Please help with another blooming "I just got a BEEB from Ebay" thread :-)

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rthorntn
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Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 5:53 am

G'day from Oz,

I'm new here, I have started collecting computers from my childhood back in the UK. I have an Apple II, Atari Mega STE, Commodore 16.

I am OK with electronics, I can solder and have access to an oscilloscope, bench power supply, hot air wand and a multimeter (I have one of those sub 100 quid USB logic analysers as well).

So I did a quick search of the forum, I didn't find what I needed.

I just got an A4000 from Ebay here in Oz, it's missing the PSU, keyboard and mouse and there was battery damage.

I removed the battery, cleaned the board with water, lemon juice, IPA and water again, the leaking battery doesn't appear to have eaten through any traces.

So obviously I want to power it on, I gather that an ATX supply will work, I have the following in addition to said supply:

Dangerous Prototypes ATX Breakout Board
Hacked up 4-pin female MOLEX cable

So I gather I need +12, +5, GND and -12 but I don't have a pinout?

Should the system power up in isolation without the battery, keyboard, disk, speaker or mouse? I have a VGA monitor that works with 15Khz?

What kind of mouse and keyboard does it use, I can only see a keyboard port it looks like PS/2, what to do about a mouse, something like the Eiffel I have for my MSTE?

Oh and what to replace the battery with?

If I'm unsuccessful in powering it up are there any useful troubleshooting resources, I'm reading through the sticky "32 bit Fault finding index"?

Is there a high resolution photo of the motherboard showing the key components and maybe a guide on where to stick a multimeter and what you should see if you stick it there?

Thanks.

Richard
Last edited by rthorntn on Wed Aug 29, 2018 6:34 am, edited 4 times in total.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by danielj » Wed Aug 29, 2018 7:03 am

Hullo, welcome!
So, A4000 schematics are here:
http://chrisacorns.computinghistory.org ... A4000.html

The cmos will be full of garbage so you'll need to reset it on boot, you do need a keyboard for this. It is non-standard unfortunately, and the mouse (quadrature) plugs into the keyboard. If you can source a keyboard there are a number of good mouse solutions, if you can't then this is probably your best bet: viewtopic.php?t=9334

In so far as booting without anything connected, I suspect the garbled cmos will get in the way and you'll at least need a keyboard to reset that. A monitor that syncs at 15khz is perfect.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 7:21 am

Thank you!

What does a garbled BIOS look like, it's a good sign, yes?

I can probably make on of these PIC16F628A things, or are they available assembled online?

Any idea what the power pinout is on PL26 (I might be losing my vision, I can't see it on the drawings), I need to wire that correctly?
Last edited by rthorntn on Wed Aug 29, 2018 7:24 am, edited 2 times in total.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by danielj » Wed Aug 29, 2018 7:26 am

Not off the top of my head - on the bus at the mo. That's why I posted a link to the schematics. Fairly sure it must be on there...

Garbled cmos will look like not booting, wrong screen mode for display, complete hang... All sorts of different things.

As far as I know you'll have to build the adaptor yourself. I don't think anyone is making/selling them :)

d.
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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 7:34 am

Thanking you, kind sir, strangely enough I'm going to be in Manchester in a couple of weeks, going to check out the RAF 100 while I'm over for a conference!

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by daveejhitchins » Wed Aug 29, 2018 7:38 am

Welcome to the Forum, Richard . . . Enjoy . . .

And good luck with your A4000 . . .

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com


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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 7:58 am

I have 10 cheap PS/2 roller ball mice so I'm happy to hack one or two up if anyone knows how?

Ebay seems to have a lot of the smallymouse2, I could get that but where does it connect to?

Ideally I would have a PS/2 keyboard and mouse that I already own connected to my A4000.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by flaxcottage » Wed Aug 29, 2018 8:00 am

Welcome, Richard. :D

When my A4000 PSU died I obtained a guaranteed replacement from CJE Micros in the UK. It was quite reasonably priced considering that they guarantee it and compared to buying a duff A4000 just for the PSU.

