anyone do vaxstation repairs?

Ture enough. There is a lot of differnce between design and repair (I've done both, and FWIW, I do not regard the former as being necessarily more difficult than the latter...). Of course there are some common skills for both -- you'd better know how the components behave, how to solder, etc. But equally, repair (or more precisely diagnosis) of a design that's worked once is IMHO very different from working out why your newly-created design doesn't work -- for one thing in the latter case I would hope you know how you inteded it to work in the former case you may well not fully understnad the circuit. ASICs bring 2 problems. THe obvious one is getting replacements, but the obvious answer to that is to raid them off old boards... The lkess obvious problem is that the behaviour of an ASIC will probably not be fully understood. Which means you may well not be able to tell which signals on the pins are correct, which are incorrect, and wheter the incorrect ones are caused by incorrect inputs or a fialure inside the ASIC. That makes fualtfinding a lot harder... If you take a VAXstatiuon board, you could produce a sort-of scheamtic. It would show the ASIC as a 200-pin (or whatever) device and show what each of the pins linked to. Some might be very understnadable (power, ground being the really simple ones). But then some might not, particularly if there are several ASICs with traces that just link them. Given that sort od scheamtic, you could, I suppose, find broken tracks (2 pins not connected that the schematic shows should be) or shorts (the reverse :-)). But other than that, it';s not a lot of help. If you stick a 'scope (or whataver) on a pin and see a particualr signal, you can't know if it's right or not, You can't know if the timing is reasonable. So how do you know what to replace? A _meaningful_ schematic (and in my experience a lot of commercial schematics are not 'meaninful' in this sense) firstly names all useful signals (clocks, address/data buses, bus strobes, etc) and secondly shoews circuits in the conventional way (e.g. a pair of cross-coupled NAND gates froming an SR flip-flop is shown just like that, you don't end up with the 2 gates on different sheets). Having done it a few times, I am convinced that producing a meaningful schematic is a lot of work... -tony