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by dp11
Wed Jun 26, 2013 4:09 pm
Forum: 32-bit acorn hardware
Topic: Strange Risc PC video fault
Replies: 45
Views: 5601

Re: Strange Risc PC video fault

The freezer spay is good for finding cracked joints and also devices which are on the edge of timing. You might have a databus buffer with a soggy output .
by dp11
Tue Jun 25, 2013 1:42 pm
Forum: 32-bit acorn hardware
Topic: Strange Risc PC video fault
Replies: 45
Views: 5601

Re: Strange Risc PC video fault

Oh yes I forgot you can't read any of the VIDC20 Regs.

I think it is a databus problem.

I would try freezer spray and see if the problem goes away, if so you can try and localise the problem.
by dp11
Mon Jun 24, 2013 8:45 pm
Forum: 32-bit acorn hardware
Topic: Strange Risc PC video fault
Replies: 45
Views: 5601

Re: Strange Risc PC video fault

The images are great. Don't rule out the possibility of more than one fault. I would be tempted to check the databus ( I only suspect the lower 8bits)to the VIDC20 . I wonder if you tried writing to the palette register the following patterns and check they read back correctly 0x55 0xAA. I would als...
by dp11
Mon Jun 24, 2013 1:15 pm
Forum: 32-bit acorn hardware
Topic: Strange Risc PC video fault
Replies: 45
Views: 5601

Re: Strange Risc PC video fault

Can you post some pictures of the screen ?
by dp11
Sun Jun 09, 2013 10:11 pm
Forum: 32-bit acorn hardware
Topic: Strange Risc PC video fault
Replies: 45
Views: 5601

Re: Strange Risc PC video fault

Sounds like an Address Line fault to the VRAM to me.
by dp11
Thu Jan 03, 2013 9:21 pm
Forum: 8-bit acorn hardware
Topic: purpose of the -5v line on the beeb psu?
Replies: 13
Views: 1826

Re: purpose of the -5v line on the beeb psu?

While people are thinking about negative numbers. Think about this.

Connect a -1 Ohm resistor across a car battery ?

Now swap positive and negative what happens ?
by dp11
Mon Dec 24, 2012 10:28 am
Forum: 8-bit acorn hardware
Topic: 23 Beebs available...
Replies: 55
Views: 5609

Re: 23 Beebs available...

more than happy to fix a few beebs, I'm on the edge of Cambridge.
by dp11
Fri Dec 14, 2012 6:56 pm
Forum: 8-bit acorn hardware
Topic: Speech Roms voice
Replies: 3
Views: 1043

Speech Roms voice

Some where I heard that the voice for the speech roms was Kenneth Kendall. is this true?
by dp11
Sun Nov 18, 2012 7:17 pm
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Re: Some stuff from a clear out

Some more stuff listed included some bits from an AMX mouse.
by dp11
Fri Oct 26, 2012 7:04 am
Forum: 8-bit acorn hardware
Topic: Advanced Battery Backed RAM Project ABR - All sold, new batch on the way
Replies: 56
Views: 9807

Re: Advanced Battery Backed RAM Project - Preliminary

I may be wrong but arent the second and fourth line on NCS effectively the same ?
by dp11
Sun Oct 21, 2012 9:47 pm
Forum: 8-bit acorn hardware
Topic: rs-confusion-432-423...
Replies: 15
Views: 2216

Re: rs-confusion-432-423...

The serial ULA baud rate generator also needs emulating.

http://beebwiki.jonripley.com/Serial_ULA
by dp11
Sun Oct 21, 2012 9:07 pm
Forum: 8-bit acorn hardware
Topic: rs-confusion-432-423...
Replies: 15
Views: 2216

Re: rs-confusion-432-423...

I'm interested in helping out

http://uk.farnell.com/nte-electronics/n ... dp/4899775

Might be worth using a CPLD instead as the 6850 has become expensive.
by dp11
Sun Oct 21, 2012 3:13 pm
Forum: 32-bit acorn hardware
Topic: Loss of Audio on an A5000
Replies: 19
Views: 2591

Re: Loss of Audio on an A5000

I would want to check the PSU capacitors next.
by dp11
Tue Oct 16, 2012 9:27 pm
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Re: Some stuff from a clear out

a few more bits and an oscilloscope now on ebay.
by dp11
Thu Aug 30, 2012 9:19 pm
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Re: Some stuff from a clear out

A few more bits on eBay (dominicp1088)
by dp11
Mon Aug 20, 2012 7:55 pm
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Re: Some stuff from a clear out

