test-drb

test-drb@ccmp.vtda.org

101090 discussions

Possibly going up to VCF, stuff I would like to sell/get to proper people pdp8/12/HP stuff

by cz＠alembic.crystel.com

Hi all! I'm thinking about going up to VCF in Wall next weekend. I haven't been to it since it was the Trenton Computer Fest (think late 1990's) so I'm not sure what the protocol is on tailgating, trading stuff or whatnot. Appears that they have a "sale room" you drop things off in with prices. Ok.... Things I could "sell" if anyone's interested: HP1000e computer, dead power supply, basic boards, no advanced memory. HP9825B likewise does not power up, but it's there. Microvax 2 boards, stuff like that. Spare 11/24 CPU boards (I have a bunch, all work, no idea why I have all them) Stuff I could bring to get out of my house and into the right hands: Big box of pdp12 schematics. This came from my olden days when I had to turn up a pdp12 because it will not fit in a station wagon. Still it looks like board locations and a lot of 12 stuff. Big box, heavy to ship, easier to drive over. Ton of pdp8/12 IO cables. These are the black circular wire ones, I think negibus. There's also some posibus ribbon cables but I'll save those for my 8/L's. If you need a set, let me know. Stuff I'd trade for: AF01 A/D converter. I don't have Negibus anymore, but I did check/reform the power supply and hooked it up and things do light up. Bunch of extra channel cards (I think it might have all 64). Would trade for a memory box for an 8/L. Back to unearthing BLT.AI.MIT.EDU....... C

3 years, 3 months

Quantum ATL-7100 DLT Changer in SLC

by Tim＠Rikers.org

I have a Quantum ATL-7100 100 tape DLT changer. Last I checked it worked fine. It's almost as big as a fridge. I have around 100 tapes for it, not all the same density. It uses fast/wide scsi-3 differential for the drives. I think I have 2 working drives in the cabinet plus one or 2 separate external drives. I think my drives are DLT-7000 or similar which gives a total capacity of 7TB. Upgraded with SDLT 220 drives and tapes the chassis would have a capacity of 22TB. Anyone interested in picking this up in South Jordan Utah? (outside Salt Lake City). The only issues I know about it, is the tape loading pivoting door is not quite rotating correctly, and I replaced one of the AT power supplies with a unit that is NOT autoswitching. So if you want to run the unit on 220V instead of 110, you will need to change the chassis and the replaced internal power supply. It's really fun to load it up with tapes, then tell it to auto-shuffle them. I have the door hot wired so you can open the door while it's operating. Easy to restore the switch if you don't want to. Photos here: https://rikers.org/gallery/hardware-atl7100 Interested, please email directly, I don't check the list very often. Tim

3 years, 3 months

RCA COSMAC MS2000 MicroDisk Development System

by Rice43＠btinternet.com

Hi all, I?ve recently come across something i?ve soon realised really quite unusual. An RCA MS2000 MicroDisk Development System. I?m very green to the COSMAC scene, with this being my first 1802 machine. I?m very interested in knowing the pitfalls i may come across in restoring such a machine. I?ve had a quick cursory look over the machine, and it seems to be complete, with 2 RAM/ROM cards, CPU card, FDC and a (3rd party?) ROM programmer board, along with the PSU and floppy disk drives. It?s my understanding that these are pretty similar to the RCA Microboard development systems, which i believe are also pretty similar to the ELF ?homebrew? microcomputer this group revolves around. I?ve found some manuals on bitsavers,, a website on the Microboard system, along with disk images on the Emma02 emulator website, so I have a reasonable undertanding over what this actually is. I have a week off work next week, so am planning on taking my time on disassembling and checking the unit over next week. I?ll endevour to upload some pictures of said machine when i tear it apart. Thanks, Josh Rice

3 years, 3 months

Bob Lucky

by brain＠jbrain.com

I don't remember seeing this here, and not sure how many of you read his articles, but: https://spectrum.ieee.org/bob-lucky-obituary -- Jim Brain brain at jbrain.com www.jbrain.com

3 years, 3 months

Any CodeWright users: still have patch installers?

