2015-04-25 Transistor Tester Kit Does More

A few weeks ago I ordered this kit on a whim, not knowing what to expect, just something to assemble and get some soldering practice (this is what it looks like). There are several Chinese vendors that sell them.  The info claimed it tested other components besides transistors. It shipped from China so it has taken a few weeks to arrive. It says transistor tester, but I was pleasantly surprised to find that it does many other things, which I talk about at the end.

This kit consists of a double sided phenolic circuit board, a back-lit display, an Atmel microcontroller and socket, a 9V battery clip, switch, trimmer pot,  and an assortment of other components.  All of the resistors, to my surprise, were 1 percent tolerance.

I would like to warn others that this kit comes with no documentation at all.  You’re completely on your own with no help at all.  For this reason I would say that it is not a beginner’s or intermediate kit; it needs a kit builder with experience.  There are some parts that don’t match the labels on the board. So if you intend to tackle it, then find someone who can help you if you find yourself lost.

I got to work and stuffed the resistors, capacitors and a few others that stayed in place, and soldered them, clipping the leads as I went along.  The 1% resistors are a blessing and a curse.  They provide extra accuracy but it’s likely that many of them could be 5% with no difference in performance.  But for the typical technician who is used to reading 5% resistors, it’s a lot tougher and slows things down a lot.  If you have any doubt about the value of a resistor, check it with a digital multimeter to find its actual value.

After I had finished stuffing and soldering the resistors and “104” and “103” capacitors, which all matched the labels on the board, I found a 102 label on the board. Well, 102 is the same as 1 nF, which was a yellow cap marked 1nfJ100 on the top. The two 22 pF holes are filled by small disk caps marked 22, nothing else. The white line on the electrolytic capacitors should line up with the line on the board. I found that the ‘lytics caps must be fully seated to allow the display to be screwed all the way down to the board.

The metal package marked 8.0 is the 8 megahertz crystal that’s close to the two 22 pF caps and the microcontroller. The power jack goes in only one way, but the pushbutton switch should have a line on one side, which goes towards the edge. Line the socket up so that the notch on the end lines up with the label on the board, which is the edge of the board. I haven’t soldered the battery clip in because I have a 9VDC wall wart adapter that fits the power socket. The jack is 5.5 by 2.1 mm. This MUST have the center pin positive. I just have to get an AC ‘wall wart’ adapter for it from my junk box. The jack says 5.5 to 12 VDC, but the wall wart I used was 9VDC unregulated, and when it is first turned on it displays the supply voltage, which read 13 point something, depending on the AC line voltage. It accepts this with no complaint.

I chose to solder the display male 16 pin connector to the board and the female socket to the display, but either way should work. I had to bend the LED out to the outside to get the display to seat completely. Some transistors were nearly touching the display so it’s best to make sure they are seated well before soldering.

When I finished with double checking the parts and making sure the Atmel chip was inserted properly, I assembled the display with the two studs and four screws provided. I checked the parts to make sure they were not preventing the display from seating fully. I had to bend the LED over a bit.

After I again double checked everything, no loose or unsoldered pins visible, I decided everything was ready for power up. I plugged in the power and the display lit up, but there were no letters on the display. I adjusted the trimpot, which is the display brightness, and the letters appeared in the display. The top row of pixels on the second line were blank, so I tried seating the display onto the board, and the pixels lit up. I’m not sure why, but if it comes back, I’ll have to resolder the pins.

I connected a few disk caps to the left and center pins of the three pin screw block and pressed the button switch. It identified the part as a capacitor on pins 1 and 2 and the capacitance was correct. I decided to add alligator clips to make it easy to change parts.

I got some 562.2 ohm, 1/10 percent precision resistors and tried one and it showed a resistor and a value of 562.8, which is very close. Some of the difference is the fraction of an ohm in the clip leads. I tried a red LED and it identified it as a diode, with 2.16 volts forward voltage. Cool! The LED blinked on and off during the test.

So far, it’s working very well on an LED, caps and resistors. I still have to try inductors, transistors and FETs. And a bunch more resistors and caps to see now accurate it is over a wide range. The inductors are my main interest because many L meters have difficulty with measuring sub-microhenry and multi-henry values.

