[cctalk] Re: Need a 1.2mb 5.25 floppy
On 2/27/23 15:50, Fred Cisin via cctalk wrote: > Could you explain [in dumbed down form], the differences between "tunnel > erase" and "straddle erase"? Is it solely that the erase head(s) are > behind, VS alongside the R/W head? How about ChatGPT's explanation? (Is this a first for CCTalk?): When recording signals on magnetic media, erasing the previous data from the media is an important step in preparing it for new data. Tunnel erase and straddle erase are two different methods used for this purpose, and they differ in how they erase the previous data from the media. Tunnel erase is a method of erasing the previous data by applying a magnetic field perpendicular to the direction of the recording tracks. This magnetic field is strong enough to create a "tunneling effect" that causes the magnetic particles on the media to lose their magnetic orientation, effectively erasing the previous data. This method is called "tunnel erase" because the magnetic field creates a tunnel through which the magnetic particles lose their orientation. On the other hand, straddle erase is a method of erasing the previous data by applying a magnetic field that is parallel to the direction of the recording tracks. The magnetic field is applied by two or more magnetic heads placed on either side of the recording tracks, creating a "straddle" configuration. The magnetic field from the heads is strong enough to erase the previous data by realigning the magnetic particles on the media in a uniform direction. In summary, tunnel erase and straddle erase are two different methods of erasing the previous data from magnetic media. Tunnel erase uses a perpendicular magnetic field to erase the previous data, while straddle erase uses a parallel magnetic field created by multiple magnetic heads. -Chuck
[cctalk] Re: Need a 1.2mb 5.25 floppy
It is also worth noting, that although not all "360K" diskettes are up to the task, they will still be much closer than "HD"/"1.2M" diskettes! "360K" diskettes are 300 Oersted "Quad density" diskettes are also 300 Oersted. The only difference is that "QD" diskettes are tested for 96tpi, whereas "360K" diskettes are tested at 48tpi. They are made of identical materials. However, if the production quality control is marginal/poor, then you could have some/many? that test OK at 48tpi, but are too flawed for 96tpi use. If they are really good quality, then the 48tpi ones should work just fine. OTOH, "HD"/"1.2M" diskettes are 600 oersted. Use of those for DD 300RPm/250Kbps / 360RPM/300kbps recording, whether at 48tpi, or 96tpi, will result in data retention longevity that is lower than it should be. Testing Roytype "HD" diskettes on TRS80 model 1 (SD/FM), gave data life of MINUTES, whereas "360K" diskettes tend to last years However, 3.5" "720K" diskettes are about 600 Oersted, and "1.4M" are about 720-750 Oersted. That is close enough that using the wrong media is something that people often get away with. I do not currently own a coercivity meter, so I can't check compliance with the specs. 45 years ago, Verbatim made some very crappy diskettes. To recover from their bad reputation, they came out with "Datalife" diskettes, which were acceptable quality. Dysan seems to have always been good. However, they "bet the company" on 3.25" disk form factor, and lost. -- Grumpy Ol' Fred ci...@xenosoft.com
[cctalk] Re: Need a 1.2mb 5.25 floppy
Then, I made the students describe how to make a 48tpi disk with a 96tpi drive. Whether to count their answers as acceptable or not was mostly just the understanding of need for "bulk erase"/"virgin disk" On Mon, 27 Feb 2023, Chuck Guzis via cctalk wrote: One thing that folks need to bear in mind is that it's the change of direction of magnetization that induces a signal in a drive head. So a DC or AC erase on the "straddling" portions of a track will work equally as well. There is some erasing done by the heads to clear some of the area around the track. BUT, that erase of a 96tpi head is not wide enough to remove all traces of a previous 48tpi recording. I wondered why they didn't incorporate TWO sets of erase heads in 1.2M drives, so that it could "clear the margins" enough for 96tpi OR 48tpi re-writing. Could you explain [in dumbed down form], the differences between "tunnel erase" and "straddle erase"? Is it solely that the erase head(s) are behind, VS alongside the R/W head? I looked at http://www.bitsavers.org/pdf/cdc/discs/floppy/75897469_5inchFDD_Fmt_Jan80.pdf but I don't understand all of it. -- Grumpy Ol' Fred ci...@xenosoft.com
