Stephen Adams plots the pitfalls of the used market
THERE ARE precautions which need to be taken when buying second-hand, as most equipment is sold "as seen". That means that you buy a computer with no comeback to the seller, as you determine whether anything works. Here is a simple list of things to check on ZX computers and it could well apply to the purchase of other computers.
Make sure you know what you are buying. Like buying any computer, first find what it is you are intending to buy. Read the advertisements and if they are for different models make sure you know what the differences are. Try, to find someone who has one and see what they think of your intended purchase. Also ask if you can try his computer to get the feel of it.
If it has some extra items, such as a printer - usually called peripherals - make sure that you know what they are like, too, as they may be offered with the computer as a package which may not be split. There is no point in having a Sinclair printer without a computer. If you have no friend to ask, try a computer shop, explaining first that you are intending to buy a similar machine and are not just wanting to play games on the shop computer.
The price of computers is falling rapidly, especially with the introduction of new models every year. ZX-81s can be bought for as little as £20 for the basic 1K model, 16K RAM pack models about £50. Prices for Spectrum 16K and 48K models are still indeterminate as Sinclair has just lowered the price to compete with other manufacturers - but never pay more than current price for the computer.
The weekly magazines are usually the best place to look for a computer, as the time between an advertisement being received and published is shorter. Check what is being offered with the computer and is included in the price - does it include postage, for instance, if you are buying by mail order?
Software should be treated with suspicion, as it is no use without the computer and costs so much initially to buy. Usually it cannot be sold on its own, so "includes £200 of software" should be treated as unimportant to the main price of the item.
It is not a good idea to buy from shops second-hand as they have to make a profit from somewhere and that usually means you, the customer.
Is the computer in its original packaging and does it include the manual and leads which are needed to operate it? If you can visit the seller, you can check the computer and equipment yourself. Look for worn jack sockets - they are difficult to replace - which are spotted easily as the plugs move about in them. That causes bad contact and intermittent power supply, crashes or loss of LOADing or SAVEing. The edge connectors can also wear out as they are only solder-plated and can be scraped away with over-use.
Ask to see the computer working for at least half an hour - that helps to detect over-heating problems - and try to SAVE and LOAD tapes using your own tape recorder, if you have one, at the beginning and end of the half-hour.
Check the keyboard for signs of wear and see if any of the ZX-81 keys are "dished inwards", indicating over-heavy use. Those keys will probably be the cursor keys and will be very difficult to operate. Also check the TV display to see if it wobbles about at the side; that is caused usually by a poor power pack or over-heating.
If you are allowed to remove the top, check for modifications to the board. On model 1 Spectrums there was an extra IC added which was sometimes soldered to the board, using flimsy wires; check that that IC is well-secured with tape and not wandering about the circuit board. On model two Spectrums an extra transistor has been added near the Z-80A; that is normal and fitted by Sinclair.
Sinclair printers are often offered as a package with the computer and are provided with a large power supply - 1.2 amps. Make sure you receive that if you buy a ZX-81 with printer, as otherwise neither the computer nor the printer will work with the original 750ma power supply and would damage it.
|'It is not a good idea to buy from shops as they have to make a profit from somewhere'|
ZX-81 hardware does not usually wear out but Sinclair 16K RAM packs seem to lose their grip with age and can intensify the original RAM pack wobble experienced with them.
I hope these hints will help you when attempting to buy a good second-hand Sinclair computer.
Remember that it is pointless having a computer unless you want to do something with it. So make sure it fits the purpose you have in mind, even if it makes you decide against a Sinclair.