ZXmore or the ZX80CORE follow-up

[pablo9]

OK, I've ran clkcfreq.p in instance 1. Pic is below. So yes you see the vertical grey lines for some of the special characters.

I checked these chips and they are correct

C21=74AC86
IC19=74AHCT74
IC9=74AHCT126
IC8=74AHTC08

I measured the resistance between IC15 pin2 and the via and it is 2k2.

IC15 pin1 is connected to the CPLD on pin 11, and is not connected to either IC22 pin 19 or IC7 pin 11

I tried adding a switch off board for the 47pf cap ... but I could never get an instance other than 0 to start. ie. I had the 47pf wired up with some wires out the side joined together (ie. I turned on with the 47pf wired in, and hadn't even tried to disconnect it yet). Instance 0 turned on, but I could never get instance 1 or 2 etc to start, so I couldn't try the test. I don't think it liked my long dangling wires. I need to have a few more goes later. I did try some other value caps directly to pin 27/29 (I don't have a spare 47pF). I still get vertical grey lines with 22pF or 56pF.

[PokeMon]

The ceramic capacitor should be wired as close as possible to pin 27 and pin 29 at the solder side with no wires at all.
Maybe this is the problem. It should be a small ceramic capacitor. What happen if you remove it complete and test instance 1 with the switch. This should work regardless if the capacitor is present or not. Instance 0 shouldn't startup at all but worth a try. Activating instances with the rom switch do directly use the ZX81 video routines without the ZXmaster (which is the only part required this capacitor).

You should run the BASIC program when activating the instances via the (mechanical !) switch as the USB loader is not present.

[pablo9]

So I originally put the 47pF in on the underside of the board directly to pin 27 and 29 with very short lead lengths (2mm or so). It's only since I've tried to put in a switch that I attempted to run long wires to one side of the cap (ie. one leg of the cap 2mm or so soldered to p27) and the other cap lead to a 10cm or so wire that hangs out the side, along with another 10cm wire to p29 (i.e. so I could wire a switch in).

But I just had another go. I wired a toggle switch in as close as possible to the p27/p29 points and propped the ZXMore up on its side. Now I have put the side 'instance' switch to start instance 1 on boot. If I set the toggle switch to include the 47pF cap and turn it on, instance 1 starts up fine. If I flip the switch to disable the 47pF, instance 1 stays running, but I still get the vertical grey lines. I just tried printing CHR$ 135 to the screen. I've flipped the toggle switch back and forth and there is no visual difference to the vertical grey lines.

[PokeMon]

Do you have these stripes when you remove the capacitor totally (with manual switching to "1").
Please do not use wires at all as these thin lines are an effect of 10-20 ns only.
Does anybody else has this issue with the new version by the way ?
The guys on the german board did not report such an issue.
Maybe this is a general issue at your board, that's why I propose to remove the capacitor at all and check if these lines have been there always (in version 0.9) but not seen yet because these chars have not been used in earlier versions or ZX81 programs you tried.

[martinjharvey]

Hi Karl,

I have the grey lines that you're discussing on my ZXmore also. I've updated to the latest software release and installed the 47pF cap and they are present on both TV's that I have used. They were present on the previous software release also in my case. I didn't mention anything as I just thought that the lines were a quirk of the system like the 'Jailbars' that can be seen on the original ZX Spectrum

I commented previously on the blurred yellow/rainbow effect that I was experiencing. I'm still getting that but since updating the software and installing the 47pF cap this is limited only to the ZXmaster instance. I will upload some photos if this is any help?

Mart

[gemby]

Hi gemby,

sorry to hear issues with your ZXmore.

First:
The latest schematic is available in this post:
http://sinclairzxworld.com/viewtopic.ph ... tic#p17474

Most known issues have been wrong or forgotten setting jumpers, be sure to use the BaseAddr set to A7 and be sure that you not put a jumper on the reset pin header (one guy really did as it was spare ). Check also the capacitors soldered at the back side and the wanted short between two pins. You may also remove IC22 and IC24 to avoid wrong latch settings. It should start up but LED should not be set anymore to white (led off). When removing the latches (IC22/24) it is not possible to switch to other instances by software (but with the switch).

You may also startup in switch position 1 or 2 or 3 to see if the ZX81 instances are working. This is a single mode and the corresponding color will be set through the switch instead of the latches. You should avoid switching around during power on. I think the flash rom is more protected against accidently beeing overwritten than the EEPROM but you never know. So switch during power off only to be more safe.

On default position 1,2,3,4,5 show ZX81 image and 6,7 show ZX80 image while 0 shows the control software.
You should also check that the wire on the background is still in position, connecting pin 1 of IC15 with pin 11 of the CPLD - see picture below showing pin 11 position on a 44 pin CPLD.
http://circuits.datasheetdir.com/389/L6515-pinout.jpg

These are the first steps to check. Unfortunately I am in a short holiday from tomorrow but are other people here to help as well I think. Points to check could be clock at pin 6 of CPU, NMI generator (NMI pulses on pin 17 CPU). Removing RAM and ROM and IC5, the CPU executes NOPs - so this way you can measure around many signals. The address bus counts upwards, giving half frequency from every address line from A0 to A15 and the control signals can be measured as well to check any possible shorts or mysterious signals.

