Search found 261 matches

by johnkenyon
Thu Feb 11, 2021 1:03 pm
Forum: 8-bit acorn hardware
Topic: RPi (zero) backpowering via gpio
Replies: 9
Views: 293

Re: RPi (zero) backpowering via gpio

If the Pi is always going to be powered by the BBC, then the easiest option is to cut the +5v USB connection. You only need ground, D+ and D- to send data, and a computer won't complain when an enumerated USB device draws zero current. One method is to cut the track on the PCB (not the method I woul...
by johnkenyon
Mon Feb 01, 2021 10:17 pm
Forum: other vintage hardware, software and languages
Topic: Tandata TD 2500
Replies: 17
Views: 1334

Re: Tandata TD 2500

Do you reckon you could also have a stab at my AlphaTantel which is the precursor to the TD2500? It's not a password crack this time but merely trying to locate the key that enters programming mode. There's a switch on the back that physically enables config mode but how you then enter new phone nu...
by johnkenyon
Wed Jan 20, 2021 2:00 pm
Forum: other vintage hardware, software and languages
Topic: Tandata TD 2500
Replies: 17
Views: 1334

Re: Tandata TD 2500

Latest discovery - a possible reset password. Found a subroutine which compares text pointed to by ($40) against that pointed to by ($42). The first call to this subroutine loads ($40) with $7A1E which contains the our previously identified "RESET!" text. So I suggest when prompted for a p...
by johnkenyon
Wed Jan 20, 2021 8:13 am
Forum: other vintage hardware, software and languages
Topic: Tandata TD 2500
Replies: 17
Views: 1334

Re: Tandata TD 2500

Attached the ROM from Tony. The ROM must map to &C000-&FFFF for the reset vector to be found, but this then jumps to &6100, so ROM must also be at &4000-&7FFF. I've started disassembly of the code. From my findings so far: The R6501 has several bus modes, and the code switches b...
by johnkenyon
Tue Jan 19, 2021 12:40 pm
Forum: other vintage hardware, software and languages
Topic: Tandata TD 2500
Replies: 17
Views: 1334

Re: Tandata TD 2500

A Google for R1702-12 will yield a datasheet for the CPU. It has onboard RAM between 0040 and 00FF. 0040 to 005F gets battery backed, and probably holds the password. There's no obvious "factory default" link, so my money is on a "hold down a key and power on to reset" style meth...
by johnkenyon
Mon Dec 14, 2020 2:45 pm
Forum: 8-bit acorn hardware
Topic: *Answered* BBC Master Repair Replace Purple Capacitor
Replies: 3
Views: 252

Re: BBC Master Repair Replace Purple Capacitor

Flat grey square capacitors with a purple top are un-polarised ceramic capacitors - identify the value and replace with any same value ceramic capacitor. Tantalum capacitors are polarised (the PCB will have one pin marked with a "+"), and are usually dark yellow or orange (really old ones ...
by johnkenyon
Sat Dec 12, 2020 7:43 pm
Forum: 8-bit acorn hardware
Topic: connecting GOTEK and a disk drive
Replies: 5
Views: 319

Re: connecting GOTEK and a disk drive

How do I make the cable up? What do I need to buy and where? Will only use the thing once to copy my discs and I’m done with it!! Usually a length of 34way IDC ribbon cable, and three 34way female IDC connectors. The connectors are crimped onto the cable (in a factory: using a specially designed pr...
by johnkenyon
Fri Dec 04, 2020 10:45 am
Forum: 8-bit acorn hardware
Topic: Prism 1000 modem cable
Replies: 21
Views: 771

Re: Prism 1000 modem cable

To identify which pins, I would take the lid off the modem and see how the serial connector is wired. If it is panel mounted, with wires to the PCB, the PCB might even have markings telling you which wire/pin is which. An examination of the PCB+connector should reveal the ground pin (usually to a la...
by johnkenyon
Sat Nov 28, 2020 5:39 pm
Forum: 32-bit acorn hardware
Topic: RISC PC 120v Power supply
Replies: 8
Views: 345

Re: RISC PC 120v Power supply

Mandatory health warning: The input reservoir capacitors on a switch mode PSU will have high voltage DC (>300v) present which may persist for some time after the equipment is disconnected from the mains supply. It may be possible to modify the existing PSU. It may have provision for a link on the PC...
by johnkenyon
Tue Nov 24, 2020 11:47 am
Forum: 8-bit acorn hardware
Topic: Help identifying this Model B
Replies: 16
Views: 699

Re: Help identifying this Model B

Is there any chance that the ROM labelled "BASIC" is actually the OS+BASIC ROM?