by dnm＠pobox.com

This is a long shot, but on the off chance anyone else on the list shares some of my particular weirdnesses, anyone got a line on the *patches* for Embarcadero (nee Borland (nee Starbase (nee Premia) CodeWright? I have the latest version Embarcadero sold (and maybe still sells?) as of not all that long ago -- 7.5 -- but it's basically patch level 3 (e.g., 7.5.3) instead of patch level 5 (e.g., 7.5.5). I'm hoping someone has the patch installers squirreled away somewhere, and that I can find that person. At least for Windows, patch installers were typically named something like "xcw753_4.exe", which would update an existing version 7.5.3 to version 7.5.4. Likewise xcw754_5.exe would update 7.5.4 to 7.5.5. Every now and again, I go looking for archives in The Wayback Machine, etc. or stashed away versions of the patch installers, but no dice so far. I've even attempted emailing folks who posted 10+ years ago or more on various fora about the patches/about CodeWright, but nothing has yet worked out there either. -- Daniel Moniz <dnm at pobox.com> [http://pobox.com/~dnm/]

3 years, 3 months

Lecture: A tour of Update's new premises, 2022-04-09, 19:00

by stueberahoo＠yahoo.de

Hi all, you're invited to the Update computer club[0] public lecture series "Updateringar"[1]! When: 2022-04-09, 19:00 CEST Where: https://bbb.cryptoparty.se/b/upd-0mo-m2u-aq8 A tour of Update's new premises In December and January 2021/2022 Update moved out of the Uppsala University IT department's basement into rooms of its own (thanks again to all our volumteers who put in a huge effort!). The new premises offer 150 m? of space for Update's collection and activities, with a dedicated area for exhibitions. What has happened since the move? With this online tour we invite you to take a peek into our new home and at what we've been working on in the last couple of months. We will give you an insight into current and future projects and show off some of our collection items. Bjarni Juliusson, Anke St?ber (Update) The lecture is free and open to everyone. Don't want to miss upcoming events? Subscribe to our low-traffic announcement list here[2]! Hope to see you there, Anke [0] https://www.dfupdate.se/en/ [1] https://wiki.dfupdate.se/projekt:updateringar [2] https://lists.dfupdate.se/postorius/lists/announce.lists.dfupdate.se

3 years, 3 months

UNIBUS powoer on/off spec

by jnc＠mercury.lcs.mit.edu

> the later "pdp11 bus hanbook" (which, as mentioned, does not seem to be > online yet, alas) Arck, I'm a moron; Paul has pointed out to me that this is, in fact, online at Bitsavers: http://www.bitsavers.org/pdf/dec/pdp11/handbooks/PDP11_BusHandbook1979.pdf It didn't show up in a couple of pages of results in a Web search for it, though. I have noticed that things on Bitsavers often don't show up high up in Web search results, unless you add 'bitsavers' to the search term. I have been told that at one point Google was 'downgrading' results that used plain HTTP, instead of HTTPS, because they were trying to push people to switch to HTTPS (this was when everyone was hyperventilating over the Snowden revelations). Given the near-ubiquitous use of HTTPS these days, I'd have thought that piece of 'information credit engineering' by our tech overlords was past its 'sell by' date, and now serves primarily to block people from finding the material they are looking for (as here). Noel

3 years, 3 months

Glass memory?

by anders.k.nelson＠gmail.com

Hey all, found this on eBay: https://www.ebay.com/itm/Corning-Glass-memory-/125087612899 I can't find any info on it - was it some kind of delay-line or magnetic laminate stack? Interesting!

3 years, 3 months

Short PDP-8 Memory Address Test..

by lbickley＠bickleywest.com

Continuing the debugging of my recently acquired PDP-8/E, I wrote an address test that's easy to enter from the front panel: --- # PDP8 Quick Address Test # Pass 1: Loads locations 23-7777 with their own address. # Pass 2: Tests each location for the correct address. If # it fails (address does not equal it's own address) then # the diagnostic halts with the error location in 22. # The contents of that location displays the error. # By Lyle Bickley # 0000 7600 CLA 0001 1021 TAD 21 0002 3022 DCA 22 0003 1022 TAD 22 0004 3422 DCA I 22 0005 2022 ISZ 22 0006 5003 JMP 3 0007 1021 TAD 21 0010 3022 DCA 22 0011 1022 TAD 22 0012 7041 CMA IAC 0013 1422 TAD I 22 0014 7440 SZA 0015 7402 HLT (ERROR!) 0016 2022 ISZ 22 0017 5011 JMP 11 0020 5000 JMP 0 (START OVER) 0021 0023 0022 0000 --- Cheers, Lyle -- 73 NM6Y Bickley Consulting West https://bickleywest.com "Black holes are where God is dividing by zero"