[cctalk] Re: Need a 1.2mb 5.25 floppy
On 2/27/23 14:14, Fred Cisin via cctalk wrote: > Then, I made the students describe how to make a 48tpi disk with a 96tpi > drive. One thing that folks need to bear in mind is that it's the change of direction of magnetization that induces a signal in a drive head. So a DC or AC erase on the "straddling" portions of a track will work equally as well. --Chuck
[cctalk] Re: Need a 1.2mb 5.25 floppy
For my students, I used analogies and visual aids. 1/48, 1/96 is a little hard for some to visualize. "48 tracks per inch, is about half a millimeter spacing, with the actual data being aabout a third of a millimeter wide. 96 tracks per inch is about a quarter of a millimeter spacing, with the cata being about a sixth of a millimeter wide" "If you make stripes with a 2 inch wide paint brush, . . . you can also make stripes with the same spacing, with aa 1 inch wide paint brush, . . . BUT, with a single stroke, can you paint over a 2 inch stripe with a 1 inch brush? No, you'd have to clean all of the old paint off first, or start with a virgin canvas." "car tires make two tracks. Motorcycles could make tracks the same spacing. But, motorcycles won't obliterate the car tire tracks." I took a wide piece of colored chalk and made a series of stripes. I held up a piece of cardboard (file folder) with a slit in it, and looked at one stripe. With a narrower piece of a different color chalk, I made a series of half width stripes, half as far apart. I used a corresponding piece of cardboard with a narrower slit. I made narrow sripes at the wide spacing. I used the narrow slit cardboard, and then the wider slit cardboard, "Maybe a little weaak, but it should do." Then I made narrow stripes down the middle of the end of the wide stripes. I used the narrow slit cardboard. "Looks fine." Then I used the wide slit cardboard. "What is this mess??" Then, I made the students describe how to make a 48tpi disk with a 96tpi drive. -- Grumpy Ol' Fred ci...@xenosoft.com
[cctalk] Re: Need a 1.2mb 5.25 floppy
Actually it's not the controller, it is the fact that the head gap on the 48 tpi drive is twice as wide as on the 96TPI drive. So the actual head sees the magnetic fluxes from two different tracks, This looks like noise to the data separator on the controller. The way around this was to magnetically erase a disk and format it and write it on a double stepped on a 96tpi drive and only read it in a 48 tpi drive. This is what we had to do when I wrote the floppy formatter for Gimix 6800 and 6809 Flex and OS/9. The floppy driver also had an option to double step the drive for normal Flex operation. On 2/27/2023 2:55 PM, r.stricklin via cctalk wrote: On Feb 27, 2023, at 10:21 AM, Mike Katz via cctalk wrote: the drive would see half the new data and half the old data. I think that explaining it this way can easily lead to an incorrect inference on the part of an arbitrary hypothetical neophyte that what is going on in the drive in such a case is that the head can equally well read either the old data or the new data but the controller can’t distinguish which is which, or might return old data, or might return new data, or might indiscriminately return some old data and some new. What the drive reads in such a case is noise, because the wider head picks up a superposition of the old (wide) 48tpi track data AND the new (narrow) 96tpi track data, simultaneously. ok bear.
