Re: Seeking a MC75325L Dual Memory Driver
On 3/11/22 07:01, Paul Birkel via cctech wrote: .snip. UTSOURCE claims to have a supplier of the ceramic part "new", with a significantly higher shipping charge. For what it's worth, I've ordered several times from UTSOURCE and the results have been perfect. So far, I obtained a number of the Harris 'pdp8' chips D1-6120-9 and 6402 uarts plus Harris's weird baud-rate generator and 6121 'port' decoder. All have been quickly delivered and were 100% tested by me only receipt and they all met operational specs within specified voltage ranges. Surprised about shopping charges, though. I'm in the US and the shipping charges were quite 'nominal'. Less than $5 on a 25 chip order of about $150. They are so far, "good guys" in my book. -Gary Before I go with the ceramic part (IMO not the sort of packaging that gets . remarked) I thought that I would check here for alternative sources. Thank you, paul -- -Gary
Re: DECTape head problem (I've uploaded pictures)
Some folks asked for pictures and information about my Astrotype DECtape project. I've uploaded some pictures and other details to the web for your enjoyment. http://xx2247.com contains some photos and first-draft information about the components. I'll update this site from time-to-time as I make progress. -Gary
Re: DECTape head problem
On 2/9/22 10:54, Michael Thompson via cctech wrote: Date: Tue, 8 Feb 2022 20:55:31 + From: Wayne S Subject: Re: DECTape head problem So it serms dectape heads are special. I don?t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? We have one from Applied Magnetics Corporation, maybe the one in Goleta, CA. I can't find them. Lots of lost info (even Bloomberg has info, but the web site listed goes to a parking 'for sale' page.) Documents suggest they "merged out" in 1987 (but no pointers to who gobbled them up.) I have sent a request for information from jrfmagnetics.com (thanks Tom!) and will see what they say. It's seems they are still 'lingering' in the head repair business, so it's remotely possible they could do a repair job. Thanks all. If anyone has a working head they aren't using, I'd entertain an offer... :-) -Gary
Re: DECTape head problem
On 2/8/22 14:14, Wayne S via cctech wrote: Searched a lille bit for Western Magnetics. Here’s a site that has some surplus heads, even a western magnetics onebut probably not the correct one. There is a corporate charter record for Western Magnetics in Minnesota dated 1964. Maybe this is the same company. There’s also a tape head from Michigan Magnetics. Maybe a merged company? https://www.surplussales.com/Equipment/magnetic-tape.html Sent from my iPhone On Feb 8, 2022, at 13:05, Ron Pool via cctech wrote: So it sermsdectape heads are special. I don’t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron Thanks. Hadn't seen the Minnesota information. Found some references but not actual company info. Did find a reference somewhere it Canada, but I couldn't tell if it was original or successor company. At any rate, no web presence nor telephone numbers found (yet.) I've dealt with the SurplusSales (of Nebraska) many times. His prices are usually pretty high (not obscene, but just not 'surplus' prices I'm used to.) However, he is a first-rate dealer and when he says something is so, you can count on it. Never had problem with anything I was willing to *PAY* for. I scanned the list you provided and found only a few 'digital' devices, unfortunately. I suspect from 7 and 9 track mag tape drives. I will scan his site and send him a ping so he'll be on the lookout. -Gary
Re: DECTape head problem
On 2/8/22 13:04, Ron Pool via cctech wrote: So it sermsdectape heads are special. I don’t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron Mine also says Western Magnetics, Glendale CA, but does not have a part number. Just serial numbers. At least I assume they are serial numbers "19984" and "19976". I've seen evidence that a few souls in the 50s managed to make magnetic heads from scratch (heck, Ivan Sutherland is claimed to have made a functioning magnet drum storage device when he was in 12th grade,) so give the modern world of CNC milling and availability of every manner of sheet metal via Internet searchers, I figured their just *might* be a possibility of growing one of these from scratch - tolerances (other than head gap) appear pretty generous, but I just don't have enough info to crack what the coil construction is to be. There may be enough information to do a stab at it, but I'm not sure I have the energy (or even the skill) to give it a credible effort. I've seen evidence of 'head repair' services, but I doubt they include digging out the wires from solid epoxy. Any information available would be appreciated. -Gary
Re: DECTape head problem
