3: Check for any damaged or leaking capacitors. Check the ceramic ones too, in case a previous owner has knocked
and damaged one. Remember to replace any capacitor with a product of equal or higher voltage rating.
Equivalent ones are nowadays frequently physically much smaller than the 1980's originals. So don't be surprisedat that.
4: examine Examine all resistors for signs or damage or discolouration. check Check resistance with a basic multi meter and replace as needed.
5: Examine all the chips for any corrosion, damage or discolouration. Virtually all the components are still available
to buy online if you look long enoughsearch thoroughly.
6: Check for damage to the tracks at the edges of the board. these can often be fixed with a few wires soldered to
nearby points, to re-route the voltage around broken tracks and back where it was supposed to go. Remember to use wires that are the equivalent thickness or greater, of the broken track.
The CRT controller UM6845R is about £4.50. They are all made by several different manufacturers, with very slightly
differing model numbers for what is actually the same product. So shop around first and check the specs/pinouts before buying one
that is over priced. Compare at the chip model numbers printed on the cpc wiki mainboard images chips on these boards: '''''http://www.cpcwiki.eu/index.php/Mainboard_Versions'''''to check see what will and wont work. For example, the same CRT chip is listed under made by three sets of models numbers and different manufacturers.
Memory (1980s DRAM(that makes your 64k memory banks) is quite surprisingly easy to source from eBay as there are a surprising number of UK suppliers who still have stocks of authentic 4164 or , 4264 and 3764 dram chips. When changing the memory, change the four 74LS153 chips as well. These support the memory operation and so may have also been damaged. Don't forget to buy your 16pin DIP socketsas well. We don't solder in chips.. Sockets are far easier. Do not buy from microchips anywhere except the UK, US or Germany. There are too many eastern European and Chinese fakes around to be worth the minor savings.
The Gate Arrays, either Amstrad 40007 or 40010, are the only expensive parts at between £8 and £15.
It's a suppliers market for these unfortunately.. Look at eBay in France or Germany too, as they were big CPC markets back in the day. ( My last 40010 chip came from southern Germany). The two models chips are NOT interchangeable btw, as they have different pinouts, even though . Although some boards made potential allowance for either chip in their designs, only one type is ever used. For the floppy control circuitry, the NEC 765 floppy disk controller can still be acquired but the SEC9420C buffer is a hard one to track down. Luckily these are virtually never needed as you are likely to have replaced everything else before getting round to that anyway. The floppy controller chips are not required for the machine to boot btw. So they would never be the cause of a core failure to boot. All the other various chips labelled as 47LSxxx are easily bought from eBay or RS, Farnell etc. Even the older ones. The last versions of the 464/6128 (1989/90) had a more modern integrated SMD chip that removed the need for a gate array. They were known as the "cost-down" boards. These chips physically cannot be swapped out and so would render any such board as scrap, if it turned out to be the SMD chip. Avoid any major expenditure on these boards that cannot be recouped back via eBay, should the board be duff. '''REMOVING CHIPS:''' A subject often treated with a fear that is unwarranted. Just observe the following: Firstly make sure you are properly earthed with a £2 anti static strap that is plugged into a proper mains socket (via the earth pin, obviously..) Then get setup on a nice clear desk with a good lamp, preferably one of those with a large magnifying glass to look through, like jewellers use. Then get yourself an Antex 25w or 15w soldering iron with a smallish soldering tip on the end. You will also need a stand for it with a sponge for wiping off crud from the tip. A simple de-solder pump with plastic tip is also needed. Maplin sell all of these, as do eBay. Now you are ready. Clean of any dust from the chip in question and carefully snip the legs off the chip at the highest point, closest to the chip itself. Remember that we don't care about the chip as it is duff anyway. The mainboard and its tracks are what we have to protect.
For Once you have snipped all the floppy control circuitrylegs, the NEC 765 controller can still be acquired but the SEC9420C buffer is chip will just fall off, leaving a hard one bunch of legs or pins sticking up. Now use a pair of tweezers and your soldering iron to track downpluck out each pin in one piece. Hold the pin with the tweezers, melt the solder with the tip Luckily these are virtually never needed as you are likely of the iron and pluck the pin out of its hole. Like plucking eyebrows, or so I am told. Then use your de-solder pump and soldering iron to have replaced everything else before getting round suck out the solder from the holes where the pins were, ready for a chip DIP socket to that anywaybe installed.
The last models of 464/6128 (1989/90) had an integrated SMD chip that removed the need for This is a gate array. They were known as the "cost-down" boards. These chips physically cannot slow process but be swapped out calm and so would render any such board as scrap, if it turnedout to be the SMD chip. Avoid any major expenditure on these boards, that cannot be recouped via eBay anywaymethodical and you wont go wrong.