WE 32K RAM Card Repair

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sun Oct 29, 2017 10:14 pm

Nope! :wink: I need to do that.

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trixster
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Re: WE 32K RAM Card Repair

Postby trixster » Mon Oct 30, 2017 6:57 pm

Hey jms2, I can send you my spare cable if you'd like to test with that?
A3020 | A3000 | BBC B + 128K RAM/ROM + 20K Shadow + Pi0 + VideoNuLA
BBC Master Turbo + DC | Atom | A1200 060 | A500 | Jaguar | A420/1
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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Mon Oct 30, 2017 7:18 pm

Thanks for the offer! :D I may take you up on that, but I'll test my cable first - I'm fairly hopeful it should be ok. Dry joints on the board are at least as likely I reckon.

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sun Nov 05, 2017 10:09 am

I've now re-tested the BBC without the ram card but with the rom board only. It works fine. I've also checked out the cable and there are no problems with that either. So the issue must be with either the ram card PCB or the chips on it (excluding the 6502).

As lazarusr found, the soldering isn't great. I've started to study the reverse engineered schematic... Crikey it's a bit complicated! I have not managed to figure out how it works but I note there is an RC clock delay plus use of phi 0, phi 1 and phi 2. I don't understand yet how it 'switches off' main ram as there are no tri-state buffers anywhere...

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Thu Nov 09, 2017 8:08 am

I've reflowed all the joints on the card, and now it works! :D :D

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Thu Nov 09, 2017 3:05 pm

o so it was a bad solder joint after all, glad you got it sorted out.

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1024MAK
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Re: WE 32K RAM Card Repair

Postby 1024MAK » Thu Nov 09, 2017 3:38 pm

And the resoldering of a Watford Electronics PCB of the week award goes to....
























jms2
Well done =D> =D> =D>

Seriously, glad that you have it working okay now. Fancy a bit of reverse engineering to keep you busy... :mrgreen:

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

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Thu Nov 09, 2017 7:19 pm

Thanks very much! :D

I didn't encounter the same bizarre solder problems as lazarusr found, but some of the joints were certainly tricky. I can only describe the solder as "bubbling", ie when melted it kind of boiled, with little bubbles erupting from the surface (usually at a single consistent point). When cooled, the solder joint looked like a tiny volcano. Some of the joints were like this from new, but when re-melted the same effect occurred again.

I fixed them by removing all the solder, adding flux, and starting again. This was needed at about 5-10 places. Everything else was OK.

I've started trying to understand the schematic and I've got a little way with it...

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Thu Nov 09, 2017 7:31 pm

But in the 1st post there is a pdf file http://stardot.org.uk/forums/download/file.php?id=26390 which if you download it you will see there is a schematic for the ram board :wink:
Peter.

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Thu Nov 09, 2017 10:10 pm

vanekp wrote:But in the 1st post there is a pdf file http://stardot.org.uk/forums/download/file.php?id=26390 which if you download it you will see there is a schematic for the ram board :wink:


Yes, that's the one I've been trying to understand! It's interesting...

cmorley
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Re: WE 32K RAM Card Repair

Postby cmorley » Fri Nov 10, 2017 8:06 am

jms2 wrote:As lazarusr found, the soldering isn't great. I've started to study the reverse engineered schematic... Crikey it's a bit complicated! I have not managed to figure out how it works but I note there is an RC clock delay plus use of phi 0, phi 1 and phi 2. I don't understand yet how it 'switches off' main ram as there are no tri-state buffers anywhere...


As previously mentioned... the schematic has been posted on this board before (lasarusr)...
viewtopic.php?t=12299#p156516

From a very quick look at it it inhibits the BBC system memory by gating the phi1 clock with the memory select. As the BBC generates OE (and other things) from buffered phi1 the system memory won't 'reply' for the given address..

It also gates R/!W so no write happens.

Quite an elegant solution but does introduce a further gate delay on phi1 & R/!W which is maybe why the Pi copro's have problems with it an long cables...

Chris

P.S. As for bubbling solder, I have seen that on old Amigas and BBCs. I think it is crusty old flux inclusions in the solder. Remove the solder and re-solder with fresh works best IMO


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