ZX80 at last....

[bola_dor]

I've received a new (to me) ZX80 after 20 days of delivery waiting...
Woe.. it is smaller than I xpected, and looks more fragile..
Externally it looks very good but a minimal cracking near one corner.
Keyboard andis glossy, shiny.. I didn't expect that neither so I wonder if it is an original Keyboard or a newly replacement.. it looks like new.. (wite marks in the picture are light reflections)
It is supposed to be a US model and I bought it from the USA..
Later I think I will open it to check inside.. and perhaps try to load something

[Moggy]

I've received a new (to me) ZX80 after 20 days of delivery waiting...
Woe.. it is smaller than I xpected, and looks more fragile..
Externally it looks very good but a minimal cracking near one corner.
Keyboard andis glossy, shiny.. I didn't expect that neither so I wonder if it is an original Keyboard or a newly replacement.. it looks like new.. (wite marks in the picture are light reflections)
It is supposed to be a US model and I bought it from the USA..
Later I think I will open it to check inside.. and perhaps try to load something 20200608_161008.jpg
20200608_160953.jpg
20200608_161222.jpg

Very nice ZX80 you have there.

The keyboard is normal as is the cracking unfortunately.
Be very careful when pushing the locking pins out of the centre of the rivets as they are easily lost!

[bola_dor]

I had no luck trying to connect it to any TV .. neither tuning nor the mod based on 555 .. I also had no success with the blind SAVE test ... you can barely hear the classic background noise but no attempt to save. So I decided to open it and test the tensions. I found that IC16 / 13 and 11 have no connection to GND. so I'm going to lift the plate and check those welds .. Hopefully it's just that.

[bola_dor]

No luck again.
the welds looked good so I tried again .. scratching a bit with the multimeter tip the continuity was OK.
With the logical probe several of the pins show pulses in those ICs .. so let's check the rest:
Z80 pins:
6,16,18,19, 21, 27 and 28 Pulses
17, 23, 24, 25 High
20 and 22 Pulses High
all address lines Pulses But A12 and A13 are Low (or pulses too low)
Data lines pulses ..
in the ROM everyone Pulses except pin 21 (I assume its A12..it pulses low I think.. low led gets a little low light)
At RAM every one is pulsing but WE that its High or pulses High..

Now I need help

[1024MAK]

Going on the marking on the modulator, it looks like it outputs on VHF channel 3.

In English, what you call ‘welds’ we call solder joints. Although sometimes we refer to voltage as tension (for example in CRT design, manufacturer, and servicing/repair, the high voltage lines/rails were often referred to as high tension, or EHT extra high tension) we mostly use the name ‘voltage’.

Mark

[bola_dor]

Going on the marking on the modulator, it looks like it outputs on VHF channel 3.

In English, what you call ‘welds’ we call solder joints. Although sometimes we refer to voltage as tension (for example in CRT design, manufacturer, and servicing/repair, the high voltage lines/rails were often referred to as high tension, or EHT extra high tension) we mostly use the name ‘voltage’.

Mark

Thanks for the teaching...

What do you think about the ZX?

How are you doing with your fever? I hope is not more than a flu.. and you are better now

[1024MAK]

Yes, rain has caused the grass pollen levels to fall so my hey fever has subsided

So looking at your photo, it looks like the only chips in sockets are the CPU and the ROM. Is this correct?
This makes it more tricky to fault find on

I presume the +5V supply is okay?
And the input voltage (+9V nominal) is at least +8V?

It does appear that the Z80 is okay, but as it's in a socket, it's still worthwhile swapping it into another known working computer AND putting a known working Z80 CPU in the ZX80 to see if it makes any difference.

Can you please test the Z80 CPU pins 4 & 5 (A14 and A15).
Also pin 8 on each of the two 2114 SRAM chips (IC3 & IC4).
And ROM (IC2) pin 20.

Apart from a multimeter and a logic probe, do you have any test gear?

Because the RAM chips in this computer are static types (hence SRAM - Static RAM), we can run it from a slow clock if needed. I assume you have some NE555 timer chips and can put together an astable multivibrator running at around 4Hz.

Mark

[bola_dor]

Yes, rain has caused the grass pollen levels to fall so my hey fever has subsided

Glad to hear that, at this times any fever looks scary

So looking at your photo, it looks like the only chips in sockets are the CPU and the ROM. Is this correct?
This makes it more tricky to fault find on

thats correct no74xxx is on sockets neitherthe rams

I presume the +5V supply is okay?
And the input voltage (+9V nominal) is at least +8V?

yes . I tested twodifferent psu and get 5v to every IC

It does appear that the Z80 is okay, but as it's in a socket, it's still worthwhile swapping it into another known working computer AND putting a known working Z80 CPU in the ZX80 to see if it makes any difference.

will do later at home

Can you please test the Z80 CPU pins 4 & 5 (A14 and A15).

they are pulsing

Also pin 8 on each of the two 2114 SRAM chips (IC3 & IC4).
And ROM (IC2) pin 20.

all pulsing but I will retest later

Apart from a multimeter and a logic probe, do you have any test gear?

not at this moment.. I am thinking about buying a cheap oscilloscope like the hantek 6022be, https://www.amazon.com/Hantek-Digital-S ... B085QGF2YM do you think it may do the job or will I waste my money ?
I could get access to an oscilloscope when the COVID-19 thing ends up, we are just aproching the winter and we are perhaps the country with longest quarantine in the human history

Because the RAM chips in this computer are static types (hence SRAM - Static RAM), we can run it from a slow clock if needed. I assume you have some NE555 timer chips and can put together an astable multivibrator running at around 4Hz.

I can do that, I have a spare 555 but I have no idea o how to make that ..

Mark

Thank you a lot.. I will name you may old computers godfather...

[bola_dor]

It does appear that the Z80 is okay, but as it's in a socket, it's still worthwhile swapping it into another known working computer AND putting a known working Z80 CPU in the ZX80 to see if it makes any difference.

Mark

I confess that I thought it wasn't going to make any difference.. but I did take apart the NEC 780C and put a SSS from one of my TS1000...
I manage to sintonice on cannel 2 (about 55400Mhz) and got a white screen with some known jailbait artitifac.. but no inverse [K]... but it was good news.. SAVE [NEW LINE] worked.. so I suspected that I had a good SYNC and IC20 but something were wrong with character video output, perhaps IC19 and a bad Z80 ..
Then I wanted to rechec the original NEC Z80 so I put it back.. pressed it well. And.. voila

Beautiful!!!
Perhaps because of the time some contacts needed some friction.. or some love, I don't know..
I have to review the 555 video mod as it just kills the computer .. I tested it with the TS1000 and worked with the only drawback of a black left border but it has a newer ULA so I though it was spected..
Now I tested with a simple BC547 and a resistor to GND .
At first I got a gray with an almost invisible K .. attributable to lack of a backporch.. I made SAVE (new line), TV went out of sync and went back with a really good Image, steady and without artifacts of any kind.. better than an emulator.. I think the TV found its way. I don't know if this will last or what will happen nex time.

I feel happy
Thank You Mark

[Muttley Black]

Well done my friend!