[cctalk] Re: Need a 1.2mb 5.25 floppy
On 2/27/23 12:55, r.stricklin via cctalk wrote: > >> On Feb 27, 2023, at 10:21 AM, Mike Katz via cctalk >> wrote: >> >> the drive would see half the new data and half the old data. > > I think that explaining it this way can easily lead to an incorrect inference > on the part of an arbitrary hypothetical neophyte that what is going on in > the drive in such a case is that the head can equally well read either the > old data or the new data but the controller can’t distinguish which is which, > or might return old data, or might return new data, or might indiscriminately > return some old data and some new. > > What the drive reads in such a case is noise, because the wider head picks up > a superposition of the old (wide) 48tpi track data AND the new (narrow) 96tpi > track data, simultaneously. Double-stepped disks written at 96 tpi are perfectly readable on a 48 tpi drive if the disks are bulk-erased first. I've done this using a videotape eraser and later, a DC eraser made up of two ring magnets from an old magnetron, spaced perhaps 3-4 mm apart with like poles facing each other. Just pass the disk around the gap. Works a treat. --Chuck
[cctalk] Re: Need a 1.2mb 5.25 floppy
> On Feb 27, 2023, at 10:21 AM, Mike Katz via cctalk > wrote: > > the drive would see half the new data and half the old data. I think that explaining it this way can easily lead to an incorrect inference on the part of an arbitrary hypothetical neophyte that what is going on in the drive in such a case is that the head can equally well read either the old data or the new data but the controller can’t distinguish which is which, or might return old data, or might return new data, or might indiscriminately return some old data and some new. What the drive reads in such a case is noise, because the wider head picks up a superposition of the old (wide) 48tpi track data AND the new (narrow) 96tpi track data, simultaneously. ok bear.
[cctalk] Re: Need a 1.2mb 5.25 floppy
As already said here most of the better DSDD diskettes could handle 48 or 96 TPI. The biggest problem I remember from that era (on 6809 Systems in the early '80s and early PC's) is intermixing 48 and 96 tpi drives and reading/writing both drives. Since the tracks are half as wide on the 96 TPI drive, if you format a disk on a 48 TPI drive and then write to it on a 96 PTI drive and then try to read it back on a 48 TPI drive, the reads may fail because the 96 TPI drive only wrote half of the track as seen by the 48 TPI drive. When reading data on a 48PTI drive, the drive would see half the new data and half the old data. Also the 96 TPI drive needed to be double stepped to read a 48 TPI formatted diskette. On 2/27/2023 12:10 PM, Christian Corti via cctalk wrote: On Mon, 27 Feb 2023, Warner Losh wrote: You should be using QD floppies, but those are rare. DD floppies from later than 1985 though work just fine (discovered empirically while a Are they? I guess that I have at least as many QD floppies as DD, if not even more. :-) However, in a PC, to write these diskettes, you need a 1.2M drive. While there is a couple of TEAC drives (55FR I think) that do 80-tracks at the DD/QD RPM and data rates, things get fussy putting them into PCs. And last time I looked they were 5x the price of ye-olde-generic 1.2M floppy drive. As long as it's formatted at the right density/rpm rates, it's fine. And RX50.SYS, if memory serves, does all that right. When giving an advise, it should be as correct as possible ;-)) So no, you don't need a "1.2M drive" (i.e. high density). You just need a 96 tpi drive. And the drive is totally (well, almost) ignorant of the data rate. It is just spinning the media at a specific velocity (300 or 360 rpm). When using a 300 rpm drive, you need a 250 kHz data rate for DD (QD is the same, it's just a marketing name for 96 tpi DD). With 360 rpm you need a 300 kHz data rate. It only gets a little bit complicated if you jumper a high-density drive for dual-speed mode (300 rpm if DD, 360 rpm if HD). Using 3.5" drives in double density mode will work, but there's a cascade of software issues you'll have to deal with. I booted my DEC Rainbow with It would be the same for a normal 5¼" double sided drive. IIRC the trick is to combine the RX50 specific drive selects to one drive select and one head select. The software should not know anything about this. Drive 0 would be side 0, and drive 1 side 1. Christian
[cctalk] Re: Need a 1.2mb 5.25 floppy