3 years, 3 months

UNIBUS powoer on/off spec

by jnc＠mercury.lcs.mit.edu

> From: Paul Koning > You might give a precise source citation on that page. Done: https://gunkies.org/w/index.php?title=UNIBUS_Initialization&curid=6842&diff… Don't complain to me if the publication data is skimpy; that's all that's in it! (I mean, we all know that DEC is in Maynard, but the book doesn't say it...) Noel

3 years, 3 months

Digital Control Applications with the TMS320 Family

by kevin.bowling＠kev009.com

Does anyone have a hardcopy of this book they'd be willing to part with? http://www.bitsavers.org/components/ti/TMS320xx/1991_TI_Digital_Control_App… USPS managed to lose the one I ordered but delivered me the damaged packaging with tire marks on it :( Regards, Kevin

3 years, 3 months

UNIBUS powoer on/off spec

by jnc＠mercury.lcs.mit.edu

So, I looked at the early editions of the "pdp11 peripherals hanbook", which have good, detailed discussions of UNIBUS operations (at the back; chapter 5, "UNIBUS Theory and Operation", in the 1976 edition), but in contrast to the level of detail given for master/slave operations, and bus requests and interrupts, the level of detail on power up/down is very low, especially compared to that in the later "pdp11 bus hanbook" (which, as mentioned, does not seem to be online yet, alas). So, I have transcribed that section, and posted it: https://gunkies.org/wiki/UNIBUS_Initialization I have yet to scan and post the associated timing diagrams (which are useful, but not critical); the desktop that runs my scanner is down at the moment, alas. (If anyone who has a copy would like to volunteer to scan them, that would be great.) Noel

3 years, 3 months

SETI@home (ca. 2000) servers heading to salvage.

by korpela＠berkeley.edu

>From here: https://setiathome.berkeley.edu/forum_thread.php?id=85870&postid=2096776#20… They are bog standard Sun Enterprise systems, drive removed and destroyed for privacy reason. They are only interesting for what they've done. By university rules, our group can essentially "permanent loan" them to a non-profit, but any sale or transfer of ownership is up to University Excess and Salvage. A bit of history disappearing, which is nothing new in this group.

3 years, 3 months

Core memory

by bmr＠ringman.ch

On Fri, Apr 1, 2022 at 10:26 PM Marc Howard via cctech < cctech at classiccmp.org> wrote: > We need to onshore Nixie production now! ;-) > Gentle plug for https://www.daliborfarny.com/.

3 years, 3 months

AlphaServer 2100s available

by a.carlini＠ntlworld.com

I have three AlphaServer 2100 systems in storage in the UK (Oxfordshire). The storage, however, is due to be demolished (soon, but no fixed date). I won't have room to store these three systems, so if anyone would be interested in offering them a home, then please get in touch! I can probably get some pictures in the next day or two. These systems were SMP Alphas and could sport as many as 4 CPUs. I'm not sure of the configuration of these systems but I can probably find that out soon. They have not been run since ~2003 so they may be in need of some TLC. OTOH they are not rusted to death so you have a chance of getting them back to life. Just so you know what you might be dealing with these systems are about: 700mm H x 430mm W x 810mm L. I can't find the weight in any of my references right now but they are very heavy. Three people can move them up a slight slope with some effort but you would not successfully lift it into a car (assuming that it would fit). I'm planning to dismantle them to move them (i.e. remove PSU/PSUs etc. until they are light enough to move). A tail-lift would probably be the sane way to go (and is, indeed, how they got to their current location. I'm hoping that someone can step forward and offer one or more of these machines a new home. Please contact me off-list (once you're sure you understand what you are getting into :-)). Antonio -- Antonio Carlini antonio at acarlini.com

