- vcf-midatlantic - lists.vcfed.org

Who's near Aston PA?
by Evan Koblentz 14 May '18

14 May '18

We need three boxes of (important) magazines picked up in Aston PA and delivered to the museum. ________________________________ Evan Koblentz, executive director Vintage Computer Federation a 501(c)(3) educational non-profit evan(a)vcfed.org (646) 546-9999 www.vcfed.org facebook.com/vcfederation twitter.com/vcfederation instagram.com/vcfederation

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Deadline for Saturday Dinner Pre-Payment for VCF East XIII
by Jeffrey Brace 14 May '18

14 May '18

I was just advised that there is a Pre-Pay deadline of Wednesday at midnight for pre-payment of the Saturday Dinner which is $29 send to paypal(a)vcfed.org. Thanks! -- ========================================= Jeff Brace Vice President Vintage Computer Federation

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VCF Saturday Dinner pay it now and get it out of the way!
by Jeffrey Brace 14 May '18

14 May '18

Cost is $29 per person. Send via PayPal: paypal(a)vcfed.org Put a note: VCF East XIII - Saturday Dinner You can bring guests if you like. Please don't wait until the last minute. Do it now, it's so quick and simple! :-D -- ========================================= Jeff Brace Vice President Vintage Computer Federation

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Overnight lodging @ VCF East
by Evan Koblentz 14 May '18

14 May '18

So far only 7 people signed up for staying overnight at VCF East. Is anyone else interesting? https://tinyurl.com/y928w6gq

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DEC RK06 Disk Cartridges
by Bill Degnan 13 May '18

13 May '18

Does anyone have an RK06 drive AND plan to go to VCF East AND would be interested in purchasing a cartidge pack or two? Reasonable offers accepted. I also have a few RA60 drive pack carts avail. Send inquiries through http://vintagecomputer.net/contact.cfm

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ANNOUNCE: VCF East XIII 8085 Single Board Computer
by systems_glitch 12 May '18

12 May '18

Some of you may have noticed that I've been extra busy/slow to reply lately. It's not just because of taxes :) This is on my bench: http://i.imgur.com/TppyO2Mh.jpg We got together on the idea of a special edition vintage computer project for VCF East last year, but there wasn't enough time between when someone mentioned the idea and the event to actually get it done. This year, I've revised my 8085 SBC design into a larger, more full-featured board as seen above. Specs as follows: * 8085 CPU * 64K Static RAM * 32K ROM available in 4K pages * Autoboot/ROM switchout circuit * 8251A USART for console port * DS1233 EconoReset * Baud rates from 300 - 38400, baud clock independent of CPU clock * GlitchBus expansion header * Single 5V power supply The board is 8x5 inches, the GlitchBus expansion stacking area provides for a 4x5 inch board. Currently I've got the prototype version running GWMON, my ROM monitor, from Ferroelectric RAM in the ROM socket. The goal is to have a customized monitor and fully functional BASIC by VCF East. This is also the first board to commit to a GlitchBus pinout/layout -- several of us have been working together offline and through IRC to get it nailed down. Eventually, you'll be able to add a storage controller (CF, floppy, etc.) via GlitchBus and boot/run CP/M! The ROM can be switched out under software control, so the full 64K of RAM will be available to user programs. The board also supports FeRAM, so it's possible to have a core-like setup for main memory. If you use FeRAM or an EEPROM in the ROM socket, the board can update its own firmware. This revision is going to be released at VCF East XIII and is a special edition that will probably be limited to the show. We'll be doing an event-long workshop to build and test the SBC at InfoAge during VCF East, just like we did with the XT-IDE and Apple II prototyping workshop last year. If you choose to assemble your board at VCF East, you'll leave with a 100% tested and working 8085 SBC. I may bring a very few CRT terminals to make available to builders of the 8085 SBC. Evan got me a high-res PNG version of the VCFed logo, which I was able to work into a copper-and-silkscreen graphic for the PC board: http://i.imgur.com/H6iJnXIh.jpg I haven't nailed down a price for parts kits yet -- that will be forthcoming. Thanks, Jonathan

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FS: Motorola MEK6800D2 6800 Trainer/Dev Kit TESTED/WORKING
by systems_glitch 12 May '18

12 May '18

link: https://www.ebay.com/itm/273207889695 This one looks like it was essentially built and never used. Nothing has been added to the prototype area, it looks like the EXORcisor bus connection was never plugged in to a socket, and there was no additional RAM in U18/U19 sockets. I cleaned it up, removed some areas of excessive rosin flux, and brought the board up on a 5V bench supply. It draws around 1A with address/data info on the displays. Ran through the sample program in the manual, which worked fine. I added two Fairchild branded 6810 SRAMs to bring it up to a total of 512 whole bytes of memory :) Didn't test the cassette interface, I no longer have a cassette recorder kicking around. If you're interested and will be at VCF East, let me know -- I'll take substantially less if I don't have to pay eBay/PayPal fees and ship. Thanks, Jonathan

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Magic smoke
by Evan Koblentz 12 May '18

12 May '18

Museum pet released its magic smoke. :( Appeared to come from front/underneath the motherboard.

