There's a difference between it running now, and the restoration methods :-) Have you read the report in Computer Resurextion? (This is the _only_ indformation I have seen on this project). There were a couple of things that really upset me... -tony

I don't have the appropriate copy of Computer Resurection to hand, but hope I've kept the meaning) 'After basic electircal safety tests we applied power and the machine appeared to start up correctly' 'However one part proved unreliable, we replaced all the PCBs, but it was still unreliavly. In the end we discovered the power supply was faulty, so we replaced that' Now, as to my problems with that: The first thing is to consider why htis machine is 'special' After all, a PDP11/73 while a nice compouter, is hardly rare. This installation may well ahve had special data input or display hardware, of course, but I would cuggest the main reason that it's significant is what it was used for -- its provenance, if you like. With that in mind : They don't say what the 'electrical safety tests' were, but I would guess it means using something like a PAT tester (an instruemtn, which IMHO should be banned, but that's another rant). That is nowhere near enough before powering up a significant machine. If it were mine, I would _at least_ completely dismantle everything that could be dismantled without damage (i.e. not open up HDAs...), then do a complete visual inspection, looking for any poissible futrue problems. Then, if there is custom hardware, consider making backups of any programmed parts (EPROMs, etc) -- if they are socketed. Note down the configuration. Reassemble the PSU and check it on a dummy load (This would have found the intermittant fault, I suspect). Check and clean (and maybe lubricate) all cooling fans. Now we come to the 'repair' : My dislike of board-swpaping in legendary here, but I find it particularly bad in this case for a couple of reasons. With an internmittant fault, the only way you can know you have cured it is to know what cuased it (and then to correct that). Swapping boards won't help. An intermittant fault could be caused by a bad connection, whcih is distured and then works well enough so that you think you've fixed it, only for it to recur some time later. And as I said earlier, this machine is significant for its provenance. In which case (in fact for any museum machine), the smallest possible part should be replaced -- the machine should be kept as original as possible. Which brings me on to the faulty PSU. Firstly, why wasn't this checked before the machine was even assembled and brought into service? Secondly, even if you take tht risk, the first thing that IMHO you do with a malfunctioning machine is check the power supply rails with a voltmeter _and 'scope_ at the backplane. And then why replace the PSU. Why not repair it? Again, keep the machine as origianl as possible. -tony

That doesn't appear to be the articel form Computer Ressurection (it says as much on the sitr). I;ve read it, and I agree that I had misremembered some details. However, I feel my 2 major commetns still stand -- that not enough checking was done (or at least it's not recorded as being done) before the machine was powered up, andthat a PSU was swapped out when it should have beeen repeiared (to keep the machine as origianl aas possible) A minor comment. If this PDP11 is like most of the more recent models that I've worked on, then eorrr code 77 doesn't mean a PSU failur. What it meansis that the CPU hasn';t tried to write to the error display latch. This could be because the PSU hasn't deasserted DCLO (I think, maybe ACLO), it might be because the CPU isnt; clocking, or has failed trotally. Inb otehr words, to me, it would indicate I should stick some test gear on the DCLO (and ACLO?) lines, then if they're OK, strt debuggihnthe CPU board, and if they're not, dive into the PSU. I disagree. It's entirely possible for somethign to break loose in shipment and cause damage when the machine is powered up again. With some PSUs desgins (I doubt the one in this machine is like that), jsut one dry joint openign up can ruin every IC in the machine. Just about every year I cart one of my HP desktop machines to the HPCC mini-conference.. And although I have been running it in my workshop the night before the first thing I do when I get it ot the meeting is test the PSU on a dummy load. I'd rather have to fix the PSU than have to fx the PSU _and replace most of the logic chips_. This has not been my experience at all. I have never had any problems dismantling and reassembling a machine. And I take my machines apart a lot more than most people would (since I demonstrate them to friends, etc and I _always_ take them apart to explain the internals). I also would claim that field service repairs and museum restorations are totally different things (if only because field service cna genrrally get any new parts they need, museums cannot). I would question that field service people are necessarily the best people to do museum restorations (as you seem to imply). There will be some that are, sure. And there will be some that just follow the CE manual and are completely helpless when they don't ahve a swap kit to hand. I don;t beleive there's any correleation between ability to repair a machine, and whether or not you work(ed) for the manufactuer a a field serviceman. -tony