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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 23rd Jul 2023, 5:41 pm   #221
Iangebbie
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Default Re: What was your first computer and do you still have it?

My first was a Sinclair Spectrum with rubber key pads, was back doing a HND at the time, and for my project, I used the Spectrum along with a HF receiver and UART (home brewed RTTY interface fitted in a tobacco tin)
It just so happened when the SCOTEC assessor was reviewing the projects in the class, RTTY information was received (50 Baud) that a minor issue had occurred in a a nuclear plant called Chernobyl.

The computer was sold off some four years later / now tend to use Apple products
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Old 24th Jul 2023, 11:17 pm   #222
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It's nice that you still have that machine that you have such fond memories of. I still own nearly every computer that I ever owned from new, and several more besides. If you ever have time you should replace the RIFA capacitor in the PSU before ever turning it on again. If all the anecdotes are true they seem to have something like 100% failure rate if left for long enough. It's not a question of if they will go bang, but when.

I own two complete BBC model Bs + disc drives but I've never really played with them properly because I bought them, as much to 'rescue' them as anything, when prices had fallen to the very bottom of Owen's 'bathtub curve'. I paid about £5 for each of them. They both worked fine at the time (mid nineties) but they will also need the RIFAs attending to before I do anything with them nowadays.

I did get to play with the BBC B when they were contemporary because two friends of mine had them, one of those two friends was interested in programming so we did a bit of 6502 coding using the inline assembler which was a useful feature in BBC BASIC. They were really nice machines, nice hardware architecture, proper keyboard, as a Sinclair man throughout the first half of the eighties I was very envious but I just couldn't justify the cost of a BBC B, especially not with a floppy drive. I think that's partly why I bought the two I have, just to be able to finally own something which I could never have afforded when they were current machines.

To be honest I feel a bit selfish for hoarding them for all of this time, but I suppose the upside is that they have survived for a further 25+ years. I'm still working at the moment but when I eventually retire I hope to be able to give them the attention they deserve.

Yes, those infamous RIFA 'PME271X' clear-epoxy cased capacitors (which I'd previously liked being able to see inside), seem to have an issue with the epoxy's formula causing it to develop splits / cracks (due to shrinkage?) in many places over the years, letting moisture from the air into the vulnerable paper! dielectric (that caused so much trouble with wax-case sealed 'Hunts' etc. capacitors in vintage valve radios etc).
This occurs even with unused New Old Stock ones, as I have some of these that have gone like that (and found a large bag of these, dumped at the end of a rally many years ago, where they'd all failed like that). Bizarrely, these are still being made, and it's not clear whether RIFA have fixed this problem with new ones / they don't have a date code on them, so rather risky buying identical make replacements off online marketplaces / buying refurb kits with these in. Wima do also produce similar-looking clear-epoxy ones, but much-more rounder, and a bit wider so can be a tighter squeeze to use these.
I already had a bag of similar vintage Blue Philips 10nF Class-X ones, with a more robust Polypropylene case, so bought a bag of NOS 100nF ones to match these, for the other one of the pair you need to change.
Although the seller did rather dodgily just describe them as 'Polypropylene', when that's only the case and the dielectric is still paper!.
However, I found you can buy true Polypropylene-dielectric class-X capacitors for only a few pence more than paper ones, at Farnell etc. And these Polypropylene one's ESR measures a lot lower than new paper dielectric ones.

It seems that when the paper dielectric gets damp it starts conducting a bit and gets rather warm / emits smoke after a short while. And once had one go bang a bit in a vacuum cleaner, but not had one get that bad in a Beeb yet.
But after hearing of so many others having this problem, I mostly just changed them first, before powering these up (many for first time in > 20yrs)
I did chance one, without changing these, and it went bang with a flash from the power-switch, at switch on! But when repairing it, I found that the small TO-92 transistor had actually gone short, taking out the emitter current-sense resistor on the main chopper transistor (which fortunately had survive, as now obsolete and fetch £10! for NOS) plus the fuse.
I also encountered a few other strange faults with a few of these, with low -5V rail caused by one of its electrolytics going high ESR. And another where the DC o/p voltages read OK but no operation of the Beeb & hum bars on blank-screen, with massive ripple when 'scoping the outputs, that was caused by one of the HT reservoir electrolytics going o/c (other one's ESR still read fine).

