WE 32K RAM Card Repair

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Fri Oct 06, 2017 5:14 pm

Would seem the cable from the 6502 socket to the ram board if faulty, if I move the board the BBC crashes, would guess it’s a bum connection on one of the crimp's connections of the ribbon cable :(

As I suspected it was the crimping of the ribbon cable going to the ram board, after gently squeezing the 40 pin plug to recrimp the cable (with a pair of pump plyers) seems to have fixed the problem for now, I can move the board and tap it without the BBC crashing, so maybe something to look at if you’re having problems with getting your ramboard working :wink:

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sun Oct 15, 2017 5:46 pm

I'm underway with repairing my "32k Ram card" BBC now. I'd just got the machine working fine without the ram card, but then some magic smoke came out! This was a surprise because I'd already recapped the PSU (back in about 2001 I think). I reckon that at the time I only replaced the affected cap (C2). Now its C1 which has popped. Now fixed. :D

The ribbon cable for the RAM card is definitely the culprit - at one end, the header wasn't properly attached to the cable and I discovered my attempts at repair from 2001, which were to cut tiny holes in the insulation next to the pin and solder them together. At the time this worked, but it didn't prove reliable (as you might expect).

I've got a question though - if I make up a new cable, what sort of maximum length can it be? At the moment it's about 30cm which makes taking the lid off the machine awkward. However, if I make it longer, could this introduce problems? I guess it's not buffered like a Tube cable...

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hoglet
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Re: WE 32K RAM Card Repair

Postby hoglet » Sun Oct 15, 2017 5:52 pm

jms2 wrote:I've got a question though - if I make up a new cable, what sort of maximum length can it be? At the moment it's about 30cm which makes taking the lid off the machine awkward. However, if I make it longer, could this introduce problems? I guess it's not buffered like a Tube cable...

Actually, on the Model B the Tube isn't buffered either.

I would expect that 30cm is getting close to the maximum, but it will all depend on what else you have in the Beeb. Modern gadgets (like Matchbox Co Pro) are much more sensitive to noise caused by crosstalk (from long cables) than the original hardware was.

Dave

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sun Oct 15, 2017 6:32 pm

There's a massive Watford 12-rom board in there, plus a 1770 daughter board. Sounds like I should be abandoning hopes of making it easy to get the lid off!

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MartinB
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Re: WE 32K RAM Card Repair

Postby MartinB » Sun Oct 15, 2017 7:02 pm

The advantage that the Tube, the 1Mhz Bus, the disc interface and indeed most ‘designed’ IDC ribbon cable-based interfaces enjoy, is that the active signal lines are interleaved with 0v (reference ground) lines and this reduces the potential for significant crosstalk on longer cable runs. ‘Evolved’ adaptor cables that re-host the cpu or roms etc. tend to lack this feature and so such enhancements are much more likely to be sensitive to cable length. There are of course other significant factors, not least the signal characteristics themselves where for example fast edge rise-times are a big contributor.

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trixster
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Re: WE 32K RAM Card Repair

Postby trixster » Sun Oct 15, 2017 7:42 pm

jms2 wrote:
KenLowe wrote:
jms2 wrote:Col's right - the card is useless really.

I disagree. As Trixter has already posted, Lancelot and a number of other Level 9 games relied on both shadow and sideways ram to get the full visual experience.

I'm keen to try those out once I have fixed it. :D


I bought a WE ram card just to play Lancelot! I remember reading the review in The a Micro User (Jan 89, same issue as Exile) and being blown away by the graphics. Sadly dad never upgraded the Beeb with shadow and sideways ram so I just stared at the advert for the game and wistfully wished for an Amiga!
image.png
image.png
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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KenLowe
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Re: WE 32K RAM Card Repair

Postby KenLowe » Sun Oct 15, 2017 8:32 pm

trixster wrote:I bought a WE ram card just to play Lancelot! I remember reading the review in The a Micro User (Jan 89, same issue as Exile) and being blown away by the graphics. Sadly dad never upgraded the Beeb with shadow and sideways ram so I just stared at the advert for the game and wistfully wished for an Amiga!

I was also the sole motivation for me to add BBC+ & IntegraB support to BeebEm!

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sun Oct 15, 2017 9:09 pm

Just measured the old ribbon cable. It was 25.5cm long before I chopped the dodgy bit off the end. Now its 24cm. This is long enough to be able to assemble the machine (I think) but it's not ideal for getting the lid on and off. I guess that's not really a show stopper though.

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Thu Oct 19, 2017 7:32 pm

Received new cable and 40 pin dip plugs [img]
20171019_210352s.jpg
[/img], can now make up a new cable for the ram board, just got to work out how I am going to crimp the cable in the plugs without damaging the pins :wink:
Peter.
Attachments
20171019_210352s.jpg

johnkenyon
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Re: WE 32K RAM Card Repair

Postby johnkenyon » Thu Oct 19, 2017 7:44 pm

vanekp wrote:Received new cable and 40 pin dip plugs [img]20171019_210352s.jpg[/img], can now make up a new cable for the ram board, just got to work out how I am going to crimp the cable in the plugs without damaging the pins :wink:
Peter.


