Internal 16K mod question

[patters]

I used the GadgetUK164 YouTube video to perform the 16K mod on my Issue 1 since the Tynemouth guide only shows an Issue 3 board. It seems to be ok (I haven't currently got a viable keyboard to try the PEEK confirmation), but I get a K prompt after a little extra delay compared to with 1K of RAM fitted. For that machine, it had a single large ROM chip so the socket which I fitted directly replaced it. I notice that on both of these motherboards the vias through the board for the unused chip positions are generally filled with solder.

I'm performing the same mod for my Issue 3, but this one had two small 512 byte ROM chips. Should I fill in the vias where these chips were before I put the turned pin socket in place? Is there a risk to continuity across the vias without solder?

[patters]

I was forgetting that I could always fill in the holes from the back of the board without the new turned pin socket obstructing , so I pushed ahead with the install without bothering.

Post upgrade the machine seems to work ok - I still get the K prompt after a slightly longer self-test, as expected. The SRAM chips might have only been £1.80 but it feels like I just did £200 worth of labour to install! Next stop WESPI...

Does anyone want to 2 x 512byte RAM chips by the way? The large 1K chip had to be removed destructively unfortunately.

[Lardo Boffin]

Good stuff! I don’t think I have ever filled in the holes and have done maybe 15 or 20 16K RAM mods.

I do this mod from Mark for 16K internal RAM. It is also easy to do 32K this way (if using a vLA81 for example):

http://8and16bit.blogspot.com/2015/08/m ... o.html?m=1

Its also pretty easy to apply to an issue 3. There is a discussion somewhere - will have a look.

Very interested to see a WESPI. I keep meaning to have a go at that one but never find the time.

Edit: 32K mod viewtopic.php?p=36251#p36251

Edit: issue 3 16K mod viewtopic.php?p=26147#p26147

[1024MAK]

If the plated-through holes are undamaged, no, they don’t need filling with solder. The reason that some manufactured boards have them full of solder is because the manufacturer used a solder wave bath to do the soldering instead of hand soldering. This will leave solder in both used and unused plated-through holes and vias.

Mark

[patters]

I had suspected this but confusingly both boards also have plenty of unfilled single vias.

[Moggy]

I've often wondered about the soldering process used since watching a documentary about Timex,Dundee where one of the female assembly line workers when interviewed held up a ZX81 and said everything was hand soldered which seems at odds when looking at the finished product.

[1024MAK]

There is no way that anyone who is hand soldering many, many boards a day is going to solder empty pads and vias.

Wave baths may miss some vias, especially if they are coated with solder resist.

Mark

[1024MAK]

I've often wondered about the soldering process used since watching a documentary about Timex,Dundee where one of the female assembly line workers when interviewed held up a ZX81 and said everything was hand soldered which seems at odds when looking at the finished product.

That may have been the case at the start. But with the ever increasing demand, they would have had to move to using some automation at some stage. And moving away from hand soldering would have been the one of the logical things to do if they wanted to continue to be a contractor for Sinclair.

Mark

[Moggy]

Agreed.

[patters]

WESPI first test. I've used the Issue 1 as my test rig but, as posted in another thread, I'm having issues with the composite mod so it's a very dark picture that I have to brighten right up. By fiddling about with the knackered ends of one of my dead keyboard membranes I was just able to type LOAD "" in order to test this. I was expecting the screen to instantly flip to the WESPI menu, but it actually squirts a tape program down the EAR to the machine so you have to wait a few seconds. So neat though...

If you're curious, this is the specific ESP32 dev board I purchased for only £7.59, and you have to option of buying without the pin headers (unwelded) to keep it flatter:
https://www.ebay.co.uk/itm/ESP32-ESP-32 ... 2749.l2649

There are so many variants of these things it was difficult to be sure I had the right one, but as you can see it works. Even this very auction is for multiple different variants - you want the "30pin ESP-32 unweld" which was my order.

For the other components I recommend https://www.switchelectronics.co.uk which had very reasonable shipping charges for small orders and they don't make you buy minimum quantities. You'll need some heat-shrink tubing. Once my keyboard membranes arrive, I'll do a new thread with proper close-up pictures of the build.