On 2/8/22 13:04, Ron Pool via cctech wrote: So it sermsdectape heads are special. I don’t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron Mine also says Western Magnetics, Glendale CA, but does not have a part number. Just serial numbers. At least I assume they are serial numbers "19984" and "19976". I've seen evidence that a few souls in the 50s managed to make magnetic heads from scratch (heck, Ivan Sutherland is claimed to have made a functioning magnet drum storage device when he was in 12th grade,) so give the modern world of CNC milling and availability of every manner of sheet metal via Internet searchers, I figured their just *might* be a possibility of growing one of these from scratch - tolerances (other than head gap) appear pretty generous, but I just don't have enough info to crack what the coil construction is to be. There may be enough information to do a stab at it, but I'm not sure I have the energy (or even the skill) to give it a credible effort. I've seen evidence of 'head repair' services, but I doubt they include digging out the wires from solid epoxy. Any information available would be appreciated. -Gary -- -Gary
Re: DECTape head problem
On 2/7/22 12:48, Marc Howard via cctech wrote: The problem would be the non-standard track size and number of tracks. However if at least one of the head's paired tracks is good you could potentially cut the drive current in half and double the read amplitude and just use one track for the affected channel. Marc On Mon, Feb 7, 2022 at 12:33 PM Wayne S via cctech wrote: I’ve often wondered if the tape heads from consumer tape devices such as cassette or 4-8 track tape players could be used or be made to be used as replacements. Anybody ever try that? Sent from my iPhone On Feb 7, 2022, at 11:51, Michael Thompson via cctech < cct...@classiccmp.org> wrote: Further, the DECTape had various track-to-track spacing. Between the the Mark track and the first data track on both edges, the spacing is at a little less than twice that between the mark and timing tracks or between each set of data tracks. Put a different way, the track spacing is: T.M..D.D.D.D.D.D..M.T The magnetic poles of each head is roughly 1mm wide with about .8 mm spacing heads The '..' in the above means there is about 1.4mm spacing (between 'M and D' and 'D and M', for example - the measurements are crude, so I could be off 20% or more.) I've searched the documents I have (many from bitsavers) and haven't yet spied a specification for the head design. I suppose if I could determine the head 'gap' and knowing the magnetic flux required of the tape (with proper margins) and knowing the stated impedance of the head and drive current, I could figure out how many turns of some size wire is required (looks to be at least as small as #40). Back when I was a bit younger and less experienced (and didn't know it was impossible,) I actually 'repaired' (for some definition of 'repair') an old 1/4 inch tape head. But all I did was pull some wire off the coil and delicately soldered a tap to this wire. It worked ok for a couple of years but was obviously failed again from rough handling. Fortunately it was 'easy' since there wasn't a bunch of clear epoxy in the way ;-) I'm not sure today I would have the temerity to even try. Hoping one will show up someday and I can make a deal as to complete my unit. Thanks to all who have replied. -Gary
DECTape head problem
In debugging my DECtape interface lashup, I found that one of my head has two open windings. Specifically, one channel has an open 'ground' with the other two lines apparently the full winding of the channel. The second channel failing has no continuity between any of the three lines. I have tested the other head and it has all the requisite continuity so I'm hoping I can at least get a single spindle running. Visual inspection of the head 'suggests' it might be caused by the age-old 'wire stress' of being captured within a polyester resin and then finally snapping due to internal stress. I see lots of internal stress cracks on this head so I'm probably toast on this one. Are there documents on how the heads are made? I.e. number of turns of number X wire; cap of X micros etc. I'm not (yet) seriously entertaining the idea of rebuilding this head, but it looks pretty low tech. These heads are Western Magnetic heads without a model number (only serial number 19976 - don't know the other head S/N as I haven't removed it yet.) And the look to be hand made... Has any ever attempted repair of one of these? -Gary
Old Micro Memory core board
Going through an old junk pile, I came across a couple of core boards: Micro Memory, Inc. PN 90360 8K*8 (MM-6800) Date code 7725 I have two boards (s/n 202 and 203) so likely purchased in pairs. Anyone have any information on these? They have 86 pin connectors so not S-100 though connector is about the same size. For years, these have sit on a shelf on my 'round tuit' list of bringing them up in one of my old S-100 boxes, so I've been cruising along thinking these were 100 pin connectors. I got them out today so I could find the manual (I have used the MMI s-100 8kx8 boards in an old company project back in 1977 and those were about the same size and form.) The core board is a daughter board on top of the board with the bus connector and is likely the same module from the S-100 board. I'm guessing the 86 pin bus is a Motorola Exorciser bus - so I can probable figure it out from there, but I would like to find a manual. I think my company had an Exorciser development system in the late 70s. These were obtained from a dumpster dive. Pity I didn't get the rest of the box, if so. As usual, google wasn't extremely helpful with old pedestrian hardware searches. -Gary
