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Hello, so the progress and findings: We've checked the all of the traces on all of the VRAMs sockets, from the VDP leg to the appropriate 4116 leg, all checked out and no shorts were found. ZD3 still gives -5.3V, but I guess this is within specifications (or would you suggest swapping it out with mo...

Hello, as promised an update. I'm not so sure that the -5V issue was the real culprit, all of the voltages check out now. We've replaced all of the 4116 video ram with modified 4164 which should not use the -5v line or 12V (we changed the ZD3 diode (second time) with one that now gives, -5.3V withou...

Sorry, I forgot to mentioned, that the ZD3 is the second diode that was replaced and R60 is also reading 1kΩ. Will check the voltage on D16 or D18 anode leads and for any other shorts. I'm sorry for asking stupid questions, should have referred to the previous post. Thank you for your input. :) I wi...

Hello, it's been almost a year of silence, but other things got in between but now it's time to get back to this wonderful project. To recap what has been done to the machine in the meantime. I recapped it, swapped all of the video RAM and socked it, changed the regulators and a diode (beside C49 an...

Thank you, I'll try this out. I'll get back to you on the results

Hello, it's me again :lol: So, first a recap: I have socketed all of the video RAM and I've replaced all of the 4116 with a known good one. the picture after it was like: IMG_20190713_123944.jpg Than i checked the voltages again, and I've figured out, that sometime during the replacement and resocke...

Good idea will also check for that. Thank you.

Will also do that, thank you.

Hello, thank you for the fast answer, yes the problem is reproducible if i turn it on and off again. I will concentrate on finding the next bad VRAM (or multiple of them). Any more tricks in helping to identify it? :) Regarding the keyboard, i have not yet come to fully debugging it, but the only th...

Hello, it's me again, reporting on progress and "progress". 1.) I managed to replace a faulty 4116 video RAM and i even managed to get it out in one piece. To determine the faulty IC i shorted the pin 14 with an 10 ohm resistor. I've added a socket and a new old stock 4116 (it's from a dif...