Insert the pins into one or more pieces of veroboard/perfboard so that the pressure is on the bottom of the connector, not the pins.

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Thu Oct 19, 2017 8:37 pm

Ahhh thanks thats a good idea :)

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Thu Oct 19, 2017 9:49 pm

How long do you plan to make your cable?

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Fri Oct 20, 2017 5:21 pm

I was thinking as short as possible would be a good idea as I find the original cable rather long.

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Fri Oct 20, 2017 6:01 pm

... and how long would that be? :lol:

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1024MAK
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Re: WE 32K RAM Card Repair

Postby 1024MAK » Fri Oct 20, 2017 7:13 pm

jms2 wrote:... and how long would that be? :lol:

Longer than too short?

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

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Fri Oct 20, 2017 7:27 pm

LOL

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Fri Oct 20, 2017 10:18 pm

Ha ha, yes OK I'm not really making myself clear I admit!

What I was getting at is trying to understand what cable lengths are in use, and what you consider to be too long, because I was originally contemplating fitting a slightly longer cable.

In reality I'll probably go down the "short as possible" route as well, I was just curious.

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Sat Oct 21, 2017 6:24 am

The original cable that is on there is 17cm but I don't see the need for it to be so long and think I can get away with one around 8cm long (about half the length), long enough that you can lay the board upside down in the BBC and also be able to get to the CPU socket to insert and or remove it.

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sat Oct 21, 2017 7:20 am

Crikey, even 17cm is radically shorter than the cable in mine. Bearing in mind that:

1. Mine has been unreliable (probably due to poor connections, but you never know).
2. Problems with the PiTube have been reported with a longer cable on the ram card.

... I'll see if I can shorten mine from its current 24cm. I've got a 12-rom board that the cable needs to snake around, but the real issue is that the board is mounted (upside down) on the case lid on those adhesive post things, so when removing the lid I can only lift it a short distance - and then have to struggle to get the board off the posts. this essentially drives how short the cable can be.

I wonder if I can mount it off the rom board instead, which would solve all these issues.

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Sat Oct 21, 2017 8:56 am

Well I think mine is original and I still find it far too long the length is going to make a difference on the speed and also you get introduction of noise across data lines, so it seems logical the shorter it is the less cross talk you will get between the wires.
I guess your idea of mounting it onto your rom board is a good idea, only don't know if it will then all fit in the case and that may be the reason that the cable was made longer to put the board elsewhere still don't think it’s a good idea.
And to do what your suggesting you would then have to remove the socket from the WE 32K ram card and put a extended socket to plug it directly into the ROM board and the ram card would have to be sitting with the chips facing up, won’t be an easy job, but it’s doable if you have the skills.
Here is a pic of my RAM card you can see the cable length (ruler)

20171021_104545.jpg

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sat Oct 21, 2017 1:07 pm

Unfortunately mounting it directly into the 6502 socket using some kind of extender is not an option. The 12 rom board entirely masks the 6502 socket. And there is also a 1770 interface nearby as well, so it's like threading a needle.

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Sat Oct 21, 2017 2:07 pm

Yes I gathered that and meant to plug the ram card with a fitted raised socket into the rom card, which I assume has a place for the 6502 to normally plug into. only not sure it will all fit under the cover like that.

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sat Oct 21, 2017 4:41 pm

Good idea, but unfortunately the rom card does not have any interaction with the 6502 socket. it plugs into the OS rom socket and the serial chip socket IIRC.

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vanekp
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Re: WE 32K RAM Card Repair

Postby vanekp » Sat Oct 21, 2017 5:26 pm

Ahh okay I though it was a rom board that plugged into the CPU socket as I use to have one like that... My bad :)

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jms2
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Re: WE 32K RAM Card Repair

Postby jms2 » Sat Oct 21, 2017 10:35 pm

I have come up with a plan... I think using double sided sticky pads it will be possible to stick the ram card upside down on top of the rom board.

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trixster
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Re: WE 32K RAM Card Repair

Postby trixster » Sun Oct 22, 2017 1:46 pm

That's similar to what I've done. I've insulated the topside of the WE card and it lays over the ram. This allows for a short cable run from the 6502 socket to the WE card.
A3020 | A3000 | BBC B + 128K RAM/ROM + 20K Shadow + Pi0 + VideoNuLA
BBC Master Turbo + DC | Atom | A1200 060 | A500 | Jaguar | A420/1
A4000/040 060 | Atari Falcon 060 | Saturn | PS1 | SNES | CPC6128 | C64 | 3DO | MD


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