Buying Second User flat screen monitors

Ask for a 1 week guarantee that it wont be Dead On Arrival, or within one week of delivery. If they are not confident to give you any form of guarantee - then it probably is not going to work..

This is important, because there are plenty of people who may sell you a monitor they know not to work well or be dead and then try to tell you "it was working when I had it". If you are able to view the item and see it working in person before handing over money, that is even better.

This is not normally necessary with new monitors because they come with a guarantee, usually for 1 year.

Monitors (yes even these flat ones) are heavy items, so shipping can be expensive. Check that you can be shipped to, and do not need to collect the item yourself unless you are happy to do so.

Also - make sure you know as much as you can before buying, as returning a monitor can be very expensive, and often, if there is a refund procedure at all, the cost of shipping is rarely included.

Getting a proof of posting or some kind of insurance is more pricey, but considering the price of a monitor itself, may be well worth it. Ask the seller how they will package it, as monitors are fragile items, and therefore need to be packaged appropriately - ensure it has been marked as fragile and that the seller agrees to cover any breakage in transit.

Try and get a consignment number and which method it will be shipped by.

Image: © Funniefarm5 | Dreamstime.com

Look at the specification. An LCD should be able to at least handle 1024 by 768, and preferably more - high end often deal with 1600 by 1200 with no problems. It should be able to display 16.7 million colours. Think about the refresh rates - if you are a gamer, you will need the highest you can find, whereas somebody who does mainly browsing/word processing could settle for lower with little consequence. Also be aware of the contrast ratio - this is how far the difference will be between the dark, and light areas of the monitor. If this is too low, your display may be a pale wash out.

A 15 inch LCD monitor as actually likely to give you a larger viewable area than a 15 inch CRT monitor.

Important note - You are strongly advised not to buy a monitor without a power supply unless you already know how to source the power supplies. Monitor power supplies tend to have high current ratings even if they are standard voltages and connectors. Some have specialist connectors or unusual voltages, or even dual voltages. Replacing these can be very difficult and expensive!

Check what comes with the monitor. Does it have a stand included? If not - how much will the required stand be. You probably wont be able to use a monitor without one. Ask for a manual, or failing that a web link to one - you will need it if you are lacking parts like the stand or power supply.

If it is a Rack Mount monitor- make sure you know how many units it uses and its heat dissipation. You will need to make sure the rack frame you get is complete. Always ask the seller about the completeness of these things.

TFT and Plasma are basically variants which are also flat screen. TFT- Thin Film Transistor technology is probably the more common type.

Check the inputs for the monitors. Are they DVI only, or can they accept VGA? They may be VGA only. Make sure the card in your computer can be connected easily with the monitor. Ensure that the required cable is easily available and standard(15 pin to 15 pin d-type) or that it is shipped with the monitor.

You will want DVI if you want to future proof the monitor. Remember - with DVI, pixels are exactly where they are meant to be, as opposed to DSUB - 15 pin where the position is approximated from the analogue signal. DVI means digital to digital and not digital to analogue and back to digital.

Some older LCD models actually require model-specific video cards, with their own connectors. Try to avoid these - they will obviously not be able to handle what your own Radeon/Geforce card can, and in the long run are a waste of space. If the monitors like these are not shipped with their adaptor card- they are also useless except for salvaging the actual display itself.

One thing also to be aware of is bad pixels. Depending on how you will use it, one or two bad pixels will hardly affect you. But run a mile if they specify black lines - when that happens - the LCD panel is pretty worthless. Ensure that you are aware of where the dead pixels are. If they are at the edge of the screen - they are not a problem, but ones in the centre will be. If you are buying the monitor from a shop or stall - ask to see it working. If they will refuse, simply refuse to buy it - a non-working bargain is a rip-off!

Some sellers will guarantee a certain maximum number of dead pixels, often they say no more than 9. Still - try and ask how many, 9 is enough to really annoy someone. Even with new monitors, this may be consider an acceptable limit with no more than 4 in the centre area.

eBay, gumtree and Dabs Auctions are a good place to start, they generally have a good range, but shop around, check out specifications on manufacturers sites as well as ads as some sellers are less than honest. Be very aware of power supplies, and push for a DOA guarantee. It may sound obvious, but try to buy from sellers who are honest, and those who list as much detail as possible.

