IBM PC AT Service and Repair Video From 1984 - Page 1
Forum section: electronics / general

author: AF6LJ
author_rank: Unknown
timestamp: October 11, 2015, 10:00:13 pm
content: I forgot my safety glasses

author: tom66
author_rank: Super Contributor
timestamp: October 12, 2015, 01:13:39 am
content: I didn't see them mention the design flaw with the power connectors on the main board. Get them in the wrong order, since they're both 6 pins and interchangeable, and the board fries...

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 01:50:13 am
content: Quote from: tom66 on October 12, 2015, 01:13:39 amI am sure the tranees were schooled on that bit of information.I suppose yhou could consider it a flaw, lots of gear have interchangable connectors, that can cause problems. This was from a time before every eight year old was building their own PC to play Quake 3 on.

author: xrunner
author_rank: Super Contributor
timestamp: October 12, 2015, 03:00:34 am
content: FRUs and CRUs - got it!

author: helius
author_rank: Super Contributor
timestamp: October 12, 2015, 03:23:26 am
content: At 16:00, the TOY clock battery is a Li-MnO2type, what Panasonic calls "CR". These were considered new at the time: they were first marketed in Japan during the mid-'70s.At 18:00, you can see that the DRAM chips are stacked piggyback.

author: bitseeker
author_rank: Super Contributor
timestamp: October 12, 2015, 06:58:44 am
content: That was fun. I thought Superman was going to fly in during the title sequence.Come to think of it, I may still have an IBM PC service manual somewhere. Came in a binder that fit into a hard sleeve. Fancy.

author: German_EE
author_rank: Super Contributor
timestamp: October 12, 2015, 04:20:18 pm
content: At the time of the IBM AT I was living and working in the UK and a friend of mine gave me a faulty CMOS battery and just said "have fun". The warning not to dispose of the battery in fire was very specific so I decided to give it a Viking funeral.In the UK they celebrate something called Bonfire Night every 5th November, it's similar to the 4th July celebration except that they also light a large fire and have lots of treats like treacle toffee. Eager to follow the local tradition I joined in a Bonfire Night event with some friends and had lots of fun, but by 10pm the party had died down and the fire was just a pile of embers, this was when I tossed the battery into the fire. The initial few minutes were disappointing. There was a brief flame as the wires burned away and then a longer burn as the plastic case met its end. Then it happened.Do you remember the end of 'Close Encounters of the Third Kind' when the mothership opened up? That bright light with the aliens hidden in the glare? Well, it was like that only brighter, and there was the loudest bang I have ever heard. For the next ten seconds I could see nothing as my eyes recovered but eventually I managed to see again and I realized that the bonfire was gone, there were only a series of small fires around the garden due to the scattered embers.A few years later I spoke to an industrial chemist and he reckoned that I was very lucky. The contents of the battery would have melted in the heat of the fire and then exposed to super-heated air when the case eventually ruptured. The chemical reaction would then be quite violent.

author: helius
author_rank: Super Contributor
timestamp: October 12, 2015, 10:43:54 pm
content: Better to watch videos than to risk life and limb with batteries, imho.This cell ruptures very suddenly when recharged with 50V (not even reverse charged, apparently):[this type is very strongly reinforced, which is why the release is so sudden. it's good because they hardly ever leak spontaneously]This is what it looks like underwater at 400fps:

author: continuo
author_rank: Frequent Contributor
timestamp: October 12, 2015, 10:57:00 pm
content: Meanwhile, at the Lithium Cell disposal facility in Mexico...

author: pickle9000
author_rank: Super Contributor
timestamp: October 12, 2015, 11:14:25 pm
content: 20 MEG HARD DRIVE!!!More space than you'd ever need in a lifetime.

author: bitseeker
author_rank: Super Contributor
timestamp: October 13, 2015, 01:12:34 am
content: Quote from: pickle9000 on October 12, 2015, 11:14:25 pmAnd lighting-fast access times via stepper motor head positioning. Ah, those were the days.

author: AF6LJ
author_rank: Unknown
timestamp: October 13, 2015, 03:18:03 am
content: Quote from: bitseeker on October 13, 2015, 01:12:34 amAnd you would never need a drive larger than 23MB.I fondly remember the days of running Debug C:800 to set the drive up.

author: bitseeker
author_rank: Super Contributor
timestamp: October 13, 2015, 03:46:37 am
content: Quote from: AF6LJ on October 13, 2015, 03:18:03 amdebug g=c800:5or c800:ccc on RLL controllersWow, you're really rattling old brain cells now, Sue.

