What to salvage from a CRT? - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: May 24, 2014, 12:00:14 pm
content: Hello,So I'm currently in possession of a couple of old CRT computer monitors and I wanted some advice on what I can salvage / reuse from a tear down.I haven't yet opened them to have a look, but I assume many of them have common components that one can find in each (transformers, etc). What should I look out for? What good components can generally be found in CRT monitors?I'm not necessarily looking to do "PhotonicInduction" type activities, but hey, who knows.Also, what should I watch out for? Such as discharging caps and whatnot? I know for a fact these monitors haven't been turned on in years, but I will still keep an eye out for things that might cause injury. Any advice on how to best tear down a CRT?And also, how should I deal with the disposal afterwards? I've got an e-junk center in my area, but should I watch out for any potential issues with the monitors once they have been disassembled?Thanks

author: jammet
author_rank: Newbie
timestamp: May 24, 2014, 12:28:05 pm
content: flyback? for fun?essentiallyheatsinksMOSFETsPower BJT'sChokes (but hell i dont know how to use them)lots of passivesvaristorsdont desolder them to the board, just get the board away. (remember to discharge caps, tube, well it wont kill you, it's just an uncomfortable spike)

author: made2hack
author_rank: Frequent Contributor
timestamp: May 24, 2014, 12:37:43 pm
content: How does one discharge the tube?

author: madires
author_rank: Super Contributor
timestamp: May 24, 2014, 12:52:03 pm
content: Yep, discharging caps and the HV anode of the CRT is a good advice. You could also keep the enamel wire from the yokes / deflection coils. Copper is quite expensive and enamel wire is very useful to wind coils. Afterwards I'd put the back cover back and bring the 'broken' monitors to the e-junk collection center.

author: madires
author_rank: Super Contributor
timestamp: May 24, 2014, 12:59:47 pm
content: Quote from: trs80 on May 24, 2014, 12:37:43 pmTake a screwdriver, add a wire to the CRTs ground and push the screwdriver underneath the round rubber at the CRT (where the anode wire goes to). I think there are some videos on youtube showing that method.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 24, 2014, 01:14:18 pm
content: Please don't call a tube monitor a "CRT".The big glass thing is a CRT .& the monitor is a monitor.Yes,I know a lot of Computer people call the whole thing a CRT------but this is an Electronics forum!

author: Evil Lurker
author_rank: Regular Contributor
timestamp: May 25, 2014, 06:20:59 am
content: Your typical computer monitor is a virtual cornucopia of components. Some of the goodies I look for are:Braided shielding wire. This is the stuff that looks like tinned desoldering braid and can be found wrapped around the tube and in the VGA cable. As it turns out, you can't desolder with it as is because solder will not wick. But if you have a little bit of sulfuric acid based drain opener like rooto you can wad up your wire into a little coil and add it into a small plastic container with a couple tablespoons of acid in it. Just enough to cover it. Interestingly enough the acid won't touch the wire. You can even add water to the acid (of course this is not good laboratory technique, do it a few drops at a time to prevent flash boiling!) and still nothing will happen. The trick is to add in a good dash of plain old 3% hydrogen peroxide a few drops at a time... the tin coating will be gone in literally a few seconds leaving bare copper braid behind. Basically you gotta change the oxidation state before the tin on the outside will dissolve. Weird but it works.Single digit and sub ohm power resistors. Typically you may never need these, but if you tinker with power supplies much you may find yourself needing a .27 ohm 3w resistor sometime.The UC384x SMPS controller. Most units will have some variant of this on board. Handy to have a few spares on hand in case you run up on a blown SMPS.Film caps. Many monitors will have film caps. Hard to determine exactly what dielectric they are made out of and their voltage rating, but the good news is they typically hold their values extremely well. Just make sure you don't overheat them while desoldering. I'm thinking that some of these film caps can be used bypassing, especially the 100nf ones. Also they are handy to have if you play with 555 timers and need some oddball yet extremely accurate value for your timing capacitor. I actually found one board that had "F" tolerance (+/- 1%) film caps.Mosfets, voltage regulators, and other IC's. IRF630's seem to be fairly common. I see a lot of boards with 7805's and 7812's along with the occasional LM324 and LM358. Outside of that there is usually a bunch of transistors and diodes that nobody has ever heard of before and probably never will again. Usually let those go.Flybacks and other inductors... kinda a pain to get off, but if you find the two magic pins on the bottom and rig up a 555 timer to drive a mosfet you can use one to throw some really nice big ozone producing sparks. You can also kill any excess mosfets you do not need this way too. Iductors... meh, not so much. Most of them are chokes with some weird permeability and low saturation currents. You might find a few power inductors mixed in. Save them I say. Still haven't figured out WTF those power inductors with the permanent magnet are for.Trim pots and potentiometers. Can't pass them up. Never know when you will need a trim pot. Also for what it is worth if you look on the "yoke" there is typically a small board with 3 trim pots on it. Usually two of these will be 10ohm trim pots. Yup, 10 ohms. Can be very handy if you need a very precise resistor value.Zener diodes. Handy to have if you work on SMPS. Can be a pain to identify though. Best way to test them is to use a LM317 rigged up as a constant current source just as you would with an LED, just turn it down to like 5ma or so for the small ones. That will give you the zener voltage and tell you if they are good or not.Ceramic capacitors. Always look out for radial MLCC caps and ceramic caps in oddball values.Hmmm lets see thats about all I can think of. Maybe snag the degaussing relay and PTC but that is about it. And they usually have some hefty through hole diodes...

author: SeanB
author_rank: Super Contributor
timestamp: May 25, 2014, 07:26:05 am
content: Inductors with the magnet on are linearity adjustment for the scan coils. They basically saturate at a predetermined current in one direction in a predictable way, and make the non linear current change required to make the beam sweep linearly across the screen. Without it the magnetics have a much higher sensitivity at the centre and lower at the outer edges, which makes circles look like ellipses. This decreases the current at the inner section ( near zero current where the inductor is not saturated) and it then increases current at the outer sections when the inductor saturates.Interesting thing to do to a working set is unsolder this and turn it around, where you will notice that it is a polarised device, as it then makes a massive difference to linearity. The inductor is in the horizontal side only, as it is easy to make a correction to the current drive for the vertical side as it is only 50/60/100/120Hz derived from a chip that uses an audio amplifier to drive the vertical yoke section with a current drive. Horizontal drive is derived from the line output transformer, as that is it's job, the power supplied generated from the flyback side are incidental, it is there to give a linearly rising current with time to drive the tube. Linearity has to be added on to the transformer, as the transistor driving it is a saturated switch.

author: made2hack
author_rank: Frequent Contributor
timestamp: May 26, 2014, 10:41:59 pm
content: @evil - I don't have any sulfuric acid or drain cleaner, I do have on hand nitric acid, some IPA, some ferric chloride, and I guess I can get 3% h2o2 from the pharmacy, any of these useful?In other tutorials, I noticed large loops of I guess copper wrapped around the base of the tube, is this the braided shielded wire you were talking about?If so, can't I keep it as shielded wire and use it in electromagnetic projects? Either as motors or generators? Or just use it when a coil is needed?