The PSU provides +5v, +12V and -5v, red, yellow and purple wires I believe. There is no fan so it runs silently.

The keyboard can be either an A5000 one or an A4000 one as they are interchangeable. I believe the A3xx and A4xx series keyboards work too, though I've not tried them.

Good luck with your endeavours.
- John

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by danielj » Wed Aug 29, 2018 8:14 am

:D Depending on what's your bag, a quick visit to the Museum of Science and Industry whilst you're here will reveal the working replica of the first stored program computer - the Manchester Baby :) https://en.wikipedia.org/wiki/Manchester_Baby

SmallyMouse turns a USB mouse into a quadrature mouse, but you'll still need an archimedes keyboard to plug it into the back of. Some PS/2 mice have quadrature outputs from their controller ICs - especially the optical ones. It's possible to hack those to work with an arc:
viewtopic.php?f=3&t=6869

Someone seems to have made a video of it here:
https://www.youtube.com/watch?v=r73GwTQbnXI

d.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 8:27 am

Thanks good call, I will of course also be making the pilgrimage to Bletchley!

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by Elminster » Wed Aug 29, 2018 8:32 am

Welcome.

Do the triple and do the computer museum at Cambridge as well! Do on the wekeend of 7th-9th Sept and a couple of Dozen of us will be there.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 8:52 am

I don't land till the 12th, bugger all chance of me changing my flights, any chance of a smaller scale reinactment the weekend after I arrive?

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 8:55 am

I should add it will be "worth it" I'm the most social guy I know ;-)

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 9:21 am

BTW I still haven't figured out which voltages on the PSU go to which pins on PL26, it's a bit of a showstopper, the images I can find of the PSU suggest 5v, 12v, ground and -12v (I can't see a mention of -5v maybe [thankfully] that was an older Acorn)?

Getting late here, my instincts tell me something might pop up while I'm asleep.
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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by danielj » Wed Aug 29, 2018 9:44 am

From the tech drawings I linked to earlier, sheet 2 of 3 (Acorn_A4000TRM_MainPCBCircuitDiagram2of3.pdf):
PLS26.jpg
That should see you right :)

d.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 9:51 am

Thanks again, I completely missed that.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by tomc » Wed Aug 29, 2018 11:07 am

Replacing the PSU in an A4000 is also something I need to do (mainly because the replacement someone fitted many years ago doesn't actually fit in the A4000 case properly, so it won't close!).

I'm trying to work out if a PSU with -12v is needed. I've looked around the circuit diagrams and can't see anywhere that uses the -12v. My guess would be an op amp needs it, but again couldn't see anything in the diagrams. I ask because a PSU with just +12v and +5v is likely to be easier to get and cheaper.

Has anyone spotted where the -12v is used?

Thanks

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by IanS » Wed Aug 29, 2018 11:54 am

tomc wrote:
Wed Aug 29, 2018 11:07 am
Has anyone spotted where the -12v is used?
Appears to be just used for the serial port driver.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Wed Aug 29, 2018 12:10 pm

-12v is part of the ATX spec so it should be very easy to replace, I found this:

5V was the back-bias voltage for 3-rail DRAMs, in the era of 16kbit DRAMs. These used 5V for the interface, 12V to power the storage, and -5V to provide negative bias to the chip substrate. Without -5V, all 16384 storage transistors turned on at once, pretty much shorting the 12V supply to ground and destroying the chip.

You needed to ensure the -5V supply was working before starting the 12V supply. However as it supplied a bias voltage, it didn't need to source a great deal of current; 5ma was enough for a whole 64k memory! (the 12V supply was somewhere close to an amp)

Later DRAMs (starting with the 64kbit generation though there were some 16k versions) generated their own -ve supply with an on-board charge pump - and possibly still do, for all I know. These were already coming into fashion as the PC started to take off, but were possibly still more expensive...

