test-drb September 2013

test-drb@ccmp.vtda.org

168 participants
203 discussions

Repairing Mac128K board - memory problems

by ethan.dicks＠gmail.com

Hi, All, A list member recently sent me a broken Mac128 logic board. I quickly found a bad solder joint from a previous repair where one of the original 64Kbit DRAMs was replaced with a socket, but I'm still having issues. The Mac does "bong" and I do get a "Sad Mac" with a hex code. It claims it's the same chip that is now socketed (G8). If that DRAM is installed, I get "Mac in Jail" bars. If that DRAM is removed, I get black pixels where that chip was. The other odd symptom is, between the bars, a semi-regular sparse grid of on-pixels. It's not a perfect pattern across the screen; it's mostly on the right side, and not always top to bottom in a column. It does look regular, as if it's every 64 bytes or some other power-of-2, and 5% of the pixels blink as if they are changing in software. I know that Apple-branded DRAMs of this era are dodgy. I could just clip them all out and replace them with fresh, *tested* chips (I have a DIP DRAM tester), but I am concerned that the fault is elsewhere since a known-good DRAM always produces a stuck-on bit (the "jail bars"). That smells to me like a bad gate upstream of the RAM field. Looking at the available schematics, unbuffered DOUT D0-D15 go several places - a pair of '244s to buffer the data bus, a pair of '166 shift registers for video data out, a pair of '161s for sound data out, and a 16R8 PAL named ASG that appears to be related to sound and diskette PWM. The DIN side of the data bus connects to the '244 bus buffers, the CPU, the ROMs, the IWM, the 6522 VIA, and the Z8530 SCC. I would think that if that side of the bus had a stuck bit, the CPU would be fetching bad data from the ROMs, so there wouldn't even be a Sad Mac. I can do some catastrophic repair by blindly pulling all the RAM and replacing it, and I can even pull the CPU and socket it so I can stick my Fluke 9010A on the board and do some serious memory tests and exercise the bus and poke at it with an oscilloscope. What I'm asking for at this point is any information that can help me target my efforts. It seems like this sort of fault would have been common in the day, but mostly when I google "Sad Mac" or "jail bars", I get stuff about replacing individual RAM chips or changing SIMMs in an SE/30. So anyone have any advice that could help me not remove and replace 320 solder joints on a multi-layer board? Yes, I can do it, but it's a lot of time to do it well. I'd just like to get this old Mac working with an original board (I have working 512K boards, but the point is to have an Original Mac in time for display next January). Thanks for any suggestions, -ethan

10 years, 8 months

accepting pre-orders for S-100 80286 CPU board PCBs

by LYNCHAJ＠YAHOO.COM

Hi! We still need 5 to 6 more pre-orders to have enough to make the PCB manufacturing order. If you are considering getting one or more of these rare S-100 80286 CPU boards please consider making a pre-order. These don't come around very often! The S-100 80286 CPU board is ready for "production". If you would like to get one or more of these exciting new S-100 80286 CPU boards please do the new usual pre-order. I will set aside your board so you get them as soon as they arrive. Here is a web page to describe the S-100 80286 CPU board http://www.s100computers.com/My%20System%20Pages/80286%20Board/80286%20CPU%2 0Board.htm The PCBs will be $20 each as per the usual arrangement. Shipping in the US is $3 for a single PCB and $2 for each additional PCB. Shipping internationally is $10 for a single PCB and $3 for each additional PCB. This is for the bare basics USPS first class postage with no tracking or insurance. The builder assumes all risk of delivery as per usual arrangement. Please send a PayPal to LYNCHAJ at YAHOO.COM and I will reserve your board(s). Thanks and have a nice day! Andrew Lynch

10 years, 8 months

substituting 7401 for 8881 in a PDP-8/E

by steve＠tronola.com

Hi Pete, >No, that's wrong. 7438 guarantees 48mA, still a little under spec, but >close, and the gates are the wrong way round. --- I suppose you're basically right, but the TI datasheet doesn't specify the output voltage at that current. It shows 48mA as being the maximum recommended sink current, which certainly guarantees being free from damage at that level. The only spec I find which guarantees the output voltage specifies just 16mA. I conservatively went with that figure. In contrast, the 7439 datasheet does specify output voltage at 48, 60 and 80mA. Steve Lafferty

10 years, 8 months

DEC TSZ07-CA 9-track Drive

by me＠GarrettMeiers.com

I have a DEC TSZ07-CA 9-track drive, in a desktop cabinet, that I got a couple of years ago. It was one of those situations where I had to have it, but had no use for it! Dug it out to play with, but it doesn't seem to power on. Anything special to get this thing to turn on? I'm assuming the PSU doesn't work, or has issues, but I've not tried to figure it out yet. Just wondering if it won't turn on because there is no tape loaded, etc. There is probably something wrong with it, but thought I'd ask. Garrett Meiers www.linkedin.com/in/theunixguy