Stripping down the Beeb's Astec-BSR made SMPSU to get to the caps is a bit of a pain, as you need to undo two nuts inside, to remove short earth bonding wires. And also cut (or carefully release, to re-use original) cable tie on power-switch wires. Plus need to bend retaining clips on the switch back in, to pull it out from PSU chassis in order to give clearance for PCB ass'y to slide to the side (after also removing its screws).
So can easily take an hour or so each, to pull apart & put back together and test (Ideally with some suitable load-resistors and a 'scope on the outputs to check for ripple).


BTW, if you have got FDD's with your Beeb's, it seems these are now getting quite expensive - especially for 5.25" ones. And that's assuming your Beeb's have the FDC Interface IC's fitted, to be able to use a true FDD / a GOTEK SSD. Although their are SD card etc adaptors, that use other existing on all Beeb Model B interfaces.
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Old 25th Jul 2023, 12:23 am   #223
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They are fully equipped with DFS and floppy drive controller as I bought them as complete working outfits. They probably have the original specified um... 8271, was it, floppy controllers rather than the WD177x ones which some third party outfits offered. Unfortunately the drives have been idle for more than 25 years so I would think they will at least need belts, if indeed they have belts. One is a Cumana unit, the other I don't remember the branding.

One of the friends I mentioned wanted to add a disc drive to his BBC B when they were still contemporary and the main Acorn dealer at the time up here was a little outfit in Gateshead whose name I have completely forgotten. It was either their policy or Acorn policy generally that they wouldn't supply a DFS ROM and a floppy controller ICs as spare parts, the only way they would let them go was as an installed upgrade which they expected people to pay them to install.

I remember I went there and spun them a sad tale of how I'd damaged my disc controller IC by poking around with a scope and needed a replacement which they grudgingly sold me. He then went there a week later and tried to buy a DFS ROM but they would have none of it, perhaps they realised what was going on, (we probably weren't the first to try it) so my friend ended up having to buy an EPROM copy of the DFS ROM from someone around the doors. Ridiculous, really.
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Old 25th Jul 2023, 12:24 am   #224
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I've been clearing my late Dads garage and it brought back a long-forgotten childhood memory. In the middle of the garage floor is a deep, proper concrete-lined car maintenance pit, normally covered with boards. As kids of around 10-12 years old this was our 'Bat Cave', and my very first 'computer' was a home-made Bat Computer!
It started as a discarded writing desk with a tambour roller opening, we painted it black, fitted it with knobs, switches, bulbs and a panel meter, all robbed from my Dad's stash. We thought it was brilliant. It had rows of coloured lights, a bell and some sort of speaker that just crackled. The Bat Computer was powered from an old car battery. Of course it couldnt compute a thing but as kids we were totally convinced! Happy days. Seems a very, very long time ago, maybe 1968 ish?

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Old 25th Jul 2023, 12:32 am   #225
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Sounds like you had a pretty cool Dad, Phil - no-one in my family was technologically inclined (my Dad was great in other ways of course) so my interest was sparked entirely by a well known 'how to make radios' book which I found in the school library. I did have a friend who got interested at about the same time so we sort of learned and taught each other as we went along. He was the one who built the very basic Elektor SC/MP system which was the very first programmable thing I ever played with, some months before the MK14 arrived.
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Old 25th Jul 2023, 8:01 am   #226
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Default Re: What was your first computer and do you still have it?

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One of the friends I mentioned wanted to add a disc drive to his BBC B when they were still contemporary and the main Acorn dealer at the time up here was a little outfit in Gateshead whose name I have completely forgotten. It was either their policy or Acorn policy generally that they wouldn't supply a DFS ROM and a floppy controller ICs as spare parts, the only way they would let them go was as an installed upgrade which they expected people to pay them to install.

I remember I went there and spun them a sad tale of how I'd damaged my disc controller IC by poking around with a scope and needed a replacement which they grudgingly sold me. He then went there a week later and tried to buy a DFS ROM but they would have none of it, perhaps they realised what was going on, (we probably weren't the first to try it) so my friend ended up having to buy an EPROM copy of the DFS ROM from someone around the doors. Ridiculous, really.
I can't imagine it was Acorn policy, as I had no problem purchasing a disc upgrade kit for my Beeb and installing it myself. This included the 8271 disc controller (single density only), but some time later I upgraded to the Watford one (WD1770?) on a daughter board to add ADFS capability.
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Old 25th Jul 2023, 8:09 am   #227
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Reaching back into the murky depths of my memory I have a dim recollection that there may have been some kind of shortage, possibly of the disc controller ICs, which might have led them to want to conserve what stock they had for the paid-for upgrades they did themselves. I've just remembered what they were called - 'HCCS'. Probably long gone.
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Old 26th Jul 2023, 10:00 am   #228
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They are fully equipped with DFS and floppy drive controller as I bought them as complete working outfits. They probably have the original specified um... 8271, was it, floppy controllers rather than the WD177x ones which some third party outfits offered. Unfortunately the drives have been idle for more than 25 years so I would think they will at least need belts, if indeed they have belts. One is a Cumana unit, the other I don't remember the branding.

