Changes
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.
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.