On 2/27/2023 12:54 PM, Chuck Guzis via cctalk wrote: On 2/27/23 09:30, Warner Losh wrote: Prior to about 1984 or 85, the failure rate for DD floppies for me was high enough that I splurged for the QD. After 84 or 85, I never had any problems using DD media. I suspect that yields must have gotten better, but maybe I just had bad luck prior to going to college... There was a lot of junk in the floppy arena in the early days. The brands that vanished were numerous. Brown, Elephant...all terrible. That's funny. I used lots of Elephant on my TRS-80's and never had a problem. Still have them and I can still read and write them without any problems. The only funny stuff I ran into was with 8" disks and the Terak. We were having problems and talked to Terak about it and their solution was that we should be buying Terak Brand Disks. Yeah, right, like they ever actually made disks bill
[cctalk] Re: Need a 1.2mb 5.25 floppy
On Mon, Feb 27, 2023 at 11:10 AM Christian Corti via cctalk < cctalk@classiccmp.org> wrote: > On Mon, 27 Feb 2023, Warner Losh wrote: > > You should be using QD floppies, but those are rare. DD floppies from > > later than 1985 though work just fine (discovered empirically while a > > Are they? I guess that I have at least as many QD floppies as DD, if not > even more. :-) > I'd guess at least as many HD floppies, likely way more. QD was a pretty odd duck, and any > > However, in a PC, to write these diskettes, you need a 1.2M drive. While > > there is a couple of TEAC drives (55FR I think) that do 80-tracks at the > > DD/QD RPM and data rates, things get fussy putting them into PCs. And > > last time I looked they were 5x the price of ye-olde-generic 1.2M floppy > > drive. As long as it's formatted at the right density/rpm rates, it's > > fine. And RX50.SYS, if memory serves, does all that right. > > When giving an advise, it should be as correct as possible ;-)) > So no, you don't need a "1.2M drive" (i.e. high density). You just need a > 96 tpi drive. And the drive is totally (well, almost) ignorant of the data > rate. It is just spinning the media at a specific velocity (300 or 360 > rpm). When using a 300 rpm drive, you need a 250 kHz data rate for DD (QD > is the same, it's just a marketing name for 96 tpi DD). With 360 rpm you > need a 300 kHz data rate. It only gets a little bit complicated if you > jumper a high-density drive for dual-speed mode (300 rpm if DD, 360 rpm if > HD). > Correct. You don't need a 1.2M drive. That's true. However, getting the 96tpi QD 300prm 250kHz drives are a lot harder these days than finding an old 1.2M drive. I recently looked for the TEAC 55FR drives that I used back in the day, and could not find them at all. Found plenty of other TEAC 55xx drives that were all either '360k' or '1.2M' drives. So it was more of a practical bit of advice, than an absolute requirement... While several of the newer drives do allow dual speed operations, the floppy cables for the RX-50 drive don't have the necessary signals to switch them. IDrives used a transistor to switch the signals properly for these drives. I opted to use drives that didn't need this signal. For 3.5" drives, there weren't any hacks needed because that signal was ignored by most of the drives. I rarely used them on a PC back in the day, so I'll defer to others on that. > > Using 3.5" drives in double density mode will work, but there's a cascade > > of software issues you'll have to deal with. I booted my DEC Rainbow with > > It would be the same for a normal 5¼" double sided drive. IIRC the trick > is to combine the RX50 specific drive selects to one drive select and one > head select. The software should not know anything about this. Drive 0 > would be side 0, and drive 1 side 1. > The trick is just to use two double sided drives, the side select stuff is there, and you just need to jumper the drives to be ID0 and ID1 to get your A & B drives. You have to use for this, though, drives that can do 300rpm at 250kHz because that's what (at least the Rainbow) RX-50 controller puts out. I ran this way for many years, though the software changes to MS-DOS were a bit flakey for me, and I never found ones for CP/M. I only got the 3.5" floppy drives that were the lower density to work, since those were also 300rpm/250kHz. I never got the high density ones to work since at least the ones I looked at didn't have the density signal, nor density jumpers. Wrote a 'driver' for it called IMPDRIVE back in the day. Some 5.25" drives would work with it (like the TEAC 55FRs), but many would not. And my old FRs are toast and I've not been able to find good replacements to try this again... Warner
[cctalk] Re: WTB Any storage for a PDP 8/A
Oh really - what a nightmare :/ - they are rare boards it seems.
