal generators, oscilloscopes, multimeters, test oscillators, calibrators, attenuators, filters, logic analyzers, frequency counters, audio analyzers and more. It is important to note that while TM500 plug-ins can be used in the TM5000 power frame, the inverse is not true: TM5000 plug-ins cannot be used in a TM500 power frame.

Part of the repair/refresh process of any TM500 power frame requires the use of a Power Module Tester which (in conjunction with some basic test equipment … Read More »



Tektronix Type 106 Square Wave Generator Refresh

Posted by Shaun Merrigan in Electronics, Restoration, Tech, Test Equipment. Comments Off on Tektronix Type 106 Square Wave Generator Refresh

20th June

Introduced in 1966, the Tektronix 106 Square Wave Generator is a signal generator which can produce fast rise (<1nS @50 ohm loads positive or negative going) or high amplitude (120 Volts, high impedance load) square waves from 10Hz to 1MHz. It is used for oscilloscope calibration, risetime testing and for triggering extremely fast rise (<100pS) tunnel diode pulsers. The 106 uses a combination of vacuum tube and discrete solid-state technology. This is the sort of equipment that was used for development and testing during the NASA Apollo Program through the 1960’s.

The cost of the Tektronix Type 106 was USD 590 in 1966 or about USD 4900 in 2021 dollars. I was fortunate enough to obtain one of these units in decent condition and I was able to restore it to better than factory specification. What … Read More »


Tektronix TM5006 Power Frame Refresh

Posted by Shaun Merrigan in Electronics, Restoration, Tech, Test Equipment. Comments Off on Tektronix TM5006 Power Frame Refresh

17th June

The Tektronix TM5006 is a 6-Bay power frame which can host and power either TM5000 or TM500 plug-ins .

Tektronix themselves had about 130 different plug-ins available which comprised power supplies, signal generators, oscilloscopes, multimeters, test oscillators, calibrators, attenuators, filters, logic analyzers, frequency counters, audio analyzers and more. In addition, numerous third parties made plug-ins for the system. The total number of different plug-ins numbered at least 200. The system was introduced in 1972 and was available in some form through at least 1995. The system is remarkably interesting from a technology standpoint because it encompasses the move from discrete transistor circuitry in early equipment, evolving through microprocessor-controlled units in later equipment. The more modern TM5000 equipment also had network interface (GPIB) capability for control and data acquisition.

In terms of cost, a basic … Read More »


Tektronix Type 114 Pulse Generator Update

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on Tektronix Type 114 Pulse Generator Update

16th June

This is an update to my previous post documenting my restoration/repair of two Tektronix Type 114 Pulse Generators. As of this writing I have completed some cosmetic work on the cabinets, front panels and carrying handles of both units. This includes cleaning and painting the cases, cleaning the front panels, knobs, BNC connectors and replacing the missing handle inserts.

Tektronix 114 Handle Insert Bottom Section Missing

Tektronix 114 Handle Insert New Aluminum Base Plates and OEM Example

Tektronix 114 Replacement Inserts and Tolex

Tektronix 114 Replacement Handle Insert and Tolex in place

Tektronix Type 114 Refinished Cabinet and Front Panel

Tektronix 114 Front Panel Cosmetics Completed

I have implemented a Maintenance and Inventory system which includes an equipment label with QR code. The code includes the Equipment Name, Serial Number, Instrument ID Number, and a summary of the latest service work completed on the unit. … Read More »


Racal 9478: Widespread Electrolytic Capacitor Failure

Posted by Shaun Merrigan in Electronics, Restoration, Troubleshooting. Comments Off on Racal 9478: Widespread Electrolytic Capacitor Failure

25th May

The Racal Dana Model 9478 Frequency Distribution System has an internal precision, oven-controlled crystal oscillator, or it can be phase locked to an external signal derived from a GPSDO or other master oscillator.  The system will automatically lock to an external signal above 100 mV, and with a standard frequency of 1, 5 or 10 MHz.  “In Lock” indication is provided.

