Fault finding index

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steve3000
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Re: Fault finding index

Postby steve3000 » Tue Mar 27, 2018 10:18 pm

Bat wrote:The noise from the speaker has certainly decreased since replacing C19 and C20 so it's improved PSU noise filtering.

Great, that's definitely worth knowing about :)

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marcusjambler
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Re: Fault finding index

Postby marcusjambler » Wed Mar 28, 2018 9:59 am

1000uf 16v 105oC axial electrolytic caps


Pretty sure these are radial type required.

Marcus

Bat
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Re: Fault finding index

Postby Bat » Tue Apr 03, 2018 8:02 pm

marcusjambler wrote:
1000uf 16v 105oC axial electrolytic caps


Pretty sure these are radial type required.

Marcus


Hi Marcus,
Yes you're right radial type!
Well spotted thank you :)
Cheers :)

Graeme Roberts
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Re: Fault finding index

Postby Graeme Roberts » Tue Apr 17, 2018 5:57 pm

1. BBC Model B+ 64K.
2. Continuous beep, black / blank screen on power up.
3. Removal of all ROMs except OS / BASIC. Then a sequential piggy backing of a known good 4164 RAM chip at each of the eight RAM positions on the motherboard starting at IC55, then IC56, 60, 61, 64, 65, 66, 67 etc.

Procedure identified IC64 as bad as the machine booted when the 4164 was put on top of this chip as shown below.

IMG_1453.JPG


4. I initially tried removing all ROMs and cleaning legs / pins. I then checked the links to make sure all were present. This procedure will work for one bad chip, however I doubt if it would work for multiple RAM chips that might also be faulty. As the B+ motherboard has no link S25, it's difficult to use the 'switch bank' technique to identify if the problem is in the first or second bank of RAM, unless one of you knows a similar feature that can be used on the B+ range?

Hope this helps.

Graeme.

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marcusjambler
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Re: Fault finding index

Postby marcusjambler » Tue Apr 17, 2018 7:29 pm

Hi Graeme

If you have access to an eprom programmer you can burn Tricky's test ROM that plugs in the OS socket.
It works in a Beeb, B+ and Master.
I've used it to diagnose a B+ RAM issue.

The ROM image is here :
http://stardot.org.uk/forums/viewtopic.php?f=2&t=10268#p139467

Marcus

Graeme Roberts
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Re: Fault finding index

Postby Graeme Roberts » Tue Apr 17, 2018 7:54 pm

Hello Marcus,

I don't have access to an EPROM burner, however I do have an EEPROM burner so I was curious to know what types of EEPROM I could use in a Beeb, assuming a 16K size with 24 pin DIL layout. Do any chips of this type exist? I could then update this machine from DFS 2.10 to DFS 2.26 as well as blow some useful software such as Tricky's test ROM image. Thanks for the tip and the link.

Graeme.

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1024MAK
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Re: Fault finding index

Postby 1024MAK » Wed Apr 18, 2018 1:10 pm

There is a whole thread about using EEPROMs in Acorn computers, so make some lots of time available and go and have a nice long read of this thread :wink:

Dave H. (A member on here) can supply the correct EEPROM chips for a very reasonable price.

Mark
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