Sinclair ZX80 / ZX81 / Z88 Forums

Also vouching for the ZX8-CCB - I've got them running in boards with the three different ULA types also. In fact (as Moggy and PokeMon will know), the one time I couldn't get a CCB to work, the ULA was faulty

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I'm starting to think my ULA chip is faulty. I've been thinking about getting a replacement and a heatsink. I don't think it's anything to do with the CCB board.
I'll try both monitors again soon and I've got a television with a video in socket I'll try that too.
Cheers Trev

Unless you're using the m/board on an open to air chassis as some of us do I wouldn't waste money on the ULA heat-sink.

As a retired builder of studio and stage audio amps heat sinking is something I have knowledge of and quite frankly in a closed system like the zx81 (yes I know it has vent slots at the bottom and holes in the side) with no ambient/cool air throughput and a nice big regulator plate raising the internal temperature even more, all that will happen is that within a short period of time the heat sink will reach thermal equilibrium with the ULA and, will at best do nothing as there is no moving air current to remove the heat from the now hot heat-sink, and at the worst may even reflect heat back into the chip at point of contact.

I know others will disagree which is cool but to my mind it's a physiological peace of mind thing, hoping to preserve a rare zeddy chip.

When ever a customer of mine requested that no heat sinks be showing externally we always had to resort to fan cooling, like computer CPU/chip-set fans as internal heat-sinking alone in a sealed system always ended badly.

I can confirm that it was the ULA chip causing some of the problem. I now have a replacement and your board is working really well.
Cheers Trev

Thanks for reply and coming back to that issue. And good that you were able to solve it.

I just wanted to thank PokeMon for such a great value piece of kit. I've returned to the ZX81 after a 35 year break. The ZX81CCP is easy to fit and provides an excellent picture on a modern display. I'm so impressed that I've just ordered another to fit to my DK-Tronics keyboard equipped machine.

It's people like PokeMon who keep the scene alive.

As there have been questions about adjusting the trimmers I will give following advices and two pictures.

* use very small screw drivers as used for watches
* don't use a crosstip screwdriver but a slot screwdriver instead
* turn the trimmers carefully with not much force
* it is possible to turn them around but not recommended in any way (there is a stop which could be felt when turning softly/gentle)
* most times adjustment is needed for R2 only (pixel trimmer) and visible on screen for about only 15 degree of 300 degrees all in all
* if a cursor is seen but unsharp or only slightly - then adjustment can be done with +/- 5 degree to find optimum sweep point

Most easy to adjust with using an old CRT monitor/TV, when using an LCD it should be calculated that there is a delay until the screen is shown - can be 1-3 seconds depending on model. The reason for that is, that modern LCDs don't show a picture at all if the signal is invalid and need some time to detect a valid signal again. When the pixel trimmer is wrong settled than it can disturb the horizontal sync signal which makes the video signal invalid. In that case it is recommended to do just a roughly setting in 1 hour steps when imaging a clock for the trimmer shown in the picture below. So try from 10 to 2 while avoiding 11,12,1. Wait a few seconds to see result on LCD TV. When cursor is seen or signal valid it can be optimized by very slightly moving it to left or right.



And here are some pictures for the proposed tools to adjust.
As you can see from the watch tool screwdriver set it is even not the very smallest driver but the second (would even work with the smaller one). Avoid using crosstip / Philips drivers as they can not get deep enough into the "hole". It may look like a crosstip to be used but a slot screwdriver is recommended.
One last hint: It is recommended to use a plastic screwdriver if available but could be done with a metal screwdriver as well. Keep in mind that the extra resistance/capacitance through your body would influence the sweep point a little bit, so can be changed when removing the screwdriver but can be corrected manually a little bit afterwards to have a non perfect optimized picture when touching the screwdriver and will get perfect when removing it again.

It sounds maybe much more complicated as it is in reality. It is not that hard but I tried to describe it as close as possible.

Pokemon - Are you still selling the ZX8-CCB boards/kits?

If so, how would I go about purchasing one?

Yes, please let us know when they are available again. I have two ZX81's with 184 ULA I can't use...

Planned to be available again in about 2 weeks.