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Re: [vcf-midatlantic] talk at VCF-East on audio cassettes for data; stuff
by Michael Thompson 11 May '18

11 May '18

> > Date: Thu, 10 May 2018 23:38:29 -0500 > From: Kyle Owen <kylevowen(a)gmail.com> > Subject: Re: [vcf-midatlantic] talk at VCF-East on audio cassettes for > data; stuff > > This may be too beyond audio cassettes, but I figured I'd share. > > I never really was interested in this portion of my first PDP-8 haul, but I > ended up with a Tennecomp Fidelipac drive. For those unfamiliar, these were > commonly used for commercial breaks in radio stations and the stations' > jingles. Similar to 8-track, but they didn't have a built-in pinch roller. > > I have yet to see if the unit is functional, and need to figure out where > the interface card is (if it came with the interface, even), as I would > like to digitize the tapes. Fortunately, I've got a friend with some radio > station cart machines, so I could possibly record them to audio files and > reverse engineer them from there. > > So yes, even a PDP-8/M, ca. 1974, and possibly prior, used an audio tape > system for data storage! > > Pictures here: https://photos.app.goo.gl/kBL9gRGF697A0xUT2 > > Kyle > There is one of those on the PDP-8/I at RCS/RI and on the Classic PDP-8 at the Computermuseum der Fakultät Informatik. Michael Thompson

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Reanimating Zorba (long)
by Mike Loewen 11 May '18

11 May '18

It's alive! http://q7.neurotica.com/Zorba1.jpg http://q7.neurotica.com/Zorba2.jpg After several extended troubleshooting sessions, my Telcon Zorba (Nomis 9) is up and running! I don't know what happened to this system, but it had some major problems. When I received the system, it did nothing: no lights, no fan, no display. My first thought was a bad power supply, and a voltage check showed that the +12VDC line was down to around 8V. No filament on the CRT, either. Unplugging the display board allowed the 12V line to pop right back up to spec. So, something was wrong on the display board. A visual check of the display board didn't reveal anything obvious. I used my DMM and a curve tracer (connects to my oscilloscope's X-Y inputs) to look for anything odd. I found a large diode which appeared to be shorted. On desoldering it, it just fell apart! No idea what caused it to short, but I ordered some horizontal output transistors just in case. The diode was a MR854 400V 3A fast recovery diode, and the HOT was a BU807. The old HOT tested similarly to the new transistors, but I replaced it anyway. I replaced the diode with an MR856 (600V 3A) for an extra margin of safety. After adjusting the power supply, I plugged everything back together, and bingo, the filament lit up and the 12V line looked good. Still no display though, so I started looking at signals. With the help of the schematics, I traced things back to the CRT Controller chip (CRTC), an Intel 8275 programmable CRTC. No signals coming out of the CRTC at all. I found an Intel P8275 on Ebay, and sat back to wait. (tip of the hat to Ian Primus for troubleshooting advice) After I replaced the the CRTC, the system immediately beeped (which it had never done before), and eventually the boot display came up, telling me to press <ENTER> to boot. A slight tweak on the horizontal hold pot was all it took to stabilize the display. So, second problem solved. However, pressing <ENTER> did absolutely nothing. There was voltage going to the keyboard (the caps lock LED would toggle), but nothing was happening. I checked the output from the keyboard on the scope (looked okay) and from the inverter going to the 8251A USART for the keyboard. Time to haul out the logic analyzer and find out what's happening on the bus. On the diskettes which came with the Zorba, there was one labeled "Gemini Zorba Source BIOS 1.7A". I imaged the disks with IMD, and was able to pull the files from them. On the BIOS disk was source code for the CP/M BIOS, as well as source for the boot ROM. I dumped the boot ROM with my Data I/O 29B and ran it through a disassembler (z80dasm). Things didn't quite match up, and it was obvious that the ROM in my Zorba wasn't exactly the same as on the disk. Working with z80dasm on the Linux side and Z80ASM on the CP/M side, I was able to create an ASM file which assembled and loaded to an exact copy of my Zorba's boot ROM. Armed with the correct assembly listing, I hooked up the logic analyzer HP (1650B) to see what was happening. The code was stuck in a loop, waiting for the floppy drives to home to track 0. The heads would move (if initially off of track 0), but the code was waiting for an interrupt from the FDC (1793) which never happened. I started checking the circuitry for the interrupt chain, and found a shorted 2N3904. After I replaced it, the code moved on, but again was looping, this time waiting for the keyboard. I intially thought the USART for the keyboard was bad, but swapping it with another 8251A on the board didn't change anything. A check of the signals going to the USART showed the proper select lines activating, but the RxRDY line never showed a character ready. I finally checked the clock line for the USART. The frequency should have been 19,230Hz, but was nowhere close. The clock comes from an 8254-2 Programmable Interval Timer, which has 3 independent counters. The 8254 is programmed early in the boot process, and counter 3 takes the 8MHz clock and divides it by 416 to provide the TX/RX clock for the keyboard USART. The USART then divides the 19,230 clock by 16 to provide something close to the 1200 baud clock for the keyboard. The logic analyer showed the correct programming sequence going to the 8254, but only random values were coming out. So, back to the order form for a couple of 8254-2 chips and some other spares for inventory. As soon as I replaced the 8254 (actually with an 82C54-2) the frequency counter showed 19,230 from counter 3, and the keyboard magically came to life. It booted! This is the most difficult micro fix I've ever had to make. The tally of bad components reads: MR854 diode (shorted) 8275 CRT controller (dead) 2N3904 transistor (shorted) 8254-2 programmable timer (dead) I ended up using the following test equipment to find the problems: Tektronix 485 oscilloscope HP 1650 logic analyzer Curve tracer module Logic probe DMM Data I/O 29B programmer Advantest TR5823H Frequency counter I also wasted some time chasing imaginary floppy drive problems. To simplify things, I was only using a single floppy drive. After chasing code with the logic analzyer and the source listing, I discovered that whoever wrote the boot ROM code decided to wait for BOTH floppy drives to interrupt when they reached track 0 before moving on. If one of the drives is bad, or not installed, the code will loop forever waiting on the bad/nonexistent drive. All told, it was an interesting journey, and I now know more than I ever wanted to know about the Zorba. :-) Mike Loewen mloewen(a)cpumagic.scol.pa.us Old Technology http://q7.neurotica.com/Oldtech/

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