Hi all,
My CPC6128 has been in storage for some time as I don't have an original monitor. I wanted to convert it S-Video and perhaps make a uC SD floppy emulator. I don't know if it ever worked.
No good lol. It doesn't boot. It did once or twice out of about 20 power cycles.
I get a mostly blank screen with a square where the active video normally is. ie white screen and black border.
I am using the composite out to a TV and a small 5 Volt switch mode PSU rated at 3 Amps.
I noticed the board was a bit dirty and there was corrosion in some of the IC sockets (CPU) so I replaced three IC sockets and cleaned the board with metho. I used snap off SIL machined pins with gold inserts.
The three sockets I replaced were for the CPU, a small PAL (Programmable Logic Array) and another chip marked 40010.
Thinking the problem may be noise from the SMPSU, I put a 100nF cap across the 5 Volt input and upgraded the 47uF 5 Volt filter cap to 220uF.
I am guessing that the CPU is running as the registers in the 6845 need to set by the CPU to get video sync and I have sync.
The 5 Volt rail is at 5.05 Volts.
My next guess would be the DRAM chips but I don't want to socket 16 chips if I don't need to.
Does anyone have some experience or advice / suggestions that mat save me some time fixing this??
Any help would be greatly appreciated.
A screenshot would be helpful. There's a good chance it's RAM, but you wouldn't have to swap all 16 RAMs, the CPC only needs the first 64K to boot, so only 8 of them would cause this problem. Are any of the RAMs hot?
Bryce.
I have a 6128 I repaired about a year ago, amongst other things, the main issue was a bad Gate Array, the IC marked 40010. If you rule out the RAM as Bryce suggests, then the GA would be the next place I would look.
Mine did the same thing showing a white screen at boot until I desoldered the GA and put a socketed replacement in, after that it booted normally the rest was some dead logic to control the FDD. I suppose if enough corrosion has built up on the GA pins it might cause some issues so maybe start by checking and cleaning them if necessary.
Good luck!