It wouldn't do any harm to move the BASIC ROM to the OS socket and see if it boots, and if it doesn't come up in BASIC see whether *BASIC works or not.
by johnkenyon
Fri Nov 20, 2020 1:45 pm
Forum: 32-bit acorn hardware
Topic: Acorn A3010 and Serial WiFi adapter
Replies: 8
Views: 454

Re: Acorn A3010 and Serial WiFi adapter

The A3000 has a weird non-standard DSR/DTR handshaking arrangement so I imagine the A3010 is the same... I worked it out with some help from serial wiring diagrams on the internet (A30x0<>PC) but don't remember what you need to connect to what. I sold my A3000 too so didn't bother to commit it to m...
by johnkenyon
Wed Nov 18, 2020 7:54 am
Forum: 8-bit acorn hardware
Topic: Loose ROM sockets
Replies: 12
Views: 510

Re: Loose ROM sockets

I keep having reliability issues with my Beeb. Mostly it manifests itself as a reluctance to start up the first time every day. Once it is up it is stable for hours on end. I am reasonably convinced the problem is loose / sloppy ROM sockets, since pressing down on the ROM tends to fix things. I sho...
by johnkenyon
Mon Oct 26, 2020 4:54 pm
Forum: 8-bit acorn hardware
Topic: Someone's pinched my econet! (Not Mine Any More!)
Replies: 30
Views: 2159

Re: Someone's pinched my econet! (Now repair help!)

If you want some spade terminals for your beeb, PM me. I bought a sack load a while back. Bear in mind they are 'fun' to fit. Well, the 'fun' has been had! Thank you very much, @Colday - really appreciate it. Given the hard life this board has had I'm amazed (but happy) to say it has survived surge...
by johnkenyon
Wed Oct 14, 2020 1:14 pm
Forum: 8-bit acorn hardware
Topic: Unknown rom
Replies: 27
Views: 1103

Re: Unknown rom

You can get them from Farnell's. Likely cheaper than eBay, And their delivery is superb. https://uk.farnell.com/murata/rder71h333k0m1h03a/cap-0-033uf-50v-mlcc-radial/dp/2990806?st=33nf Based on my experience over 30+ years - RS wins hands down for delivery. RS - next day ~99% - - Farnell next day ~...
by johnkenyon
Fri Oct 09, 2020 11:06 pm
Forum: 8-bit acorn hardware
Topic: Unknown rom
Replies: 27
Views: 1103

Re: Unknown rom

And what this is, there are lots all over the board, marked A, this one has broken off . Decoupling capacitors - they are wired between 5V and ground, and (put simply) provide a local reservoir of energy when the IC nearby temporarily pulls more current from the 5V line. If these capacitors weren't...
by johnkenyon
Sat Aug 22, 2020 8:19 pm
Forum: general
Topic: Today I received.....
Replies: 6137
Views: 702058

Re: Today I received.....

Nice pizza box Stephen! They do come up occasionally for reasonable prices. I scored an IPX with keyboard and Sun monitor for postage as the owner was moving house and wanted rid. It's ex Bath Uni Maths department. Just needed a battery hack for the NVROM and it's a good 'un. I was given an UltraSp...
by johnkenyon
Thu Aug 13, 2020 4:09 pm
Forum: other vintage hardware, software and languages
Topic: Picked up some unusual equipment today
Replies: 16
Views: 1518

Re: Picked up some unusual equipment today

[*]the monitor socket looks like nothing I've ever seen before - certainly a cross between DVI and something else). A 13W3 ? Popular on Sun and SGI back in the day https://en.wikipedia.org/wiki/DB13W3 Note: Sun and SGI DB13W3 to VGA adaptors are not compatible with each other, despite having identi...
by johnkenyon
Tue Aug 11, 2020 4:16 pm
Forum: 8-bit acorn hardware
Topic: Clearing EPROMS/EEPROMS
Replies: 59
Views: 2470

Re: Clearing EPROMS/EEPROMS

That could explain why it doesn't work at all in any beeb.... So I need to write the test ROM code to 0xC000 instead of 0x4000? Ok, I'll give that a go next. I do not think this is going to make any difference with the dishwasher beeb. But we shall see. My personal rule is to program N images into ...
by johnkenyon
Tue Jul 21, 2020 8:31 am
Forum: 8-bit acorn hardware
Topic: Model B - possible faulty cassette interface?
Replies: 30
Views: 2178

Re: Model B - possible faulty cassette interface?

https://en.wikipedia.org/wiki/Crystal_earpiece My tool of choice when trying to trace where a low level audio signal has disappeared. Use the tip of the 3.5mm plug as a probe, the thing is so sensitive, you don't need to provide a return path. Play a signal (an audio cassette will do) into the casse...
by johnkenyon
Sun Jul 12, 2020 4:00 pm
Forum: 8-bit acorn hardware
Topic: Faulty ROM sockets
Replies: 9
Views: 650

Re: Faulty ROM sockets

Test with the power switched off using the 200 ohm range on your multimeter. You are looking for a resistance of less than 1 ohm. Always test with a ROM chip fitted in the sockets and test the very top of the IC leg/pin. Pinging off at a tangent (as is my wont)... I'm a bit paranoid about using the...
by johnkenyon
Thu Jul 09, 2020 10:53 am
Forum: 8-bit acorn hardware
Topic: Econet High Pitched Squeal
Replies: 3
Views: 383

