Changing the ZX81 ULA, newbie question

[sl07h1]

Hi guys, I have a ZX81 that have an old ULA (ULA2C184E) and I have problems connecting it to all TV sets I have, I get a very dark, blurry and noisey image, you can barely see something turning the bright all the way up. I learned that there's an issue with this ULA that hasn't this "back porch" thing in the video signal and newer TV's can't tell black from white. I got an ULA2C210E, I want to replace it and I have some questions:

1. The new ULA is a Ferranti chip and comes with a heat sink. The ULA I have now has no heat sink. I guess that I should install it with the heat sink, but I find this a little strange, the new ULA gets hotter? Why the difference? There are voltage differences or something? or maybe the heat sink is not really necessary?

2. Is there another thing I should have in mind to replace the ULA given this differences (if they exist)? or it should be just like remove the old, and put on the new in the socket with the heat sink and that's it? or there's more to do?

3. Besides the video thing, what other differences are between these 2 ULAs?

Thanks in advice!

[mrtinb]

Someone sold you a ULA and a heat sink.

Sinclair ULAs always turns hot, so someone insists on putting a heat sink on. This has been a huge disagreement in this forum, so we don’t want to start that again.

The advocates against the heat sink is that there is no air flow in the small case, so the heat on the heat sink cannot get away. Thus the heat sink preserves the heat instead of removing it.

[1024MAK]

Hi guys, I have a ZX81 that have an old ULA (ULA2C184E) and I have problems connecting it to all TV sets I have, I get a very dark, blurry and noisey image, you can barely see something turning the bright all the way up. I learned that there's an issue with this ULA that hasn't this "back porch" thing in the video signal and newer TV's can't tell black from white.

Yes, the first two ULA versions do not include circuitry to produce the part of the video signal known as the ‘back porch’. Black and white CRT TVs (which the ZX81 was intended to work with) don’t care about this. But a lot of colour TVs use the ‘back porch’ part of the video signal to calabrate their circuits to the normal black video level. Hence as the first two ULA versions don’t produce the correct signal at this point of the video signal, the TV calibrates to the wrong level. This completely messes up the displayed image.

The last ULA version does generate the ‘back porch’ part of the video signal. Or there are circuit modules that can be added that also generate the ‘back porch’ video signal.

I got an ULA2C210E, I want to replace it and I have some questions:

1. The new ULA is a Ferranti chip and comes with a heat sink. The ULA I have now has no heat sink. I guess that I should install it with the heat sink, but I find this a little strange, the new ULA gets hotter? Why the difference? There are voltage differences or something? or maybe the heat sink is not really necessary?

Sinclair Research did not supply or fit heatsinks for ANY ULA in any of their computers. ULA chips use a technology that results in them running warm and this is normal. The ULA2C210E does not run hotter than the previous two versions. I go into greater detail about all of this elsewhere on this forum. This post being the most recent, and it contains links to other posts where the subject is discussed.

2. Is there another thing I should have in mind to replace the ULA given this differences (if they exist)? or it should be just like remove the old, and put on the new in the socket with the heat sink and that's it? or there's more to do?

Leaving the argument about the heatsink to one side, you can just remove the existing ULA and put the replacement in. The later version is backwards compatible with the previous versions.

Is the ULA soldered on your ZX81? Or in a socket?

3. Besides the video thing, what other differences are between these 2 ULAs?

Nothing significant. It was Sinclair policy to make the minimum changes.

Mark

[sl07h1]

Is the ULA soldered on your ZX81? Or in a socket?

The ULA is in a socket, so it would be very easy.


So, I will put the ULA without the heat sink and see what happens.

Thanks guys!!

[1024MAK]

Do extract the existing ULA carefully, using a flat blade screwdriver or blunt knife. Lever up each end a bit at a time, and keep a finger on top of the chip, but lever between the plastic of the socket and the chip, not against the PCB (you don’t want to cause any track damage). If you are too energetic or you try to use a IC removal tool, there is a great risk of bending or breaking one or more of the chip pins at one end of the chip.

As you are removing a working ULA chip, these have value. You can either use it as a spare, or sell it. Definitely don’t bin it.

Mark

[Moggy]

Couldn't resist sorry!

[sl07h1]

Do extract the existing ULA carefully, using a flat blade screwdriver or blunt knife. Lever up each end a bit at a time, and keep a finger on top of the chip, but lever between the plastic of the socket and the chip, not against the PCB (you don’t want to cause any track damage). If you are too energetic or you try to use a IC removal tool, there is a great risk of bending or breaking one or more of the chip pins at one end of the chip.

As you are removing a working ULA chip, these have value. You can either use it as a spare, or sell it. Definitely don’t bin it.

Mark

Ok, I will have that in mind, thanks for the tips.

Couldn't resist sorry!

[sl07h1]

I was reading the posts about the heat sink, my gosh! It's really a controversial / sensitive subject in this forum

[Moggy]

No not at all sl07h1 no one here has ever fallen out over anything in fact this is probably one of the most friendliest retro forums out there.

Occasionally I get on my high horse over something then there is a bit of argy bargy, a bit of to and fro as it were but fall out never.

Life's too short and there is too much going on in the world at the moment to fall out over an old computer.

Also as Mark has said do hold onto that other ULA because when used with one of the many composite video boards available that provide the back porch it suddenly becomes very precious I have at least three that are using the older ULA/comp' board combination and they work very well.