Ding-Dong my ULA is dead (ZX81)

[abaffa]

Hi folks,

I'm trying to bring my zeddy back to life but I guess my ULA is dead. I've read all topics about this but I still have some doubts about it.

For example: My ULA has oscilation from the XTAL (6.5mhz) between 3v and 4v on pin 35 but I have zero volts on pin14.

Is it posssible that maybe it's caused by the capacitor and the ula is not reading clock sinal?

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Also... about recreating ULA using CPLD... Andy Rea did a great job and also there is the vLA81 but I could not find any source code or instructions... are there proprietary solutions? Is there some open source solution? I am forever grateful to them for the work but I'm worried 'cos both ULAs are out of stock... we must have some open solution to keep our zeedies running in the future...

[1024MAK]

What do you have on pin 16 of the ULA?

Also, what test gear are you using?

Mark

[Moggy]

If your ULA does end up being found to be dead after following Marks advice, and you still wish to create your own,then both Andy and RetroTechie have details regarding their ULA's available on the forum which a quick search would have lead you to.

Zip files for both ULA's can be found here...

viewtopic.php?f=8&t=1862&start=10#p21120

[abaffa]

What do you have on pin 16 of the ULA?

Also, what test gear are you using?

Mark

Hi Mark,

used probe 10x on pin 35 - getting osc 6.5mhz and min/max about 3v-4v

I've disconnected pin 14 from my board (just lifted the pin) and it's 0v (1x or 10x... nothing)

pin 16 had response but now its 0v also...

[abaffa]

If your ULA does end up being found to be dead after following Marks advice, and you still wish to create your own,then both Andy and RetroTechie have details regarding their ULA's available on the forum which a quick search would have lead you to.

Zip files for both ULA's can be found here...

viewtopic.php?f=8&t=1862&start=10#p21120

Hi Moggy,

yeah... I've read that topic but it's missing details about the PCB... I guess it was on broken links.

The schematic and CPLD code I've already downloaded.

[abaffa]

I'd like to gather all information in one place and with simple details (maybe create a gerber file), so that everyone could build ur own.

But also, crediting authors and with their authorization.

Another way is for me to create my own project but it should take longer. If those who already did it could help I would be very grateful (and the zeddy community too)

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I know there are many informations about testing ULA and building one but I am committed to gathering all the information in one place for everyone to consult (crediting original authors). - This is my quest

[1024MAK]

The older ULA replacements based on CPLDs are obsolete due to the CPLDs becoming hard to get, or end of line.

The production of Charlie Ingley’s vLA81 is being limited due to the COVID-19 Corona virus outbreak rather than anything else.

Okay, it’s not looking good for your ULA. But before condemning it, first off, if it’s soldered in, check every pin for dry joints, broken/cracked tracks. If it’s in a socket, as well as checking for for dry joints, broken/cracked tracks, also check the pins of the chip are clean, and that the chip pins actually make contact with the contacts in the socket. Both by visual inspection and by testing with the power off using the continuity range on your multimeter.

One other thing to keep in mind, although you are using a X10 probe with your ‘scope, the master oscillator pin (35) is very sensitive and the slightest loading can disrupt the oscillations.

Mark

[1024MAK]

But also, crediting authors and with their authorization.

Once you are able to send private messages (PMs), you can try to contact the authors. At the moment, they don’t visit the forum that often, but if they have their account set up to send them a email when they get sent a PM, one or more may respond.

Andy Rea and RetroTechie have already said they don’t have a problem with the available details being available on this forum. But yes you should definitely ask them for permission if you intend on hosting the files and details elsewhere.

I don’t know the status of Charlie Ingley’s vLA projects. You would have to ask him. He’s also a member here.

Mark

[abaffa]

But also, crediting authors and with their authorization.

Once you are able to send private messages (PMs), you can try to contact the authors. At the moment, they don’t visit the forum that often, but if they have their account set up to send them a email when they get sent a PM, one or more may respond.

Andy Rea and RetroTechie have already said they don’t have a problem with the available details being available on this forum. But yes you should definitely ask them for permission if you intend on hosting the files and details elsewhere.

I don’t know the status of Charlie Ingley’s vLA projects. You would have to ask him. He’s also a member here.

Mark

I couldn't find Charlie Ingley on the member list. Could u tell me his username?

[1024MAK]

I couldn't find Charlie Ingley on the member list. Could u tell me his username?

He introduces himself here

Mark