I had forgotten that 75 years ago, Oct. 3, 1950, the transistor was
invented leading to integrated circuits making possible personal computers
and the interest of our love of computing. Where would we be without
Bardeen's, Brattain's and Shockley's invention?
Happy computing,
Murray 🙂
I just purchased an old Gimix computer (now if only I can get it from
Orlando to Chicago before my friend goes down there for Christmas).
It has an OMTI 20C-1 MFM hard disk controller with a IMI 5018 19MB hard
disk drive in it.
I am thinking of trying to upgrade the hard drive. The Gimix System
that I worked on had a half high 20MB drive and a Syquest removable 5MB
drive.
Does anyone have an old MFM drive laying around (half high or full
height but larger than 18MB) and/or an MFM removable cartridge drive
with cartridges?
I am also going to try to rebuild a Vector Graphic Dual Store Dual 8"
drive enclosure that I picked up at VCFMW. It suffered some dampness
damage and I'm not sure the drives will come up. If you have a dual 8"
drive setup (double sided drives, and enclosure) that you need a good
home for, please let me know.
I'm in the Chicago Area.
Thanks,
Mike
bitwiz(a)12bitsbest.com
> From: Jim Davis <jim.p.davis(a)gmail.com>
> Subject: [cctalk] Re: MFM Hard Drive & 8" Double Side Drives
> Was anything MFM or RLL with a removible cart build in the 80's-90's?
> I never heard of such a thing, Carts were scsi early 90's Syquest and
> others?...
>
Yup
https://en.wikipedia.org/wiki/SyQuest_Technology
The early ones were ST412 type interface
> From: Doc Shipley <doc(a)vaxen.net>
>
> Pretty sure Mr Gesswein is on this list but I don't see him post often.
> Anyway, he designed a very handy MFM drive emulator:
>
> https://www.pdp8online.com/mfm/mfm.shtml
>
Yup but try not to hawk my board. When they say they want a drive I don't
suggest alternatives.
I also get the digest so most questions have been answered before I see them.
Thanks all for the kind words.
I am trying to resolve a problem with a H7842 PSU from a DEC Rainbow. The AC OK output is not being asserted. I am looking at Tony Duell's schematic https://bitsavers.org/pdf/dec/rainbow/duell_schematics/psu.pdf and specifically at the Power OK circuit.
I am using a test load of 1R on the 5V output and 6R on the 12V output, which is within the spec of the PSU. I see that under load the 5V output is only 4.4V, so I suppose it is to be expected that AC OK is not asserted. If I (briefly!) remove the load from just the 5V output, the 5V output is 5.27V, but the AC OK output is still not asserted.
Using Tony's schematic, I looked at the input to the inductor on the secondary side (sheet marked "H7842 PSU Sheet 3") and it looks like this: https://rjarratt.wordpress.com/wp-content/uploads/2025/10/h7842-5v-secondar… I can't tell if that is correct or not. If I remove the 5V load the peaks narrow but are slightly higher.
However, the puzzling thing is the 5V Pulse signal, it doesn't pulse, it is a steady 32V. I see that the 12V Pulse signal *does* pulse. The name would suggest it is supposed to pulse and its inputs do pulse as shown in the trace pictured above. I don't see how it is possible for 5V Pulse to be at a steady 32V, even if the diode or resistor that create the 5V Pulse signal was somehow bad. I guess this non-pulsing might be the problem, but I don't really know what to check here, I have lifted the diode and tested it, it seems fine.
Does anyone have any suggestions please?
Incidentally, for those who helped me with my Olivetti M24, I had already reassembled it and got this PSU out to look at next before receiving further suggestions on the M24. Once I have the H7842 sorted out I will go back to the M24 again.
Thanks
Rob
Hi everyone,
According to historians, and I consider myself one, let us consider what
classic/vintage computers were: The 1970s saw the three amigos: Apple II,
TRS-80 and Commodore PET and the OS was DOS and its ilk + CP/M. The 1980’s
saw the Dells, HPs and many others with MS-DOS & IBM PC-DOS from QDOS. We
saw this and behold ’bring on the clones’(I just had to say this!) The era
of old computers saw one generation building on the shoulders of giants who
designed these wayback computers(with apologies to Wayback Machine).
Today’s PCs and ARM machines are just the latest iteration of this
theory(by the way not mine).
Happy computing
Murray 🙂
The VCF swap meet is in three days. Are you ready? Click here for more
information: https://vcfed.org/vcf-swap-meet/
Take care!
Jeff Brace
VCF Fundraising Manager
Going through my endless piles of *stuff* I have come across some
manuals that might already be scanned, might not. So anyone know if
these are archived somewhere?
* TSX Plus: 4 RX02 floppies. Version 6.40, 6.5
o Along with release notes for 6.40 dated Jan 16, 1989
* SDC-RXV31 floppy controller manual: Sigma information systems, 1984
* DHV11 Technnical manual
* DLV11 users guide ek-dlv11J-ug-001
* RA80 disk drive service manual (booklet, tough to scan)
* RLV12 disk controller user's guide
* MSC4806 Expansion memory board User's manual (10-29-1982)
o MSC is Monilithis Systems Corporation
o I think I have some of these boards
* Computer Products: Instruction manual, Model 307 Clock Calendar
* GTSC: Instruction manual, Model 304 Serial IO board
* Fortran 11 reference manual (unsure of title)
Thanks!
Chris
