Shaun Merrigan's Information Pages



HP 8903B Audio Analyzer PCB Pad Replacement

Posted by Shaun Merrigan in Electronics, Test Equipment. Comments Off on HP 8903B Audio Analyzer PCB Pad Replacement

18th August

HP 8903B Audio Analyzer PCB Pad Replacement

Visual inspection of my recently acquired HP 8903B Audio Analyzer revealed that the polymer pads on the bottom side of the main PCB were seriously deteriorated:

 

 

 

Besides making an unsightly mess, this residue may form corrosive products which, over time, could damage the PCB.  Also, the pads no longer perform their bottom cover to PCB isolation function.  So all the old pads and residue had to be removed and new pads installed.  Lintless wipes, isopropyl alcohol, and nitrile gloves were the chosen tools.

 

 

 

The residue cleaned up completely, and new pads were installed. I won’t need to be concerned with this failure mode again.

 

Thanks for reading.

 

Shaun Merrigan

 


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 »


The uTracer Tube Tester and Curve Tracer

Posted by Shaun Merrigan in Electronics, Vacuum Tubes. Comments Off on The uTracer Tube Tester and Curve Tracer

14th August

The uTracer Tube Tester and Curve Tracer

I have completed building my uTracer (micro Tracer) computer based vacuum tube tester and curve tracer.  This unit, designed by Ronald Dekker described on his website:

The uTracer is much more than a simple tube tester; it is also a curve-tracer. It measures both the anode as well as the screen currents for a range of specified bias conditions, and arranges the measurements in meaningful sets of curves. From these curves parameters like the transconductance or the output resistance can then be extracted and plotted as a function of bias. Alternatively the uTracer can be used as a tester which extracts important parameters like Ia, Rp, gm and um in your favorite bias point in a matter of seconds. http://dos4ever.com/uTracer3/uTracer3_pag0.html

Ronald Dekker makes this tester available as a kit, with detailed assembly and testing instructions.  One of … Read More »


Tektronix DSA602A Digitizing Signal Analyzer

Posted by Shaun Merrigan in Electronics, Oscilloscopes. Comments Off on Tektronix DSA602A Digitizing Signal Analyzer

14th August

Tektronix DSA602A Digitizing Signal Analyzer Part 1

I recently had the opportunity to purchase one of these units, and I am thoroughly enjoying the process of  checking its operation and getting to know how to use it.  This unit is a laboratory grade, very accurate digitizing oscilloscope from about 1990.  From the Tek Wiki entry:

Inputs
3 amplifier bays, up to 12 channels (using 11A34 plug-ins)

Resolution
8 bits; averaging of N acquisitions increases by log2(N) up to 14 bits

Display resolution
50 pixels/Div

Sample rate
DSA601, max 1 GS/s; DSA602, max 2 GS/s (one channel, left plugin)

Record length
512 to 32768 samples

Sweep rate
50 ps/Div  to 100 s/Div

ENOB
7.2 bit up to 10 MHz, 6.3 bit @ 250 MHz, 5.7 bit @ 500 MHz, 4.5 bit @ 1 GHz

Screen
magnetic deflection color computer monitor, 10″ diagonal (130 mm × 168 mm), 552×704 pixels, 22×11 infrared touch-screen grid

Power
90-132 V or 180-250 V, 48-72 Hz, 465 W (DSA601A) / 585 W (DSA602A)

Features

Automated signal measurements (rise, fall, period, frequency, width, delay, phase, duty … Read More »