• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

Weekend fun: SE/30 RAM fix

This is my first serious post in 68kmla. I only started playing with old Macintosh since this year and I already have good collection of compact one and a big pile of “pizza boxes”. I just spent this Saturday trying to fix an SE/30 I just got from eBay with a description of “recapped, having issues”. The logic board is in surprisingly good condition, much better then my previous two that have corrosions everywhere.

The machine will play dead chime as soon as powered up then simasimac. At least I know the CPU, ROM and Sound is working. Something is wrong with the RAM and it remains the same no matter I put what memory on the slot. I pulled out another working logic board from another SE/30, removed all SIMMs and measured key control signals with oscilloscope. I can see even without SIMM and machine is dead after dead chime, the ROM will keep accessing all SIMMs in a loop, all CAS and RAS signals are toggling with fixed interval on all SIMMs.

Now go back to the bad logic board, After probing same CAS and RAS signals (Second pin in each SIMM from left and 4th from right), one CAS and one RAS in Bank0/1 are missing! I then traced back to UD1 (Inverting buffer to generate all RAS and CAS signals) and all signals are there. I remove the RP1 and still connect find where is broken until I checked each pad one by one under magnifying glass only to find a tiny gap right on the neck of one pad.

I rewired enough signals for Bank1 with discrete resistors to continue the test. Still dead chime. I then realized that I need Rominator-II in my situation that I only have SIMMs in Bank1. The board is booting after that. I am waiting for a real resistor-pack to be delivered from digikey then I can fully recover this.

A list of “essential” tools for anybody who is really serious fixing SE/30 logic board issues:

1. A BlusSCSI dongle for hard disk emulation, internal 50-pin version or external DB-25 variation
2. RGBtoHDMI dongle with TTL/DB9 hook up to the logic board directly with a Molex Mini-fit 14-pin receptacle, then you don’t need analog board and CRT and trying to put logic board in a impossible location when measuring signals around. I have to revert to last firmware in 2023, the latest one will just keep flickering.
3. A set of bench lab power supplies to provide all power rails to the same Molex connector.
4. Floppy drive emulator from Bigmessowire. It is really wonderful.
4 a speaker that I hook up to the headphone jack to hear the bong, or dead chime.
5 good magnifying glass with light.

Really appreciate great guys in the forum, those knowledges are priceless. Especially thanks to those YouTube videos from techknight.

Good night.

Attached some pictures of the logic board, gap near the pad and my bench. Hope you enjoy this.

IMG_0009.pngIMG_0673.jpegView attachment IMG_0671.jpeg


Well-known member
Many people use an ATX extension cable to be able to power the board outside of the chassis for diagnostic work, that might eliminate the need for the RGB->HDMI dongle, though I do see how that would be a nice setup.