Search found 246 matches

by johnkenyon
Sat Aug 22, 2020 8:19 pm
Forum: general
Topic: Today I received.....
Replies: 5956
Views: 587193

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: 918

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: 52
Views: 1111

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: 1434

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: 406

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: 277

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: 556

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: 1096

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: 1434

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've now ordered replac...
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: 1490

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: 842

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 capacitors in series gives y...
by johnkenyon
Sat May 16, 2020 12:12 pm
Forum: 8-bit acorn hardware
Topic: ROMS - lots and lots
Replies: 39
Views: 1899

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 following * 2764...
by johnkenyon
Sat May 16, 2020 11:10 am
Forum: 8-bit acorn hardware
Topic: ROMS - lots and lots
Replies: 39
Views: 1899

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: 769

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 actually a...
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: 769

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 double density ...
by johnkenyon
Thu May 14, 2020 9:04 am
Forum: programming
Topic: Below page free space (DFS)
Replies: 27
Views: 1501

Re: Below page free space (DFS)

If you want the soft keys cleared before chaining the program, your !BOOT file becomes *BASIC *K.0*FX18|MCH."MYPROG"|M *FX138,0,128 I thought I'd tried that some time ago and I vaguely recalled that it didn't work. I just tried it again now in BeebEm and I can confirm that it doesn't seem to work: ...
by johnkenyon
Wed May 13, 2020 10:27 pm
Forum: programming
Topic: Below page free space (DFS)
Replies: 27
Views: 1501

Re: Below page free space (DFS)

*BASIC *K.0CH."MYPROG"|M *FX138,0,128 Rather than running the chain command from "inside" the EXEC loop, define a function key, and then insert it into the buffer for execution after the EXEC loop has ended. Thanks, that's a neat trick! @AJW, sorry for hijacking this thread, but if I may just add t...
by johnkenyon
Wed May 13, 2020 3:28 pm
Forum: programming
Topic: Below page free space (DFS)
Replies: 27
Views: 1501

Re: Below page free space (DFS)

I've seen something along the lines of

*BASIC
*K.0CH."MYPROG"|M
*FX138,0,128

Rather than running the chain command from "inside" the EXEC loop, define a function key, and then insert it into the buffer for execution after the EXEC loop has ended.
by johnkenyon
Wed May 06, 2020 7:25 am
Forum: 8-bit acorn hardware
Topic: BBC micro black linear PSU repair
Replies: 27
Views: 2169

Re: BBC micro black linear PSU repair

Perhaps the iss7 boards used a single rail PSU - a single 7805 with PNP power transistor to give a single 5V 3A power rail with multiple outputs to avoid high currents via the PCB traces.
by johnkenyon
Sat Apr 04, 2020 5:45 pm
Forum: other vintage hardware, software and languages
Topic: Atari 2600 - doesn’t like switching PSUs
Replies: 13
Views: 954

Re: Atari 2600 - doesn’t like switching PSUs

A common fix for SMPS noise is to clean the SMPS output by feeding it into a linear PSU. For example, for a device expecting 12v regulated, feed 19v from a laptop PSU into a 7812 regulator+heatsink. Note that the laptop PSU will already have sufficient output capacitors to strip low frequency ripple...
by johnkenyon
Fri Mar 06, 2020 9:07 am
Forum: 8-bit acorn hardware
Topic: Sync issue with Master + Panasonic Viera TV
Replies: 10
Views: 612

Re: Sync issue with Master + Panasonic Viera TV

Does anyone know of a cable which goes from a 6 pin DIN to three phono connectors (see photo of an Atari compatible cable) for connecting to the rgb input of a TV? Have searched but can’t find one, which says to me that it can’t be done...? F8136A66-B6D3-4982-8EE8-95859151E026.jpeg If you want to u...
by johnkenyon
Thu Feb 20, 2020 2:49 pm
Forum: 8-bit acorn hardware
Topic: Re: BBC model b serious sound issue
Replies: 5
Views: 435