10 years, 8 months

For Sale: Original Early Model Macintosh 128K, TRS-80 48K Model III, Mattel Aquarius, and more!

by me＠GarrettMeiers.com

Doing some more cleaning, and found some more items that I would like to sell. These are all items that I had good intentions of playing with, but feel it's best to find new homes so they can be enjoyed. I'll be going to VCFMW, so can bring items there instead of shipping. However, I'd like to not bring them unless they are sold. Whether or not I will ship is listed next to each item, and the approx. weight. Shipping would be from 54914. TRS-80 Model III. 48K, 2x Floppy Drives, Optional RS-232-C Expansion. Fairly low serial number. Will not ship. https://www.dropbox.com/sh/9zj7ycsezrmu3o9/lD4_E7urDP One LOBO Systems MAX-80 Left, Unit only, no Documentation (Available as PDF though). Can Ship. 15 lbs. https://www.dropbox.com/sh/tpg7qi9vh1ggxu1/u0kdZSU9Jm 8x IBM Diskette Magazine P/N 2462521 filled with 8, likely unreliable, IBM 8" floppies. Can ship. 1 lb, 15oz, ea. https://www.dropbox.com/sh/ypu3bfafp3yi215/ZoXD3MnTTL Atari 400/800 Programming Language Pilot. CX405. Pocket Ref, Cart. 2x Cassettes, User's Guide, Student Guide, Pilot Primer, in binder. Can ship. 5 lb, 8oz. Mattel Aquarius Computer and Game System. In original boxes. Comes with Mini Expander, 2x Joysticks, Data Recorder, etc. Does not have any games, unfortunately. Can ship. 13 lbs. https://www.dropbox.com/sh/9r3vr6bupytp5vh/6F-AYuMegR Original Apple Macintosh M0001 128K -- early model with just "Macintosh" on the rear badge (later models say "Macintosh 128K"). This is a functional machine, but I think the floppy drive will likely need to be replaced. I got it with a floppy stuck in it, and the floppy is now out, but the drive doesn't appear to be aligned with the hole on the case. Probably what was making the floppy stick. The drive might be fixable, not sure. It's probable that the eject motor is bad due to it having a stuck floppy. It's in pretty decent shape otherwise. There is some corrosion on the battery terminals, but at least the terminals are still present! Probably a quick fix with a replacement floppy drive. Will not ship (unless you are willing pay to have this professionally packaged, insured, and shipped). https://www.dropbox.com/sh/0debci7ynuxp0gy/kIPjC-hqXX Logical Devices PROMPRO-8X MOS EE/EPROM/MICRO Programmer, with manual, software. This is an ancient programmer that connects to an IBM PC via serial. It also comes with a couple extra ZIF sockets, and a Logical Devices C-51 add-on, which allows intelligent programming of AMD/Intel 8751 Micro's and the AMD 9761. https://www.dropbox.com/sh/uwi9jwb8uu57ngx/ZBtxMBUcO7 Indus GT Floppy drive for Atari. Not 100% sure that is that is the original power supply, but I believe the specs are the same. Brochure, Plastic Hard Case (no inserts), data cable. Will ship. https://www.dropbox.com/sh/0od87p9yg98sj0a/AilVqFncQD 3x or 4x Apple eMate 300. I have power supplies for these. The hinges are all mostly too loose, and would need to be fixed/replaced. No stylus, and the batteries are not going to hold a charge. But, they are fun, and my kids love playing with them. Will ship. https://www.dropbox.com/sh/98mu014osrr39tp/moM1fzbNpZ 30x or 35x Sun Microsystems SunRay 1 Thin-Clients. Google them, they are pretty fun. I do have a copy of the SRSS Software for Sun and Linux if you need it. Will ship. I've been selling these for about $20, but can give you a deal if you want a bunch. Will ship. https://www.dropbox.com/sh/i8otfj01orwsu78/Kexq_v_S5C 4x Compaq Portable (Luggable) Model: Compaq. One has a hard-drive, but pretty sure it doesn't work. I believe they all need some work. I can't remember if one of them worked or not. Looking, ideally, for someone to talk all 4 of them. You can probably make one dual-floppy model work at least. Two of them have the padded compaq carry case. One is missing a handle, I'm sure there are parts missing from the others. Will not ship. https://www.dropbox.com/sh/ccsysqtgygkukte/NFe-QS3n21 Morrow Micro Decisions (MD-2?) Computer. Chassis Rev C, Rom 2.5. Matching Morrow MDT-60 Serial Terminal. 2 Floppy drives, can add two more. Parallel port, and an extra serial port for modem/serial/host connection. Box or two of software. Bunch of manuals. Couple issues of Morrow Review magazine. Fun little CP/M machine. Will not ship. https://www.dropbox.com/sh/bessw7ftud7l99a/X4ctyRFJ3U Apple III Computer and Apple Monitor III. This is a functioning system! I have one other one that I am keeping for parts, or a future restoration project, but I might be willing to let that go too if you are interested. Both are 128K models. Will not ship. https://www.dropbox.com/sh/h2d7rpageaj52oi/OoVYnOtAnI Commodore 64's. I have quite a few Commodore 64's. Probably at least 7 or 8. About as many 1702 Monitors, and should have at least one 1541 drive for each. I sold a couple setups with one each of the above last year for a special price of $64. But with inflation, I'll probably need a little more this year -- hey, the hotel rooms used to be $64, but now they are much more... even more with a hot tub. Also, I have lots, and lots, of TeleVideo stuff as detailed in an earlier post. If interested in anything, please contact me via private e-mail. NOTE: When replying, please add your name, and what you are interested in, to the subject line, so gmail doesn't brainlessly group everything into one thread. (Mutt gets it right, not sure why gmail can't). Thanks, Garrett Meiers ?? www.linkedin.com/in/theunixguy

