Re: ICL OPD 3 vertical white stripes fault
Posted: Mon Jan 22, 2024 11:39 pm
Sorry, it's confusing as I'm talking about 2 different OPD's (both being used with one sort-of working CPU board). Here is the progress, or lack of it, from today.
The one with 5 white stripes: On the SRAM chip /CE2 is at batt voltage with no power turned on and it goes low when powered-on. /CE1 goes high when powered on. As far as I understand it, that's normal so is fine. I found a flow chart for the OPD and gleaned that the SRAM has connections/inputs with the ULA (IC21), the 74HCT257 pair of chips (IC23 and 24) and with a 74HCT245 (IC22). I've checked all those and they all checked fine. So I'm a bit lost now. Could the Sinclair ZX8301 be dud and could that cause an SRAM error? I have a couple of spares of those. And also, I suppose one of the RAM chips could be messin' things up if dud.
The one that goes into a boot loop: I will certainly check the stability of the 5v rail tomorrow. I've also ordered another known working ROM pack, as that doesn't seem to do anything when plugged in.
The one with 5 white stripes: On the SRAM chip /CE2 is at batt voltage with no power turned on and it goes low when powered-on. /CE1 goes high when powered on. As far as I understand it, that's normal so is fine. I found a flow chart for the OPD and gleaned that the SRAM has connections/inputs with the ULA (IC21), the 74HCT257 pair of chips (IC23 and 24) and with a 74HCT245 (IC22). I've checked all those and they all checked fine. So I'm a bit lost now. Could the Sinclair ZX8301 be dud and could that cause an SRAM error? I have a couple of spares of those. And also, I suppose one of the RAM chips could be messin' things up if dud.
The one that goes into a boot loop: I will certainly check the stability of the 5v rail tomorrow. I've also ordered another known working ROM pack, as that doesn't seem to do anything when plugged in.