Query on a Issue 1 ZX81

Discussions about Sinclair ZX80 and ZX81 Hardware
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RetroMike
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Query on a Issue 1 ZX81

Post by RetroMike » Mon Jun 16, 2014 3:42 pm

Hi all,

I've just opened up my new purchase, which is also the first time i've opened a ZX81, and inside I've found an Issue 1 board with wiggly traces that's all very psychadelic! :roll: My reason for opening it was to slap a heatsink on the ULA and change the keyboard membrane for a new item due to some wear and the fact that I've got a new ZXPand interface module. Ok... question now (sorry about the rambling), what on earth is going on with the Z80 chip? What's the stand-off board doing soldered onto the pins, and do I need to do anything to it? The unit seems to be in working order, but I'm not sure this is standard kit, a user bodge, or some kind of internal upgrade. Also, I've not seen the big heatsink on the (I guess) MOSFET before, and was wondering if this is a gen1 thing?

Second question: Is there anything to watch out for with Issue 1 boards, other than the psychadelic traces? Weaknesses, etc.? There's a bit of brown goo on the underside of the board in the third pic, and I can't decide if it's flux or corrosion, and the traces look... erm....wrinkly? :shock: Also, should I be worried about the wear on the edge connector?

Image

Image

Image

Any help gratefully received :)

XorA
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Re: Query on a Issue 1 ZX81

Post by XorA » Mon Jun 16, 2014 4:03 pm

That addon board is actually a rom patch and is detailed on these forums in another thread.

The bad news is your zxpand will not work quite right unless you remove the patch and change the rom chip :-( I have tried a zxpand on such a machine and it almost works but not quite.

G

XorA
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Re: Query on a Issue 1 ZX81

Post by XorA » Mon Jun 16, 2014 4:04 pm

A link to the thread where I brought this up.

http://sinclairzxworld.com/viewtopic.php?f=7&t=867

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RetroMike
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Re: Query on a Issue 1 ZX81

Post by RetroMike » Mon Jun 16, 2014 4:17 pm

Ooer... trust me to get a tricksy one! :( So if I desolder the stand-off board I'll have a faulty ROM, so the sensible option is to replace it? I've just had a squint through eBay and SellmyRetro to no avail. Any clues where I could find one?

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RetroMike
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Re: Query on a Issue 1 ZX81

Post by RetroMike » Mon Jun 16, 2014 4:44 pm

I've spoken to Rich @ RWAP, and even though he doesn't think it'll be an issue, I've ordered a new custom flashed ROM anyway. One problem down, how many to go? :roll:

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RetroMike
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Re: Query on a Issue 1 ZX81

Post by RetroMike » Mon Jun 16, 2014 5:17 pm

Good job I erred on the cautious side, as I've just run a simple test with the board in:

Code: Select all

10 PRINT "CHRISTOPHER ";
20 GOTO 10
When I ran it, the error C/8514 was displayed. Bleh! :cry: More expense :(

Moggy
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Re: Query on a Issue 1 ZX81

Post by Moggy » Mon Jun 16, 2014 11:01 pm

Welcome aboard Wiffleplop.

I notice Your zeddy also has the issue 1 ULA chip (2C158E). which lacks the "back porch" signal required for modern and even the old CRT colour TV's. You may want to update it unless you are using old B/W TV.
See Rich for replacement alternatives

The crinkly bits are normal and that boards looks very clean I have to say, I also think it's had little use as the pins of the onboard ram chip still look shiny.
The pins on Mostek ram chips have a tendency to go discoloured when the zeddy has been used for some time, I have found over the years.

The mosfet you refer to is the 5volt regulator and tends to run hot with the original power supply, try one with an output nearer to 9v than the Sinclair one which kicks out about 13 volts which makes the regulator get a bit hot and bothered!

Try re tinning the edge connector so the expand seats firmly as that could be the cause of your error message/non running etc.

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1024MAK
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Re: Query on a Issue 1 ZX81

Post by 1024MAK » Tue Jun 17, 2014 2:13 am

This thread may help with your hunger for Zeddy knowledge... :D :lol:

Mark

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RetroMike
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Re: Query on a Issue 1 ZX81

Post by RetroMike » Tue Jun 17, 2014 3:53 pm

Thanks for the info chaps :) I've been speaking to Rich and it looks like my Zed is taking a trip to chez SirMorris to be stared at and pondered over with a view to resolving the issue that early Issue 1s have with the ZXpand. He's also going to flash and install a later ROM for me while it's there :D

As to the back porch, I've today received a ZX8-CCB from Pokemon, which I'll install when I get 'er back from her trip away. Doubtless I'll have loads of stupid questions on that later :roll: I'm also going to install a micro-switch in the side of the casing so I can switch black/white modes at whim, rather than soldering the pins and losing my option. That's all a way down the line for now....

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GCHarder
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Re: Query on a Issue 1 ZX81

Post by GCHarder » Thu Jun 19, 2014 7:07 pm

I read this article by Dr. Logan from Sinclair User just last night, pretty fortuitous! It explains that add-on board nicely.

With only 20,000 produced it might be better to keep it intact and get another one.

Regards;

Greg
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