Re: Question about DECtape formulation
On 1/25/22 12:24 PM, Chuck Guzis via cctalk wrote: On 1/25/22 06:18, Paul Koning via cctalk wrote: On Jan 24, 2022, at 10:27 PM, Gary Oliver via cctech wrote: ... As to the real reason I was doing this: Most of my tapes are un-boxed and have suffered being in a dusty area (before I got them) with the dust forming a sort of 'crust' on the outside of the tape. It's only on the first wrap or so, but it's enough that it keeps those handy vinyl cohesive tapes from sticking. For that reason, I was trying to find something to clean of this dusty gunk so the vinyl strip would hold the tape into a spooled condition. It was the side-effect of this effort that lead me to the discovery if this "removable layer" on the DECtape. BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue very-flexible vinyl without any adhesive. They rely only on the cohesive properties of vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from Cricut (the plastic decal printer company.) They have a couple of colors without adhesive that they call "window cling" but they aree only 4 mills thick and a bit flimsy, though so-far they are holding ok. There's a children's toy I remember: shapes cut from vinyl, intended to be stuck to windows to make pictures. That seems to be the same stuff. The term of art is "cling vinyl" or "static cling vinyl". Most art stores carry the stuff--mine is a package of this: https://www.grafixplastics.com/materials-plastic-film-plastic-sheets/commodity-plastic-film/vinyl-sheets-film/grafix-cling-pvc-film-2/ Cut the strips with a paper cutter and you'll have enough in a package to last you well into your sunset days. --Chuck My search results were dominated (even with 'advanced search') by Amazon and Ebay (naturally) but also by a couple of vendors (Cricut as example) and I never found anything coming up for .10 inch or equivalent in mm. This appears to be .10 inches without adhesive so I'm going to give this a try. Thanks VERY MUCH for this link. -- -Gary
Re: Question about DECtape formulation
On 1/24/22 4:25 PM, David Gesswein via cctech wrote: On Sun, Jan 23, 2022 at 03:09:53PM -0800, Gary Oliver wrote: Taking the bits of tape, I exposed them to various concentrations of isopropanol/water (from about 25% to 99% iso) and found than in all cases, some of the data side of the tape came off on the wipe.? The remaining tape fragment appears intact - the brown oxide was still there but both sides were now the same color, rather than the data side being darker (as were all my tapes before the test.) I had done the careful test to find something safe to clean DECtape. One time I grabbed the wrong bottle and that removed the coating. Tape was now totally unreadable in that location. Didn't have any luck with cleaning helping data errors so stopped trying. This was a long time ago so I don't remember if my incorrect cleaning result matched your description. As to the real reason I was doing this: Most of my tapes are un-boxed and have suffered being in a dusty area (before I got them) with the dust forming a sort of 'crust' on the outside of the tape. It's only on the first wrap or so, but it's enough that it keeps those handy vinyl cohesive tapes from sticking. For that reason, I was trying to find something to clean of this dusty gunk so the vinyl strip would hold the tape into a spooled condition. It was the side-effect of this effort that lead me to the discovery if this "removable layer" on the DECtape. BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue very-flexible vinyl without any adhesive. They rely only on the cohesive properties of vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from Cricut (the plastic decal printer company.) They have a couple of colors without adhesive that they call "window cling" but they aree only 4 mills thick and a bit flimsy, though so-far they are holding ok. -Gary -- -Gary
Re: Question about DECtape formulation
On 1/24/22 12:42 PM, Noel Chiappa via cctalk wrote: > From: Gary Oliver > Paul - thanks for the bitsavers reference. Ahem! In any case, it's Al who really deserves the credit, for finding that document, and putting it up. Noel Clearly Al is to blame :-) Yes, thanks to all of Al's work in this regard. I found all of the other technical details I needed (and more!) -- -Gary
Re: Question about DECtape formulation
