Blog Archives

Optoma HD20 DLP Projector – Dark Spot Repair

It Could Be Caused by a Burnt Lens That is Easily Fixable

Can You Find the Dark Spot Problem In This Image?

Can You Find the Dark Spot Problem In This Image?

Optoma HD20 DLP Projector

Optoma HD20 DLP Projector

The Optoma HD20 is a fairly popular DLP projector with a 1920 x 1080 native resolution and an attractive price tag. It also seems to be afflicted with an unusual tendency to suddenly develop a diffused dark area (sometimes inaccurately described as a blurry area) that may obscure part or nearly all of the projected image.  This sudden darkening may also be accompanied by a strong smell of melting plastic, because as in the case described here, plastic is actually melting and charring.

I had been looking for a full HD projector to use to build a high-resolution 3D printer, and I ran across this unit suffering from the dark spot problem on Craigslist for $100.  I was aware that projectors with this problem could be user-repairable, and when I looked at the unit I was able to see enough to determine that the large dark area on the right side was indeed caused by a melted inner lens.

Almost Unbelievable Meltdown of Internal Plastic Lens

Almost Unbelievable Meltdown of Internal Lens

The cause of the dark region on the projected image is an oddly-shaped aspherical plastic lens that is the final element in an optical path that channels light from the reflector lamp on the left front of the unit. … Read the rest

Tags: , , , , , , ,

A Milling Machine Spindle Camera

Modified Webcam Provides Tool’s-Eye View of Work

 

Camera Mounts in a 1/2" Collet In Milling Machine Spindle

Camera Mounts in a 1/2″ Collet In Milling Machine Spindle

It’s been a busy home-project summer (as in home-maintenance) but there have been a few shop projects that I have not had time to write about. One of these projects was the fabrication of a video camera that could be swapped for the milling cutter and used to precisely place a target under the cutter visually rather than by the numbers.

Sometime last spring I got the urge to buy and perform a CNC conversion on a small Grizzly G0704 milling machine.  Before beginning this project I knew there would be a need to machine stepper-motor adapters and other hardware components to a higher degree of precision and accuracy than I routinely care about.  And since many of the parts would have to mate with the machine castings, I needed a way to measure dimensions and hole spacings more accurately than by simply using a dial caliper.

Many other DIYers have built spindle cameras (I’m calling this one a mill-cam from here on), and a web search turned up several different approaches.  I incorporated many of their ideas into this design and added a few of my own, including the ability to adjust the tilt the vertical axis of the camera.… Read the rest



Unauthorized Streaming of Your TV Subscription Service?

Devices No Longer In Your Possession May Still Access Your Accounts

Reset or Deauthorize Any Streaming Accounts Before Selling or Returning Network TVs or Streaming Media Players

Reset or Deauthorize Any Streaming Accounts Before Selling or Returning Network TVs or Streaming Media Players

Okay, maybe the rest of the world knows about this, but I didn’t until a few days ago. And at least a couple initial levels of Amazon tech support didn’t recognize the source of the problem either…

To be more specific, the unauthorized streaming discussed here refers to a situation where your legitimate streaming account is being accessed and used by a party not known to you, the streaming account holder. This party can view your watchlist and your list of recently viewed movies, and you can view theirs. It’s an unwillingly shared account where you are the only one paying the subscription fee. The freeloading party almost certainly knows that they are tapped into someone else’s account; however it is possible that you may be unaware that anything is wrong if you don’t access your viewing history.

We subscribe to both Amazon Prime and Netflix streaming accounts, both of which have a recently watched category that displays any past movie or TV program that was played long enough to register. Netflix gets used the most in our house and has this list on its main movie page (at least on my Roku XS – other devices may differ), so it is visible every time you browse the movie lists.… Read the rest

Tags:

Homebuilt Video Camera Stabilizer

Preventing the Blair Witch Jitters

Homebuilt Stabilizer with Canon HF-M301 Camcorder

Homebuilt Stabilizer with Canon HF-M301 Camcorder

One downside to the ultra-miniaturization camcorders and other video recording devices is the increased difficulty in holding the camera steady. The earliest camcorders, despite their awful video quality by today’s standards, did from a pure stability standpoint have the inherent advantage of larger size and mass going for them. Resting a heavy camera on the shoulder tames some of the worst jitters, but palm-sized cameras simply aren’t large enough in any axis to stabilize against the body.

Using even the simplest video stabilizer with a camcorder can result in a large improvement in picture stability. Optical and digital stabilization in camcorders can only fix a limited amount of camera mishandling – it pays to have a stable platform to start with. Learning to balance and operate a stabilizer effectively will take a fair amount of practice, but even if your movements do initially wallow around a bit when tilting and panning, the worst jitters will be gone almost from the moment you start using it.

I probably shouldn’t start off trying to explain physics behind video stabilizers – it’s a topic that is well-covered elsewhere, and you may want to skip this beginning part if you are more interested in the project.… Read the rest

Tags: , , , ,

Edge-Lit TVs Are Like a Box of Chocolates…

Displaying LCD Technology in the Worst Possible Light

composite_LR

Top Left – Clouding
Top Right – Dirty Screen Effect

I would guess that LCD TV enthusiasts, owners, and potential buyers that lean more toward the videophile/home-theater end of the spectrum represent a fairly small percentage of the overall market. If you are part of this minority and follow discussions on AV forums dedicated to such topics, you will learn about quality control issues that plague just about every make and model of flat-panel TV on the market. In some cases you will learn about flaws that you may never have noticed on your own, and once they are seen they usually can’t be unseen. But it is better to be able to spot a problem immediately within a return or warranty period than to suddenly discover it on your own when it is too late. Being informed can assist you in making a better choice in selecting a TV; it can also cause frustration to find out that no matter what make or model you choose, luck almost always plays a role.

It is pure speculation on my part, but it seems plausible that the Edge-Backlit LCD TV business model has settled on this general quality control philosophy:

If it lights up and displays a picture, ship it.Read the rest

Tags: , ,

Equalizing CRT Phosphor Wear Patterns

Re-Use or Extend the Useful Life of CRT Projector Tubes

Proj A_green tube mod 533

Phosphor Wear Pattern on Face of One of Two Green CRT Projector Tubes.
The Effect of This Wear Was Reduced Using the Procedure Outlined Here

Note: this article is several years old but may still be of interest to some home theater enthusiasts.

CRT (cathode ray tube) projectors may be a dying technology, but they are not dead yet. Despite their size and weight compared with digital projectors, CRT projectors have some advantages that an enthusiastic subculture of home-theater aficionados cannot abandon, at least until something truly better comes along. CRTs can produce the deepest and most uniform black levels, and tube life far exceeds the lamp life of a digital. CRT projectors, despite their complexity, are highly repairable compared to a typical digital projector where even the replacement of the lamp may be cause to abandon the whole unit and buy another.

In a CRT projector three separate images produced on the faces of red, green, and blue tubes are converged and projected via separate lenses onto a screen to create a full color image. The light is actually produced by an electron beam striking a phosphor coating on the faces of the tubes.… Read the rest

Tags: , , , ,