Hi to all,
2 year ago i have turned on my C128 and after 3 hour of gaming in C64 mode i have turned off it...Again, in the same day, i have returned it on but without use it, only stay on in C128 mode. About after 10 minute the screen going to black, in both mode C64 or C128. This with a normal LUMA CHROMA output, but same with RBG.
I have checked power supply and replaced with another one, but all are ok and all respective point on the board have a correct power value.
I have fast checked it, replaced socketed rom but nothing and i have decided to store it. One Week ago i have decided to try rapair the board....................but.....................it's impossible..........Why?
I have replaced the RF modulator but nothing.
I have replaced and socketed all RAM and tested on C64 and all are ok but replaced with another 16 new tested chip, i have replaced all ROM and reburned new in a 27c128 EPROM but nothing (tested originale and burned in other 128 and all ok)
I have replaced and socketed Zilog Z80 CPU and tested original in a different computer (KAYPRO II) and it's working perfectly.
I have replaced and socketed MOS 8502 CPU with four new one tested in another C128 and all working perfect.
I have replaced and socketed video RAM and tested it in another computer and its working perfect.
I have replaced the MOS 8563 and MOS 8566 video chip but nothing, tested in other C128 and working.
I have replaced the MOS 8721 PAL and MOS 8722 MMU but nothing, tested in other C128 and working.
I have checked clock signals, present but i have replaced both oscillator nothing changed, replaced regulator capacitor on video section, nothing changed.
At this point i have decided to replace the 74LS06 and check on a reset circuit but all is ok, Then i have...........................socketed and replaced ALL, very very ALL logic chip on the board, but nothing same problem.
With the Diagnostic Cartdidge setted for C64 mode i have a correct tools border and background colors but garbage and colored character, then in C128 mode settings i have same black screen.
With the Jupiter Lander cartridge it's try to start bud i have a garbage screen, smilar at C64 with a broken kernel rom.
I have printed schematics on paper and i have starded a trace check................................................i have checked all trace, dataline, address line, power, logic, very very all trace, section per section.....all trace are ok!!
Then i have passed all data line on CPUs, MMU, PLA, SID, RAM and CIA chips with scope...........and:
When i insert Jupiter Lander cartridge i have pulse in all dataline of 8502 SPU and in all Address Line of it.
When i isert a Diagnostic Cartridge and system stays in C64 mode with previouse mentioned garbage screen i don't have any pulse in Address line, or little oscillation at 5 volt, and nothing in dataline.
Then i have tried to turn on it or reset system frequently and i have noted the addressline, in any case pulse, and in other case pulse one second and then stuck.
Now i have lost all ideas!
I have repaired other C128 o C128D or C64 and more and more different computer, but this is impossible!
Can anyone help me?
Thanks
Emanuel
2 year ago i have turned on my C128 and after 3 hour of gaming in C64 mode i have turned off it...Again, in the same day, i have returned it on but without use it, only stay on in C128 mode. About after 10 minute the screen going to black, in both mode C64 or C128. This with a normal LUMA CHROMA output, but same with RBG.
I have checked power supply and replaced with another one, but all are ok and all respective point on the board have a correct power value.
I have fast checked it, replaced socketed rom but nothing and i have decided to store it. One Week ago i have decided to try rapair the board....................but.....................it's impossible..........Why?
I have replaced the RF modulator but nothing.
I have replaced and socketed all RAM and tested on C64 and all are ok but replaced with another 16 new tested chip, i have replaced all ROM and reburned new in a 27c128 EPROM but nothing (tested originale and burned in other 128 and all ok)
I have replaced and socketed Zilog Z80 CPU and tested original in a different computer (KAYPRO II) and it's working perfectly.
I have replaced and socketed MOS 8502 CPU with four new one tested in another C128 and all working perfect.
I have replaced and socketed video RAM and tested it in another computer and its working perfect.
I have replaced the MOS 8563 and MOS 8566 video chip but nothing, tested in other C128 and working.
I have replaced the MOS 8721 PAL and MOS 8722 MMU but nothing, tested in other C128 and working.
I have checked clock signals, present but i have replaced both oscillator nothing changed, replaced regulator capacitor on video section, nothing changed.
At this point i have decided to replace the 74LS06 and check on a reset circuit but all is ok, Then i have...........................socketed and replaced ALL, very very ALL logic chip on the board, but nothing same problem.
With the Diagnostic Cartdidge setted for C64 mode i have a correct tools border and background colors but garbage and colored character, then in C128 mode settings i have same black screen.
With the Jupiter Lander cartridge it's try to start bud i have a garbage screen, smilar at C64 with a broken kernel rom.
I have printed schematics on paper and i have starded a trace check................................................i have checked all trace, dataline, address line, power, logic, very very all trace, section per section.....all trace are ok!!
Then i have passed all data line on CPUs, MMU, PLA, SID, RAM and CIA chips with scope...........and:
When i insert Jupiter Lander cartridge i have pulse in all dataline of 8502 SPU and in all Address Line of it.
When i isert a Diagnostic Cartridge and system stays in C64 mode with previouse mentioned garbage screen i don't have any pulse in Address line, or little oscillation at 5 volt, and nothing in dataline.
Then i have tried to turn on it or reset system frequently and i have noted the addressline, in any case pulse, and in other case pulse one second and then stuck.
Now i have lost all ideas!
I have repaired other C128 o C128D or C64 and more and more different computer, but this is impossible!
Can anyone help me?
Thanks
Emanuel