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Category Archives: Electronics

I don’t think I’ve ever been accused of being loose with my spending. In fact, I believe my wife has the opposite complaint. As I understand, this is a common trait of the engineering type, whether it be from the inherent desire to cost optimize my life, or from the overzealous and overconfident way I say to myself, “Oh yeah, I can do that.” Which leads us to the topic of today’s post. What is the easiest way to aquire an expensive item? Buy a broken one cheap and fix it of course!

Today’s subject is a Nikon DSLR 55-200mm 1:4-5.6 AF-S VR camera lens. Prices vary only (as I believe the VR (vibration reduction) is now on VRII in the latest lenses), but around $100-140 USD. The main reason I wanted this, was that I had just picked up a Nikon D3200 setup and that package only came with the non-VR lenses. The supposed advantage to VR is reducing blur on shaky freehand shots, particularly useful on the 200mm zoom as your movements are amplified. This in turn allows for faster shutter, etc. The VR itself works by using accelerometers inside the lens, and compensating for movement by adjusting one of the internal lense elements. I picked one up on EBay for about $30, listed as ‘for parts.’

The listed issue was a stuck aperture. This is easy to test on the unit. Despite all the fancy electronics jammed into the lense for auto-focus, zoom position, and vibration reduction, the aperture is controlled by a mechanical lever that sticks out the back and interfaces with the camera. The lever doesn’t want to move, and the aperture is fully closed. No use waiting, time to open it up and look for the problem.

Nikon Lense Aperture Lever

Nikon Lense Aperture Lever

Aperture

Aperture

First step is to grab a thick piece of paper, like an index card, and a pen. I acutally picked this tip up in the comments section of a Hackaday article on IPhone repair. As you remove the tiny screws from the item, draw a diagram on the paper and punch the screws into it at the corresponding location. Much more effective than the ‘take a picture’ method (for screws anyways), and thick paper does a good job at holding them too, so they don’t roll off of your work bench.

Screw Card

Screw Card

While the most prominent screws are the three on the back side facing up, I’m going to remove the ones around the perimiter of the mounting ring. This frees the inner plastic pieces, and importantly, the connector piece. This prevents you from pulling this up with the rest of the mount ring and damaging the flat flex cable. However, when removing the mount ring from the back, there is a separate ground pin, connected by a screw on the back side and a single wire that can be damaged if you are not careful.

After all the screws around the inner perimeter of the mount ring are removed (5 in total), and the three larger screws on the face of the mount ring are removed we are ready to get inside. Be cautious when handling the lens at this point, as there is nothing holding the rear housing onto the rest of the lens anymore. An attempt to pickup the lens by the rear housing (where the model number is stamped) could be very surprising and disastrous. First thing you want to remove is the piece that sits inside the mount ring. This will free up the connector peice so you can move it out of the way and get the mount ring off.

Nikon Aperture Ring Disassembly

Nikon Aperture Ring Disassembly

Now, the aperture lever has an external arm that interfaces with the camera and an internal one that does the work. These two are in different spots, connected to a spring loaded ring that rotates along the inside of the mount ring. Remembering that ground wire I mentioned, the internal part of the aperture lever is far too long to be able to simply lift the whole assembly off the lense without damaging the wire. You can separate the metal aperture ring from the plastic mount ring by rotating it to a position that allows it to be freed. However, with the aperture stuck, well have to move the mount ring instead. First, to make it easy on yourself, remove the spring. I used a small flat screwdriver to guide the one side off the plastic anchor attached to the mount ring. You should only be able to move the ring one direction, the way that would have tensioned the spring. Once it gets past its normal range of motion, it should simply fall off.

Nikon Aperture Ring Disassembly 2

Nikon Aperture Ring Disassembly 2

For further repairs, or if you are doing this to replace the mount ring itself, you should detach that ground pin. I’m leaving it hanging off to the side with a little support underneath to avoid putting pressure on the wire. Replacing the mount ring only is actually a common repair, and you can find a lot of lenses on EBay with broken mounts. Commonly the camera is dropped and the plastic on the lens gives way to the metal mount on the camera. Replacement mount rings can also be purchased on EBay in the 1 to 2 dollar range with free shipping from China.

At this point you’ll notice several pieces of metal, which I believe are simply shims. Note the position and remove them if they are in the way. Now, carefully maneuver the connector piece out of the way and slid the aperture lever assembly up and out. This is were I noticed the potential problem in my lens. The inner lever has a slot in it, and there appears to be a lever with a pin inside the lens. As I was able to pull the part right out of the lens, it seemed obvious that these two parts should be mating, but were not. A quick probe with the screwdriver proved that that the lever with the silver pin operated the aperture. So now it is time to mate these parts up and reverse the disassembly process. The only thing I’m worried about now is that someone had trying to repair this lense already and reassembled it wrong, and I was going to discover another, more sinister problem.

