As some of you may be aware I am trying to find a fault in a Rainbow H7842
PSU. I am using Tony Duell's schematic from here
I have been testing the Control Module by using a bench PSU to supply 15VDC
to the input of the 7812 regulator (p2, PSU Sheet 1).
My diagnosis shows that the control module is shutting down the PWM (p6,
Control Module Sheet 2) because it is detecting an overcurrent in the -12V
side (E3d on Control Module sheet 1, although I have determined that it is
This seems to be because I measure a steady 0.6V on pin 6 of the transformer
(p4, PSU Sheet 3). I just can't imagine where it might be coming from as the
chopper won't be running. I had previously removed the transformer and there
are no shorts between the pin 5-pin 6 winding and any of the other pins on
the transformer. I checked all the DC outputs of the PSU when powering the
7812 from the bench, both on a working PSU and the non-working one. They are
all at zero except the -12V output on the non-working PSU, which is +0.6V.
But the voltage can't come out of nowhere.
I am stumped and would appreciate any suggestions.
I saw this old post while searching for stuff related to the CPT Phoenix word processors. I was an engineer at CPT Corp. from 1978 thru 1989 and helped design the CPT 8100, 8500, 9000, and Phoenix systems.
The original monitor that I have has burned-out and I am searching for a replacement. You seem to have found/acquired the exact monitor that I have been looking for!
Would you care to sell the monitor, and keyboard too, to me? I would be most appreciative. It would certainly find welcome home, back with one of its original designers.
As you know I've recently restored a couple of CP/M luggable
computers. I also have many other machines with floppy disk drives,
3", 3.5", 5.25" and 8"
The machine I connect to the internet with is a more modern laptop
runnng Windows 8.1. Essentially its only interfaces are USB ports.
I would like to be able to :
Download disk images (I assume in .IMD or .TD0 format) and write them
to real floppy disks to use in my old machnes
If possble, for the more common filesystems like MS-DOS or CP/M, be
able to work with these images on the modern PC at the file level. For
example, if I download a CP/M progam as a .COM file I'd like to be
able to put it into a disk image of a Philips P2000C disk, then
transfer that image to a real floppy and put it in a drive on the
I understand there are designed based on a modern microcontroller that
connecct to a USB port and a disk drive. Software on the PC translates
between the disk image and the accurately-timed pulses corresponding
to flux transitions on the disk. This unit links to a real disk drive,
you run the software and it reads/writes a real disk in said disk
Now... I can handle a 'scope. I can handle a logic analyser. I can
handle a soldering iron. I can handle an engineer's lathe. I can
rebuld and align floppy disk drives. I can program most 8-bit micros
along with PERQ microcode, PDP11 mahine code, etc BUT I don't have a
clue when it comes to modern PCs, modern microcontrollers or USB
So what I am asking is for people to describe what to do as in :
Buy this microcontroller board
Buy this blank PCB and solder the components given in the BOM to it.
Download this software and install it by doing this.
Connect a standard floppy drive to this connector
Run the software, specify the disk image file and sit back.
I'd rather not put a customer through the throes of sending a 10.5" reel
of tape written on a S/370 mainframe through international shipping.
Anyone in the Barcelona area with the equipment and ability to handle
reading this thing? Besides, I'm up to my ears in work.
I have an HP 2875B paper tape drive that I want to interface to. It has
a 50 pin block connector (using well under 1/2 the pins). The connector
manufacturer was Continental.
I have already discovered, the hard way, that it is not a winchester
connector - the pins on the 50 pin Winchester connector I just obtained
via ePay that otherwise fits are too small in diameter and won't make
contact. I *could* increase their diameter using solder - but -- yuck.
The other connectors of this sort I am familiar with that have the same
general overall size and pinout were made by AMP. Does any one know if
the AMP connectors and the Continental connectors would be compatible?
On 5/28/23 09:17, Tony Duell wrote:
> I've come across the former and have the datasheets. From what I
> recall it was common to use it a control store sequencer and have
> microcode ROMs wider than the 8X300 needed, the extra bits were used
> to directly control hardware.
Power hog (well, it was bipolar) with a 3-bit opcode and a somewhat
strange programming model. You could usually spot one by the 50 pin
cerDIP and the external pass transistor. I think I still have a loose
one in my hellbox--and at least two in old systems.
Amidst all the floppy archiving discussion, here's a slightly different
The weather is warmer now where I live, so it's starting to be a good time
to do messy work outdoors. I have some mouldy floppy diskettes that I'd
like to try to read (mostly 5.25"), plus a good flux reader. What is the
best way to attempt to image these floppies?
My thinking right now is that for each floppy I can attempt this procedure:
- remove the mouldy cookie from the infected disk jacket; discard the latter
- give the cookie the best clean I can (how?) and allow to dry
- place the cookie in a clean disk jacket
- attempt to image
- clean floppy drive heads
Does this seem like a sensible plan? If so, what would be the best way to
clean as much mould off the cookie as I can? Tools that come to mind are
distilled water (tap water here is full of chalk), dish soap,
cyclomethicone, and of course more fearsome solvents. I have kimwipes,
microfibre cloths, and... 200-grit sandpaper, I guess :-)
Thanks for any advice,