new here

One thing about taking it apart: before you do, record what card is in which slot. If you have multiples of a given card (for instance, more than one core memory card set), mark them somehow so you can put them back the way they came out. (N.B. for memory card sets: they ARE sets, calibrated as a unit - don't mix and match!) On the Omnibus, you should be able to put most cards into any open slot - it says so right here. But there is also documentation suggesting the ordering, such as the PDP-8 Maintenance Manual set (which is available on BitSavers). You may find that the cards are actually not in the "best" order. But if you record the original sequence, you can always get back to a situation where the machine probably once worked. When you check voltages, don't just look at levels. If you have or can borrow an oscilloscope (a good tool to own for this hobby), look at the power lines for AC component. A small ripple can be accepted, but the filter capacitors in these machines are well beyond their lifetimes. If you are the cautious sort, disconnect the filter caps and perform a leak-down test, replacing parts that fail. If you're really cautious, just replace them - that's what we do with power caps if they're over twenty years old. There's a date code on the part. Once you have the machine reassembled, take another look at the power buses. If you see a lot of higher-frequency noise on the power lines, some card has bad bypass caps. This can lead to frustrating intermittent failures, as digital logic interprets noise as signal. Core memory is particularly noisy. Just some things I've learned restoring these things.... -- Ian ________________________________________ From: cctalk-bounces at classiccmp.org [cctalk-bounces at classiccmp.org] On Behalf Of Tony Duell [ard at p850ug1.demon.co.uk] Sent: Sunday, April 24, 2011 7:39 AM To: cctalk at classiccmp.org Subject: Re: new here You;re in the right place, then :-) Ask away :-). I know what _I_ would do, it's the same for jsut abotu any clasisc computer. My procedure is basically ; 1) Take apart anything that will sensibly come apart. No, I don't mean to deoslder all the ICs from the PCBs. But pull out all the boards, remove covers, things like that 2) A visal inspuction (and cleanup), looking for burnt/borken parts, cooling fans tht don't run freely, open-circuit light bulbs, blown fuses, etc. Anything taht can be easily checked, is... 3) Electricla safety check. Check the contiuuity of the earth (ground) wire, and the iunsulation resistnace between live parts and the case (at at least twice the mains voltage, I normally use 1000V). 4) Assemble the PSU section only, and if necessary connect it to dummy load resistors. Power up and check the output voltages. Don't go any further until they're cortrect 5) Assemble a 'mimimal system'. CPU + front panel + one memory board, something like that. Get that working (at least ot the extent of running a simple program entered on the panel). 6) Add the remaining parts one at a time and check. If you cna run the manufacturers diagnostics, do so. But be warned that in soem cases such diagnostics will tell you if soemthing is wrong, but may not be too useful in actually findign the fault. DEC ones are normally OK, though. -tony