Aperture Lever Pin

Aperture Lever Pin

Using the precision flat screwdriver again, I pushed the pin gently to the interior of the lens to make room to slide the aperture arm in such that the pin would enter the slot. Re-aling the shims, and flip the mount ring back into position. The problem I ran into here was that it was quite tricky to get the metal ring back into its channel on the mount ring in this position. The connector piece seems to find itself in the way, and the bits you need to align are on the blind side. I ended up moving the metal ring temporarily above the connector so they wouldn’t interfere with each other, and used a long nose pliers to pull the ring up into the mount. The entrance to the channel is in the position where the aperture is fully open (counter-clockwise), so you also have some new spring resistance from inside the lense while doing this. Once it’s in the channel, let it rotate all the way to rest (clockwise). Now you can put the other end of the spring back on its anchor. I do this by putting the small flat screwdriver inside the loop and letting it slide of the end onto the anchor.

Here you can put the three mount ring screws back on, provided the shim holes are still aligned. Now you should be able to give the lever a little test. I had to remove the ring and re-adjust the flat flex cable as it was somehow interfering with the ring travel. Now replace the one other piece you removed and insert all the screws as shown in your diagram.

On first test, everything worked! My only concern is the sound the autofocus was making, not loud, but much more audible than the ‘silent focus’ is supposed to be. But hey, what do you want for $30?

Thanks for reading, good luck, and happy repairs!

I just got in my new boards for the scoreboard project, and I was super excited to test out my plain old, unmodified toaster oven for some old fashioned reflow soldering. So I taped down the stencil and jig I had ordered from OSHStencils, and applied the solder paste to the board.

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One of my first concerns when settings up this first go at reflow soldering, was how expensive the solder paste was. Well, just as i had thought, it takes very little paste to cover all the little pads. I was concerned about waste, and while there was some paste left on the stencil and the spreader tool (a plastic card that also came with the OSHStencil order), I was able to collect most of the excess paste with the tool and place it back in the container. Since this was a large board, I started with a small gob of paste and worked the board in sections, alternating between thick spreading, and scraping it back up with the edge of the card.

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Placing the parts wasn’t too bad, I’d say it was easier than normal soldering with the 0603 resistors. I did expect the paste to be tackier, and while the parts did stick in place, it took very little effort to move them, so a stead hand is still needed to place and position. On the SOIC parts, the paste did seem to mingle between pads, but that wasn’t an issue at all. Once all the parts were down, it was into the oven.

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I tried to keep with the same methodology as the last post, although this time around I had black PCBs (since its an LED display, a dark background is preferred). While I’m only speculating, these boards reached much higher temperature much faster, I believe due to extra IR absorption. So this time I set the oven to 300F/150C on the convection setting (fan on). I let it heat until the thermostat clicked off, and waited until it clicked back on to turn the oven up to 400F/200C. This is were I was suprised. The black board started to flow as it approached this temperature setting, where the red board I had tested earlier flowed on its way to the 450F setting. Using a bright light, I was able to see the metallic shine of melted solder on all the joints. So once the thermostat clicked off, I shut the oven down and opened the door to let it cool. The board looked great, all the joints looked solid. There were a few were I could see that there possibly wasn’t enough paste on the pad, but the connections were still solid. The shift registers looked good, with no solder bridges.

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And the best part is, it worked!

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Even the digit chaining worked as expected.

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I think a proper diffusing sheet would make the final product very easy to read.

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And lastly, the Arduino code I used for the testing the digits.

/*
|***F***|
A       E
|***G***|
B       D
|***C***|

*/
const int D1 = 2;
const int CLK = 4;
const int STROBE = 3;

byte digitMap[10] =
{
	B11111100,
	B00011000,
	B01101110,
	B00111110,
	B10011010,
	B10110110,
	B11110110,
	B00011100,
	B11111110,
	B10011110
};


void setup()
{

	/* add setup code here */
	pinMode(D1, OUTPUT);
	pinMode(CLK, OUTPUT);
	pinMode(STROBE, OUTPUT);

	digitalWrite(STROBE, LOW);
	digitalWrite(CLK, LOW);
	digitalWrite(D1, LOW);


}

int state = HIGH;
int count = 0;
void loop()
{

	for (int i = 0; i < 100; i++)
	{
		byte Data2 = digitMap[i / 10];
		byte Data1 = digitMap[i % 10];

