User:Deriss
Bought a 464 or 6128 from eBay ? Broken or not working right ? Read on..
Firstly, make sure you have a 5v regulated power supply and that your monitor / tv are working ok. (You'd be surprised...)
Make sure your power supply provides a minimum of 2A continuous current. Some PSUs can be very "optimistic".
On the 6128, you don't need a 12v feed for anything except the 3" disk drive. So it can be omitted for testing.
Earth yourself to prevent static damage or better yet, get an anti-static strap. It's a 30 year old machine remember...
Now carefully remove the case.. Be VERY careful with any keyboard membranes. You CANNOT buy these anymore.
eBay is The best source for spare chips and other replacement components that I have found, btw.
The obvious things on the board to look for first are:
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. Equivalent ones are 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 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 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 :
Capacitors and resistors are too cheap to mention. FYI: buying a bag of 5 is frequently little more expensive than buying just 1 or 2. Then you have spares as well. 85c rated parts are fine. 105c is excessive and a waste of money.
The Z80 cpu can be easily replaced for as little as £3 new, as can the 8255AP-5 interface chip and the AY-3-8912 audio chip. The CRT controller UM6845R is about £4.50. They are all actually 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. Look at the chip model numbers on the cpc wiki mainboard images to check what will and wont work.
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.. The two models NOT interchangeable as they have different pinouts, even though some boards made potential allowance for either chip in their designs.
For the floppy control circuitry, the NEC 765 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 last models of 464/6128 (1989/90) had an 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 via eBay anyway.
