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Fun thing I just realized tonight that I’ll share… prior to replacing the ram the 22.184mhz crystal would only work after booting up without the turbo switch on, but after the ram upgrade to 100ns uniform ram it’ll boot with it on. So maybe it was worth it regardless of the faster crystals not...

@clifford did you make any other modifications to be able to get that 24+mhz crystal to work? I also am fully populated w/ 100ns ram, so wondering if there are other factors at play...

Good news and bad news... Good news is that the memory upgrade worked and we're running fine w/ the 100ns ram... Bad news is that the 24mhz crystal didn't work. :-(

WOOHOOO!!!!! It was U45 pin 15........ trace lifted ever so slightly! Re-chipping now... brb! Massive thanks for the invaluable resource that is https://www.minuszerodegrees.net/manuals/IBM_5150_Technical_Reference_6322507_APR84.pdf! 😅

@modem7 Do you have a photo or schematic that shows the top traces? I can't seem to find a clear photo where the traces aren't hidden under the chips to be able to test for continuity...

Didn’t change any of the dip switches, I should have tested more thoroughly at first and started with one bank at a time, but oh well… I’ll figure it out eventually!

Reflowed the connections and didn’t make a difference… checked continuity on the back traces and everything checked out, no cross-joins either… still need to check the front traces and also check voltages… I kind of suspect a power issue as well but not sure. Seems odd, but starting to feel like...

Would I expect the monitor to get power regardless of the motherboard?

Yup, tried that… same result. Also took out the pc-sprint and put the 8284A chip back in to take that option out of the loop…

Ok, update time… desoldered the bank 0 ram, put sockets in, loaded it up with new ram, and…. computer not booting properly. Here’s where I’m stuck… my monitor (5151) isn’t turning on at all now/not getting power it seems, board kicks on and isa slots are getting power (leds on)… I hear the...

Ok, just bought 50 KM4164B-10 chips... will take a few weeks to get here though... meanwhile I'll pivot to some other work on the computer!

Looking at the other chips that are in the sockets, some are clearly 200ns which won't cut it... also seems that I probably can't feasibly push the system beyond where 100ns would even matter... 100ns would work w/ 10mhz hypothetically which I don't think is realistic... eBay here I come!

Ya, seems like the soldered ram is probably the issue at the moment...

Didn't change anything, still hangs...

I think that's the issue though, like I can't actually disable those banks due to the bug...

Only Bank 0 which is 150ns... I still can't figure out what the other 3 banks have in them and google isn't producing any hits at all... Mystery chips!

https://www.minuszerodegrees.net/5150/misc/5150_27OCT82_less_than_4_ram_banks.htm <- info re: the BIOS bug...

I suppose that the 10/27/82 bios actually prevents me from doing what I was thinking now that I look at the docs... Maybe someone more knowledgable than me can confirm?

Ok, the 24mhz does the same thing... freezes immediately when I enable the turbo... I have another thing to try though... If it's a ram speed issue, I currently have the Lo-tech 1MB ram board in the system, but I'm using the ram on the motherboard vs. the ram on the card... I wonder if I can...

24.576mhz immediately caused the system to hang... moving down to a 24mhz crystal now... will let y'all know how it goes in a bit!