On 1/24/22 11:09 AM, Chris Zach via cctalk wrote: It sounds more like some sort of sprayed-on coating of some sort of abrasion-resistent material. It might well be porous, which would be a possible explanation for the oxide coming off when rubbed with solvent. paul Is it possible we're looking at something called "dirt"? C Not likely, as it's on all of my tapes, including the four 'unopened' (well, there opened now...) tapes I had in my stash. Brand spanking 'new' in blue plastic boxes, still with seal on tape. I even had an unused 'scotch' brand that had the seal on the tape, though that one came in a paper box, so conceivably it could have been 'contaminated'. But it still looks the same. Also, in reference to another comment: the 'oxide' isn't coming off exactly. I did have one tape with some really ragged ends on it, and on that one, the oxide did flake a bit. But that tape had other damage on the leader end. For the rest of them (tried so far) all I can say is the oxide appeared 'exposed' but on several different tapes I tried 'scraping' this exposed layer with an exacto knife and all that happened is some scratches appeared on the 'overcoat' layer. No oxide residue on the knife. Sorry if it appears I implied the oxide was degrading. May on one or two, but this is not a feature of the other 100-ish tapes. I'm guessing it *is* some kind of spray-on 'extra' lubricating coating, so I'm just trying to figure out what it is. Obviously it's extremely soluble in iso, but that's the 'strongest' thing I've tried. As I think I mentioned, even water will degrade this layer with some rubbing, but alcohol takes it off quickly. 'Dry polishing' the tape doesn't seem to degrade the coating, though I do seem some 'smudges' left on the kimwipe. This issue isn't standing in my way of completing the project - I was just checking the 'collective conscience' here if any knew some unpublished secrets or where they were published if not secret. Thanks for all the replies. -Gary
Re: Question about DECtape formulation
On 1/24/22 7:30 AM, Paul Koning via cctalk wrote: On Jan 23, 2022, at 8:40 PM, Noel Chiappa via cctalk wrote: From: Gary Oliver I've always thought the physical tape wound on a DECtape spool was a fairly conventional 'sandwich' of mylar/oxide/mylar ... Was there some kind of 'lubricating' coat on the data side? It makes sense, but none of my DEC documents or Googling has any mention of lubrication ... If someone has some detail information on the tape construction, I'd am curious to see it. Dunno if you know of this: http://www.bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf but it doesn't mention any lubrication, just a "Protective Overlay" layer, over the "Coating" (which I assume is the oxide). I'm a bit surprised that "some of the data side of the tape came off on the wipe", though, unless the "various concentrations of isopropanol/water" dissolved the Protective Overlay. Noel Depending on how much the tape has been used, it's possible that the top layer has worn through. I have known that to happen on highly used tapes, though not many got enough to wear that far. It also might be oxide tranferred from one tape to the head to other tapes, if the heads weren't cleaned enough. paul I also have tried the alcohol wiping on a piece from a 'fresh' tape (never used - still with tape seal) and the results were the same. The procedure was to slightly dampen a piece of lint-less paper towel (e.g. kimwipe) with the alcohol solution and wipe with minimal force over a small portion of the 'data' side of the tape. (I used 25%, 50% and full strength alcohol and all were identical except for time required to remove the layer.) Removing the dark brown/grey 'coating', allows the brown oxide to show. After this step, the top and bottom of the tape looked identical (a medium color iron oxide.) This 'exposed' oxide did not seem to be any easier to scrap off using a sharp exacto knife (no oxide residue when scraping, but clearly left scrape marks on the tape) suggesting there is still a robust protecting layer left on the tape. Also, after removal of the layer with alcohol, there was no apparent thickness change. I haven't used a micrometer yet to verify, but the 'fingernail' test doesn't indicate any thickness layer boundary between the 'cleaned' and 'uncleaned' portions. Paul - thanks for the bitsavers reference. I thought I had copied all of the DEC documents relating to DECtape, but clearly missed that one. -- -Gary
Question about DECtape formulation
I've always thought the physical tape wound on a DECtape spool was a fairly conventional 'sandwich' of mylar/oxide/mylar, but a recent 'test' makes me think there is something else involved. I have a number of tapes I'm cleaning (removing dust, etc.) to make ready to read on a restored (apparently) Astrotype dual DECtape drive and I was 'dressing' the leaders of the tape (removing ragged bits from old use.) After trimming a wee bit from several tapes (.5 to 1 inch) I did a test. Taking the bits of tape, I exposed them to various concentrations of isopropanol/water (from about 25% to 99% iso) and found than in all cases, some of the data side of the tape came off on the wipe. The remaining tape fragment appears intact - the brown oxide was still there but both sides were now the same color, rather than the data side being darker (as were all my tapes before the test.) Was there some kind of 'lubricating' coat on the data side? It makes sense, but none of my DEC documents or Googling has any mention of lubrication, other than the "...hydro- dynamic lubrication, relying on the viscosity of air to entrain it with the tape and provide the flotation medium." found in an "ELECTROMECHANICAL COMPONENTS & SYSTEMS DESIGN" from November, 1964. All of my tapes, including DECtape brand, Scotch brand and even a couple of old "Microtape" brand from DEC (before 'dectape' name change) have this feature, so this doesn't appear to be something that appeared recently (as in late in DECtape production or due to old-age in the tapes.) If someone has some detail information on the tape construction, I'd am curious to see it. Thanks,
