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New IIsi project - any tips?

JC8080

Well-known member
Check for chip enable on the ROM chips. There is crud around W1?
Check for bad traces around C34. Not only the nearby transistors/diodes, but also the CPU pins around 50/51.
I checked pin 82 of the MDU (shown as /ROMOE on the developer notes, and ROM SEL on the Bomarc schematics), it starts high and stays high. I also checked a couple address and data lines, all started high and stayed high, though admittedly I am not exactly sure what you should see on a address/data line.

This weekend hopefully I will have time to take a closer look for broken traces under a microscope, and also R&R the chips @imactheknife pointed out.
 

JC8080

Well-known member
Repaired! Though I say that with cautious optimism, since it is an IIsi, so "repaired" may be a temporary state.

I pulled off all ALS245s, and the upper and lower RAM chips closest to the ALS245s. The solder on the RAM chip closest to the cap by the power connector looked quite grungy compared to the rest. The ALS245 closest to the power connector had one broken trace and one that had continuity but looked highly suspect. I repaired the two broken traces, cleaned all the pads thoroughly, and re-installed the ALS245s and RAM chips. Powered it on and got a chime. I hooked up a monitor with fingers crossed, and sure enough it came up to the grey screen with the mouse cursor. I hooked up a mouse and BlueSCSI, and booted to the desktop.

@imactheknife and @David Cook, thanks for your help, as well as others that helped earlier.

ALS 245 broken traces 2.jpgGrungy RAM removed.JPG
 

imactheknife

Well-known member
Repaired! Though I say that with cautious optimism, since it is an IIsi, so "repaired" may be a temporary state.

I pulled off all ALS245s, and the upper and lower RAM chips closest to the ALS245s. The solder on the RAM chip closest to the cap by the power connector looked quite grungy compared to the rest. The ALS245 closest to the power connector had one broken trace and one that had continuity but looked highly suspect. I repaired the two broken traces, cleaned all the pads thoroughly, and re-installed the ALS245s and RAM chips. Powered it on and got a chime. I hooked up a monitor with fingers crossed, and sure enough it came up to the grey screen with the mouse cursor. I hooked up a mouse and BlueSCSI, and booted to the desktop.

@imactheknife and @David Cook, thanks for your help, as well as others that helped earlier.

View attachment 61566View attachment 61567
excellent:) glad we could help!! Always good to hear the chime:)
 
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