Vertical bands on screen

[Lardo Boffin]

I have just got a zeddy and it is a bit poorly. I believe the ULA is dead amongst other things - I put the ULA in a known working zeddy and it produces a white screen with no cursor.

Having put in a working ULA I get the following:-

IMG_6071.JPG

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I have done the following so far:-

Swapped out the ULA (to get the cursor)
Swapped the Z80
Swapped the ROM
Plugged in a 16k RAM pack to bypass the onboard RAM

The PCB is in lovely condition:-

IMG_6072.JPG

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Could it be the modulator? I haven't had time to fit a ZX8-CCB yet.

Any further suggestions? I don't have a 'scope or anything that sophisticated!

Also there is some of the keyboard strip stuck in the KB2 connector - not me being clumsy! The ribbon was already broken when I opened it. Any suggestions as to how best to remove it without destroying the contacts?

Thanks

Lardo

[sirmorris]

The modulator might have a tiny tuning pot - you could wiggle that. That pattern also kind-of reminds me of a power issue I once had. Do they move or are they static?

[Moggy]

I have had black banding albeit horizontal when the power supply or regulator is giving up the ghost so assuming a good power pack the only thing I can suggest,Lardo is to multi meter the regulator and check for a steady 5volts, taking care not short anything.

As for the broken ribbon try using two jewellers screwdrivers of the smallest size if you posses them in a pincer like fashion to tease the cable up taking care not to damage the contacts.

[Lardo Boffin]

The modulator might have a tiny tuning pot - you could wiggle that. That pattern also kind-of reminds me of a power issue I once had. Do they move or are they static?

They are pretty static - I am using a good quality power pack and will replace the regulator with a new one.

I have never wiggled the modulator before! Very liberating. I tried various setting and after re-tuning the telly got this:-

image.jpg

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It is an early ULA I am using so a black output is not unexpected I guess. Maybe a combination of composite mod and new regulator will sort it. I will find out when I have time to dust off the soldering iron!

I also need to find out where I can buy a reasonably priced ULA! If there is such a thing these days.

Lardo

[Lardo Boffin]

I have had black banding albeit horizontal when the power supply or regulator is giving up the ghost so assuming a good power pack the only thing I can suggest,Lardo is to multi meter the regulator and check for a steady 5volts, taking care not short anything.

As for the broken ribbon try using two jewellers screwdrivers of the smallest size if you posses them in a pincer like fashion to tease the cable up taking care not to damage the contacts.

I have a set of jewellers screw drivers so will give it a go. I managed to do similar before (my fault that time) and stuffed up the connector in the process - I bent one of the contractors back. Had the replace the whole connector which was a pain.

Edit - removed the last remaining bit with no damage!

[MaFli]

I also need to find out where I can buy a reasonably priced ULA! If there is such a thing these days.

Lardo

You can try here: viewtopic.php?f=8&t=2386
Not sure if these are already sold, but you could give it a try!

[Lardo Boffin]

I also need to find out where I can buy a reasonably priced ULA! If there is such a thing these days.

Lardo

You can try here: viewtopic.php?f=8&t=2386
Not sure if these are already sold, but you could give it a try!

Thanks. I had seen those a while ago but at £28 each I was hoping to find something a little cheaper if possible!

[gozzo]

£28 each is far too expensive, especially as they are not fully tested and seller wont give refund if found partly duff..

[gozzo]

your machine has the earliest ula and this is lacking the 'back porch' part of the signal, so WILL give poor dark picture on a colour tv, even if its perfectly ok... it will usually be ok on a black & white set..the zxvid or zxccb will cure it by adding the back porch..dont worry too much about the 'bands' at the moment, they will most likely also disappear with a zxvid /zxccb

[Lardo Boffin]

Having fitted a ZX8-CCB all is well. I now need to tune it in properly and find a replacement ULA.