June 2019 - vcf-midatlantic

Museum report
by Evan Koblentz 08 Jun '19

08 Jun '19

A bunch of visitors to InfoAge today, but mostly for the military stuff because they had a D-Day 75th anniversary event. Highlight for us was a guy in his 30s who is part of the 2600/HOPE community. Between visitors I did some cleaning in the workshop + replied to VCF emails. Evan Koblentz Executive Director, Vintage Computer Federation evan(a)vcfed.org / (646) 546-9999 www.vcfed.org @vcfederation

1 0

Festivus December 7 & 8, 2019
by Jeffrey Brace 07 Jun '19

07 Jun '19

Mark your calendars. The infamous VCFestivus party has been scheduled. Signup here: < https://docs.google.com/spreadsheets/d/1x0oSxqZXh8tmqqbUsP3KS3OywiNsEAOOmtq… > -- ========================================= Jeff Brace Vice President Vintage Computer Federation <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campai…> Virus-free. www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campai…> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

3 4

Re: [vcf-midatlantic] PDP-11/10 PSU Repair/Warning
by systems_glitch 07 Jun '19

07 Jun '19

Apparently some of the other DEC power supplies include a fuse on the AC input for the 5411086 board! I guess they discovered the problem in the field, too. It is a little ironic that the board that generates power fail blew up :) That's why I'd suggested the analog circuit that generates AC LO/DC LO -- both of them had gone away on the backplane. I also find it interesting that DC LO really has nothing to do with the output of the various independent regulator modules. You'd think since DC LO is open collector, each module would be able to pull it down and it'd only be released when all modules were stabilized. That is of course one of the issues with memory write-protect lockout on nonvolatile RAM on S-100: you have to wait til all three supplies stabilize, and then factor in enough time delay for each board to also have stabilized before releasing *PRESET and/or memory write lockout. I guess that's why they built a signal in for just that purpose on IEEE-696! The current draw through the connector should be 2-3 A, the combined output from the 5411086 board's +15V and +8V supplies isn't supposed to exceed 4A and is fused at 5A. It's switchmode (albeit kinda weird early switchmode, using a uA723) so current out should be less than current in, even accounting for efficiency losses. A 1A load on the +15V supply didn't register on the (granted, somewhat insensitive) power meter I was using on the AC transformer primary side. I plan to include a 0-15A AC current meter on the "actually in a box" version of my AC test supply, for finer measurement of module consumption at given loads. I've also seen various old computers and other machines with fuses bypassed, or something that's not a fuse in the fuseholder (cut off pieces of bolt or rod are common). Not a good choice! I did once see a military computer power supply with "battle fuse" switches -- the switches bypassed the power supply fuses, presumably so that you didn't lose computer power in a critical situation from a fuse breaking due to concussion from a shell hit or something. Thanks, Jonathan On Fri, Jun 7, 2019 at 11:29 AM Herb Johnson via vcf-midatlantic < vcf-midatlantic(a)lists.vcfed.org> wrote: > This caught my eye, so I looked at the schematic. Ironically, the > shorted full-wave rectifier is shown on the "power-fail" circuit > drawing. But the rectifier supplies all the unregulated DC voltage. > Unfortunately the fuse F1 is *after* the rectifier and not before. Thus > adding a fuse before the rectifier is wise. > > Bypassing the now-destroyed edge-connector pins is also wise. Did you > determine the normal AC current on those pins? I suspect a few amps, > thus those pins are at risk anyway. > > Thanks for calling this repair out. It's a cautionary tale about vintage > power supplies in general; look for AC-side fuses, install if not. I"m > looking at an IMSAI; the prior owner bypassed the AC fuse holder! ;( > > Shocked, > Herb > > > -- > Herbert R. Johnson, New Jersey in the USA > http://www.retrotechnology.com OR .net >

1 0

PDP-11/10 PSU Repair/Warning
by Herb Johnson 07 Jun '19

07 Jun '19

This caught my eye, so I looked at the schematic. Ironically, the shorted full-wave rectifier is shown on the "power-fail" circuit drawing. But the rectifier supplies all the unregulated DC voltage. Unfortunately the fuse F1 is *after* the rectifier and not before. Thus adding a fuse before the rectifier is wise. Bypassing the now-destroyed edge-connector pins is also wise. Did you determine the normal AC current on those pins? I suspect a few amps, thus those pins are at risk anyway. Thanks for calling this repair out. It's a cautionary tale about vintage power supplies in general; look for AC-side fuses, install if not. I"m looking at an IMSAI; the prior owner bypassed the AC fuse holder! ;( Shocked, Herb -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net

