Sinclair ZX80 / ZX81 / Z88 Forums

I forget which wire I used. Most likely 0.63mm dia or 0.9mm dia solid tinned (silver in colour) wire. The 0.9mm is better. If you have any spare off-cuts of telephone cable, or network cable (the type used for fixed wiring), strip the insulation off and that should do.

I use fine round-nose pliers to form the curles in the wire - makes a better stronger joint.

Also note that whichever way you do it, you will need something to temporarily hold the DC-DC converter/regulator in position while soldering.

Yes, the ROM chips arrived okay. Currently sitting in my "recently received pile"

Mark

Thanks Mark. I'll have a look but I have had a clear out recently (well, a couple of years ago) so may struggle with the those - I think I only have flexible cable knocking around.

On another note I bought some caps for the zeddy and the 1uF cap has no obvious polarity markings (again, I know).

Any ideas or have I wasted a few pence?

Lardo

Lardo Boffin wrote: ↑Fri May 12, 2017 8:16 pm On another note I bought some caps for the zeddy and the 1uF cap has no obvious polarity markings (again, I know).
Any ideas or have I wasted a few pence?

Usually the shorter lead is the "minus". And perhaps that is what the (M) marking means in the second picture.
But... don't quote me on this one.
Another option would be to measure voltage across the leads. Usually electrolytic caps have the tendency to build up some charge due to their chemical nature. Even though they are not connected to anything. You could try with a multimeter.

Long lead is positive. Saying that, not all electrolytics are polarised.

The 'NP' marking indicates that it may be a non-polarised electrolytic capacitor. What did the description in the listing from where you bought it say?

Non-polarised electrolytic capacitors can be fitted either way round. They are intended for AC circuits (e.g. audio), but should work okay in a Zeddy.

If you don't have any wire, some component lead off cuts may do. The best are the leads from rectifier diodes, or resistor leads (where they use the thicker gauge wire, not the thin leads)

If you are really struggling, I can send some wire to you.

Mark

1024MAK wrote: ↑Sat May 13, 2017 12:50 am The 'NP' marking indicates that it may be a non-polarised electrolytic capacitor. What did the description in the listing from where you bought it say?

Non-polarised electrolytic capacitors can be fitted either way round. They are intended for AC circuits (e.g. audio), but should work okay in a Zeddy.

If you don't have any wire, some component lead off cuts may do. The best are the leads from rectifier diodes, or resistor leads (where they use the thicker gauge wire, not the thin leads)

If you are really struggling, I can send some wire to you.

Mark

Hi Mark. Sorry managed to miss your post on this one. Busy week!

It was this one:-

http://uk.farnell.com/multicomp/mcnp100 ... 7-00001003

Suspect I may have shown my electronic ignorance again...

I have found various bits of wire now thanks, some of which may suit. Just got to find time to use them!

As an aside what parts do I need to buy for the RAM mod (16k, your process). A socket should be fairly straight forward but not sure about the RAM chip.

Thanks as ever!

Yep, that's a are non polarized electrolytic type.

The RAM is a 32k byte x 8 bit (256k bit) 28 pin DIL chip (we use half, as you will not find a 16k byte chip). The normal type number is 62256.
Farnell currently offer these.
I would either go with an older chip if you have one (or find a working cheap one elsewhere), or buy the CYPRESS SEMICONDUCTOR CY62256NLL-70PXC chip. One person has reported a problem when using a modern SRAM chip in the past. But I don't remember where.

Edit: found the thread where there was a problem, it's here.

Mark

But that was a CMOS CPU not a CMOS RAM that caused problems
Reichelt offers these at 1,60€:
https://www.reichelt.de/DRAM-FRAM-SRAM/ ... ARCH=62256

Paul wrote: ↑Thu May 18, 2017 2:48 pm But that was a CMOS CPU not a CMOS RAM that caused problems

Yeah, my memory forgot that. Having posted the comment about one person having a problem, I thought it best to go back and edit my post to link to the whole thread.

Thanks for clarification though.

Mark

That's the caps done. Nothing expoded so thanks for the polarity advice!

Next up to order some RAM chips and do the memory mod when I am brave enough!

As an aside the longer legs I cut off the caps look like an ideal size to make the 'bridge' for the regulator and I have plenty of them lying around now.