1: check the 5v power and 6pin display sockets for dry solder joints. A dab of fresh solder will fix this.
2: check the rest of the board for dry joints too. This can be tedious but is worth it in the long run. Never touch the soldering iron tip to a joint for longer than 2 seconds to avoid damaging sensitive components.
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. Equal Equivalent ones are now nowadays frequently physically much smaller than the 1980's originals. So don't be surprised.
4: examine all resistors for signs or damage or discolouration. check resistance with multimeter multi meter and replace as needed.
5: Examine all the chips for any corrosion, damage or discolouration. All Virtually all the components are still available to buy online if you look hard long enough. 6: Check for damage to the edges of the board. these can often be fixed with a few wires to re-route broken tracks.
'''REPLACEMENT PARTS :'''
The Z80 cpu can be easily replaced for as little as £3 new, as can the 8255AP-5 interface chip Capacitors and the AY-3-8912 audio chipresistors are too cheap to mention. The CRT controller UM6845R FYI: buying a bag of 5 is about £4frequently little more expensive than buying just 1 or 2.50Then you have spares as well. They 85c rated parts are all made by several different manufacturers, with very slightly differing model numbers for what is the same productfine. So shop around first before buying one that 105c is over pricedexcessive and a waste of money.
Capacitors The Z80 cpu can be easily replaced for as little as £3 new, as can the 8255AP-5 interface chip and resistors the AY-3-8912 audio chip. The CRT controller UM6845R is about £4.50. They are too cheap to mentionall actually made by several different manufacturers, with very slightly differing model numbers for what is actually the same product. FYI: So shop around first and check the specs/pinouts before buying a bag of 5 one that is frequently little more expensive than buying just 1 or 2over priced. Then you have spares as wellLook at the chip model numbers on the cpc wiki mainboard images to check what will and wont work.
The gate arraysGate Arrays, usually either Amstrad 40007 or 40010 , are the only expensive parts at between £8 and £15. It's a suppliers market for these unfortunately.. They are The two models NOT interchangeable as they have different pinouts, even though some boards made potential allowance for either chip in their designs.
The last models of 464/6128 had an integrated SMD chip that removed For the floppy control circuitry, the need for NEC 765 controller can still be acquired but the SEC9420C buffer is a gate arrayhard one to track down. Luckily these cannot be swapped out and so would render any suck board are virtually never needed as scrap. In you are likely to have replaced everything else before getting round to that case cannibalise it and sell the partsanyway.
One common fault is probably someone having plugged a 12v PSU into the 5v socket. This usually fries some or all The last models of the ram 464/6128 (memory1989/90) and may sometimes damage had an integrated SMD chip that removed the need for a few ceramic capacitors along gate array. They were known as the way too"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 via eBay anyway.