Re: Econet High Pitched Squeal

If you want more randomness ;)

Code: Select all

   10 M%=&800
   20 REPEAT
   30 FOR A%=0 TO 47
   40 B%=RND(256)-1  
   50 M%?A%=B%
   60 NEXT
   70 UNTIL FALSE
by johnkenyon
Thu Jul 09, 2020 10:42 am
Forum: 8-bit acorn hardware
Topic: Unreliable ROMs / sockets in BBC B
Replies: 12
Views: 816

Re: Unreliable ROMs / sockets in BBC B

After that, I was able to remove the pins and clear the holes individually, by standing the board vertically, applying the soldering iron to the underside and pulling the pin out with pliers from the top side. That was much easier than trying to get all 28 holes clear before moving the socket. My t...
by johnkenyon
Sun Jun 28, 2020 10:17 pm
Forum: 8-bit acorn software: other
Topic: Writing a service rom - it's not recognized
Replies: 21
Views: 1562

Re: Writing a service rom - it's not recognized

I believe the Acorn data lives here in the Electron MOS ROM: \ Electron Acorn bitmap for Ctrl-Break \ ------------------------------------ .LC42B EQUB &18:EQUB &3C:EQUB &3C:EQUB &7E EQUB &7E:EQUB &00:EQUB &7E:EQUB &3C \ ...**... \ ..****.. \ ..****.. \ .******. \ .**...
by johnkenyon
Sun Jun 28, 2020 3:33 pm
Forum: 8-bit acorn hardware
Topic: Model B - possible faulty cassette interface?
Replies: 30
Views: 2178

Re: Model B - possible faulty cassette interface?

OK. Thanks. Since my last post, I've run the following test program: 10 CLS 20 *MOTOR 1 30 PRINT "ON" 40 FOR N=1 TO 5000: NEXT N 50 *MOTOR 0 60 PRINT "OFF" 70 FOR N=1 TO 5000: NEXT N 80 GOTO 20 On running the program, I can confirm there is NO motor light OR sound ('click'). I'v...
by johnkenyon
Wed Jun 24, 2020 6:30 pm
Forum: 8-bit acorn hardware
Topic: Here are some scans of the Barson computers Electron Econet interface CCT and blank board
Replies: 33
Views: 2356

Re: Here are some scans of the Barson computers Electron Econet interface CCT and blank board

No collision detection I note.
The circuit between the 68B54 and the Econet socket is more or less a direct lift from the original ("issue 1") Master Econet module.
by johnkenyon
Thu Jun 18, 2020 3:29 pm
Forum: 32-bit acorn hardware
Topic: AKF17 repair - whining noise, no screen
Replies: 13
Views: 1206

Re: AKF17 repair - whining noise, no screen

Watch out for the 4.7uF 50V bipolar electrolytic! These seem to be NLA. I've chucked a poly film cap on my order to try in place of it. You can make a bipolar electrolytic from two "normal" electrolytics wired in series, wired "like to like". Remember that two identical capacito...
by johnkenyon
Sat May 16, 2020 12:12 pm
Forum: 8-bit acorn hardware
Topic: ROMS - lots and lots
Replies: 39
Views: 2683

Re: ROMS - lots and lots

Possibly an adaptor to put two 2764's into a single 27128 socket. What would be the reason to do this? Probably one of * The mask programmed ROM 's won't be along for a few weeks. * "We have to ship 1.00 now, and then replace with the 1.20 ROM when it's finished." and/or one of the follow...
by johnkenyon
Sat May 16, 2020 11:10 am
Forum: 8-bit acorn hardware
Topic: ROMS - lots and lots
Replies: 39
Views: 2683

Re: ROMS - lots and lots

Colday wrote:
Sat May 16, 2020 9:14 am
Or this...

image.jpgimage.jpg

The part number (203,011) looks like a Acorn product.
Possibly an adaptor to put two 2764's into a single 27128 socket.
(i.e. "top half" in one socket and "bottom half" in the other)
by johnkenyon
Sat May 16, 2020 8:22 am
Forum: 8-bit acorn hardware
Topic: 6502 and IC's on daughter board
Replies: 17
Views: 1113

Re: 6502 and IC's on daughter board

I presume this is some sort of disc controller8DC2E9E6-DE8C-4830-9493-C9E9DBA68AB7.jpeg The "8272" marking on the board seems to tally with a double density controller. So if this an 8272 why does the chip have what looks like a covered window as one might expect on an EPROM? Is the 8272 ...
by johnkenyon
Fri May 15, 2020 5:56 pm
Forum: 8-bit acorn hardware
Topic: 6502 and IC's on daughter board
Replies: 17
Views: 1113

Re: 6502 and IC's on daughter board

I presume this is some sort of disc controller8DC2E9E6-DE8C-4830-9493-C9E9DBA68AB7.jpeg Microware DDFS? Looks like the item pictured on page 9 of Beebug Jan/Feb 1984 available at http://www.computinghistory.org.uk/downloads/14544 The "8272" marking on the board seems to tally with a doubl...

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