3 years, 3 months

The Vertical Plane

by trash80＠internode.on.net

This may be of interest to some list members, particularly those who have an interest in the BBC computer or just like Twilight Zone type stories. Apart from being extremely interested in classic computers I also like the old stories that surround these old machines. A while ago I stumbled across a story about a BBC computer (this is the short version) that had been lent out from a school l think (as they did in those days due to the cost of machines back then) and this BBC, despite apparently not being connected to anything, started displaying messages from the past (a previous land owner) and someone in the future. As I said this is the short version of the story - it's also referred to as the Dodleston Messages or even the Dodleston Files if anyone wants to Google it. One of the claims was that this BBC proved the existence of time travel - WOW, a big claim. So the story eventually found its way into a book, The Vertical Plane by Ken Webster (1989). I believe the book gets its title from the way scientists describe time. So being interested in the stories I started my world-wide hunt for a copy. That was tough. A new copy unobtainable, an electronic copy not to my liking - I like the real thing, used copies were monumentally expensive (apparently the first edition was highly collectable). So I resigned myself to maybe one day I would stumble across a copy in a used book shop or an Op Shop (aka Thrift Shop) or a second hand shop. I visit these regularly because its amazing what pops up in them. Much to my surprise in February this year a Second Edition of The Vertical Plane was published and of course obtained for me by my local bookshop. My take - a good yarn - yes, do I believe the story - no. Please note, I have no connection with the editor or the publisher. Kevin Parker

3 years, 3 months

Looking For HP-UX 5.1 9000/200 Series Kernel Disk

by tangentdelta＠protonmail.com

Hello. I have an HP 9000/217 (9817) machine that I'd like to install HP-UX 5.1 onto. In order to do this, I need to find the boot disk containing the correct kernel, which has the part number "A98680B", and is described as "Multi-user kernel for S200". Alternatively, I could run just the single-user version of HP-UX 5.1, which has the part number of "A98670B". The disk images for HP-UX 5.1 on bitsavers.org and hpmuseum.net do not have this disk. I found these numbers in the HP-UX administrator manual. Page 370 lists the kernel disks and their contents. http://bitsavers.org/pdf/hp/9000_hpux/1985/97033-90049_HP-UX_System_Adminis… If anyone can point me in the right direction, it'd be greatly appreciated! Thanks.

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

> From: "Rob Jarratt" > I did plug the connector back in, so that DCLO and > LTC are connected, I just removed the ACLO pin. Ah, OK, good. Pulling the pins from those Mate-n-Loc shells without the right tool is tricky; glad you did it, because as Brent Hilpert pointed out, having a working DCLO is important, to reset everything to a known state on power-on. > I didn't look for replacements last night. Is there a modern > equivalent? Not that I know of. Even if you found something with the same pin-out, supposedly DEC selected ones that were 'good enough'. I've never had an issue with NOS ones that I bought from vendors, though. > I may have found a source of NOS. Great; get several, they're a useful chip to have around; the QBUS uses them, as well as the UNIBUS. If the same place has DS8640's (the receiver), save on shipping (and ordering delays) and get a couple of those too. I say that because depending on what else you had plugged into the UNIBUS post ACLO failure, the -15V may have damaged them too. The M9312 (not sure if you had one of those, but the -11/24 manual says it's common in them) uses ACLO (via a DS8640). The KY24 seems not to (as far as I can tell from a quick look - negative results from a quick print scan aren't 100.00% reliable, whereas positive ones are), oddly enough. In EUB memory (not sure which you have), the MS11-L and MS11M MS11-P don't seem to, whereas the MS11-P _drives_ ACLO (through an 8881) - probably to prevent CPU startup until the ECC is cleared). Etc, etc. > I always marvel at how neatly those wires are done, I wish I knew how > to do such a neat job. The same way the old joke says one gets to Carnegie Hall, I expect! :-) (I wonder what the UK equivalent of the Carnegie is - the Royal Albert, probably?) Noel