author: AF6LJ
author_rank: Unknown
timestamp: October 13, 2015, 03:56:58 am
content: Quote from: bitseeker on October 13, 2015, 03:46:37 amThat's It!My first hard drive was a 65MB drive on an XT clone I had to do a low leve partition since the OS couldn't recognize a drive that large. (DOS 5.0)I had the computer for three years and in 1990 bought the drive and controller.

author: bitseeker
author_rank: Super Contributor
timestamp: October 13, 2015, 04:05:26 am
content: Quote from: AF6LJ on October 13, 2015, 03:56:58 amMine first "IBM PC" was an AT clone, but I could only afford a 20MB (Seagate ST225) hard drive. Holy smokes you can still buy themon eBay!After that, I upgraded it to a 72MB Miniscribe. Full height, 5-1/4", boat anchor of a drive.

author: Halcyon
author_rank: Unknown
timestamp: October 13, 2015, 05:10:39 am
content: Quote from: bitseeker on October 13, 2015, 04:05:26 amSimilar to this drive I have?....(Shown here next to a 2.5" disk with over 2300x the capacity. It still works fine to this day!)

author: bitseeker
author_rank: Super Contributor
timestamp: October 13, 2015, 05:52:13 am
content: Quote from: Halcyon on October 13, 2015, 05:10:39 amYes, similar size. Here's a photo of the 40MB version (pretty short defect list on that one). The 72MB model has the same housing.

author: German_EE
author_rank: Super Contributor
timestamp: October 13, 2015, 10:28:20 am
content: Given the current state of hard drive technology with 6TB 3.5 inch hard drives I wonder how much we could now store in a 5,25 inch full height device? Every PC I have ever seen has had multiple 5,25 inch drive slots just sitting there and doing nothing apart from (maybe) giving a DVD or Blu Ray drive a home.I am however glad that MFM and RLL drives are no longer around and I can't remember the last time I had to set heads, cylinders and sectors when doing a drive install.

author: AF6LJ
author_rank: Unknown
timestamp: October 13, 2015, 12:37:55 pm
content: Imagine one 5.25" drive four platters each being 6TB...

author: helius
author_rank: Super Contributor
timestamp: October 13, 2015, 12:48:16 pm
content: Larger platter diameter limits the rotational speed that can be safely achieved. And rotational speed is the defining factor for access latency, so a larger diameter platter will have poorer latency than a smaller one, given the same motor and head technology.

author: zapta
author_rank: Super Contributor
timestamp: October 13, 2015, 01:23:09 pm
content: The video mentions a clock backup battery, what was used in previous models to keep the clock running?

author: German_EE
author_rank: Super Contributor
timestamp: October 13, 2015, 02:04:17 pm
content: Previous machines (the IBM PC and the IBM PC-XT) didn't have CMOS memory or a clock chip, if you wanted the time then you looked at the clock on the wall. There were some add-on cards that offered a clock but this meant using up one of the expansion slots.

author: bitseeker
author_rank: Super Contributor
timestamp: October 13, 2015, 09:33:56 pm
content: Quote from: zapta on October 13, 2015, 01:23:09 pmNothing. If you powered it off, you'd have to set the time again after booting.

author: AF6LJ
author_rank: Unknown
timestamp: October 14, 2015, 12:48:10 am
content: Quote from: helius on October 13, 2015, 12:48:16 pmWhich is why those big drives with many platters use to interleave between sides and platters.The stepper motors took half a day to get from the inside to the outside of the platters.Thank GOD for IDE and the soft'er tracks and the meter movement like head actuator.I am spoiled now, I could never go back to using a spinning drive for my boot up drive, cold storage of date... Yah, that wouldn't be a problem.Having an SSD is like going from a floppy drive to a hard drive in the old days.

author: VK3DRB
author_rank: Super Contributor
timestamp: October 14, 2015, 12:49:15 am
content: I was an engineer at IBM in a town called Wangaratta where we made the PC-AT for Australasia. They were prosperous days, and the profitability back then was big for IBM because there was not much competition. The ISA bus timing specs were not made public, so the IBM clones often were not IBM compatible. Besides, in those days there was a mantra by IBM - "No one ever got fired for buying IBM.", so sales were strong.I don't remember too much about the 80286 motherboard. I think it has a trim cap for the 14.2818 MHz oscillator that was adjusted using the HP3065 ICT. Every board was burned in for 12 hours, dynamically tested up to 70 deg C in Blue-M chambers.Oh, yes, the advanced diagnostics diskette. I had the source code to the advanced diagnostics, the BIOS and DOS, stored on a massive 200MB hard disk.The plant was a great place to work, where we were like one big family. Colleagues even came out to help me build my house on 5 acres not far from the plant. We all looked out for one another and there was a level of camaraderie and passion for success in the business you would not see too much today. The social club there was like no other. The plant is long gone, IBM is long gone, the people are long gone and the electronics manufacturing scene in Australia is a fraction of what is used to be.Ironically, that plant was the biggest exporter of non primary produce in the entire country in 1995. Five years later it was closed and anyone who remained lost their job.

