ZX80 trouble shooting

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

ZX80 trouble shooting

Post by Lardo Boffin » Wed Sep 04, 2019 5:05 pm

Hello all

I have a test ZX8-CCB set up as below:

79EA42D1-7CD8-4E88-98A1-48F31ED4B0DB.jpeg

I use this for testing ZX81s before connecting them to my chroma81. The leads are numbered for the ZX81 ULA pins.

Are there points where I can connect these to a ZX80?

Below is the motherboard:

84BC268F-F96D-4CC4-9331-AA840124EA15.jpeg

I cannot get this to tune in normally so not sure whether it is working or not. Various chips warm up when switched on and my glass screen telly nearly gets a picture so I am hopeful!
Last edited by Lardo Boffin on Thu Sep 05, 2019 1:57 pm, edited 1 time in total.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX80 - where to connect my test ZX8-CCB

Post by Lardo Boffin » Wed Sep 04, 2019 5:51 pm

Looking at the ZX80 I can see that TR1 is not present. I have no idea if that is a problem or not.

00A5E087-BC5B-4088-A909-265C9729E68C.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX80 trouble shooting

Post by Lardo Boffin » Thu Sep 05, 2019 3:28 pm

I decided to cut out the middle man and just fit a ZX8-CCB as there were instructions for that. So I did. :D

I got nothing. :cry:

So I decided to do some chip swapping as that is pretty much all I have the facilities to do.

And having replaced the Z80 and ROM chip I got this!

AB9F318E-D689-484C-8E0B-8A7FC0C1BB41.jpeg

Its alive! Sadly the ROM is from a ZX81.

So now all I need to do is find a ZX80 ROM. At least that should be easy!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX80 trouble shooting

Post by Lardo Boffin » Thu Sep 05, 2019 4:53 pm

This doesn’t switch on with any known working peripherals, e.g. a RAM pack or my ZXPand (which I believe should work on an ‘80 with an ‘81 ROM).
I have cleaned the edge connector.

I had a similar case a while back with an ‘81 and it worked fine after replacing the voltage regulator.

Is it the same for these? I.e. just use the same replacement type that the ‘81 uses?

Many thanks!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

User avatar
1024MAK
Posts: 2539
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX80 trouble shooting

Post by 1024MAK » Fri Sep 06, 2019 2:34 am

Hi

Which RAM pack did you try? Not all are necessarily completely compatible with a ZX80...

Sir Morris did a special version of the ZXpand for the ZX80, but I can’t remember what the differences are. But do keep in mind that the ZXpand has an overlay ROM included. The overlay ROM has to be based on the ROM version in the machine. Also the ZX80 does not have a ROMCS line on the edge-connector, hence external devices can’t switch out the on board ROM chip :(

I was hoping to reply to your earlier posts, but have been busy with work, so sorry about that. Glad to see that you have got yours going.

Have you tried putting the ZX80 ROM back in to see if it does indeed work?

The ZX80 and ZX81 both use a 7805 or equivalent voltage regulator. Or a suitable DC/DC converter with a 5V output.

Mark

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX80 trouble shooting

Post by Lardo Boffin » Fri Sep 06, 2019 10:24 am

Thanks Mark.

I tried a Sinclair 16K RAM pack amongst others. I guess I need to find one that states that it works with ZX80 as well! Or I could try and build one if there is one simple enough...

I put the ROM back in and got nothing sadly. I see that RWAP does a modern one for £15 so if I can’t get an original one I guess I will have to go modern!

Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

User avatar
1024MAK
Posts: 2539
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX80 trouble shooting

Post by 1024MAK » Fri Sep 06, 2019 10:48 am

The Sinclair 16K RAM pack is I believe, one type that should work.

What voltages do you get on the +9V and +5V rails with the ZX80 running on its own, and then with the RAM pack attached?

It is possible to use an EPROM, but pin compatible EPROMs that are suitable are a lot less common compared to the EPROMs used in later machines (like the BBC Micro).

Does the ZX80 ROM that you have, have a sticker on top that is covering a window? In other words, is it an EPROM? Or is it actually a windowless mask ROM chip? If it is actually an EPROM, it may be possible to reprogram it.

The EEPROM module from RWAP works well, I’ve used one when I was repairing Richard’s ZX80. Make sure you ask him to program it with the ZX80 code ;)

Mark

Moggy
Posts: 1866
Joined: Wed Jun 18, 2008 2:00 pm

Re: ZX80 trouble shooting

Post by Moggy » Fri Sep 06, 2019 11:34 am

To use the spand on the 80 requires the modern EPROM equivalent provided by rwap which contains the extra code required for the spands commands etc. Also a couple of pins have to be soldered to the classic spand board just under the sd card slot.
When a jumper is placed on the pins then it's in 80 mode, remove the jumper for 81 mode.

Just a thought Lardo.

When I want to experiment with different EPROMS on the 81 I burn whatever image to a 2764 EPROM, rewire the pins and off you go kind of thing. A while back the lads on the German forum showed how to turn a ZX81 into a ZX80 by burning the 80's ROM code into a 2764 add a few resistors to the CPU and lo instant ZX80.

My point being is I still have that EPROM and if you can bide a while I'm willing to try it in my own 80 and if it works you can have it with my blessings.

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX80 trouble shooting

Post by Lardo Boffin » Fri Sep 06, 2019 1:04 pm

1024MAK wrote:
Fri Sep 06, 2019 2:34 am
Hi

Which RAM pack did you try? Not all are necessarily completely compatible with a ZX80...

...

Have you tried putting the ZX80 ROM back in to see if it does indeed work?

The ZX80 and ZX81 both use a 7805 or equivalent voltage regulator. Or a suitable DC/DC converter with a 5V output.

Mark
Thanks Mark.

I tried an original Sinclair RAM pack which I was sure was working. Turns out it is now a dead parrot and is indeed pining for the fjords.

I also have these:

17563E8D-DC5C-4C6C-9CFF-77FA1F966F74.jpeg

They all work on my zeddies.

I put the ROM back in but it is very dead. It is a mask ROM not an EPROM. :(

Where do I get the 5 and 9V rails on an 80? I’m not familiar with the layout of these.

Many thanks.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX80 trouble shooting

Post by Lardo Boffin » Fri Sep 06, 2019 1:07 pm

Moggy wrote:
Fri Sep 06, 2019 11:34 am
To use the spand on the 80 requires the modern EPROM equivalent provided by rwap which contains the extra code required for the spands commands etc. Also a couple of pins have to be soldered to the classic spand board just under the sd card slot.
When a jumper is placed on the pins then it's in 80 mode, remove the jumper for 81 mode.

Just a thought Lardo.

When I want to experiment with different EPROMS on the 81 I burn whatever image to a 2764 EPROM, rewire the pins and off you go kind of thing. A while back the lads on the German forum showed how to turn a ZX81 into a ZX80 by burning the 80's ROM code into a 2764 add a few resistors to the CPU and lo instant ZX80.

My point being is I still have that EPROM and if you can bide a while I'm willing to try it in my own 80 and if it works you can have it with my blessings.
Thanks for the info and very kind offer Moggy!

Would I have to modify my 80 to get the EPROM to work?

I assume I would still need to get an RWAP EEPROM to get the ‘spand up and running?
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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