[cctalk] Re: PDP-8/A FPP8/A
Hi Bob Thanks - thats very interesting. I guess there was quite a bit of overlap with the 11 and the 8/A so 'marketing' stepped in :-)
[cctalk] Re: Need a 1.2mb 5.25 floppy
On Mon, 27 Feb 2023, Warner Losh wrote: You should be using QD floppies, but those are rare. DD floppies from later than 1985 though work just fine (discovered empirically while a Are they? I guess that I have at least as many QD floppies as DD, if not even more. :-) However, in a PC, to write these diskettes, you need a 1.2M drive. While there is a couple of TEAC drives (55FR I think) that do 80-tracks at the DD/QD RPM and data rates, things get fussy putting them into PCs. And last time I looked they were 5x the price of ye-olde-generic 1.2M floppy drive. As long as it's formatted at the right density/rpm rates, it's fine. And RX50.SYS, if memory serves, does all that right. When giving an advise, it should be as correct as possible ;-)) So no, you don't need a "1.2M drive" (i.e. high density). You just need a 96 tpi drive. And the drive is totally (well, almost) ignorant of the data rate. It is just spinning the media at a specific velocity (300 or 360 rpm). When using a 300 rpm drive, you need a 250 kHz data rate for DD (QD is the same, it's just a marketing name for 96 tpi DD). With 360 rpm you need a 300 kHz data rate. It only gets a little bit complicated if you jumper a high-density drive for dual-speed mode (300 rpm if DD, 360 rpm if HD). Using 3.5" drives in double density mode will work, but there's a cascade of software issues you'll have to deal with. I booted my DEC Rainbow with It would be the same for a normal 5¼" double sided drive. IIRC the trick is to combine the RX50 specific drive selects to one drive select and one head select. The software should not know anything about this. Drive 0 would be side 0, and drive 1 side 1. Christian
[cctalk] Re: Need a 1.2mb 5.25 floppy
> On Feb 27, 2023, at 9:50 AM, Warner Losh via cctalk
> wrote:
>
> On Mon, Feb 27, 2023 at 12:06 AM Chuck Guzis via cctalk <
> cctalk@classiccmp.org> wrote:
>
>> ...
>> I thought the Pro 300 series used RX-50 drives; i.e. 400K 96 tpi DD
>> media. So even with your 5.25" HD drive, you should be using DD
>> ("360K") floppies.
Yes, the Pro uses RX50 drives.
> You should be using QD floppies, but those are rare. DD floppies from later
> than
> 1985 though work just fine (discovered empirically while a poor college
> student,
> reconfirmed recently when I made all those Venix disks).
>
> However, in a PC, to write these diskettes, you need a 1.2M drive. While
> there is a couple of TEAC drives (55FR I think) that do 80-tracks at the
> DD/QD
> RPM and data rates, things get fussy putting them into PCs. And last time
> I looked they were 5x the price of ye-olde-generic 1.2M floppy drive. As
> long
> as it's formatted at the right density/rpm rates, it's fine. And RX50.SYS,
> if memory serves, does all that right.
I don't understand that. I have a plain old Gateway PC with a twin floppy
drive (3.5 and 5.25 pair). It defaults to PC format 9 sectors per track, of
course. But it's quite happy to be told to do 10 sectors per track, reading or
writing. I first did so using DOS with INT13 I/O, then in Linux with a fdparm
operation, and finally in C or Python by issuing an appropriate FDSETPRM ioctl.
Works great.
You can find the machinery in my "flx" utility (for operating on RSTS file
systems); it handles both container files and actual RX50 format floppies.
