ZXpand and the ZXpand-AY Sound Module wobble?

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djp
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ZXpand and the ZXpand-AY Sound Module wobble?

Post by djp »

I own a refurbished ZX81 along with a ZXpand and the ZXpand-AY Sound Module. It's a rather flaky set up as I continually have issues with the "white screen of death" (a term I learnt from the forum! ;)). The ZXpand and the ZXpand-AY Sound Module are enclosed in a replica Memotech case. I've used contact cleaner on the connections, which is nice and tight and also added some Blu Tack between the case and the ZX81. This does seem to have improved things. My worry is, while searching for answers to my problem in the forum, I came across the following comment:-
by PokeMon » Sat Jan 12, 2013 9:32 pm wrote:Many people think it comes from the connector and avoid external ram packs. The same people use the ZXpand beyond doubt and without any problems I think.
I realise this was written over 6 years ago, but I just wondered if I should be experiencing any issues at all with the ZXpand and the ZXpand-AY Sound Module, taking into account the above quote?

:?
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1024MAK
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Re: ZXpand and the ZXpand-AY Sound Module wobble?

Post by 1024MAK »

Can you see the wings of fly moving in real time with your eyes? The answer is no.

With any mechanical connector where movement is possible, like the expansion port edge-connector, it is possible for movement to cause one or more of the contacts to momentarily break for a very short time. Far too briefly for a human to notice, but long enough to affect the electronics.

PCB cards with special “edge-connector” contacts were originally designed for rack mounted systems, to mate with a edge-connector socket mounted at the rear of the rack. The cards fit into slides at the top and bottom, or on either side. And are often held in place with a screw or other mechanical fixing so that they cannot move. These are very reliable.

But on a home computer, where there are no mechanical fixings, the edge-connector ends up being a pivot point.

Blu-tack is good. A long strip of foam backed, double sided sticky tape is better ;-)
Oh, and the edge-connector contacts need to be completely clean.

The Sinclair 16K RAM pack was worse, due to its shape and dimensions.

Mark
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Re: ZXpand and the ZXpand-AY Sound Module wobble?

Post by mrtinb »

I’ve started replacing the edge connectors with stackable pin-headers, like we know from Arduinos. They are more tight. Unfortunately 20-pin stackable pin-headers are rare, and thus more expensive.
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djp
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Re: ZXpand and the ZXpand-AY Sound Module wobble?

Post by djp »

Thanks for the responses Mark and Martin.
by 1024MAK » Tue Oct 15, 2019 11:24 pm wrote:Blu-tack is good. A long strip of foam backed, double sided sticky tape is better ;-)
The long strip of foam backed, double-sided sticky tape sounds like a plan!
by mrtinb » Wed Oct 16, 2019 4:19 am wrote:I’ve started replacing the edge connectors with stackable pin-headers, like we know from Arduinos. They are more tight.
Clever stuff! Have to admit, just using double-sided sticky tape will stretch my abilities! ;)

To be honest, I'm more than happy to accept the limitations of using the expansion port. I just wanted some clarification as to whether or not my experience was common. I never had the good fortune of owning a ZX81 back in the day. I'm now a proud owner of one, along with a 48K ZX Spectrum and BBC Micro, Model B. Have to admit, it's the ZX81 that has had the most use, despite it's limitations. I think it's the fact that something with such limited resources can manage to amaze so much in relation to what it can achieve. :shock:

Once again, thanks for the advice guys.
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Re: ZXpand and the ZXpand-AY Sound Module wobble?

Post by Moggy »

I have three xpands with AY and 2 xpand+ and the ONLY time I get the white screen thingy is when the SD card Isn't inserted firmly enough (or I'm stupid enough to knock the workbench!)

The xpand + seems especially prone to this and pulling out the SD card then a firm push back into place cures it for me.

My spands are used 7 days a week primarily the AY ones which I use for studio recording and I find that cleaning the ZX81's edge connector once a fortnight with alcohol and cotton buds is also beneficial.

One point worth noting is that onboard the spand is a small regulator chip and when used with the standard Sinclair power pack this gets very hot especially in an enclosure like the one you are using and may actually be cutting put under high temperature. If possible try and source a good quality regulated power pack of suitable current capacity (2amp at least) preferably with a 7.5v out-put so as to spare the tiny regulators feelings and make for more stable running.

This is more pertinent for the spand + which has two such regulators onboard and when used with the Sinclair power pack they get uncomfortably hot and to be frank I cannot see them having a long life span when used with said power pack.
Using the aforementioned 7.5v unit makes them much cooler in operation.

I would finally add that without the enclosure the spand is much more stable mechanically as it doesn't touch the work surface and has a fairly tight connection, so a key press tends not to cause a flexing between the spand and the edge connector whereas with the enclosure which I believe touches the work surface there will always be a slight flexing when ever a key is pressed.

I find that because it hangs freely with a fairly tight connector it works in it's favour unlike the old RAM packs which because they also touched the work surface suffered the same flexing problem as described above.
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