embBambooLounge
Member
I am looking for a little help bringing a Macintosh Plus analog board back from the dead. When I first got the Macintosh Plus and plugged it in there was not much of anything happening. So, I decided to recap the board using the kit from Console5 as a first step. The sleeve on the side of the analog board has "heavy duty upgrade" written on it so it looks like they did the upgrade as suggested in Larry Pina's book. After the re-cap I was getting the bong from the motherboard after adjusting the voltage but I wasn't getting any high voltage to display. After inspecting the board I noticed that CR1 was cracked in half completely. I ordered a few replacements of CR1 and replaced the cracked CR1 and did CR5 while I was desoldering. I still wasn't getting any high voltage and after a bit of testing decided to check CR21 out of circuit and it tested as bad. I ordered the heavy duty upgrade replacement (CR20 was already upgraded) and when that part came I replaced CR21. Now, the computer powers up and has a long extended weird "bong" that sounds awful and after about 10 seconds R2 will start to smoke and fry followed by R3. Frustrated by this I decided to just order the "PicoPSU Adaptor for Macintosh 128K / 512K / Plus" and skip dealing with the analog board. So, I replaced R2 and R3, built the PicoPSU, plugged it into the motherboard and it works great as the voltages check out on the rear floppy port. I cannot hear a bong testing this way but using an oscilloscope it seems to be running as there's activity on the CPU and ROMs. After that test I hooked up the analog and boom - same issue. Extended crazy "bong" from the computer and R2 started burning up after 5 - 10 seconds (but high voltage comes on as I can hear the static). So, now I am at a bit of a loss. I've checked everything I can in circuit I could prior to replacing CR21 and now before taking another few hours to try and go through everything again I figured I would ping this group to see if there was any advice. Thank you for your consideration! Have a great day!