-12V was necessary for proper RS232 serial port levels; I can't think of any other purpose for it in a PC.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by tomc » Wed Aug 29, 2018 1:30 pm

@IanS - thank you! Looks like you are right. I've been wondering about that for some time!

@rthorntn thanks for the info. Yes, the bodge job that is currently in there is a small ATX supply, although still slightly too big, with the appropriate molex pin for the motherboard rewired to -12v. Also has a fan which it would be nice to not have. I haven't found any ATX supplies that would fit, without a fan, and are also cheap! Maybe I'm asking for too much and should just get a genuine replacement. They are not overly expensive afterall.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by 1024MAK » Wed Aug 29, 2018 5:34 pm

The recommendation to neutralise the alkaline leakage from the cell (battery) is to wash the area with ‪vinegar‬. Don't use the brown stuff. Use the clear stuff - see this thread. Use it neat, that is, do not dilute. Leave it on for five to ten minutes before washing off with tap water. Finally, if your tap water has additives or is 'hard' (has dissolved limestone), do a final wash using distilled/demineralised water (often available from car/vehicle shops for use in lead acid batteries).

Mark

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by danielj » Wed Aug 29, 2018 5:47 pm

Yup - I personally would generally discourage lemon juice (I've been seeing this more and more on facebook groups, I have no idea where it started) - simply as it's gunky/sugary and has loads of other stuff in it along with the citric acid. The other thing besides vinegar that would be fairly effective would be to mix up some tartaric acid powder (lots of people who bake have this) in a little water and get that on, but key is using something that's not going to leave any additional residue. Likewise, you can do a final rinse after the water with IPA - it'll help the water evaporate faster, but it's not essential for anything. IPA is good for removing flux/grease/things that dissolve in alcohol. Doesn't do much with the chemicals from batteries.

Anyway, hopefully it's all looking good now.

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by aotta » Wed Aug 29, 2018 6:00 pm

I always use lemonjuice, because I can't stand vinegar smell... Next time, I will try with effervescent aspirina (if the important thing is using an acid solution.. 😜)

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by flaxcottage » Wed Aug 29, 2018 6:11 pm

Instead of lemon juice use citric acid. It is easy to get hold of and is definitely non-toxic - where would sherbet be without it? :lol:
- John

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by danielj » Wed Aug 29, 2018 6:14 pm

Dispersible aspirin isn't particularly acidic (otherwise you'd be in agony gargling with it for a sore throat!). If you don't like the smell of acetic acid, then tartaric acid as described above would be fine. Lemon juice is sort of like using Metaxa when you want to clean something with ethanol :D...

(or Citric acid powder as John says! :))

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by aotta » Wed Aug 29, 2018 7:22 pm

i have to study further about the ph of aspirina... anyway, i intended the "C" vitamine added ones, to sum the effort of ascorbic acid to acid acetylsalicyic one.... :lol: :lol: :lol:

But out of joking, do you use some cotton stick, or toothbrush to clean the pcb? i used a toothbrush for my a5000, and i am afraid i made more damage to tracks than alkaline overflow... :?

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by 1024MAK » Wed Aug 29, 2018 11:15 pm

Yes, use a clean toothbrush (cheap new one maybe) to gently clean the board. If the track is good, the toothbrush will not cause any damage. However, if the track has been damaged (e.g. by the leakage from the battery, or other corrosion), the track is likely open circuit already. Or so weak that any cleaning will finish it off.

Same goes for the components.

Mark

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by rthorntn » Thu Aug 30, 2018 5:15 am

It's alive!!!

RISC OS 4096K
No keyboard present - autobooting
Supervisor

#

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Re: Please help with another blooming "I just got a BEEB from Ebay" thread :-)

Post by aotta » Thu Aug 30, 2018 5:24 am

Good! Welcome on board! :wink:

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