I connected a BUZ71A to the three leads and it gave me the polarity, pinouts, the Vt=3.43V, and the C1.18nF.

I connected BC550C to the leads and it gave the pinouts, polarity, the beta and the Vf, presumably base to emitter.

I connected a 1N5817 Schottky diode and it gave me the pinouts, junction capacitance was zero and the Vf (forward voltage)=208mV. With a rectifier like the 1N4002, it gives the junction capacitance which is an indication that if the capacitance is high, say a few hundred pF, then it’s not a high speed, fast recovery rectifier.

The great thing about this tester is that I have many house numbered devices such as power transistors that I have not bothered to use because I’m not sure of their polarity and/or pinouts. Now I can connect one up, press the button, and in a few seconds it gives me the polarity, pinouts and tells me if it’s a transistor or whatever. I have already found one power transistor that is shorted and open so the tester thinks it’s a zero ohm resistor on two pins.

To throw it a curve, I turned it on first. Then I connected a 1.2 V rechargeable NiMH cell to it and pressed the button. After a much longer test time, it blurted out “Cell!” Heh, I thought I could fool it!

I haven’t tried any inductors yet, so here’s my next batch of tests.

I tried a 0.1 uh or 100 nH coil, but it tested as a 0 ohm resistor. Seems there’s a minimum value for coils that the tester can detect – it will test at least a .02 mH or 20 uH choke. I then tested a few 180 microhenry chokes and the test showed their resistance, about 2.1 ohms and the L, about .17 to .19 millihenry. I tested two 1mH chokes, and it said 1.01 mH and 4.8 ohms. I tried a few 100 uH chokes and it said .09 to .10 uH, but with only 2 digits of accuracy, the resolution isn’t very good. I then tested a 33 uH choke and it said 0.1 ohm and .03 mH. It read the value of the choke, but again with poor accuracy; the actual value could be from .026 to .034 mH and it would still read .03 mH. So I would say that it’s not very useful with any value below .1 mH.

I tested a winding of a transformer on a ferrite core, on which was written 3.6 mH, 1.5 ohms. The test gave 3.4 mH and 1.5 ohms. Pretty good.

I tested at least a dozen chokes of various values, most of them less than 1 mH. The results were consistent, but due to the two digit values, the values were of limited accuracy.

This component tester is very useful since it combines so many component tests into one piece of equipment. I find it interesting and useful. Its performance is good and it’s inexpensive but it is a kit that must be assembled. If you can buy it assembled, I would recommend it for the hobbyist since it does so much for such a reasonable price. But as a kit with no instructions, it’s a lot tougher than one might think.

There is a plastic box for sale separately, but I plan on mounting it in a box I have.

I’ll try to find docs online.

Update May 1 – I ordered a second kit online from a different vendor in China. It arrived a day ago so I assembled this kit today. All of the resistors were 1 percent, as were the ones in the first kit. I stuffed some resistors into the board and I came to one resistor that was orange, orange, black, red, brown. This is 3, 3, 0, two zeros, and brown equals 1%. That’s 33,000 or 33 k ohms. The board didn’t have a label for 33k, but it had 3.3k. So I left it for later.

After I finished with the other parts, I had the 33k resistor and an unfilled place on the board labeled 3.3k. I measured the resistor and it was 33k, not 3.3k, so the kit came with the wrong value resistor. When I started, I noticed that the first kit had some part numbers where the battery is supposed to lay. But this second board has no numbers, so my guess is that this is a “knockoff” kit made by someone who stole the plans from the originator. I think the resistor is part of a voltage divider that goes to one pin of the Atmel microcontroller, and is probably important as a voltage reference. So I need to scrounge through my box of precision resistors and find a replacement. I found a 1% 3.3k resistor and soldered it in. Bingo! I powered it up and put a 187 ohm 1% resistor across 1 and 2, and it said 186.2 ohms – Good! Very close!

So now I have two of these little beasties up and running. One for the test bench and another for tossing in the tool box or as a backup. For that, it really should have a case. I saw one online, so I’ll have to check into getting one or two. Or else getting one of the boxes out of my collection and hand making one. Too little time and too much money so I’ll probably buy one.

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