author: AF6LJ
author_rank: Unknown
timestamp: October 14, 2015, 01:01:37 am
content: The electronics business was a lot different back then. I have fond memories of working at the division of oral Corp I worked at.Thanks you brought back some fond memories.

author: zapta
author_rank: Super Contributor
timestamp: October 14, 2015, 02:47:21 am
content: Quote from: VK3DRB on October 14, 2015, 12:49:15 amI designed once a medical diagnostic image processing system on an AT computer. Coming from the Motorola 68000/Unix world I naively assumed that we can buy as much memory as we need. I was very disappointed when I installed a memory card with a few megs of memory and the program got only 760K or so of RAM. We had to implement memory block swapping between main memory and extended memory that required bios trickery and CPU reset on each swap. I never appreciated the X86 architecture. It was kludgy.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 14, 2015, 03:20:04 am
content: After they finally changed the BIOS to support an external device, our first hard drive for the PC was the Corvus. Maybe 10 - 14" platters? Seems like two of them in the drive. Guessing 5 meg of storage for our DBASE application?I was using a pair of Quantum Q2080s with the SA2000 bus on my AT. These were 8" drives.With IBM making the BIOS and schematics available, I hacked these machines for many years to come.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 14, 2015, 04:25:58 am
content: The two 8" drives, located on the right, were as large as my AT computer.

author: bitseeker
author_rank: Super Contributor
timestamp: October 14, 2015, 05:08:22 pm
content: Those drives are whoppers alright. My AT had the same case.

author: VK3DRB
author_rank: Super Contributor
timestamp: October 15, 2015, 06:49:22 am
content: Quote from: zapta on October 14, 2015, 02:47:21 amToo right it was cludgy. In those days I had to write programs occasionally in Assembly Language, right up until the 80386. Segmented addressing was a pain. I don't know if Intel's i7 for example still supports real mode (ie: run a genuine version of DOS. I guess one could try to load up an original IBM of Microsoft DOS and see if it works.... too much bother maybe. I don't think these newer processors could boot up in real mode and then switch to protected mode as in the old days.IBM should have gone with the much superior 68000. From a programming and performance perspective I think using the Intel x86 was a mistake.We are getting old. I had a drongo from India phone me alleging he was from "Microsoft Help Desk" and my computer was infecting the entire Internet. I followed his instructions but I told him I cannot find the start menu button, and that I am running the very latest version of Microsoft DOS. The idiot and his Indian Mafia boss had absolutely no idea what DOS was. They told me DOS does not exist and to open an internet browser. After confusing the heck out of these tossers, they eventually hanged up on me just after telling me I am a f*@%$&! who knows nothing.I diverge, but another trick is to put on 90 year old's voice and tell them for example "We don't have one of those silly computer things in Happy Acres Nursing Home. If you tell me what one looks like, maybe I can phone up my grandson to find one and we can call you back." They hang up immediately.

author: helius
author_rank: Super Contributor
timestamp: October 15, 2015, 03:13:43 pm
content: Quote from: blueskull on October 14, 2015, 01:35:28 amPerhaps not the first; IBM had patents on MCM technologies in the '60s (Shockley had some even earlier). But they are an interesting last-minute kludge. The top and bottom packages have different pads bonded out so that they can be soldered directly together.Now we have Hybrid Memory Cube and HBM where the dies are thinned and stacked together quite deep, making 3D microcircuits a reality.

author: Halcyon
author_rank: Unknown
timestamp: October 16, 2015, 03:16:02 am
content: Quote from: VK3DRB on October 14, 2015, 12:49:15 amWe get these from time to time at work and you can tell they are just using an auto-dialler. The phones in our office have more or less a sequential numbering plan, so after each hang-up you'll hear the next phone ring with the same rubbish, that'll continue for about 5 minutes. They're quick to hang up when you tell them that they've called a government department.In this day and age, I don't know why law enforcement, banks and telcos can't get together and create some "bogus" credit card numbers which they can give to the scammers and trace the transactions in almost real time.