Dan,

Do you want my spare at the 8 quid the other sold for ?
by dp11
Sat Aug 18, 2012 10:26 pm
Forum: 8-bit acorn hardware
Topic: Another faulty BEEB with the long Beeeeeeeeeeeeeee
Replies: 5
Views: 1309

Re: Another faulty BEEB with the long Beeeeeeeeeeeeeee

Just checked all the pins should be the same except pins1,20,27
by dp11
Sat Aug 18, 2012 10:22 pm
Forum: 8-bit acorn hardware
Topic: Another faulty BEEB with the long Beeeeeeeeeeeeeee
Replies: 5
Views: 1309

Re: Another faulty BEEB with the long Beeeeeeeeeeeeeee

I don't have the circuits to hand. Could you start by metering between the os socket and the next socket. From memory and but pin20 should be the same. Ie pin1 should connect to pin 1
by dp11
Fri Aug 17, 2012 9:15 pm
Forum: 32-bit acorn hardware
Topic: Repair tip for old A305 A310 A440 etc floppy drive
Replies: 12
Views: 2914

Repair tip for old A305 A310 A440 etc floppy drive

Over time these appear to stop working. These are recoverable with a little care. 1 remove the floppy drive from the computer. 2 with a disc watch how the head moves as the disc is inserted and ejected. 3 notice the copper coloured piece of metal connecting to the head mounting plastic. This springy...
by dp11
Thu Aug 16, 2012 1:52 pm
Forum: 8-bit acorn hardware
Topic: Electron Second Processor project
Replies: 235
Views: 32155

Re: Electron Second Processor project

A 1MHz signal through an RC of 470R and 470pf will give the levels you are seeing.

At 1MHz 470pf has and impedance of 339R.
by dp11
Thu Aug 16, 2012 7:40 am
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Re: Some stuff from a clear out

Hi dan

Happy to lend you my spare for a few months to see how you get on. Just make the results public.

dp11
by dp11
Tue Aug 14, 2012 9:47 pm
Forum: 8-bit acorn hardware
Topic: Poorly beeb needs power!
Replies: 28
Views: 2992

Re: Poorly beeb needs power!

Your temporary repair, can you explain a little more. The beeb is sensitive to voltage drop, so make sure the wire is short and thick.

Does the splash screen say 16 or 32 k?
by dp11
Tue Aug 14, 2012 9:05 pm
Forum: 8-bit acorn hardware
Topic: Poorly beeb needs power!
Replies: 28
Views: 2992

Re: Poorly beeb needs power!

Okay I've moved to iPad and chrome browser for the evening , it appears to turn the image upside down. Main computer is fine .

So anyone reading ths in the future the correct way up for the image is with the text vcc the correct way up. Basicly dont trust the iPad .

Sorry for the confusion .
by dp11
Tue Aug 14, 2012 8:16 pm
Forum: 8-bit acorn hardware
Topic: Poorly beeb needs power!
Replies: 28
Views: 2992

Re: Poorly beeb needs power!

Photo appears to have been rotated since I last looked the thick track is now below the hole. The track is very close to the hole. If you very gently remove the white silk screen you will see what I mean. I would too also guess the nicked tracks are okay, but no harm in checking.
by dp11
Tue Aug 14, 2012 7:16 pm
Forum: 8-bit acorn hardware
Topic: Poorly beeb needs power!
Replies: 28
Views: 2992

Re: Poorly beeb needs power!

the VCC3 hole connects to the fat track on the top side just above it.
by dp11
Tue Aug 14, 2012 7:01 pm
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Re: Some stuff from a clear out

Some books this time :

Book MY BBC MICRO AND ME by Meyer Solomon
http://www.ebay.co.uk/itm/230838484668

32 Bit Microprocessors Edited By H.J. Mitchell
http://www.ebay.co.uk/itm/230838489951

The above contains a few pages about the ARM processor.
by dp11
Mon Aug 13, 2012 8:12 pm
Forum: for sale / freebies
Topic: Some stuff from a clear out
Replies: 9
Views: 2231

Some stuff from a clear out

I'm listing stuff on ebay I've never really used. Still keeping my master and RISC PC. Issue 2 Econet card : http://www.ebay.co.uk/itm/230837673160 Computer Concepts ROM RAM Podule for Acorn RISC OS Archimedes : http://www.ebay.co.uk/itm/230837621948 Acorn Desktop C Compiler For Risc OS : http://www...
by dp11
Mon Aug 13, 2012 7:49 pm
Forum: 8-bit acorn hardware
Topic: Casette cables
Replies: 4
Views: 961

Re: Casette cables

The extra two pins control the motor. Most tape recorders don't have motor control so you have to do it yourself. So 5pin to 5pin din lead is fine. MIDI and econet cables work fine.

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