One of the friends I mentioned wanted to add a disc drive to his BBC B when they were still contemporary and the main Acorn dealer at the time up here was a little outfit in Gateshead whose name I have completely forgotten. It was either their policy or Acorn policy generally that they wouldn't supply a DFS ROM and a floppy controller ICs as spare parts, the only way they would let them go was as an installed upgrade which they expected people to pay them to install.

I remember I went there and spun them a sad tale of how I'd damaged my disc controller IC by poking around with a scope and needed a replacement which they grudgingly sold me. He then went there a week later and tried to buy a DFS ROM but they would have none of it, perhaps they realised what was going on, (we probably weren't the first to try it) so my friend ended up having to buy an EPROM copy of the DFS ROM from someone around the doors. Ridiculous, really.

Very few 5.25" FDD's had a belt - Only really some of the oldest Full-height ones, and Cumuna probably used more-modern TEAC FD55 etc Half-height drives in many of their units.

I'm sure places / Acorn dealers like Watford Electronics (Maybe their own one / possibly with a WD1770 converter PCB as 8271's were very expensive at > £40 as well as being discontinued?) sold DIY Floppy Disk interface upgrade kits, as only had to plug a few IC's in and change an interrupt pin on the Model B. (Although with the £100-cheaper 16K Model A, they also saved money by not fitting most of the ports connectors. I don't think there was an official Acorn-produced DIY Model A to Model B upgrade kit, but Watford etc. sold a kit of all parts at approx. £70).
I know you could buy the 8271 by itself from many places like that, who listed it in their magazine adverts, but not sure if Acorn supplied their DFS (EP)ROM separately. There is an old advert (but includes ADFS, so must be a bit later in the 80's - around time of BBC B+ / Master) listing the complete Acorn kits (and 8271 etc. separately) here: https://www.4corn.co.uk/archive/show...ice%20List.pdf

Acorn only used 8KB 2764 EPROM's for the original DFS 0.9, so quite common to see these in Beeb's (usually with a hand-written version number on a round Orange / red coloured sticker over the UV-EPROM window) - but they later moved onto the combined with Econet NFS (+ Tube host code) DNFS 1.2, (which they often supplied free with second processors etc.). This old Acorn dealer is still around, selling used ones for £19 (amongst many other used etc. Beeb peripherals & spares - although often cheaper elsewhere): https://www.cjemicros.co.uk/micros/p...8bithard.shtml


I know Acorn did later-on did produce an official WD1770 DIY-upgrade kit for the Beeb, that included the WD1770 on an adaptor PCB to fit the 8271-socket (and some solid wire links to fit into IC-sockets for some IC's that were only required when using the 8271 FDC IC), as well as a later DFS 2.x 1770 DFS.
It seems 8271's are still obtainable from the Far East on online marketplaces etc. for only around £10, and have found to be generally OK and not fakes.
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Old 26th Jul 2023, 11:11 am   #229
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Now that's a complicated device for the late 1970s.

https://scarybeastsecurity.blogspot....ed%20in%201981.

22k transistors for an FDC.
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Old 26th Jul 2023, 12:02 pm   #230
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Default Re: What was your first computer and do you still have it?

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Very few 5.25" FDD's had a belt - Only really some of the oldest Full-height ones, and Cumuna probably used more-modern TEAC FD55 etc Half-height drives in many of their units.
Actually the 1/3rd height Epson drives (used in the QX10 and TF20, for example) are belt driven. These are the beautiful liittle drives with voice coil positioners and an optical transducer for feedback, like a miniature RK05.

The 2/3rd height BASF drives that are common in RML380Z machines are also belt driven (just looked in the service manual).

Were there any full-height 5.25" drives that weren't belt driven? I can't remember one off the top of my head.
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Old 26th Jul 2023, 3:03 pm   #231
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Default Re: What was your first computer and do you still have it?

Another one for the ZX Spectrum 48K Rubber key machine here.

I still have the machine and PSU, but unfortunately no longer have any of the cassettes. Last I tried it, the computer still came to life and I was able to tune into it with my old GEC.