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

> The 'unused' gate in E52 is the one that the added wires from the ACLO > ECO went to; I wonder if it was damaged by the -15V, somehow? So, I checked, and the wire that goes from the plated-through hole next to the etch cut on E70p1 winds up at E52p4 (the bus line on that transceiver), thereby connecting the latter directly to UNIBUS ACLO (on pin BF1). So that's almost certainly what caused other gate(s) in E52 to fail. I think I have managed to trace where all the other two wires to that 'new' gate in E52 went to/from, to see exactly what the ECO is. Given that E52 is a transceiver, it was likely substituted for E70 so that the KDF11-U could also _drive_ BUS ACLO. I discovered that E52p5 (the new transceiver's input) is connected to E73p13 (an DS8640 quad NOR used as a bus reciver); that's in the upper left corner of K2. It's BUS PB L NOR BUS PA H - i.e. a parity error has been detected in memory - so it apparently then power-fails the system! The incoming BUF ACLO (E52p6) goes to a PTH next to E70p8. On the bottom, there's a trace from that PTH that goes to E66p13 - which is the inverter shown on K2 which converts BUF ACLO H to POWER OK H. So that probably the answer to my plaint about E70p1 being left floating: perhaps theres an etch cut somewhere that disconnected E66p13 from E70p2, so the former can now be driven by E52p6. I can't see one, but there's a trace from that latter PTH that dives under E70, and I can't see it well, but it looks like it goes to E70p2. It would be interesting to know what they did about the E70p2 -> E66p13 connection. Noel

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

> does [disabling the MCLK counter via DCLO, asserted by the two > E126 monostable chain from ACLO] happen just on power-down, or on > power-up too? I'd need to understand how that two monostable chain > works in both cases, which I currently don't. (I only understand > monostables when pulses trigger them, not edges, which is a big part of > why I don't completely understand it.) So this was bugging me, so I hauled out my TI TTL databook and looked up the LS123. According to that, the 123 is triggered by the rising edge on the B (non-inverted) input, when the A (inverted) input is low (which it will be here; it's tied to ground). (Also by the falling edge on A when B is high, which we can ignore.) So I think that chain is probably triggered only on power-down, which will produce a rising edge on P FAIL. (Power-up will produce only a falling edge on P FAIL, once power is up and good.) (Note that the second monostable is triggered, also on B, by the -Q output of the first; i.e. by the 'falling' edge of the first's pulse. But see also at the bottom, below.) So that should happen (if I have correctly understood this, which is not certain, I'm just a software person :-) is that some time after P FAIL goes high - a delay set by the first 123 - the second 123 produces a pulse (of a width set by its RC pair) - which via E52 produces an assertion pulse on DCLO. WTF? (Not that we care in this machine's case, since i) it only happens on power-down, and ii) it's just a pulse, so it's affect on MCLK will be very transient; it can't cause it to stay off. My curiousity has been piqued, is all. :-) The TM does not, after a _thorough_ search (although there are a few mentions of power u/down, but not this), explin why, alas. (The TM for some _other_ -11 CPU, one which contains a similar circuit might, but I'm not _that_ curious! :-) My _guess_ is that the intent is to reset all devices to a good idle state, _before_ power actually goes out. (Don't ask me why it just doesn't use INIT, though!) The potential fly in the ointment of complete understanding is that a 123 can _also_ produce a pulse on a rising edge at the clear input - and there is some circuitry driving the clear input on the second 123. (The clear input on the _first_ 123 seems to be left hanging in space - odd!) It seems to be set off by the mysterious DGP03 signal, generated by the microcode - but the GP table on pg. 4-21 of the TM doesn't contain an entry for '3'? Unless it has a typo - there are two '5' entries. In which case it could be 'Toggle the HALT flip-flop (K6)' (which I don't see on K6, unless it's E78) but yah, pulsing DCLO will probably clear it, wherever it is! This machine is making my head hurt. Disconnect the bad ACLO, power it on, and see if the CLK LED comes on. if not, then we'll have to work out why not. Noel

3 years, 3 months

Core memory

by paulkoning＠comcast.net

When I looked at that ebay listing of "glass memory" it pointed me to another item, https://www.ebay.com/itm/265623663142 -- described as "core rope memory". Obviously it isn't -- it's conventional core RAM. Interestingly enough, it seems to be three-wire memory (no inhibit line that I can see). It looks to be in decent shape. No manufacturer marks, and "GC-6" doesn't ring any bells. paul