Re: BBC model b serious sound issue

If the computer is freezing then that indicates something on the "digital side" of the sound generator First port of call is the system VIA Then working your way from the CPU towards the speaker IC3 System VIA IC32 74LS259 IC99 (Speech processor - if installed, extract it to test) 76489 IC17 LM324 I...
by johnkenyon
Sun Feb 16, 2020 1:59 pm
Forum: 8-bit acorn hardware
Topic: Help Finding Replacement AC/DC Adapter
Replies: 4
Views: 311

Re: Help Finding Replacement AC/DC Adapter

Two "cheapo" suggestions: 1) Keep the original adaptor, and glue on a modified "socket protector"/"plug socket cover" (like: https://images-na.ssl-images-amazon.com/images/I/51Yob6yTRDL._AC_SX466_.jpg ) Find one that has an earth pin long enough to open the shutters, then do some trimming. The aim o...
by johnkenyon
Sat Feb 01, 2020 8:53 pm
Forum: 8-bit acorn hardware
Topic: Master 128 (No1) - Short Circuit
Replies: 12
Views: 893

Re: Master 128 - Short Circuit

What do the ceramic decoupling capacitors look like? If they are coated in a dipped blue covering, that's where I would look first. On another product with the same issue I would power up the board, monitor the 5V supply and then cut each decoupling capacitor in half with the power on until the shor...
by johnkenyon
Fri Jan 31, 2020 5:26 pm
Forum: 8-bit acorn hardware
Topic: Cub Monitor Question
Replies: 36
Views: 1983

Re: Cub Monitor Question

16A08184-2B6B-4047-AC79-6AE997A999D9.jpeg For a three position switch, the typical wiring is as follows: The three connection solder tags in the centre are labelled A, B and C. A is the common pin for the outer ring solder tags numbered 1, 2, 3 and 4. B is the common pin for the outer ring solder t...
by johnkenyon
Fri Jan 24, 2020 3:25 pm
Forum: wanted
Topic: WANTED ColourCard Gold f. A440/A310
Replies: 3
Views: 503

Re: WANTED Concepts ColourCard Gold for A440 A310

A gentle hint - use "Wanted: <name of item>" as a title for wanted posts
That way people like me who don't have a ColourCard Gold don't need to read your post only to find out that they can't help...

/john
by johnkenyon
Tue Dec 24, 2019 12:41 pm
Forum: general
Topic: Today I received.....
Replies: 5956
Views: 587193

Re: Today I received.....

Lardo Boffin wrote:
Tue Dec 24, 2019 11:40 am
A new ULA for a ZX81. In an A4 sized postal box!


F248CAEC-73B7-487C-B2BF-0D56CB0E6735.jpeg
One way of stopping a postman from ramming a package through a letter box..
by johnkenyon
Fri Nov 29, 2019 12:16 am
Forum: 8-bit acorn hardware
Topic: 1MHz Bus adventures
Replies: 15
Views: 919

Re: 1MHz Bus adventures

Keep in mind that if you have say a three input NAND gate and you are only using two inputs, the third input should be tied to the appropriate logic level, in this case a logic high. states don’t matter (unused gates), you can tie the inputs to either logic level. If you are using a "spare" 3 input...
by johnkenyon
Tue Nov 05, 2019 11:55 am
Forum: 8-bit acorn hardware
Topic: Master sideway ram question
Replies: 7
Views: 746

Re: Master sideway ram question

Hi, I know the BBC Master has 4 banks of sideways ram. I have two pascal roms, if I install them (for some reason they appear as one in the *ROMS list) will they occupy one of the banks of sideways ram - leaving me three left? I've tried to get the ROMS to appear at position 0, but I cant. I think ...
by johnkenyon
Tue Nov 05, 2019 11:40 am
Forum: 8-bit acorn hardware
Topic: ROM Burner/Programmer
Replies: 7
Views: 797

Re: ROM Burner/Programmer

You might find it easier/cheaper to get hold of 27256 devices compared to 27128. If you "double up" the image, you can use a 32k device in a 16k sockets on the BBC B mainboard and IC27 on the Master. In both cases, A14 is tied to +5v so only the upper half of the device is used. Your mileage may var...

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