By Carl H. Babcoke
This month, the report is about the model 59C Semi-analyzer transistor/junction tester from Electronic Design Specialists. Model 59C is a combination of passive testing and breakdown voltages with noise testing. The two are not compatible, so they are not done together; instead, they are completely separated--an interesting concept that works fine.
The 59C is intended primarily for testing diode and transistor junctions, although tests can be made on a few other components.
Physically, the unit is moderately small, except for the outside-type handle that functions as a tilt stand. Width and depth are 9 inches (plus the handle); depth is only 3 inches. Power is supplied by 120Vac only.
The digital readout appears to have 2 1/2-digit operation with automatic range selection and 1/2-inch red LED digits. During the various tests, red LED words such as OPEN, PNP, SHORT or any of six others can be flashed on the screen to indicate the conditions.
There are only two basic test positions: JUNCT with the switch out (condition of the junction), or BRKDN (breakdown mode) when the switch is locked in. The breakdown mode measures leakage of the junction. That switch is next to the power switch.
At the right side of the panel above the two switches is a grille that resembles a giant salt shaker; the various sounds originate here.
Two jacks for the test probes are located at the center bottom.
Testing silicon junctions Here are the simple steps for testing the junctions of an average silicon transistor:
1. With the black lead at the base, touch the collector with the red lead. The screen should read: SINGLE JUNCT NPN. If it does, the first test has been passed. A defective junction might have read OPEN, LEAKY or SHORT. Any of these conditions reject that junction.
2. With the black lead on the base, touch the emitter with the red lead.
The screen should read: SINGLE JUNCTION NPN (the same as for the collector test). This indicates a normal base/emitter junction.
3. Touch the red and black test leads to the emitter and collector.
The reading should be OPEN JUNCTION. If so, reverse the test lead polarity and touch the emitter and collector again. This reading should also be OPEN JUNCTION. These open emitter/collector readings are normal, and any deviation probably indicates the transistor is defective.
Of course, these previous tests were all made with the mode switch in the junction position. Before using the breakdown voltage, you should know that this voltage can shock you, because it might be any do voltage up to about 180Vdc.
Of course, the current is limited to 10mA, but that much can really shock you. And any shock is worse when you are not expecting it. Use care when handling the test leads during the breakdown mode.
There are some problems. Do not leave the breakdown switch activated (switch locked in) but switch it off to the JUNCT position after each use. Otherwise, you might accidentally place the probes across a sensitive circuit, causing damage. But there is more. The dcv/dcv converter that supplies the breakdown voltage should not be operated for longer periods of time. Be on the safe side for both reasons and turn off the breakdown voltage after each use.
Testing voltage breakdown
With an NPN transistor, touch the red test lead to the collector and the black lead to the emitter.
If the junction is good, the avalanche voltage will be less than 150V, and the speaker will have some faint hiss without popping or crackling. That is the avalanche or breakdown voltage of the collector/emitter junction. One test transistor showed 51.1V, which is the top voltage limit for its operation. The same test can be performed with the red probe touching the emitter and the black probe touching the base. Of course, this is reverse bias for the junction, which then acts as a zener to limit the voltage drop. With the test transistor that voltage was 5.6V. Miscellaneous Bias diode for a power transistor often has a box with two, three or four diodes in series. Any or all of these can fail. Use the basic transistor C/E method and the readout will show the number of junctions that are working.
Darlington or high-gain transistors show the usual single junction between base and collector, but usually will show dual junctions when measuring base to emitter.
In-circuit junction testing
The 59C is said to be very rapid and accurate when used for in-circuit tests. Of course, the breakdown test would not be used unless that transistor was disconnected temporarily from the circuit.
According to the instruction manual, circuit loads as low as 109 will not affect the readings, although the LEAKY sign might be lighted at times. I tested a silicon base/emitter junction, obtaining SINGLE JUNCT NPN normal reading. A 96-ohm resistor was connected between base and emitter, then the test was repeated. This time the readout. was LEAKY SINGLE JUNCT NPN. No attempt was made to find the effects of lower resistances because transistor junctions that light the NPN or PNP legend usually are not defective (just obscured by circuit load). But if a transistor shows LEAKY JUNCT without the PNP or NPN flag, it probably is defective. Remove it from the circuit for more testing.
Testing zener diodes
When the diode is out of circuit, the 59C will show the correct zener dc voltage. Connect it the same as any diode breakdown test (red probe to the anode, black probe to the cathode) and read the zener voltage on the screen. The 10mA of regulated current makes this possible for zeners of all voltages.
Testing capacitor leakage
Out-of-circuit film and aluminum-electrolytic capacitors up to 1,000µF can be tested for leakage and the maximum voltage that each can endure, using the voltage-breakdown mode.
As the capacitor charges, the voltage reading races upward, slows down, levels off and then begins to go down. Because this is the voltage-breakdown point, notice what the voltage reads, then instantly disconnect the capacitor from the 59C test leads.