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

> It was quite a struggle to separate those nylon connectors, is there a > trick to it? You mean the Mate-n-lok's? Not really; just make sure the catch is released. What did you do about DCLO? (Oh, I think I see the answer, below.... looks like you're relying on the pullup on K3...) > When I powered on, the CPU LEDs did not light up. Two of them ('0' and '1') are just bits in a special register, and thus only do anything when the bootstrap code fondles them. When you get ODT running, you can amuse yourself turning them off and on manually! :-) > I did notice that the CLK LED flickered on briefly when I powered it > off. Interesting. Not sure exactly what we can deduce from that; but interesting. > I put a scope probe on TP1 (p152 of the PDF), there was no activity, > the pin remained high. Yes; the signal there (MCLK H) is more or less the same one that drives the 'CLK' LED (MCLK L); so no big surprise there. Still, that reduces the problem space to a small part of K1. > The problem now is that I expect I will need to probe various pins to > find out what is going on. But I don't have a Unibus extender and I am > reluctant to remove the backplane. From what I can tell in the > Technical Manual you can't install the CPU in other slots Basically right; the backplane and CPU are designed to have it go in slot 1. It _might_ work in other MUD slots, with some loss of functionality (e.g. slot 2 doesn't have grant lines; MUD slots won't have the 'UNIBUS Map board pesent' line - pin FE1, on K11, UB TO MA VIA UBMAP) but I wouldn't want to chance it, there might be a clash. > I am forced to tack solder probe wires to the chips, which works but is > time consuming. Any other ways? Sorry, I don't have any experience to suggest any; too well supplied with extender cards, so I've never had to resort to alternatives! > I *think* I have found something. There could be a fault in E52 (sheet > K6, p157 of the PDF). While K6 BUS DCLO L is +5V, I am measuring K6 BUF > DCLO H at an average 1.64V Yeah, that's wrong. E52 is bad, and will have to be replaced. (From the +5V on BUS DCLO, I guess you're relying on the pullup? DCLO on the UNIBUS, with the resistor network on the M9302, should be about 3.5V - but now I'm confused, even with the P/S connector unplugged, it should still be 3.5V or so. Oh well, it's late, the brain is powering down... :-) The 'unused' gate in E52 is the one that the added wires from the ACLO ECO went to; I wonder if it was damaged by the -15V, somehow? > logical 0 output should be 0.4V max Which is what you should be seeing. > I also measured K6 BUF DCLO L to be always low, suggesting it thinks > the K6 BUF DCLO H is a logical 1. Yup; and that definitely explains why the clock isn't running - BUF DCLO L is clearing E41 on K1. Anyway, you'll have to replace E52 (which will be a bit of a pain, with the 3 ECO eires tacked to it). The DS8641 is an old chip, no longer in production, so the usual suppliers may not have it, but there are some on eBait. Noel

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

Finally found time to get to this one... > From: Rob Jarratt > However, there is a puzzle. On the CPU I found that the track from the > pull up resistor to E70 has been cut. I don't know about the "pull up resistor" part, but I have several KDF11-U's, and _all_ of them have the trace on the bottom of the card connected to pin 1 of E70 cut, in the exact same place (about 1/8" from the pin). This suggests that it's not a local mod (as you suggest below), but an 'official' DEC ECO. > This would suggest that E70 pin 2 is floating, which I think means that > K2 BUF ACLO H is also floating The input (pin 1) will be floating, but not the output (pin 2); TTL doesn't work that way, I think. I may have this wrong, but I think open TTL inputs float high, so BUF ACLO should be low. I looked, and I don't see any other traces (e.g. on the top side) going to pin 1. So I'm a bit puzzled that DEC allowed that input to float, as open inputs can lead to erratic operaton; they're usually tied high, or to ground. > K2 BUS ACLO L however has been patched to E52 pin 4, which is the > output of a gate on sheet K6. Can't say I understand why. Me neither; that's an unused (on the prints) driver in the DS8641 (center bottom of the page) - although that gate seems to have been fully wired up (wires to pins 4, 5 and 6) as part of the ECO. There is an ECO list on pg. 167 of the -11/24 prints (2 pages after K14), but I don't see an E52 in it anywhere. The puzzle here, if E70p1 is cut, and the output is low, is why the CPU clock isn't running. The -15V on BUS ACLO shouldn't have taken out any other semiconductors; it's not attached to anything else. (It will have run C6, on the lower right of the card, the wrong way, but i) I think that's a non-polarized item - and 100V rated, per the prints, and ii) I don't think that goes anywhere else, even if it's not.) So what's stopping the clock from running, then? Noel