In many cities and towns computer fairs do have traders which supply these. Make sure you get a DOA guarantee, or better still see them working. One fairly confident trader in London always has the stock turned on so you can see the relative quality. Ask about dead pixels, power supplies and see how new they are or if they are second hand.

Flat Screen monitors and a steady stream of older CRT monitors are now going on FreeMesa and FreeCycle, so check out your local freecycle mailing list and you may get dibs in on a freebie. People do not tend to give away the best, but some of middle range ones that people have replaced do go. Lets face it, there is no better bargain than free. You should be prepared to travel a bit to collect them with a car.

Make sure you get a power supply with it. There is a good reason LCD's without power supplies are so cheap. These DC power supplies tend to be expensive, high rated (in amps) and very hard to find.

Monitors may use standard plug types(ask this from the seller), but probably have pretty high current requirements. Many rate at 12v, 4-5 amps. The 50-60 Watt Power supplies required for these monitors tend to be pretty expensive.

Some, like Compaq monitors, have much less standard connectors. Take a look below for information on the Compaq TFT monitor.

One word of caution- fiddling with power supplies is only for the confident and experienced. Never use one that is over voltage, and always be aware of the required polarity for any device you are applying power to. Never use a power supply with a rating in watts below that of the devices requirement- you stand a good chance of blowing the supply and device- and at worst starting a fire.

Some particularly confident robot-builder/maker or tinkerer may be happy to remove the LCD panel itself from defunct Laptops, and these specialist monitors. If you are buying parts to do so, make sure you are able to get hold of the specifications you need easily - if you cannot find them online - don't buy the part. There is a good chance that the only controller chips are the ones embedded in the laptop chipset - and not general purpose at all.

There are some very clever folk who have used salvaged screens with removed backlight and backplanes with OHP's to make large projectors. However - if you do this, you must be very aware of the colour settings. It is fairly hard to get a really black black with this setup.

First hand from Dabs, Amazon and other online retailers can be interesting, as they sometimes have many ranges in stock. There are many people who have bought monitors online expecting certain features and not finding them. The most pertinent being DVI - generally, check carefully if monitors do both Analog and DVI, and if you buy one advertised as such, you may find they are analog only. Beware of other optional connectors like audio and USB, which are probably not present.

Monitors online can have a long lead time and stock problems due to their relative size and expense.

PC World can be expensive, and have a bit of a markup over other internet traders both in store and online. However - if you go instore, you can probably request product demos and see what you are buying. This means you can check all the connectors are there, as well as ensure you are getting the power supplies and video leads - these are another thing which online stockists may catch you out on if they are sold separately.

Dell Monitors tend to be a little on the expensive side, but they tend to look fairly good and be feature full. Dell also seem to ship with the least parts missing.

Most of this is common sense, and care, that should be taken when buying anything of value. Monitors are an expensive investment, and devalue quickly. Second hand ones are very cheap, but can be a risk. But do not take it as read that first hand monitors are always correct - be careful and aware in both cases.

Currently Flat Screen prices are changing rapidly- so watch you are not paying more than the going first hand rate for a second hand monitor.

All of this said - there are some seriously good bargains out there for these devices, have a look around, shop around, ask questions and get to know what you are buying.

Monitor title image and Jolly Roger are from morguefile.com.

Dead pixels demo image is based on image from FreeDigitalPhotos.net.

Power adaptor image from © Newlight | Dreamstime.com

Power supply image derived from Wikipedia and is distributed under the Creative Commons By Attribution Share Alike 3.0 license. In short: you are free to share and make derivative works of the image under the conditions that you appropriately attribute it, and that you distribute it only under a license identical to this one.

This was based on a blog post I made many years ago, and needed some revisions to bring it up to date, although plenty of the advice still stands - especially around guaranteeing you really know what you are getting. Monitors are seldom a cheap purchase, are fragile to ship and are very difficult to return - use this guide to make sure you've asked all the right questions from a seller before buying that screen!