Spent many an hour copying the tapes on my dads HiFi system.
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Old 27th Jul 2023, 9:30 am   #232
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Very few 5.25" FDD's had a belt - Only really some of the oldest Full-height ones, and Cumuna probably used more-modern TEAC FD55 etc Half-height drives in many of their units.
Actually the 1/3rd height Epson drives (used in the QX10 and TF20, for example) are belt driven. These are the beautiful liittle drives with voice coil positioners and an optical transducer for feedback, like a miniature RK05.

The 2/3rd height BASF drives that are common in RML380Z machines are also belt driven (just looked in the service manual).

Were there any full-height 5.25" drives that weren't belt driven? I can't remember one off the top of my head.

I hadn't realised their was a 2/3rd-height size of 5.25" drives, and that the RML380Z had these (even though I have one!). But it looks like these are quite similar to the original full-height ones, so carried on with similar mechanics.

Whereas moving to a Direct-drive 'continuously-pulsed stepper' motor with integrated 'flywheel' (to smooth-out speed? / for circular array of coils underneath to magnetically drive this) , that many later VCR's etc. used for capstan motor, allowed a much lower height than original quite tall brush motor and centre spindle bearing support.
So it is surprising that there were even thinner 1/3rd height ones, that still managed to use a belt (Although all 3" and some much taller 3.5" FDD's also used a belt)

I did wonder if the the classic full-height ones in the IBM 5150 PC had a belt. Rather than pull mine apart to check, I did some online searching and it seems these used a Tandon TM100 FDD, with quite a lot of info (inc. alignment without an alignment disc?) / brochure / user & service manuals etc here:
https://retrocmp.de/fdd/tandon/tm100-2a.htm
And user manual does refer to a belt - which if anything like those in 3£ drives, has probably perished in the 40yr old ones I have.
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Old 27th Jul 2023, 10:32 am   #233
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The full-height drives in the IBM 5150 PC and 5160 PC/XT are certainly belt-driven.

Were there any belt-driven half-height 5.25" drives? I can't think of one by model number but I thought I'd seen one somewhere. Maybe an Alps chassis?
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Old 4th Aug 2023, 12:45 pm   #234
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Default Re: What was your first computer and do you still have it?

Newbie to the forum, so figured this was a good place to start. Very impressed with the posts I've seen so far.

My first micro was a SoC MK14 in 1979. After a few years I upgraded to an Acorn Atom which I had for many many years.

Both have long since been consigned to the rubbish dump :-(

A few years back I purchased a JMP replica MK14 Issue II pcb, and this is now up and running. I'll post some pics of it and the assorted mods I've applied later.
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Old 4th Aug 2023, 12:56 pm   #235
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Hi Terry, welcome on board. Shame you didn't keep the Acorn Atom and the MK14, if you had still had them, you could have sold them and had yourself a decent holiday with the proceeds.

(Easy to say with hindsight, of course.)

Sounds like your MK14 may have been an issue IV or V if you bought it in '79.
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Old 4th Aug 2023, 1:03 pm   #236
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... and of course, if the majority hadn't been junked, they wouldn't have the value now!
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Old 4th Aug 2023, 1:07 pm   #237
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The board was supplied with the later version proms, so yeah - likely a later issue pcb. I didn't do too much with it in terms of expansion. Just added single step, and the twin CPU mod.

LOL yeah, hindsight is a wonderful thing. Never mind, I've got my replica to play with.

So far got the prom shadow addressing sorted as the JMP pcb is (I think) an issue II, and added the popular ram expansion / cassette interface card. Next added a single step mod, and dual CPU's (which I had on my original). The latter is more of a novelty but neat and was always useful to check on tape loads .

Now I need to find something to do with it.
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Old 4th Aug 2023, 1:11 pm   #238
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if the majority hadn't been junked, they wouldn't have the value now!
Not sure actually, because there weren't really that many made in the first place (MK14s, I mean). As opposed to (say) ZX81, over a million sold, apparently.

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Old 4th Aug 2023, 1:14 pm   #239
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Default Re: What was your first computer and do you still have it?

First "computer" I had any dealings with was a UK101 by Compukit, the boss had bought one & I was "volunteered" to build the thing, a mere strip of a lad at 18 years old. It took a while but worked first time. He got fed up with it after a few weeks & gave it to me. Being a cash starved individual it got sold on. Wish I'd kept it!
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Old 4th Aug 2023, 1:38 pm   #240
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and dual CPU's (which I had on my original).
Sounds like you've been more ambitious with your modern replica than most. Actually, just finding two SC/MPs to put on it was quite an achievement...

Should have mentioned, as a new forum user your posts will be held for moderation for the first few, but that should wear off after you've made a small number of posts.
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