Hi from Peterborough, CAMBS

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NilByMouth
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Hi from Peterborough, CAMBS

Postby NilByMouth » Sun Nov 26, 2017 12:23 pm

Hi,

Having gleaned some help from a few helpful board members, I thought it was probably about time I introduce myself.

I'm an IT consultant who recently returned to my first love as a teenager - electronics. There's nothing like the smell of solder fumes and composite perf board to get the nostalgia buzz going. I got a bit bored tinkering with Raspberry Pi and Ardunio / Atmel chips, so I bought a few 8-bit CPUs (6502, 8080, Z80, 6809) with the intention of putting some circuitry around them just for the fun of it.

Back in the 80s I had built the school's Acorn Atom from a kit and then later on built my own 6502-based CPU board using wire wrap prototyping. Those were the days when component-level repair was viable in the field and my first jobs involved doing just that. When the PC came along, and then everything becoming surface-mount, costs went down and so did demand for my skills. Boards were swapped and disposed of or sent away for repair. I moved on to supporting the software side and didn't touch a soldering iron for decades.

As I'm looking to move house, the CPU projects went on the back burner, and I decided to just buy a ready-made CPU board in the form of a BBC Model B to have a play with. I wanted to test it was fully functional, so the purchasing escalated into getting a WE dual floppy drive, Cub monitor and cassette player (later on a broken Acorn data recorder because the cassette player has no tape counter). I had problems with the floppy drives until I realised that the power switch (although the same type as the Beeb's) switches in the opposite direction :roll: - there's no power LED to tell you when it's on and the drive LEDs only flash when you turn the power off. The Beeb also doesn't load from tapes. After borrowing another Beeb from a friend and swapping ICs around, it turns out that the serial ULA is faulty. I have a replacement chip on order from Retroclinic.

My friend's Beeb also needed work - the PSU caps had gone and one of them was producing a rather acrid smell. Unfortunately he's left it on for quite a while and so the whole computer is tainted with the smell. I've replaced the caps and gave it a bit of a clean as a thank you for letting me borrow it. He has a second machine with a missing Return key, so I suggested he let me do the caps and source a replacement key switch and key cap. This one has a WE ROM/RAM board and when I went to pick it up, it wasn't completing the POST (continuous low beep). I reseated the chips on the expansion board and it seems to work okay now. While I was troubleshooting, the 100n cap decided to blow (I know - I should have replaced them before doing anything else), so I he has 2 smelly Beebs now :oops:. There's just one anomaly - when you power it on the first time, it does the expected POST beeps. If you turn it off and on again with less than 1 minute pause, the first low beep is overlayed with a higher frequency beep - sometimes higher than the second beep.

So, this foray into the Acorn world has become a little bit more involved than just writing a few BBC Basic programs :D

Malc

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Multiwizard
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Re: Hi from Peterborough, CAMBS

Postby Multiwizard » Sun Nov 26, 2017 12:38 pm

Hi Malc,

welcome to this great Forum... :D


Greetings from my little Dutch Acorn Attic, Wim... :-)

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Hi from Peterborough, CAMBS

Postby 1024MAK » Sun Nov 26, 2017 12:45 pm

Welcome on board Malc!

:D :D :D

List your Acorn machine vitals (including Acorn expansions) here :D
Please go now and make your confession here here
You can put yourself on the map by sticking a pin in it at this link :P

Yes, tinkering with hardware is fun.
IMG_5721.JPG
6502 / 65C02 chip testing board complete with a NOP generator!

Yes, I know that there is not a CPU in sight. That's because the ZIF socket (itself plugged into a stamped pin DIL socket) is currently in a Acorn model B computer along with a CPU on test...

Using a separate test board enables easier current (and therefore power) measurements at different clock speeds...

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

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hoglet
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Re: Hi from Peterborough, CAMBS

Postby hoglet » Sun Nov 26, 2017 12:46 pm

NilByMouth wrote:There's just one anomaly - when you power it on the first time, it does the expected POST beeps. If you turn it off and on again with less than 1 minute pause, the first low beep is overlayed with a higher frequency beep - sometimes higher than the second beep.

Welcome!

I have an issue 3 Beeb that does exactly this as well. I put it down to a different batch of SN76489 sound chips that don't initialize in quite the same way on power up.

Dave

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NilByMouth
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Re: Hi from Peterborough, CAMBS

Postby NilByMouth » Sun Nov 26, 2017 2:07 pm

hoglet wrote:
NilByMouth wrote:There's just one anomaly - when you power it on the first time, it does the expected POST beeps. If you turn it off and on again with less than 1 minute pause, the first low beep is overlayed with a higher frequency beep - sometimes higher than the second beep.