		//Write to display 
		for (int j = 0; j < 8; j++)
		{
			digitalWrite(CLK, LOW);
			digitalWrite(D1, Data1 & 0x01);
			Data1 = Data1 >> 1;
			digitalWrite(CLK, HIGH);
		}
		//Write to display 
		for (int j = 0; j < 8; j++)
		{
			digitalWrite(CLK, LOW);
			digitalWrite(D1, Data2 & 0x01);
			Data2 = Data2 >> 1;
			digitalWrite(CLK, HIGH);
		}
		delayMicroseconds(10);
		digitalWrite(STROBE, HIGH);
		digitalWrite(STROBE, LOW);

		delay(1000);
	}
}


Yeah I know, everyone is doing it. Reflow soldering with a standard counter-top toaster oven. While it’s not too exciting, I did want to document my successful test at using a cheapo oven I picked up at Goodwill for $10, completely unmodified. I had picked this up in preparation for some boards I’m going to make as part of my scoreboard project. While I was initially going to try to go for the ever popular reflow conversion, most of the modules out there for purchase seemed quite expensive ($60+, I’m cheap, I know). My own ballpark cost of making one myself came out to be $25-$30 (less if I skip the pesky mains isolated power supply for the micro). So while looking at the unit I had acquired, I figured it was at least work testing with built in front panel controls.

So the particular oven I picked up was a Black & Decker Toast-R-Oven 1500W, model TRO4075. Part of the reason I choose this oven over a $5 unit that was also for sale was that this one can the ‘Convection Bake’ feature, which means it includes an air circulation fan on the inside. From what I have read previously about reflowing, this can be extremely helpful for even heating and preventing hot spots.

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Oven Markings.

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Knobs.

Also looking at the front panel controls, it also already had its own temperature control and timer. Before the first test, I already knew the temp control wasn’t going to be very accurate, and the timer knob resolution not really useful as the first official marking (after light and dark toast) was 10 minutes. So for the first test I simply placed a board in the oven, set the temp to the 400F/200C mark, selected convection bake, and set the timer for dark toast.

The board I used was a 10cm square board that is almost the same board that I’m going to be assembling. The board is a double digit, seven segment LED numerical display. Foolishly I hit order to quickly on the first set, and being the amateur I am, wired the three LEDs of each segment in parallel instead of series. I only noticed after I tried doing the calculations for the resistor value and power ratings did I notice that I messed it up. While technically these boards would still work, having the LEDs in parallel can lead to current imbalance that can shorted the life of the individual LEDs as well as use 3x the power of the series configuration. The only major difference in the new boards, and I’m hoping this doesn’t have to big of an effect on the infrared heating, is that the test board was DirtyPCBs.com’s default red, and my new boards are coming in with the black solder mask. My other realization was that bright red would make a terrible background for a LED display, especially with red LEDs.

Anyways, back to the test. It was clear that the oven heats up pretty fast, probably faster than the recommended profile from the solder paste I’m planning to use. It wasn’t long before the existing solder on the pre-tinned pads began to wet. Now, I don’t have a thermocouple to measure the board temp with, so I only had my trusty el-cheapo infrared thermometer. Once the ovens own thermostat clicked the elements off, I measured the board at about 221C. Just over the melt line of the profile, but I do not have reason to suspect that the measurement was accurate by any means. I let it cook for a bit untill the timer clicked off and pulled it out of the oven after a short cool down. At first inspection all went well, no burn marks, scorching or other visible damage to the PCB. The only thing I had noticed was a bit of upward warping while the board was at peak temperature. On this board I had most of the wiring on the top layer and bottom layer is almost solid copper, so I’m guessing its a bit of thermal expansion of the bottom side that cause this. Not a big deal, it only appeared to be about a 2mm deflection at the one corner.

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For the next test, I just wanted to see how some of my extra 0603 resistors would handle it. I didn’t break out the stencil yet, so I just dabbed some paste on 8 footprints spread about the board. Pretty ugly, but the resistors stuck to it.

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In this test, I tried to follow a bit of a profile to keep the board from heating too fast. I started by setting the temp to the 300F/150C mark, then waited for the thermostat to click the elements off. I waited a few seconds, then crept the temp up the the 400F/200C mark again. I did the same by waiting for the thermostat to click off in the toaster. While this is enough melt the solder, the profile called for a peak temp of around 230-249, so for the final bit I set the temp on the toaster to its max setting, 450F/230C. After the thermostat clicked off again, I shut it down and took another temperature measurement of about 235C. I waited about 20 seconds and then removed the board from the oven to cool quickly. The results where not that bad, other than the slightly excessive amount of paste that was put down for the pads. Again no board scorching, discoloration, bubbling, or other faults. The resistors looked as though they survived as well, all measuring close to the promised 1K Ohms.

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Now as soon as my new boards get here, I’m going to be ready to try out my stencil and push a few boards through.