ZXmore or the ZX80CORE follow-up

[PokeMon]

I don't think that R11 maybe help in this case as it is important for the LOAD interface only.
Maybe you could try to make a good hires picture with a digicam, upload it somewhere and post the link here (or send me as PM) - so I could take a personal view on it and may find something. Would be good one pic from the component side and one from the solder side.

[1024MAK]

On mine, I have noticed that the oscillator based on X1 (the ceramic resonator coloured blue just to the right of the Altera EPM3064 chip) no longer starts at the correct frequency, at least, not as far as my Sharp Aquos TV is concerned. Still get the start up / menu display, but displayed with each successive line displaced compared to the previous line, so it looks like the whole picture slopes diagonally. I must get a picture, as it's hard work describing it

It was okay before I fitted the keyboard. Not sure why fitting the keyboard made any difference... Anyway, if I touch the X1 ceramic resonator with my finger for about two seconds, it locks on to the correct frequency. When I get some free time, I will attach my 'scope and frequency counter to see how far it is out.

Mark

[Becky]

Hi Karl,

I have taken a few digital photos. They are high resolution, so should zoom well. Just to explain a couple of things I messed up. C4, I damaged the mounting holes and have connected it on the back of the board between r18 and D11. I also messed up the mounting for the rom switch and tried to fix it with some pieces of wire. The smd resister moved when I was soldering it, as it was still connected to the correct pins, I just left it. It looks wrong, but it is okay.

Thank you for taking a look.

http://www.lodelane.co.uk/zxmore-becky.zip

[1024MAK]

Three quick and simple questions:
If you press and hold the reset switch, does this change in any way the image on the TV/monitor?
If you use a suitable slotted screwdriver, does the LED light up and show different colours with the ROM switch in positions 1 to 7? [See manual for the colours]. Does any of the switch positions change the image on the TV/monitor? [positions 1 to 5 are ZX81 modes, positions 6 and 7 are ZX80 modes].

Okay, one more, what test gear do you have? E.g. digital multimeter, logic probe, etc...

A tip - you can clean the flux (brown sticky stuff left over from soldering) by cleaning the board with Isopropyl alcohol (IPA) or a flux remover commercial product (not used this, but is listed as a flux cleaner). I use an old toothbrush (clean it first ). It will not harm properly soldered joints. But be careful with the jumper/patch wire that was fitted to the board when supplied and the SMD resistor that was fitted.

See some discussion here and here.

Mark

[PokeMon]

Thank you for taking a look.

http://www.lodelane.co.uk/zxmore-becky.zip

The first thing I see - you missed to jumper the io address range for the internal functions J12, Baseaddr, near the edge connector.
In this version you may jumper only A7 (fixed in software).

Try to use first jumper setting J16 (VIDPIX) to the upper position for white background with black pixels/chars.

Are you sure C16 is 47pF (named with 470) ? It looks bigger than mine when viewing from top.

At the keyboard some switches look a bit like some cold solder joint and the switch with the dot "." looks like one pin is connected to the case.
This is not important to get the board run but would give problems when trying to input something.
You can measure the keyboard later with a multimeter/connection tester to be sure if there are problems with the keyboard.
Anyway the ZXmore should give a picture on the video output even with shortened keys.



The solder side looks a bit weird. Hard to say if this is all correct and good.
If the jumper didn't help I would suggest first the following measures:

IC24 - looks like a possible connection of pin 9 and 10. You should remove some solder.

C2 looks like one leg not soldered - shouldn't be very important but I would try to fix.

IC2 (cpu) - you should maybe resolder pin 32 and 31. Doesn't look good on the pic.

IC23 - pin 9 and 10 - I would remove the big solder bridge and use a wire instead.
There is a track between both legs and I am not sure if there is still enough coating to isolate the track under.

The 3 color led should be resoldered or at least remove tin with desolder wick. There should be enough left to make the contact.
The pins are very near and not easy to solder. Maybe the best way for you is just removing solder here.

You should buy some desolder wick somewhere for this repair action.
If the LED does not work correctly the switch positions are not shown correctly.
If you turn the switch you should get the following colors:
0=no color / dark
1=blue
2=green
3=cyan
4=red
5=violet
6=yellow
7=white

The switch should be wired carefully as here are adress lines controlled (A16-A18).

By the way there is some solder at the edge connector but this could removed later with desolder wick.

Good luck, keep your fingers crossed.

[Becky]

Thanks for the suggestions guys. I'm going away for a week on holiday, so won't get time to have a play until I get back. Again thank you for the suggestions.

Cheers,
Becky.

[PokeMon]

So next week I will publish the first update - something around version 1.5 to 1.7 while I planned to release 1.9.
I changed a lot of (internal) things and added new features, one was change of charset to 128 (different) chars (ASCII 7 bit).
Usually the ZX80/81 did support only 64 normal chars plus 64 inverted chars.

I used the technique from Kelly Murta (at least found on his website I think) while the use of 64 or 128 chars is controlled with bit 0 of index register I. If bit 0 is set to 1 the second half of chars are selected which follows just the first 64 chars. I didn't change that behaviour with inversion when bit 7 is set, so the upper half of the character set has to be inverted manually. This could be easily done in 3 steps with an editor and using Find&Replace with 0=>2, 1=>0, 2=>1 when used in binary format like in the ZX80/81 assembly listings:

Code: Select all

; $00 (graphic char toleco)
	db    %00000000
	db    %00000000
	db    %00111111
	db    %00100000
	db    %00100000
	db    %00100111
	db    %00100100
	db    %00100100

128 charsets have to be aligned to $400 (multiple of $400 as start address) and the I register has to be set to this address and added 1. If you use $5400 as address for the charset you should write $55 in I register. Charsets can be read either from ROM or RAM - doesn't care.

zxmaster3.jpg (177.72 KiB) Viewed 4274 times

I added some additional graphic chars for creating some new effects and screen masks and added also the Pound and € sign and a special "ZX 81" combination pressed in 2 chars (due to some request from the german board). Anyway you may create your own charsets easily and put them into a BASIC/assembler program as well, easily to define starting addresses/points with the ZX-IDE.

Have fun.

zxmaster4.jpg (210.22 KiB) Viewed 4274 times

[PokeMon]

Not quite alive yet:



It's not running properly, but powers up and no chips are running hot. Any ideas guys?

Hi Becky,

how is it going on with your ZXmore ?
Didn't hear anymore about here and would like to see your ZXmore running as well and of course help as best as I can.

[Rishi]

any ideas, well i'd pop all chips out and check all connections for shorts with their neighbors and then check all connections on proper connecting. I'd use a multi-meter with a beep (i can't look at the board and at the LCD display at the same time) soldering something and have it working the first time is like running a computer program error free the first time, it does happen...

[Becky]

Hi Guys,

I'm still around. Just had a weeks holiday followed by a busy time at work. Hopefully get back to the ZXmore in a few days and continue checking it over.

Cheers,
Becky.