From a 2003 trip to the States, I brought home five name-brand servos. They were given to me from a friend, and although they were installed in one of his planes, they had never been used. When I returned to Blighty I installed them in my trainer plane. That's when I discovered that four of them were bad. One of them didn't work at all, while the other three each had 'dead spots' at certain positions of their travel. Maybe they were damaged in transit, maybe they were bad from new. I figgered I was just unlucky. So 'twas decided to test any future store-bought servos before parting with my hard-earnt. Something was needed that was small, portable and wouldn't cause any funny looks from the bloke in the model shop.
The following circuit for such a tester was born.

The circuit is simplicity itself. It's just a two-transistor square wave oscillator, pumping out a series of variable 1mS - 2mS pulses over a 20mS frame rate. i.e: the standard used for most all servos. With the component values shown, the on-board 5K pot will rotate the servo arm approximately 90 degrees. The rotation is pretty linear, glitch-free and VERY smooth.
Since it had to be portable I stuck a +5volt regulator there, allowing the unit to be powered from a standard 9v battery.

Although there are 14 components in total, and one servo socket, the unit can be built on a square piece of stripboard measuring just 15 holes by 15 strips (fig.1).

Prepare the board by making 4 breaks in the copper strips as shown. Flip the board over and - with a 3mm drill bit - make these breaks at the following locations:

Next, add six wire links. Figure 2 shows their locations.

Now insert the five fixed-value resistors.

Next, solder the four capacitors. The two 22nF caps are monolithic types, so can be inserted with their legs either way around. The two 4.7uF caps are elerolytics and can only be inserted one way. Be sure to insert the longest legs (+) in the locations shown.

First, the two 22nF caps. Solder these at:

Now for the semiconductors. Start with the LED. Insert the Anode at B12 and the Cathode (denoted by a 'flat' on its body) at C12. Since you'll know when the unit is powered (by the movement of the servo), the LED serves no purpose other than it looks good.
Next, add the two BC182 transistors. Insert the left-hand tranny first. Solder the Collector at J3, the Base at K3 and the Emitter at M3. Solder the Collector of the right-hand tranny at K12, the Base at L12 and the Emitter at M12.

The last semi is the 100mA 5v regulator. Solder its output leg at L7, the ground leg at M7 and the input leg at N7.

If you use a 1A regulator, remember to transpose the input / output legs.

Fig.6 show the locations of the last three components. Start with the servo connector. Solder this at locations A1 (signal), B1 (pos.) and C1 (neg.). I robbed mine from a defunct PC modem board, but they're easily available from ESR or Maplin, etc. - as too is the tactile pushswitch. The switch I used is of the vertical type. I found it easier to hold the unit and press the switch with a thumb than if it were the horizontal type. The only reason you see a horizontal there is because it was easier to draw.
If you do use a horizontal, solder it at locations N2 and Q2. If it's a vertical, solder it at N1 and Q1.

The on-board 5K pot was robbed from a mashed servo. This is the feedback pot that couples directly to the servo output shaft. The same/similar sort of pot is also used in transmitter gimbal sticks. I'm not sure if they're available commercially but their small size are spot-on for this sort of stuff.
Solder this at locations:

Finally, the battery connector. Solder the black wire at M14 and the red wire at Q13.

No setting up is needed. Refering to fig.7, simply connect the battery, a servo, press the switch, then tweak the pot. Since the shaft of the pot is quite skinny, I pushed a small knob on there, making it feel better to turn. Or, otherwise known by our colonial cousins as, 'ergonomically-enhanced user deluxe version". Full rotation of the pot from left to right, and depending on component tolerances, will turn the servo approx 45-degrees either side of center.

'Twould be a sad world without veroboard, but there's no denying that it's not as versatile, or tidy-looking, as a dedicated PCB. Building with veroboard is sometimes seen as the poor man's alternative. But sometimes a simple circuit does not justify the hassle of etching a one-off board.
On the plus side, it can be made to look a tad more elegant by using a parts-placement overlay. With this, all you have to do is stuff the board where the components are already shown. Another advantage is that it reduces the likelihood of soldering components in the wrong locations.

The image shown on the right is obviously too large in the real world. It has to be reduced in size first. So once you've copied it to your drive, and in order to have the printout match the actual board dimensions, you need to set your printer reduction to 54%.
When you get your first printout, hold it, and the board, against the light, then align the holes nearest the corners. If you're lucky they should be pretty much spot on. If not, try adjusting your printer setting just one per-cent plus/minus either side. It's a case of trial-and-error for each individual printer. But starting with 54% will put you in the right numbers.
Once you're armed with the correct setting, make a final printout on gloss photo paper. Roughly trim it to size, but leave approx 5mm around the perimeter. Paste the board and the printout with Pritt-Stick, then align / stick them together. Try not to get glue on the printed side, because it sticks like you-know-what and looks pug-ugly.
Trim off the excess overhang.

Pushing them skinny legs of resistors, etc, through plain-paper overlay is easy. Pushing them through gloss paper isn't. Jab a needle through there first.

I've built five or six of these since -- gave 'em all away. But the image you see here is the very first version, and it differs slightly in that the stripboard is a tad larger from that shown in the above drawings. This one has a TO-220 type 1A regulator. The '220 is uglier and larger than the TO-92 version, but it does fit in there okay. If you do use one of these, remember that it's input/output legs are reversed. Later versions used the 100mA type.

A dab of hot-melt gunge is used to keep the pot sitting firmly on the board -- ditto on the tactile switch and red/black power leads. The finished unit, and battery, are both stuck to a scrap piece of PCB material with double-sided tape. And to make it even more ergonomically appeasing, the PCB material is shaped that it accommodates the width of the board, and then tapered where it meets the battery. It makes the whole caboodle more comfortable to hold and easier to operate. And I could make a living selling sand to the Arabs.