Firstly, make sure your 5v '''REGULATED''' power supply and monitor / tv are working ok. (You'd be surprised...)
Check it with a multi meter and make Make sure it your power supply provides a '''minimum ''' of 2A continuous current. Some PSUs can be very "optimistic".
Some modern switch mode PSUs are very optimistic in their "ratingsOn the 6128, you don't need a 12v feed for anything except the 3"disk drive. So it can be omitted for testing.
You donEarth yourself to prevent static damage or better yet, get an anti-static strap. It't need s a 12v feed for anything except the 3" disk drive30 year old machine remember.. So it can be omitted for testing.
Earth yourself to prevent static damage or better yet, get an anti-static strap. 30yr old machine remember...
Now carefully remove the case. Be bl00dy careful with any keyboard membranes. You '''CANNOT''' buy these anymore.
The obvious things to check first are:
1Btw: check eBay is one of the 5v power socket and DIN6 display socket best sources for dry solder jointsspare chips and replacement components.
2: check the rest of the board for dry joints too. Never touch the soldering iron tip onto a joint for longer than 2 seconds. This is to avoid damaging components.
3: Check for any damaged or leaking capacitors. Check The obvious things on the ceramic ones too, in case a previous owner has knocked one.board to look for first are:
41: Examine all check the chips 5v power and 6pin display sockets for any corrosion, damage or discolourationdry solder joints. A dab of fresh solder will fix this.
The most common fault 2: check the rest of the board for dry joints too. This can be tedious but is probably someone having plugged a 12v PSU into worth it in the 5v socket and damaged 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 one. Remember to replace any capacitor with a product of equal or higher voltage rating. Equal ones are now frequently physically smaller than the 1980's originals. 4: examine all resistors for signs or damage or discolouration. check resistance with multimeter and replace as needed. 5: Examine all the chips for any corrosion, damage or discolouration. The main Z80 cpu can be replaced for £3 and is always socketed. The rest can be sourced for between £2 and £6 each from eBay, if you look around. Capacitors and resistors are too cheap to be even worth mentioning. The gate array (40007, 40008 or 40010) is the only expensive part at between £9 and £15. (Suppliers market for those unfortunately..) The most common fault is probably someone having plugged a 12v PSU into the 5v socket. This usually fries some or all of the ram (memory) and may sometimes damage a few ceramic capacitors along the waytoo.