1 0

PDP-11/10 PSU Repair/Warning
by systems_glitch 06 Jun '19

06 Jun '19

full writeup here: http://www.glitchwrks.com/2019/06/05/pdp1110-psu-repair I finally fixed the power supply in my PDP-11/10S, it turned out to be a shorted bridge rectifier on the 5411086 board, which provides +15 VDC, LTC, and AC LO/DC LO. Unfortunately, when it failed, the rectifier burned up the edge connector traces for the AC input to the board. I ended up cutting the edge connector traces away (what was left) and soldering on a pigtail to connect to the Mate-n-Lok coming from the AC transformer. I added a 15A inline fuse, in the repair. For those who have original 5411086s that haven't failed yet, you might want to make up a little pigtail with an inline fuse holder. It'd be easy to make up such that it could plug into the existing harness without permanent modification, and it'll save your edge connector traces if the rectifier shorts. It can happen in the other regulator modules too, but they use a Mate-n-Lok instead of an edge connector, so any damage would be repairable. Anyway, the PDP-11/10S is back up and running! Thanks, Jonathan

2 2

Museum report
by Evan Koblentz 05 Jun '19

05 Jun '19

It was slow-ish at the museum today. Visitors included a man who last saw our exhibits a few years ago, and a family of five (three middle-school kids) who took a solid tour and asked smart questions. Wednesdays always get busy in the summer when school is out and families come to the shore on vacation. I'm looking forward to that. Docent days are more fun when there are lots of visitors.

1 0

Re: [vcf-midatlantic] Workshop report
by Jeffrey Brace 03 Jun '19

03 Jun '19

On Mon, Jun 3, 2019 at 11:24 AM Sentrytv via vcf-midatlantic < vcf-midatlantic(a)lists.vcfed.org> wrote: > I spoke to both of them briefly. > > The boy did not seem especially interested in the Commodore 64. > He (or maybe it was his mom) was more interested in what Jeff G. was > working on and his testing procedure and programming. > > Too bad his mother doesn't want him to buy vintage computers. > > If they live locally, I would encourage them to come to the workshop more > often. > Even if it's to see what's going on there, to help and learn. Yes. They live locally in Toms River. Evan had met them at the local maker faire and told them about VCF museum. Not sure if he mentioned VCFe. The boy, Justin, was interested in a variety of machines and I got him interested in trying BASIC programming by typing in the bouncing ball program from the Commodore User’s Guide. > > By the way the barbecue and grilling was fantastic and a very good idea! > > Mike R. > > Sent from: > My extremely complicated, hand held electronic device. > > > On Jun 3, 2019, at 11:14 AM, Jeff Galinat via vcf-midatlantic < > vcf-midatlantic(a)lists.vcfed.org> wrote: > > > > Hi Jeff, > > The young man’s name is Justin and I am pretty sure his mom’s name is > Tracy. Since he seemed pretty interested I told them all about VCFE which > they did not know about. > > Jeff Galinat > > > > Sent from my iPhone > > > >> On Jun 3, 2019, at 10:56 AM, Jeffrey Brace via vcf-midatlantic < > vcf-midatlantic(a)lists.vcfed.org> wrote: > >> > >> One kid about 12 years old visited the museum and was highly interested > in > >> vintage computers. He knew many things which he learned from YouTube. > Some > >> accurate, some not. His mom said that he was bored from modern scratch > >> programming. I had him try out BASIC programming on the C64. He wants > to > >> buy vintage computers, but his mom won’t let him. He also checked out > the > >> repair workshop. He really enjoyed! > >> > >> ========================================= > >> Jeff Brace > >> Vice President > >> Vintage Computer Federation > > -- ========================================= Jeff Brace Vice President Vintage Computer Federation

1 0

Warehouse helpers needed
by Evan Koblentz 03 Jun '19

03 Jun '19

Everyone, We need a lot of help in the warehouse this summer. The work is mostly sorting and organizing, under my direction. There is some, but not a lot, of heavy lifting involved. What's in it for you: glory, lunch, and a sense of accomplishment. We need people who can give us a full day at a time. Wednesdays are best. Weekends are also possible. What's good: planning ahead for specific days. What's not so good: last-minute changes, unreliable people, inability to follow our guidelines/policies. Apply directly to me via evan(a)vcfed.org. -- Evan Koblentz, executive director Vintage Computer Federation www.vcfed.org evan(a)vcfed.org (646) 546-9999 VCF is a 501(c)(3) non-profit organization

1 0

Tanday Assembly comments
by Mike Loewen 03 Jun '19

03 Jun '19

I'm thinking about exhibiting at the Tandy Assembly in September. For those of you who attended last year, how did you like it? Mike Loewen mloewen(a)cpumagic.scol.pa.us Old Technology http://q7.neurotica.com/Oldtech/

3 2

Workshop report
by Jeffrey Brace 03 Jun '19

03 Jun '19

We had about 10 or so people working on various systems. This time we did a BBQ Saturday night and Sunday afternoon. Everyone liked it. We are going to do it again in August. Evan switched out the Amdahl in the featured artifact and put in the Canon Cat. He also put back most of the newly acquired artifacts. One kid about 12 years old visited the museum and was highly interested in vintage computers. He knew many things which he learned from YouTube. Some accurate, some not. His mom said that he was bored from modern scratch programming. I had him try out BASIC programming on the C64. He wants to buy vintage computers, but his mom won’t let him. He also checked out the repair workshop. He really enjoyed! Next workshop is August 24 & 25. @Evan: Do you want to add anything? -- ========================================= Jeff Brace Vice President Vintage Computer Federation

3 2