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So I made a small discovery.. and I feel a little silly.. The system is still broken but I found out what was causing the strange signal on the ram data lines. During testing I've had the monitor only plugged into the troublesome board, and no monitor plugged into the good board.. If I swap the...

The only way I found these broken traces was studying the Bomarc schematics and checking that every pin on all those buffer chips went to where they're meant to. Good luck!

Ok so I've just been checking the /IPL pins on the cpu. /IPL0 is constant 4.9v on the faulty board, and has a 6mhz (approx) pulse on the good board. /IPL1 is constant 4.9v on both boards, as is /IPL2 if I force the good board to crash, its /IPL0 pin tests at a constant 0 volts, versus the...

Thanks Melkhior, I've tested all those pins and here are my findings: /AS is held at 5v on the faulty board, and has a pulse on the good board. /BR is held at 5v on both boards. /BG is held at 3.9v on faulty board, 3.8v on good board. /BGACK is held at 5v on both boards. so does that mean...

Just a quick update on this Mac II, 6 months later and it's still running great! Something interesting though, I bought another Mac II because I have no self control, and it had exactly the same symptoms as this one - no nubus slots working. Turns out it had almost the same fault as this one...

the HALT pin on both boards is testing around 5.0v

Thanks, I'll check that tomorrow

Thanks for your reply David, on both boards the CPU reset pin 64 is approx 4.8v pdf

So I picked up another Mac IIsi (this brings the total to 3!) but I can't get it to work. I have it and another working IIsi sitting side by side on the bench and have been checking the signals on a scope and comparing between the two. Both have a good 20mhz clock signal at the cpu. The working...

Not too sure to be honest, I just assumed it was their own thing

Both the SE/30 and the Wallstreet are running Timbuktu 4.0 to allow screen sharing. Ah yes it does seem to vary a lot hey. I've done a few more speed measurements copying files over the network: (various system software versions etc) Wallstreet copying from SE30: 62k/sec Wallstreet copying...

Thanks for the info about the card. Using system 7.5.5 it will download at around 48kbytes per second from Macintosh Garden with Navigator 2.02

Thanks for that info, its very interesting. Oh, just using Timbuktu

Hi, I have an SE/30 with this A-series ethernet card (possibly originally for a IIsi) that works fine and has been working fine for years. It seems to work ok with no special drivers installed but transfers seem a bit slow. Does anyone know if there's specific drivers for this card that, if...

Oh yes it was a great feeling. The machine is reassembled now and has been running solidly. I've been experimenting with multiple nubus video cards and discovering some don't play so nice with each other lol. Also have an Ethernet card on the way for it 😄

Success!!! After many many hours of studying the Bomarc schematics and checking continuity of a seemingly endless list of pins and connections I found the connection between UC7 pin 6 and RP4 pin 14 was incomplete. I quickly ran a bodge wire for testing and it freaking works!! What a great...

No solutions yet but I’ve been painstakingly beeping out all the data and address lines between the chips, so far so good. Next step will be checking every pin on every chip one by one and hopefully finding something. Borrowed a thermal camera from work and had a look.. the only thing that stood...

Thanks David, that is a huge help. It definitely seems like I’ve been barking up the wrong tree in the wrong forest 😂. I’ll study Melkhior’s suggestions now and dig deeper. I’ll post my findings

Thank you David!

Thanks so much for your very thorough reply! Those measurements were taken with and without a card in a nubus slot. Voltages were measured before, during and after boot. There wasn't any noticeable change in the readings (keeping in mind I'm only using a multimeter). Resistance was checked with...