And check if all pins are correct in the sockets and no pin accidently bended during inserting - just to be sure.
If you never find out the problem I offer you to ship the board to me and let me find out (next year).
So you can be sure it will run finally - so or so. Money never lost. Just have to pay the postage both way in that case. Up to you.

Good luck,

Karl

Well, here is small update, finally got hour or two to play around with zxmore, did not got scope, but have some freq meter so..

- Pin6 of CPU has nothing
- pin6 of AC86 ( IC21 ) has nothing
- across R16 i have nothing

No led activity, no picture at all, nothing

Every now and then i got it to oscillate but it is not stable at all

When i remove IC12 ( HCT125) i have firm 6.410 MHz and notice some activity on led when i connect freq meter across pin 12 and ground and got something on screen ( not a picture, some pattern - bars out of sync, but something is here )

So, when IC12 is removed:
- pin6 of IC21 ( ac86 ) has 6.410 MHz
- pin12 of ( now removed ) IC12 ( hct125 ) has 6.410 MHz
- across R16 i have firm 6.410 MHz

So, is HCT125 have died somehow or it is DOA and it preventing ac86 to oscillate properly? Is it normal to have 6.410 MHz instead of 6.5 MHz?

[PokeMon]

Hi Karl,

I have the grey lines that you're discussing on my ZXmore also. I've updated to the latest software release and installed the 47pF cap and they are present on both TV's that I have used. They were present on the previous software release also in my case. I didn't mention anything as I just thought that the lines were a quirk of the system like the 'Jailbars' that can be seen on the original ZX Spectrum

I commented previously on the blurred yellow/rainbow effect that I was experiencing. I'm still getting that but since updating the software and installing the 47pF cap this is limited only to the ZXmaster instance. I will upload some photos if this is any help?

Mart

Hi Mart,

yes please upload some photos to see.
Am I right, that you see some color effects ?
Maybe there is an issue with the horizontal sync and the back porch.

Could you check the capacitor under IC8 (74AHTC08) pin 10 and pin 7 ?
Is this sure 470pF (named as 471 not 470) ?
Maybe you could also post a higher resolution picture of the board solder side to check something I don't think about at the moment.

Thanks,
Karl

[PokeMon]

Every now and then i got it to oscillate but it is not stable at all

When i remove IC12 ( HCT125) i have firm 6.410 MHz and notice some activity on led when i connect freq meter across pin 12 and ground and got something on screen ( not a picture, some pattern - bars out of sync, but something is here )

So, when IC12 is removed:
- pin6 of IC21 ( ac86 ) has 6.410 MHz
- pin12 of ( now removed ) IC12 ( hct125 ) has 6.410 MHz
- across R16 i have firm 6.410 MHz

So, is HCT125 have died somehow or it is DOA and it preventing ac86 to oscillate properly? Is it normal to have 6.410 MHz instead of 6.5 MHz?

First the frequency is normal - could be +/- 1 or 2%. This is not very important.
HCT125 is used to maybe stop internal oscillator and to use an external oscillator.

Can you please measure voltage at pin 10, IC12. Should be 5V around.
And you could measure frequency at pin 12, IC9. Must be half of 6.410 MHz - so around 3.2 MHz.
CLK is the most important thing and you should measure a mixture between 6.4 and 3.2 MHz at pin 6, IC2 (CPU, Z80).

You could remove IC12 completely now when you remove just pin 6 of IC23 and do a resistor (1k to 10k) between pin 4 and 5 of IC8 or just a wire or solder connection. A resistor would be better when you forget later to remove this connection and put pin 6 of IC23 back which would get some hot then with a direct wire.

First goal to measure a valid frequency at pin 6 of CPU. This modification with pin 6 of IC23 would let it run on half frequency (3.2 MHz in your case) and produce a valid video signal if all other is correct.

So remove IC12, bend out pin 6 of IC23 a little bit out of the socket and make some connection between pin 4 and 5 of IC8 for the first time.
Anyway an oscilloscope would be better than a multimeter.

[PokeMon]

So i asked in our german forum. 3 other users don't have these stripes with update to V1.7.
What about other users here owning a ZXmore ? Andy, Erik,Mark - i know from my mind by now ?
Did you ever use another LCD monitor or TV to test if it is an issue with a specific display only ?

I don't have these small stripes at the start screen on my high resolution SONY broadcast monitor and nothing similar to see on my 42 inch plasma TV I used yesterday for chatting in IRC Zeddy chat. Strange.

[1024MAK]

I have not found time to do the upgrade / update yet, so I can't help at the moment. Sorry

Mark