Got my first ZX, unfortunately not working!

Discussions about Sinclair ZX80 and ZX81 Hardware
Magnus
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Got my first ZX, unfortunately not working!

Post by Magnus »

I'm new to the Sinclair computers and I just bought my first one. I use to read about the ZX-80 / ZX-81, but I ended up with an Atari 400 as my first computer. Now that I have some time to get into the retro computing hobby I thought I'd take a look at these.

I found a Timex Sinclair 1000 on eBay, but unfortunately it looks like it's not in working condition. When I plugged it in after connecting to my TV all I get is an odd black and white pattern on the screen. I never get the reverse K prompt.

I don't know much about these yet, but is there anything I can do to diagnose the problem? From what I've read there's only 4 chips and a handfull of discrete components inside. Any chance I could get her running again? I'd really like to fire it up and load some tapes!

Thanks in advance for any help or pointers :)

Cheers!
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Paul
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Re: Got my first ZX, unfortunately not working!

Post by Paul »

Welcome on Board.
You seem to have taken the First step. Something Appears on your screen.
Next Thing we Need is a Bit more of information. Is the Pattern you get Quite Stable?
Is it fine Lines or rather Big squares (Size of a Charakter) you Might Even Append a Small Photo.
Do you have the Minimum Konfiguration? Do you own a 16k RAM Pack?
The easiest Way of Making Progress is to meet someone near your Location who Might Be able to Test with known good components. What Part of the World do you live in?
Sometimes there are Retro Computing Meetings/Shows. They also have repair Corners.
I Hope you manage to get it Running.
Cu Paul
In theory, there is no difference between theory and practice. But, in practice, there is.
Magnus
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Re: Got my first ZX, unfortunately not working!

Post by Magnus »

Hi Paul :) Thank you for the welcome!

The pattern displayed on the screen seems to be constant for the most part. After pressing keys for some time it does eventually turn to a white screen with some static like noise. Restarting it brings the pattern back. Left alone it seems to be mostly stable. Here's a photo of the pattern:

Image (click for larger image)

The unit I purchased came with a 16K RAM pack, but I'm not able to test it currently. If I'm able to get the system working then hopefully the RAM pack will be in working condition. Both are physically in good shape, so my hope is it's not a major problem.

I currently live in the US, not far from Washington, DC. From what I've seen browsing the net, the ZX computers didn't seem to do well here, but it would be great to find a local group.

I don't have a lot of electronics equipment besides a soldering iron and a multimeter, but I'm not afraid to open the system up if there's anything I can find visually or with the multimeter.
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Paul
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Re: Got my first ZX, unfortunately not working!

Post by Paul »

Please don't Open the computer!
As the Keyboard still Shows Response in any Way it seems to work.
The keyboard is connected to the pcb with two Plastik ribbons that are very likely to Break After 30 Years if the Case is opened.
As you have a RAM Pack it would Be very interesting if the behaviour is the Same with and without RAM attached.
Unfortunately I cannot See the image attached by you.
From what you described it seem As if the RAM Might Be Broken. Attaching a working expansion RAM would solve this.
In theory, there is no difference between theory and practice. But, in practice, there is.
Magnus
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Re: Got my first ZX, unfortunately not working!

Post by Magnus »

Unfortunately I tried attaching the RAM pack when testing, but the computer behaved the same. I also don't know if the RAM pack is any good, so that may still be the problem.

Thanks for the warning about the the ribbon cables. I won't try to open it up for time being.

Is the image still broken? I can upload it somewhere else if the imgur link isn't working.
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Paul
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Re: Got my first ZX, unfortunately not working!

Post by Paul »

The image is now working.
But we have to wait for someone Else to Interpret this. I have Not Seen this before, except when the tv is Not tuned in perfectly. You Might try to Manualy fine tune the tv. Modern tv Sets have difficulties with Tuning in.
Is the Channel you tuned in near where it is supposed to Be in the US?
I have "Shadows" like this on VHF when the exact Channel would Be in uhf.
But maybe someone Else has suggestions?
In theory, there is no difference between theory and practice. But, in practice, there is.
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iturbez
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Re: Got my first ZX, unfortunately not working!

Post by iturbez »

Hi, Magnus. Welcome to the Forum.

First of all: NEVER CONNECT OR DICONNECT THE RAM PACK WITH THE COMPUTER ON. This would destroy both the computer and Ram pack.

Second: Have you tried to "fine tunning" the signal? ZX TV signal is "bad" for newer TV stes. If you can try the Zeddy with an old TV set, you coud kknow if it's working...

You can see also:

viewtopic.php?t=266

Regards.
sirmorris
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Re: Got my first ZX, unfortunately not working!

Post by sirmorris »

Unfortunately this looks like a broken ULA. I've seen a few machines like this in the last few days. Sorry to be the bearer of bad news. It's back to eBay I'm afraid.

There's a vanishingly small chance it's the processor but the ULA is, in my experience, always the thing to go.

:cry:
RWAP
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Re: Got my first ZX, unfortunately not working!

Post by RWAP »

If it is the ULA - there is a good chance it is in a socket as this is an American ZX81.
Magnus
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Re: Got my first ZX, unfortunately not working!

Post by Magnus »

@Paul and iturbez: We haven't had any fine tuning controls on our TV sets for many decades. My grandparents had this on sets they had from the 50s and 60s but I haven't seen this on a TV built in my life time (I'm older than the ZX-81 :lol:). Until the switch to digital TV two years ago our TV standard hasn't static, so the channels should be on the same frequency. My TS 1000 seems to be set up for VHF channel 2 or 3. Most of our old game systems used this setup, sometimes using Channels 3 or 4 instead.

A video might better illustrate it, but the image is solid and stable. There doesn't appear to be any static or interference of any kind. It just seems to be what the computer is outputting.
iturbez wrote:First of all: NEVER CONNECT OR DICONNECT THE RAM PACK WITH THE COMPUTER ON. This would destroy both the computer and Ram pack.
No worries there. I wouldn't plug / unplug anything to a vintage system while it's powered. After using a C64 for a long time you learn even simple things like plugging in a joystick while powered can kill chips depending on how the computer was designed.I still have hesitations with USB devices and SD cards because of this :lol:
sirmorris wrote:Unfortunately this looks like a broken ULA. I've seen a few machines like this in the last few days. Sorry to be the bearer of bad news. It's back to eBay I'm afraid.
Is the ULA like a PLA? If so, is there a source of replacement ULAs (or an alternative component) other than another TS 1000?
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