I recently repaired two Racal 9478 units. What I found was widespread electrolytic capacitor failure such as I had never encountered before. A summary of the issues found in both units follows:

Virtually all electrolytic capacitors in both units (nearly 90 in all) had failed, showing either very low capacitance and/or very high ESR. Interestingly enough none showed short circuit failure.All the failed electrolytic capacitors were made by Philips in late 1980’s The -15v regulator was originally bolted … Read More »


Tektronix Type 114 Pulse Generator Repair

Posted by Shaun Merrigan in Electronics, Restoration, Tech, Test Equipment. Comments Off on Tektronix Type 114 Pulse Generator Repair

22nd May

I recently completed repairing/refreshing and calibrating two Tektronix Type 114 Pulse Generators. This is a solid state pulse generator with variable pulse width (100ns – 10ms) and period (1us to 100mS). It can produce pulses of both polarities (-10v to +10v into 50 ohms). It was introduced in 1965. The two examples I obtained were SN 001791 and SN 003460. Initally, both units were produced output, but the waveforms were distorted (rounded square waves) and far out of specification in terms of period, pulse width, and risetime.

Tektronix Type 114 SN 003460 Front Panel

Tektronix Type 114 SN 003460 Overview

Tektronix Type 114 Pulse Generator SN 001791 Front Panel

Visual inspection also revealed damaged components and mechanical damage. A summary of the issues found follows:

Pulse width and period were out of specificationNegative pulses and square waves were … Read More »



Cubic CDR-3250 Receiver Power Supply Refresh

Posted by Shaun Merrigan in Electronics, Radio. Comments Off on Cubic CDR-3250 Receiver Power Supply Refresh

9th January

The Cubic 3250 VLF-HF receiver is a 10kHz – 30 MHz DSP based radio receiver with 51 IF bandwidths and 7 receive modes. It falls into the category of professional/military grade equipment and the build quality certainly reflects this. According to Fred Osterman’s book, “Shortwave Receivers Past and Present, 3rd Ed.”, it was manufactured from the mid 1990s until at least 1998 (possibly later). I have found that the audio recovery and readability of this receiver is outstanding.

As both of my units were made in 1995/96, they are 25 years old and likely have thousands of hours of use. So I elected to replace all the electrolytic capacitors in the power supply with (arguably) an abundance of caution. I first measured the voltage and ripple on the output rails:


Cubic CDR-3250 Display Replacement

Posted by Shaun Merrigan in Electronics, Radio. Comments Off on Cubic CDR-3250 Display Replacement

9th January

The Cubic 3250 VLF-HF receiver is a 10kHz – 30 MHz DSP based radio receiver with 51 IF bandwidths and 7 receive modes. It falls into the category of professional/military grade equipment and the build quality certainly reflects this. According to Fred Osterman’s book, “Shortwave Receivers Past and Present, 3rd Ed.”, it was manufactured from the mid 1990s until at least 1998 (possibly later). I have found that the audio recovery and readability of this receiver is outstanding.

These receivers have a VFD (vacuum fluorescent display) as part of the front panel/human interface. The VFD in one of my units must have had many, many hours on it because it was quite fuzzy and dim, to the point of being blurry:

Aged, dim, blurry VFD

The old display on the CDR 3250 showed considerable burn in when viewed using … Read More »


HP 3245A Capacitor Replacement

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on HP 3245A Capacitor Replacement

4th January

The HP3245A Universal Source (datasheet is copyright HP/Agilent) is a precision AC/DC voltage and current source that can provide a wide range of precise and repeatable voltages and currents up to +-100vdc and 100mA dc. It can also provide sine, square and arbitrary waveforms up to 1Mhz and 200vpp. Such an instrument is extremely useful in the lab for calibrating meters, driving current and voltage amplifiers and checking equipment. The particular units I have were built in 1992/1993 which means the electrolytic capacitors are approaching 30 years of age. I had decided to replace the RIFA line filter capacitors in (documented here) both my units and performed routine power rail voltage and ripple checking as part of that. For example:

+5.0840 4.4mv+15.194 30mV+18.625 29mV-18.691 28mV

The other power rails and HV Amp power supply also measured good, using an … Read More »