This is how I write disks for my Pro to consume.
paul
[cctalk] Re: Need a 1.2mb 5.25 floppy
On 2/27/23 09:30, Warner Losh wrote: > > Prior to about 1984 or 85, the failure rate for DD floppies for me was > high enough that I splurged for the QD. After 84 or 85, I never had any > problems > using DD media. I suspect that yields must have gotten better, but maybe I > just had bad luck prior to going to college... There was a lot of junk in the floppy arena in the early days. The brands that vanished were numerous. Brown, Elephant...all terrible. If I look at my 5.25" archives, most early survivors are 3M, Dysan or Verbatim. A few Xidex. All of the off-brands have eventually failed and been weeded out. Wabash was legendary in its awfulness in the 5.25" area. Of course, if you're going to use DD floppies in an RX50 drive, you'll need to purchase some stick-on arrows... --Chuck
[cctalk] Re: Need a 1.2mb 5.25 floppy
On Mon, Feb 27, 2023 at 9:30 AM Chuck Guzis wrote: > On 2/27/23 06:50, Warner Losh wrote: > > > You should be using QD floppies, but those are rare. DD floppies from > > later than > > 1985 though work just fine (discovered empirically while a poor college > > student, > > reconfirmed recently when I made all those Venix disks). > > Speaking from experience and consultations during the 1970s with > engineers from Dysan (we were using 100 tpi drives), the only difference > between QD and DD floppies is QA step--QD ones are usually verified at > 96 or 100 tpi, the DD ones at 48 tpi. The brown goo spread on the > doughnut is exactly the same. > Prior to about 1984 or 85, the failure rate for DD floppies for me was high enough that I splurged for the QD. After 84 or 85, I never had any problems using DD media. I suspect that yields must have gotten better, but maybe I just had bad luck prior to going to college... > If one purchased factory-formatted diskettes for a specific platform, of > course the formatting would be different depending on the platform. > True. For the Rainbow I was always reformatting because nobody sold pre-formatted Rainbow disks at a price that was sane. > Similarly SS and DS diskettes are identical; early on, ones with > verification errors on one side were "flipped" accordingly and sold as > SS. As techniques improved, the only difference became the label. > I believe that.. Warner
[cctalk] Re: Need a 1.2mb 5.25 floppy
On 2/27/23 06:50, Warner Losh wrote: > You should be using QD floppies, but those are rare. DD floppies from > later than > 1985 though work just fine (discovered empirically while a poor college > student, > reconfirmed recently when I made all those Venix disks). Speaking from experience and consultations during the 1970s with engineers from Dysan (we were using 100 tpi drives), the only difference between QD and DD floppies is QA step--QD ones are usually verified at 96 or 100 tpi, the DD ones at 48 tpi. The brown goo spread on the doughnut is exactly the same. If one purchased factory-formatted diskettes for a specific platform, of course the formatting would be different depending on the platform. Similarly SS and DS diskettes are identical; early on, ones with verification errors on one side were "flipped" accordingly and sold as SS. As techniques improved, the only difference became the label. FWIW, Chuck
[cctalk] WTB: Accutech Gobi (Gobi7 or Gobi8)
Well, the weekend of hardware sudden death continues. The reason for getting the UltraBook IIi out was to do some more work on kOpenRay, the free Sun Ray server software I very occasionally maintain. Among other devices I use(d) two Accutech Gobi laptops to talk to it since they have an oddball VPN setup that used to cause problems. Unfortunately, neither will configure their network interfaces anymore and just hang. The board is of course a cheap mass of unrepairable components. If anyone has an Accutech Gobi (either the 7 or 8 model, both will suffice, I don't need the 3.5G module but will use it if it's there) sitting around gathering dust, I'd love to buy it off you. I have the power supply and batteries already. Southern California. -- personal: http://www.cameronkaiser.com/ -- Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckai...@floodgap.com -- And now for something completely different. -- Monty Python
[cctalk] Re: Need a 1.2mb 5.25 floppy
On Mon, Feb 27, 2023 at 12:06 AM Chuck Guzis via cctalk <
cctalk@classiccmp.org> wrote:
> On 2/26/23 16:42, Chris Zach via cctalk wrote:
> > Oi.
> >
> > So after finally getting things going I started copying the Pro/380 OS
> > files to a bunch of 1.2mb floppies. Great. However after a bit I started
> > getting errors, and found that the disks were getting gouges in the
> > tracks. Sure enough disassembly of my 1.2mb Teac showed that debris had
> > become embedded in the disk head and cleaning is not possible.
