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your welcome, remember ram of that age has no static protection like they do these days, so just handling them can easily give them a static shock which can kill them immediately, or in months to come as they damage easily, you are not aware thatch even happened, but it can and does kill ram and old MOS chips, you don't even have to be moving to create static in excess of 2000v

Yeah, get stuck in there. I reckon you'll fly through the next one. Remembering what I was saying about the diags, it would have probably told us straight away what the issue was by firing one of the triacs. There's about 5 or 6 different checks it does on initialisation and if any of them fail it fires it's designated triac so you know where to go looking. Still we got there in the end and that's what matters. Thanks to Andrew too, two heads are always better than one especially my one.

I doubt it was your fault bob only thing I can think it broke pushing in other ram? It was pin7 anyway it’s now on soak test in adders and running fine thanks again to you and Andrew for the help dare i start board number 2😵

Or Bob even... Blimey Ronnie it's certainly giving you the run around. Which pin on IC7? I'm always really careful when removing chips although the odd track does get broken once in a while but instantly repaired. Is this top or bottom of the board? I always inspect the joints afterwards (underneath) with my microscope just in case. At the end of the day though I do apologise if it's something I missed.

Well if it still doesn't boot without the 6840 then it's not that. The chip could still be faulty though but it's unlikely. Backtracking a little, I know you said you swapped out the RAM but are you 100% sure the other RAM was good and did you also try the RAM from this board in another board to confirm it was OK? I suspect you've done all this but just in case.

if there is shorts between those it would have shown up on the scope as lower waveforms as they would be battling against each other, but you checked that

Hmm, this could be one of those ones where you swap out all the 6821's and it still doesn't boot. Trouble is you won't know till you get there. Been here a fair few times I can tell you. Other things I've had to check in the past were any shorts between any of the Address lines and also between any of the Data lines. The worst thing when you can see that the 6821's have been changed is that someone was chasing a fault and maybe never found it. Don't you just hate them for not putting sockets in too!! This is where running the diags can be really useful but hey ho.

She lives! Not got any sound but getting there