I have an issue 3 Beeb that does exactly this as well. I put it down to a different batch of SN76489 sound chips that don't initialize in quite the same way on power up.


His is an issue 4. I would try mine in his board, but it's soldered in.

Malc

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NilByMouth
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Re: Hi from Peterborough, CAMBS

Postby NilByMouth » Sun Nov 26, 2017 2:14 pm

1024MAK wrote:Yes, tinkering with hardware is fun.
IMG_5721.JPG
Yes, I know that there is not a CPU in sight. That's because the ZIF socket (itself plugged into a stamped pin DIL socket) is currently in a Acorn model B computer along with a CPU on test...

Using a separate test board enables easier current (and therefore power) measurements at different clock speeds...



When I built my 6502 board, I didn't think about creating a NOP generator. I had ROM and RAM all wired up before doing any testing. Seems an obvious thing to do as a first step.

Malc

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flaxcottage
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Re: Hi from Peterborough, CAMBS

Postby flaxcottage » Sun Nov 26, 2017 2:28 pm

Welcome, Malc. :D
- John

Currently running Level 4 Econet with BBC B, BBC B+ 128K, Master 128K, 4Mb A3000, 4Mb A3020, 4Mb A4000, 4Mb A5000 dual FDD; UK101; HP41CX setup; Psion 3a, 3mx and 5mx; Z88; TI-58c, TI-59 and printer, HP-16C programmer's calculator

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CMcDougall
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Re: Hi from Peterborough, CAMBS

Postby CMcDougall » Sun Nov 26, 2017 2:36 pm

welcome Malc :)
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DutchAcorn
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Re: Hi from Peterborough, CAMBS

Postby DutchAcorn » Sun Nov 26, 2017 3:07 pm

Welcome to Stardot! Enjoy messing about with 8 bit hardware :D
Paul

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davidb
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Re: Hi from Peterborough, CAMBS

Postby davidb » Sun Nov 26, 2017 4:20 pm

Welcome! :D

cmjones01
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Re: Hi from Peterborough, CAMBS

Postby cmjones01 » Sun Nov 26, 2017 5:09 pm

NilByMouth wrote:There's just one anomaly - when you power it on the first time, it does the expected POST beeps. If you turn it off and on again with less than 1 minute pause, the first low beep is overlayed with a higher frequency beep - sometimes higher than the second beep.

That's normal. The sound before the proper beep is just the cacophony made by an SN76489 which hasn't been initialised yet. There's no hardware reset signal to the sound chip so its registers contain random junk at power up, so the noise it makes is unpredictable. After an off/on cycle the register contents may well be different than from a really cold start so the sound will be different.

Other applications of the same sound chip have the same behaviour. I've got a 'Star Force' arcade PCB which uses three SN76489 chips and that makes odd noises for a moment while the software starts up.

Chris

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tricky
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Re: Hi from Peterborough, CAMBS

Postby tricky » Sun Nov 26, 2017 6:15 pm

Welcome,
I've just been doing a bit of soldering myself (in my usual ham-fisted way) and got the IDC connector upside down again, so no extra sound for me, I'll update my thread when I can get my phone to talk to my PC to upload some photos.

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NilByMouth
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Re: Hi from Peterborough, CAMBS

Postby NilByMouth » Sun Nov 26, 2017 11:55 pm

tricky wrote:I've just been doing a bit of soldering myself (in my usual ham-fisted way) and got the IDC connector upside down again, so no extra sound for me, I'll update my thread when I can get my phone to talk to my PC to upload some photos.


Do you have a desoldering station? Makes removing chips and IDC connectors a lot easier.

Malc

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tricky
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Re: Hi from Peterborough, CAMBS

Postby tricky » Mon Nov 27, 2017 8:10 am

I do have a desolder station, but you haven't seen how I solder idc connectors :lol:
http://stardot.org.uk/forums/viewtopic.php?f=3&t=12869&hilit=mmc#p165772

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NilByMouth
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Re: Hi from Peterborough, CAMBS

Postby NilByMouth » Tue Nov 28, 2017 4:05 pm

tricky wrote:I do have a desolder station, but you haven't seen how I solder idc connectors :lol:
http://stardot.org.uk/forums/viewtopic.php?f=3&t=12869&hilit=mmc#p165772


Works of art!


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