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Great advice! And yes this is a linear power supply in this machine. The 22v rail is responsible for powering the inbuilt CRT. I haven't started going over the chassis yet but I think this will be the culprit. I will test crt using Bench power supply with inbuilt protection once power supply is...

Thanks for your reply. This is on a centre tapped transformer within the power supply. Being used for Vcc rectification to the power regulator. I was going to try 1n series diodes with regulator isolated and see if Vcc comes up...

Hi all, Have a Sanyo MBC-775 on the bench for repair. Have managed to resolve issues with 5v and 12v rails, but the 22v rail is being problematic. In the process of isolating components for testing one of the following diodes legs detached when removing from circuit. Could anyone help me ID a...

Hey All, Had a win and the apple now boots and shows Apple ][ on the screen. I ended up removing and socketing all the ram ic's and replaced a few bad ones. The diagnostic ROM passes both RAM and ROM checks. Now I have a problem with keyboard input. The reset and control keys work to reset...

Hi Folks, I have a couple of Apple IIe's for restoration. I have made a start on the first system. I have got to the point I am now getting random characters on screen. I assume it has faulty RAM on board. The 3x2764 mask ROMs all failed to read properly and have been replaced already. I...

Hi All, Just a quick intro for myself. I am in Australia, Brisbane to be exact. I'm into repairing micro systems, just as a hobby. Currently working on getting a 1980's S100 working again. I am looking to purchase a new logic analyser as it's about time for an upgrade. Open to all and any...

Hi Mike, Thanks again for your help. The card lives! I have managed to get it booting and talking over RS232. A couple of things: The board is marked SBC-780 (Rev-A) but the MON code for the 880 so far works. I replaced the MC1488/MC1489 Serial Driver/Receiver chips with a MAX232. This means...

Hi All, I have a S100 Z80SBC board from the 1980's that I am restoring as part of a larger S100 system. Problem is the 2708 ROM on board has lost it's contents and returns garbage when read using multiple eprom programmers. The manual for the card can be found online here...