Re: Owens Illinois Digivue technical info
Sorry: I goofed and sent the message to the list (too many different MUAs and I forget their defaults...) I have a set of four manuals for the Digivue 512-60 plasma display screen as from at least one version of a Plato terminal (with rear-projection capability.) They match the unit I have which was from 'broken' Plato terminal of some kind - all I got was the keyboard and display - no power supplies. The unit looked like it had been 'drop tested' but the display was intact. Never fired it up, but did talk to an engineer at Corning (who supplied the manuals) and was told that power supply sequencing was "very" critical. I have this notion I sent a copy of these to AK to add to bitsavers, but it was some time ago. I had two professionally photocopied copies made and seem to have only one left - hoping the other is with Al. If not, I can make more: the originals are still around somewhere. If there is interest, I'll make an effort to get a copy to to AK but given his workload, I hate to add to the pile... He's already done me a number of favours getting some of my old stuff onto bitsavers and I hate to be a bother... FYI I have no capability of doing any sort of 'quality' scanning myself. -Gary On 10/04/2017 05:42 PM, Paul Koning wrote: It would be great to get those scanned. It seems that documentation of the O-I display devices and related power supplies is quite rare, so it would be good to make sure whatever is available gets collected. I have power supply documentation (copies), will try to get those scanned. paul On Oct 4, 2017, at 8:27 PM, Gary Oliver via cctalk <cctalk@classiccmp.org> wrote: I found the manuals for my unit, but it appears older than yours - perhaps one of the original units. The hardware manual describes the model "512-60 DIGIVUE display/memory unit, D141." The electrical connections are .1 inch dual-row edge-connector style; 60 pins for data/control (half are grounds) and 30 pins for power. The connectors are described as "Amp Twin Leaf Printed Circuit Edge Connectors." However, it does have copious schematics, so you may get some use from it. I should be mailing it out by this weekend. -Gary On 10/02/2017 10:25 PM, Josh Dersch via cctalk wrote: Hi all -- I find myself with an Owens Illinois Digivue plasma display, model designation MDXVI. This appears to be a later model than the ones used in the PLATO IV and V terminals and I can't find any real information on it. This one has two D-sub connectors on the rear -- a 15-pin for the power supply and a 25-pin for everything else. Love to know what the interface specs are so I can make the display do something interesting. Schematics would also be nice. Anyone have any docs stashed away? Thanks, Josh -- -Gary -- -Gary
Re: Owens Illinois Digivue technical info
I found the manuals for my unit, but it appears older than yours - perhaps one of the original units. The hardware manual describes the model "512-60 DIGIVUE display/memory unit, D141." The electrical connections are .1 inch dual-row edge-connector style; 60 pins for data/control (half are grounds) and 30 pins for power. The connectors are described as "Amp Twin Leaf Printed Circuit Edge Connectors." However, it does have copious schematics, so you may get some use from it. I should be mailing it out by this weekend. -Gary On 10/02/2017 10:25 PM, Josh Dersch via cctalk wrote: Hi all -- I find myself with an Owens Illinois Digivue plasma display, model designation MDXVI. This appears to be a later model than the ones used in the PLATO IV and V terminals and I can't find any real information on it. This one has two D-sub connectors on the rear -- a 15-pin for the power supply and a 25-pin for everything else. Love to know what the interface specs are so I can make the display do something interesting. Schematics would also be nice. Anyone have any docs stashed away? Thanks, Josh -- -Gary
Re: Directory of old computer collectors
What is the age requirement to be eligible for inclusion in the old 'computer collectors' list? :-) -Gary
Repairing an DEC LA424 Printer
I've inherited an LA424-A2 printer that had been stored for a while but now has obvious problems. Powering up 'jogs' the paper feed motor, flashes the three green LEDS on the panel through a rapid sequence, but then it stops with the display showing what appears to be a fault code. Unfortunately, one of the other parts that is failing is the LCD (16 char I think) that should be showing a fault code. It appears to be "CO " but I can barely make out the "CO". Is this LCD use a traditional byte-wide interface and can it be replaced with one of the current crop of cheap LCD modules? Once I can see the fault code, I can begin to determine what else is failing, though the manual doesn't seem to be much help on error codes: they seem to be simple state-of-operation codes. Thanks, Gary
