I have to say a special thank you to Todd- who performed my first actual fix for the repair days. I've mostly been helping install Irix on SGI and giving away stuff- but I decided to come yesterday and try and get some things actually fixed. Todd not only identified 2 bad caps, but he had extras, and then helped installed them. He really did it all while I watched. The repaired PSU worked and it powered up my new-from-ebay DEC Personal DECstation 5000. It was an amazing feeling and I learned a bit to id these bad caps. I'm going to get some equipment and try to do some myself. Here are my photos from the day: https://imgur.com/gallery/ANp00f1 <https://imgur.com/gallery/ANp00f1> I hope everyone close by can make some time and attend these days as they are a great way to share knowledge and experience between members. -andy

On Mar 31, 2019, at 4:07 PM, Jeffrey Brace via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:

We had about a dozen members working on their machines and VCF machines Saturday and Sunday. Most did two days while some did one day. Bill Dromgoole and Duana Craps had worked on the Univac 1219B in the museum for the past week. They can give an update later as to their progress. David Gesswein worked on the museum's PDP-8. He will send a report later. There were others working on various projects. I got there midday and wasn't able to work on anything Saturday. Sunday I took VCF's turn at the InfoAge front desk. Evan can fill you in on what he was working on as well as the others.

This time we went to a new place: MJ's for Saturday dinner. Everyone liked it. Afterwards we played Cards Against Humanity which is always a fun time. Sunday morning we went to a new place: Mariner's Cove for breakfast. Also great food!

The next workshop is April 13 & 14.

-- ========================================= Jeff Brace Vice President Vintage Computer Federation

On Sun, Mar 31, 2019 at 04:07:37PM -0400, Jeffrey Brace via vcf-midatlantic wrote:

David Gesswein worked on the museum's PDP-8. He will send a report later.

Had the annoying two steps forward and one large step backward. The goal for the weekend was to install the reader run modification to the teletype which allows the PDP-8 to stop the tape reader and to fix the bulbs not working right on the front panel and test using the tape reader. End result is new faults developed so the machine isn't useable without more repairs. I ran all the diagnostics when I started and all passed without error. I had made the reader run board at home and tested it so it was supposed to be easy. I got it installed without problem but when loading FOCAL programs I got 11.35 errors which are input buffer overflow. In doing some research this seems to be a design error in FOCAL. Normally when reading a tape it prints everything received. It uses interrupts to read the tape into a small buffer which feeds the loading into memory and printing. The reading of the tape does not use the reader run control to stop reading when the input buffer is getting full. If the printing which is controlled by the transmit clock and any software delays is slower than the reading which is controlled by the mechanics of the teletype you will get an overrun. I need to check further but I don't think the tape reading speed is adjustable. The transmit clock had pots so I may be able to adjust it slightly faster as long as the teletype is ok with it. I also made a tape with nulls to try to slow down the reading but was unable to test due to faults that developed. I was able to load the FOCAL interpreter from tape and it ran fine. The teletype also had a capacitor go open that caused buzzing noise and operation problems. One of the workshop attendees had a capacitor that was usable to fix that problem. I moved on to the front panel issues. I finally tracked down cause of a bulb that would come on at varying brightness when it shouldn't to a diode on the cards that have the wires that go to the front panel. I checked the rest of those cards and found two more suspect diodes and replaced them also. Now that everything was supposed to be working I tried to load FOCAL again and it looked like it loaded fine but didn't run correctly. I tried to load diagnostics and they wouldn't run. Ran the moving AC light demo program and the bits disappeared when going into AC bit 3. Symptoms tended to change some as I was troubleshooting but did find moving the AC3 card to another AC bit moved the problem. I was unable to determine the failing component on the card before the end of the day Sunday so the machine is currently non functional unless the problem decides to go away on its own for a while. I'll bring an AC card to VCF to replace it and hopefully that will get it working again for VCF. I'll then take the card home and see if I can get it to fail in my machine so I can fix it. It has 123 diodes, 12 transistors, 63 resistors, and 23 capacitors. The diodes are the normal fault but none measured suspect so I will need to use the test equipment and schematic to figure out what is going wrong after I can reliably get it to fail.