Refurbing an issue one zeddy

[Lardo Boffin]

My zeddy now has 16k of RAM!

It turns out desoldering the existing RAM was significantly easier than trying to cut the tracks with a craft knife and screwdriver...

I also learnt the hardway that I needed to make a bigger allowance for the cable underneath that goes near the screw hole - I allowed for the hole but not the material of the case where the screw fits. Had to shape it to fit!


So it now has:-

16k of RAM
New power regulator (badly soldered in - first one I did)
New capacitors

IMG_6316.JPG

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I have not had chance to test it thoroughly but it takes a few extra seconds to switch on and I can just about make out (ZX8-CCB required) DIM A(3000) working so looking good.

It still needs:-

New keyboard
ZX8-CCB (hoping for some to come on sale soon!)

But these are both pretty trivial to apply (get me!)

Thanks to all who passed on their knowledge.

Lardo

[1024MAK]

Well done

Mark

PS, next, the why wait mod? Link #1, link#2, link#3

[Lardo Boffin]

Well done

Mark

PS, next, the why wait mod? Link #1, link#2, link#3

Just when you thought it was safe to go back into the water...

Looks interesting though! What do I need to buy for this one? Answers aimed at the idiot level please...

[Lardo Boffin]

Well done

Mark

PS, next, the why wait mod? Link #1, link#2, link#3

Hi Mark

Having read the threads a few times would I be right in saying I need to do the following: -

WhyWaitMod.JPG

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Desolder R1 from point 2 to point 1. Do I need to remove the modulator to get to the ground? I can just see a small amount of it exposed.
Solder new transistor TR3 pin C to pin B of TR1 (point 3)
Solder new transistor TR3 pin B to pin C of TR1 (point 4)
Solder new transistor TR3 pin E to new resistor R35 (point 5)
Solder new 10K resistor R35 to motherboard (point 6)

I assume C2 is not affected by this work?

What are the part numbers for the transistor and resistor? Looking on CPC a 10K resistor gives a number of matches and I cannot find the transistor at all based on the part number PN2907A (or NTE2362 from the second link). Not having a working knowledge of this stuff I have no idea what the modern equivalents are.

Many thanks!

Lardo

[gammaray]

http://sinclairzxworld.com/viewtopic.php?f=7&t=1935

See if this helps you should be able to find one.

There is not a PNP from the manufacturer of the OEM transistor onboard for TR1 (I forget the company name) I looked trying to make the upgrade more authentic...

nte2362.jpg (74.01 KiB) Viewed 4630 times

[1024MAK]

I've found where I posted some pictures and there are some additional details - follow the link, follow, follow the yellow brick road link
(sorry, brain failure, just done a night turn...

It would be better if a transistor with a fast turn off time is used, but PNP plastic types like this are hard to find
I used a BC307 because it was not too high a gain, and I had some in my spares stockpile

I have an idea on using another type, but I would like to test it first, and it's waiting behind other projects at the moment...

Mark

[1024MAK]

Having read the threads a few times would I be right in saying I need to do the following: -

Desolder R1 from point 2 to point 1. Do I need to remove the modulator to get to the ground? I can just see a small amount of it exposed.
Solder new transistor TR3 pin C to pin B of TR1 (point 3)
Solder new transistor TR3 pin B to pin C of TR1 (point 4)
Solder new transistor TR3 pin E to new resistor R35 (point 5)
Solder new 10K resistor R35 to motherboard (point 6)

I assume C2 is not affected by this work?

What are the part numbers for the transistor and resistor? Looking on CPC a 10K resistor gives a number of matches and I cannot find the transistor at all based on the part number PN2907A (or NTE2362 from the second link). Not having a working knowledge of this stuff I have no idea what the modern equivalents are.

1. R1 details - correct. No need to remove the modulator. Do need a powerful iron though.
2. Too early(late) for my brain to confirm the transistor pin-outs - will check later...
3. 10k ohms resistor - yes correct. Any 1/4W carbon film, or 250mW/400mW/600mW metal film type, 1%, 2% or 5% type will do
   I can send you a 10k resistor and a BC307 transistor if you want.
   Or later I can browse CPC...
4. No capacitors are harmed in the making of this modification. Absolutely no testing on farm or native wild life animals. Only tested on humans...
5. Ahh! Yes, don't bother looking for those transistors, I tried a few years ago. I went for a BC307 to see if it worked. It does. Not sure if the Zeddy is as fast as Wilf's, but then I forgot to test the ZX81 before the mod. After the mod, the ZX81 is faster than another issue 1 board that I tried, when running a BASIC test program.

Mark

[Lardo Boffin]

Hi Mark

If you can let me know the modern equivalents that would be great thanks!

I suspect it may be a while before I give this one a go - my soldering iron is only a 40w cheapie.

Lardo

[gammaray]

I looked up a cross reference and there are no exact ones for parameters

I am US and am able to get NTE2362...

Remember has to be a switching PNP...though I bet most any will do. $5 down!

nte2362 crossref.jpg

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[Lardo Boffin]

I looked up a cross reference and there are no exact ones for parameters

I am US and am able to get NTE2362...

Remember has to be a switching PNP...though I bet most any will do. $5 down!


nte2362 crossref.jpg

I did see one 2362 for sale on eBay but was put off by the cost of postage from USA.