> >
> > Terrific. Tossing the drive, this is not the first time I have had this
> > problem with these disks so I am dumpstering all of the old floppies and
> > just bought 40 new ones in sealed boxes.
> >
> > However I'm now in need of a 1.2mb floppy drive. Anyone have a good
> > working spare that I can beg/borrow/buy in the MD area?
>
> I thought the Pro 300 series used RX-50 drives; i.e. 400K 96 tpi DD
> media. So even with your 5.25" HD drive, you should be using DD
> ("360K") floppies.
>
You should be using QD floppies, but those are rare. DD floppies from later
than
1985 though work just fine (discovered empirically while a poor college
student,
reconfirmed recently when I made all those Venix disks).
However, in a PC, to write these diskettes, you need a 1.2M drive. While
there is a couple of TEAC drives (55FR I think) that do 80-tracks at the
DD/QD
RPM and data rates, things get fussy putting them into PCs. And last time
I looked they were 5x the price of ye-olde-generic 1.2M floppy drive. As
long
as it's formatted at the right density/rpm rates, it's fine. And RX50.SYS,
if memory serves, does all that right.
Using 3.5" drives in double density mode will work, but there's a cascade
of software issues you'll have to deal with. I booted my DEC Rainbow with
these and some hacks from someone in the Jemez Mountains to do double
sided on MS-DOS (which reminds me, I have the hacks still, and they also
have a now lost-ish BIOS listing for 3.10b, so I should see if I can post
that for the few people still interested).I've never done it on a PRO
though.
I'm out in Colorado, or I'd happily give you one of my spares.
Warner
[cctalk] Re: Research machines RM 380
On Mon, Feb 27, 2023 at 10:29 AM jake utley via cctalk wrote: > > I’ve been restoring a RM380 I picked up not long ago and it’s been good news > and bad news. All the cards are in wonderful condition and the case is > presentable however the two BASF 6106 floppy drives are highly corroded and > probably won’t work again but this isn’t what I’m wondering, the original > supply is a little rough but looks tone perfectly restorable with the > exception of the key lock been stuck (problem to solve later) and I can get > all the parts needed to replace the three filters but it is a 70s linear > supply and if my s-100 experience has told me anything they might not be the > most reliable. What would you all recommend restoring it and keeping it > original or fitting some modern SMPS in its place. It is a low serial number > as well (691) but saying I want it to be reliable I’m torn. I would certanly recomend keeping it original. My experience is that a linear supply, although less efficient than a switch mode one, is a lot more reliable. There's a joke about the crazy PSU in the Zenith ZVM1220 MDA monitor thst said unit combines 'The reliability of a switcher with the efficiency of a linear'. It's also a lot easier to fix a linear supply than a switcher and there are not high voltages on any of the semiconductors. Getting back to the 380Z, there's a schematic of one version in the service manuall. But even if it doesn't agree, you can trace out a schematic in under an hour and that's going slowly. It is a very simple unit using normal 3-terminal regulators in the standard way. I'd 'megger' the transformer just to be safe as the machine seems to have been stored in poor conditions. Then power it up with a 'lamp limiter' on the mains input and no load on the output (unplug the cables from the driives and the 1 or 2 10-way ribbon cables from the PCBs). Most likely it will be fine, even with the original smoothing capacitors. -tony
[cctalk] Research machines RM 380
I’ve been restoring a RM380 I picked up not long ago and it’s been good news and bad news. All the cards are in wonderful condition and the case is presentable however the two BASF 6106 floppy drives are highly corroded and probably won’t work again but this isn’t what I’m wondering, the original supply is a little rough but looks tone perfectly restorable with the exception of the key lock been stuck (problem to solve later) and I can get all the parts needed to replace the three filters but it is a 70s linear supply and if my s-100 experience has told me anything they might not be the most reliable. What would you all recommend restoring it and keeping it original or fitting some modern SMPS in its place. It is a low serial number as well (691) but saying I want it to be reliable I’m torn.
