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 🙂
>
>
> Message: 6
> Date: Fri, 24 Oct 2025 20:29:07 -0400
> From: Murray McCullough <c.murray.mccullough(a)gmail.com>
> Subject: [cctalk] The transistor invention
>
> 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 🙂
>
>
Did you know the role of Camp Evans in the invention of the transistor?
Find out here: https://youtu.be/6wFIVvb-5yQ
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
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
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
I was poking around eBay and up came a listing for a DEC "mini exchange", DFMSA. What is that? The name doesn't sound familiar. It looks like a box with a bunch of DB25 connectors on the back, but that doesn't help much.
paul