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

> From: Tony Duell > A short in FET Q15 on the bias/interface board in the PSU could do it. > The gate of that FET is driven from an LM339 comparator the -ve supply > of which is -15V. Ah; I hadn't even looked at the P/S prints. (Like I said, I'm really weak on analog: for digital, I have the advantages that i) although I'm basically/mostly a software person, the MIT CS department is part of the EE department, and they made sure that all the CS people had a decent grounding in the fundamentals of digital hardware; and ii) in my early years, I was involved in a number of actual hardware projects, including a UNIBUS DMA network interface that tuned into an actual product. So I'm pretty good with a digital circuit diagram, like these CPU prints. But analog stuff is still a mostly-closed book to me! :-) Anyway, I'm happy to let you provide the analysis of the P/S... :-) > From: Rob Jarratt > [Perhaps] something else on the CPU caused Q15 to fail (if indeed it > did). I'd guess 'unlikely' (if Q15 has failed); UNIBUS ACLO is connected, on the CPU card, to only a single gate (on K2), and that 383 ohm pull-up (on K3), and the 1K pF cap there (the purpose of which I still don't understand, unless it's just a smoother). Although I suppose that if that cap failed, shorted, maybe that could have taken out Q15 somehow. > Perhaps I should ... and disconnect ACLO, DCLO and LTC, they are all on > the same connector Now why didn't I think of just un-plugging that whole connector! Duhhhh! My only concern would be leaving inputs floating... DCLO, no problem; it has that pull-up on K3. (Ditto for ACLO, if the buffering input gate isn't dead.) LTC, let's see... It's on K6, upper left corner. I'm too lazy to work out what leaving that input floating will do, and, if it has bad consequences, trace out all the places it goes (it should be connected up to cause an interrupt, somewhere), but there's no point; the KW11 has an 'interrupt enable' that has to be set by software before it can do anything; so at the moment it's safe to just ignore it for now, and stay with a focus on getting the main CPU clock running. (LTC is not on the UNIBUS, so there's no pull-up on the M9302 for it the way there is for ACLO & DCLO.) So unplug that connector, and see if E70 (on K2, lower right corner) is OK. (Remember, the pull-up will give it an Ok input with BUS ACLO disconnected.) If yes, great, go check the main CPU clock. If not, time to i) see how far the rot has spread (e.g. have other gates in that package died - not sure what else is in there; not just looking at things connected to the output - on pin 2), and ii) decide how to repair or temporarily bypass. (Ditto for anything else that got taken out.) I'd be tempted to bypass it (since I doubt you stock 8837's - although I do :-) - ACLO handling isn't needed to get the CPU running. Tie BUF (not BUS!) ACLO to ground, I'd say, and we can move on to look at MCLK. > If that works then I think repair ACLO and see if anything on the CPU > is bad or anything else that might cause a short on the ACLO signal of > the bus. Well, your call, but i) working ACLO isn't needed to get the CPU running - and, in particular, to look for other problems that might be preventing it >from running, and ii) fixing ACLO isn't guaranteed to make the CPU work. I'd recommend 'keeping the eye on the ball', and focus on the main CPU clock, getting ODT running, etc. The ACLO issue(s) can be cleaned up at your leisure. Noel

3 years, 3 months

PDP 11/24 - A Step Backwards

by jnc＠mercury.lcs.mit.edu

> and there is some circuitry driving the clear input on the second > 123. Never mind this section. I mis-read the print; the clear input is connected to an _input_ of the flop below (which is also tied high). Noel

3 years, 3 months

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test-drb