Ithaca Intersystems DPS-1 w/ front panel, 2016 Restoration

This Web page created April 3 2016, updated April 20 2016. It is part of a series of Ithaca DPS-1 Web pages as decribed below. There's many such web pages, as linked from my repair and restoration home Web page. I also have a home page for my S-100 Web pages. I have a general Ithaca Intersystems Web page at this link..

Introduction

I started work on this Ithaca Intersystems DPS-1 system in early September 2009. On another Web page, you can see how I cleaned it up, worked from the CPU and front panel to get the two functioning, and then added and tested the remaining cards. I had a failure - blown fuse, damages - which I fixed. But it still had problems, and I put it aside. See what I did: false leads, blind alleys and all! Failures are more educational than successes, you know. I went back to it later in June 2012, to discuss and photograph the DPS-1 front-panel toggle switches.

In March 2016, I successfully repaired another DPS-1 and several Ithaca boards. That gave me a working DPS-1 (without front panel) and a good set of boards for it; plus other boards in varying condition. I identified the good set as "#1" boards" for that DPS-1 system. Then on March 21st 2016, I proceeded to test and refine another set of working CPU, floppy controller, and I/O card, to be my "#2 set". But the remaining memory cards were not reliable. Here's some running notes of my board work on both sets of boards. This Web page has details and photos from those notes, as I produced another working set to run in this DPS-1 front-panel S-100 mainframe; and clarified the operations of an Ithaca BIOS and CP/M.

I exhibited both DPS-1 systems and 8-inch drives at "VCF-E XI" or the Vintage Computer Festival - East XI (not VCF-E 11), on April 15-17, at the Infoage Center in Wall, NJ USA. Exhibitors on Sat and Sun, talks on Friday, and a vendor/consignment area. Hundreds attended. I was a vendor part-time and an exhibitor full time. Here's my Web page on my exhibit and on the event.

- Herb Johnson

Ithaca boards prep

Here's some running notes of my board work on both sets of Ithaca boards on the previous DPS-1 (no front panel) system.

Mar 23, 2016: I cleaned the edge connector on spare 64K card with DeOxite and paper towel. I got some dark stuff off the connector as photographed. I reseated all chips on card, and tested again in the working DPS-1 chassis. The card performed better afterwards. Still is not 100% reliable on first power, but it improved.

So the second set of cards, which I labled #2 white sticker, are:

I/O card spare yellow
floppy controller Robinson green
64k spare #2 card yellow
CPU board 2012 sys red

The red sticker cards, were from this DPS-1 chassis as worked on in 2009. Green, was from the system as recieved from Robinson which I repaired earlier. Yellow are cards I had in inventory. Again, details of this scheme is on my repair page for that system.

Test in DPS-1 w/front panel

March 25th - Pulled out DPS-1 front-panel chassis and FP. I powered the empty chassis (front panel and motherboard) from Variac, slowly raised voltage, to restore the power capacitors and check the voltage regulators on the motherboard. No problems occurred.

I added 2nd set of DPS-1 cards. Had problems with booting, isolated them to two effects.

1) S-100 connectors on DPS-1 chassis probably dry and slightly corroded. Cleaned indirectly by coating the four boards with DeOxit and reinserting a few times. Helped memory board in flexure to run better.

2) the #2 I/O card S-100 edge connector is damaged, has gold missing. but many of those pins are not connected. Someday I'll have to address this. Meanwhile, I cleaned again with Deoxit.

Results were more promising. I have my 2nd Ithaca chassis with front panel running now, with the 2nd set of DPS-1 boards; and booting from the same Zenith-cased drives as my other repaired DPS-1. Tests show it needs a front-panel reset repair, probably some jumper setting or toggle. But it boots and runs CP/M memory and drive diagnostics.

Front panel reset repairs

Front panel reset did not work. Removed front panel board and confirmed problem was bad clear/reset switch, by ohms testing reset to ground. I happened to have a physically compatible DPDT center-off switch except it's not momentary on both ends, only one end. Doesn't matter for use.

I removed reset/clr switch. Took most of an hour to desolder and remove carefully.

March 26th - replaced reset/clear switch on front panel. System boots and reboots OK except on boot from reset, the startup message has several initial garbelled characters, as if the UART was not well initialized??? This was not a problem on my #1 set of cards on my no-front-panel system.

(Later, I read in the manual how the ISTARTUP BIOS reads the front panel switches, to set the baud rate. Since I had no front-panel in my first working system, the default was 9600 baud. When I set the data switches to the 77H, designated for 9600 baud, that removed the garbled text.)

Bootable CP/M with Ithaca BIOS 4.c; Ithaca disk drives

I discuss on my repair Web page for my other DPS-1 system, my bootable and running CP/M disks, with Ithaca BIOS version 4.d.

I tested more software programs. I have two ISYSGEN programs, they copy some memory image into system tracks. I have two FORMAT programs, both work, one also copies system tracks. Need to do more testing of Ithaca utility programs, and to determine how or if they need to have modified CP/M images to match my booting CP/M image and ISTARTUP for 4.C BIOS.

On another Web page, I'll discuss repairs of a pair of Shugart 800's in an Ithaca DPS-1 drive chassis. Here's a photo of the running DPS-1 front-panel chassis, atop the Ithaca 8-inch dual drive chassis.

- Herb

Copyright © 2016 Herb Johnson