10 years, 8 months

substituting 7401 for 8881 in a PDP-8/E

by peter.turnbull＠york.ac.uk

My PDP-8/E stopped working at the weekend, which is a bit of a nuisance as I need it working for the DEC Legacy event at Windermere in October -- and I'm going on holiday on Friday so won't have much real time to deal with it and prepare my talk before then. In the meantime I've "fixed" the problem by replacing a dead 8881 bus driver (E23 on the display board, drives D0-D3 from the switches) with an SN7401. It works with M8300+M8310 CPU, M8330 timing board and M8320 bus loads, but probably doesn't have enough drive capability for a full system. IIRC an 8881 should be capable of sinking 70mA with Vol=0.8V, while a 7401 is only guaranteed for 16mA. I've calculated the terminators alone need 23mA plus around 1.6mA per load (20 loads in a medium system?), and DEC sometimes used selected 7401s marked 97401 presumably for this reason. Anyone got practical experience of substituting for an 8881? -- Pete Peter Turnbull Network Manager Information Directorate, University of York DD: +44 1904 323804

10 years, 8 months

substituting 7401 for 8881 in a PDP-8/E

by steve＠tronola.com

Hi Pete, >Anyone got practical experience of substituting for an 8881? --- The SN7439 is commonly taken as a proper replacement for the DEC8881. I see a couple 7439's available on eBay at the moment. Also, questcomp.com is showing DEC8881 in stock at $10 each at quantity-two. Some have mentioned substituting 7438 as a lower spec version. I see from the datasheet that it does have the same schematic as the 7439. However, it doesn't actually guarantee more than 16mA output sink current. Steve Lafferty http://www.tronola.com/

10 years, 8 months

Anyone here going to Maker Faire New York this weekend?

by ethan.dicks＠gmail.com

Hi, All, I am just curious if anyone here is planning on attending the World Maker Faire this weekend. I'll be in one of the tents in the 3D Printing Village. Drop by and say hello! -ethan

10 years, 8 months

cctalk and cctech

by peter.turnbull＠york.ac.uk

At the risk of seeming a Grumpy Old Uncle Pete (as my nieces frequently address me :-)), I'd like to remind people they don't need to post to both cctalk and cctech. They're not two separate lists, but two views of the same list. So if a message is deliberately addressed to both, it appears twice on cctalk and often cctech: anything addressed to cctech is automatically also delivered to cctalk subscribers. If it's also addressed to cctalk then it appears there a second time, and if deemed on-topic it's also delivered to cctech a second time. cctech subscribers might not always notice this, but cctalk subscribers do. This is explained in the first paragraph of http://www.classiccmp.org/cctech.html and http://www.classiccmp.org/cctalk.html -- Pete Peter Turnbull

10 years, 8 months

Making perfect Keytronic replacement keypads

by dm561＠torfree.net

Original Message: > Date: Tue, 17 Sep 2013 17:28:27 -0700 > From: Josh Dersch <derschjo at gmail.com> > On Tue, Sep 17, 2013 at 5:06 PM, Al Kossow <aek at bitsavers.org> wrote: > >> I had to fix some Lisa keyboards, and here is what I finally came up with >> after a week or two of experimenting that produces perfect pads. >> ... >> So far, I've identified the following systems that need pad replacements >> >> Apple Lisa >> Corvus Concept >> Terak >> Genrad Futuredata >> SOL-20 > That's very cool, thanks for sharing the results of your research > ... > I'll add a couple of systems to your list: > > - Compaq Portable (the original and the II at the very least, not sure of > others in the line). Perhaps not really a classic, but I like mine... > - The TRS-80 16-bit line (II, 12, 16, 6000). The II may not have used > foam, I do not recall for sure, but I know the others did. Also: Dynalogic Hyperion

10 years, 8 months

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test-drb September 2013