Hi, I've recently got cost down 6128 but one resistor is burnt (R123). Does anyone know some schematics of Z80330 (with resistors values) or correct value of R123?
The schematic you're looking for is in Amstrad CPC464-6128-GT65-CTM644-MP3-CT1 Amendment Service Manual (http://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.zip) P21.
R123 is a 2.2k resistor, but if it burned, I have little hope you that can bring the 6128 up again.
It's a pulldown on ROMDIS from the expansion port, so a voltage much higher than 5V must have been applied to burn it and the ASIC might not have survived too.
To burn a 1/4W 2.2K resistor you'd have to connect at least 25V directly across it for more than a few seconds. If the rest of the PCB survived that I'd be extremely surprised, however, if it really is burnt I'd expect more visible damage on the board. Are you sure it's burnt or is it just baked on dirt? Have you measured it's resistance?
Bryce.