author: German_EE
author_rank: Super Contributor
timestamp: October 16, 2015, 10:37:39 am
content: Here are some credit card numbers to get you started:https://www.paypalobjects.com/en_US/vhelp/paypalmanager_help/credit_card_numbers.htmhttps://www.auricsystems.com/media/filer_public/87/dd/87ddca0f-1d22-4ea8-8865-95f7e9d4c541/samplecreditcards.pdfhttp://www.getcreditcardnumbers.com/Have funOne thing I miss living in a non-English speaking country (well, officially) are the scam callers. I've never had a call from Heinrich or Helmut at Microsoft telling me that my copy of MS Windows has a problem but then I run Linux so that would only confuse them.

author: VK3DRB
author_rank: Super Contributor
timestamp: October 16, 2015, 12:21:40 pm
content: Quote from: Halcyon on October 16, 2015, 03:16:02 amThe solution to this endless barrage of Indian scam merchants is simple. The Australian government should block all incoming calls from India, except those on a new "Do Call Register" specifically targeted at India. Therefore the Indians who live here and have relatives overseas simply place their relatives number on the register so it is not blocked. Numbers without caller ID from India are blocked. The "Do Call Register" stays until the Indian government cleans up the problem.

author: AF6LJ
author_rank: Unknown
timestamp: October 16, 2015, 12:59:17 pm
content: The easiest answer is to to simply tell them you do not have Windows, you live in a mud hut.If they still don't get it. Put them on hold with the sound track from a slaughter house.

author: idpromnut
author_rank: Unknown
timestamp: October 16, 2015, 03:11:41 pm
content: I still have the grey book (technical reference I think it was?). Interesting read

author: SeanB
author_rank: Super Contributor
timestamp: October 16, 2015, 05:31:56 pm
content: With the IBM PC you could also get a very nice clock kit, which did not use up any of those scarce ISA slots to hold a clock with battery back up. Dallas Semiconductor made a clock socket, where you simply removed any 28 pin EPROm and put it back in with this socket installed. then you knocked using a special sequence of accesses, and you got a serial data stream on D0 where it held the lime as a clocked binary stream. Writing the data was the same simply using a write to the EPROM ( non volatile so it never did anything, but was still going to have /CS on the chip which was all that mattered along with the pattern of data on the address and data lines).Had a small program on the hard disc which would simply be run during boot which did the knocking, got current time and date then set the PC clock using it, then it just left a DOS hook that handled the clock setting built in DOS instruction instead of the default one.Was pretty expensive IIRC, and was superceded soon after release by the inclusion of a RTC in the 80286 application note. Dallas then made a battery backed RAM that replaced this chip, and this was very popular, still in production today and it, and it's variants, are in a lot of equipment as battery backed RAM and a clock.Interesting aside, I did get a digital counter, that was supplied in a low power state to give long storage life of the internal lithium cell. Display was working from manufacture, just showed the word "Sleeping" until you pressed the front panel reset, which turned on an internal high value pull up on the count line. When I do have to change the battery ( it might do 15 years though) it will probably go back to that display again.

author: bitseeker
author_rank: Super Contributor
timestamp: October 16, 2015, 07:34:50 pm
content: Quote from: idpromnut on October 16, 2015, 03:11:41 pmThat's the one. I never tried finding scans of them, but they're probably around.

author: bingo600
author_rank: Super Contributor
timestamp: October 17, 2015, 02:13:29 pm
content: I still have the "Blue book too" XT-Ref i thinkAnd this one as pdf : 1502494_PC_AT_Technical_Reference_Mar84.pdf (27MB)Saw it here :http://bitsavers.trailing-edge.com/pdf/ibm/pc/at/1502494_PC_AT_Technical_Reference_Mar84.pdf/Bingo

author: bitseeker
author_rank: Super Contributor
timestamp: October 18, 2015, 03:42:57 am
content: Thanks, Bingo!

author: Halcyon
author_rank: Unknown
timestamp: October 18, 2015, 03:47:11 am
content: Quote from: VK3DRB on October 16, 2015, 12:21:40 pmAll well and good however a lot of these calls are made over VOIP services, which can appear to originate from a domestic number.

author: bitseeker
author_rank: Super Contributor
timestamp: October 18, 2015, 03:52:11 am
content: I've heard that they get really bent out of shape if you lead them on. I look forward to the day they call me. Maybe I'll boot up my Atari 800XL.