All capacitors produce noises when the voltage is near the breakdown point. Look for a capacitor that is breaking down at a lower voltage than the marked value (or the working peak voltage in the receiver). Thumping noises or wildly varying voltage readings are valid reasons to reject that capacitor.
Noise tests of transistors are performed exactly as leakage tests are, except attention is focused on the volume and quality of the noise. Good semiconductor junctions will show a stable voltage and have a steady hissing sound (pink noise). Intermittent or noisy junctions produce an erratic voltage reading along with all varieties of popping noises. Leaky semiconductors often do not have excessive noise, but always will show a voltage lower than the rating.
Testing neon and LED lamps
With the instrument switched for the breakdown mode, touch the test leads to the LED or neon lamp (observing polarity when LEDs are tested) and the voltmeter will show the correct voltage for that LED or neon. In many cases the test can be made in-circuit with good accuracy. This is possible because of the regulated (constant-current) voltage supply.
Remember, for all these tests the machine being tested must be unplugged and without ac or do power.
Note: Do not test the voltage breakdown of any tantalum capacitor. Tantalum capacitors have very low leakage but they have a tendency to short on any voltage beyond their rated limits. Do not test them.
Model 59C is not intended for testing germanium junctions.
However, most germanium junctions can be tested with reduced accuracy. One germanium tested single junction with a breakdown voltage of 129V. One red and one black test lead are furnished with the machine.
They have no resistances, capacitances or inductances in series or parallel with the test leads, but the operating manual seems to indicate some important characteristics. The operating manual says: "The junction tester portion of the EDS-59C has been calibrated to sharp stainless-steel probes with exactly 36-inch long leads. If you use any test leads other than the ones recommended, the tester may give inaccurate circuit conditions." I have no comment.
Audible signals
Audio tones that accompany some transistor junction tests are not mentioned in the operating instructions and owner's manual that details all the other tests. Perhaps the manual I have was one of the early ones that was intended for revisions as needed. Anyway, the machine produces a pleasant low tone for normal junctions, a slightly higher tone for Darlington base readings or bias-diode junctions, a shrill high tone for shorted junctions, or a low buzz for leaky circuits. Of course, the audible signals cannot be used during breakdown tests because the audio channel is busy with noise analysis.
It has been said that after using the 59C instrument while noticing the various audio tones for each read-out, a technician should have no difficulty in using the junction analyzer by listening for the various tones, rather than by watching the read-outs. Of course, this can be a time-saver.
Figure 1. Block diagram of the unit. The first part of the unit probes semiconductors
in circuit to indicate condition, type and number of junctions. The second
part finds the component's breakdown voltage and amplifies junction noise.
Comments
Every item of test equipment has limits on the things that safely can be done with or to it.
The junction mode of the 59C supplies all necessary signals for the tests; no outside power is needed or desired. Therefore, the machine being used for in-circuit tests must be unplugged from the 120Vac power. Further, all B+ lines near the test site should be grounded for a few seconds each to ensure that no B + is stored there.
Do not switch to the breakdown mode and leave it there, even after the test has been made. One reason is the danger of shocks. The pointed test probes have up to 180Vdc between them (although limited to 10mA). I haven't been able to check out the following statement, so it is printed verbatim:
"Besides, the DC/DC converter consumes a lot of power, and leaving the 59C in the VB mode for more than a few minutes at a time will shorten its life considerably."
It is recommended, therefore, that you use the breakdown mode for the test or tests and then move the switch to junction position until the breakdown mode is again needed.
Incidentally, the only clue about how the instrument operates was found in a press release that said, in part:
"sends out a special current-limited sine wave through its test leads to the circuit under test; the circuit and the component under test will distort the sine wave in a certain way. This distorted sine wave is converted by an 8-bit analog-to-digital converter, and the 8-bit word is presented to a 16K PROM, which has been programmed to recognize and display the results of just about any situation it may encounter."
Sample readings The EDS-59C Semi-analyzer is said to display up to 25 different combinations of circuit parameters. These will be self-explanatory.
Shorted junction--the reading is less than 0.6V (one junction) in both directions.
Leaky junction--readings under0.6V in one direction, and one or more junctions in the other direction.
These will give you two samples of the screen readouts possible on the 59C.
Comments
During the time I have examined the EDS 59C, I have grown fond of it. At first, I was not enthusiastic because I had samples of almost every commercial transistor tester ever made and a few I had hand-built. But I particularly like the breakdown and noise tests, which are unique. Each technician will have a different preference. Another might like the panel readouts best; there is something for everyone.
The EDS 59C has several highly unusual features, and merits a thorough evaluation. After all, it is the equivalent of two testers in one with almost all functions automated. The only adjustment on the front panel is the junction/ breakdown switch, and it is the one that changes from one type of testing to another. (EDS is located at 951 SW 82 Ave., North Lauderdale, FL 33068.)
Also see:
What do you know about electronics?--Model behavior