Sinclair ZX80 / ZX81 / Z88 Forums

I have an issue one zeddy that I thought I would try and refurb (it's one of too many I bought recently but this one is cosmetically too poor to sell on with good conscience).

I am planning on:-

1) Changing the regulator - done this before but want to do it 'properly' this time though! Last time I cut off the legs of the old one and soldered onto those.

2) Recapping

3) Possibly fitting an internal RAM upgrade. Although the current chip is not socketed so this may be beyond my skills.

I have a question about item 2 - recapping. How do I know the alignment of the existing caps? Below is a photo but the caps only have an arrow on the side rather than positive / negative. I don't want to fit them the wrong way round!

If I was to guess I would assume that the arrow is the positive side but hopefully someone knows for certain?

Thanks

Lardo

The arrow is the negative side

Paul wrote: ↑Fri Apr 28, 2017 2:21 pm The arrow is the negative side

And that is the reason, why there is a very big '-' sign inside the arrow

siggi wrote: ↑Fri Apr 28, 2017 2:34 pm

Paul wrote: ↑Fri Apr 28, 2017 2:21 pm The arrow is the negative side

And that is the reason, why there is a very big '-' sign inside the arrow

And this is why I never actually assume! It never occurred to me that the block inside the arrow was a negative sign.

Clearly this predates the concept of poka-yoke.

Lardo

You can always 'buzz out' the pins with your multi meter. Negative is nearly always ground.

why change the regulator? is it faulty? if not, leave the original in... and as for capacitor polarity..i have come across some that have a + sign within a red arrow , but they were quite old, probably some of the first of that style..?!

gozzo wrote: ↑Fri Apr 28, 2017 4:45 pm why change the regulator? is it faulty? if not, leave the original in... and as for capacitor polarity..i have come across some that have a + sign within a red arrow , but they were quite old, probably some of the first of that style..?!

There is a whole discussion about heat being generated inside the zeddy elsewhere in this forum (it makes interesting reading) and it was considered that the regulator is a major contributor to heat generation. It's certainly my experience that the one zeddy I have replaced it in does not get as hot as the one where I have not.

Lardo

If anyone mentions heat-sinks I shall unleash Brenda the hound from hell!!

Moggy wrote: ↑Fri Apr 28, 2017 5:11 pm If anyone mentions heat-sinks I shall unleash Brenda the hound from hell!!

You just did!!! Stone him!

Touché Lardo consider me stoned.