My Klyball 600D build

[ronin47]

Evening all.

So, I have been away from the 600D build for a bit, since it was getting super frustrating.

In the meantime I built an Altairduino and uKENBAK-1 from adwaterandstir:

IMG20240317124618.jpg (2.75 MiB) Viewed 297 times

And it's got me in the right frame of mind to get going on the 600D again.

Given that I know 'something' is happening and I can see what looks like pixels on my micro B&W tv, I think I need to start going through the video circuit with a fine toothcomb.

I know I am getting what looks to be a good video signal, and I know that it's not a PAL/NTSC issue since my Dell display will do either and using an NTSC -> PAL adapter didn't help either.

So I am going to identify all the IC's from the video circuit and do some close up checking for bent pins and then check all the power/gnd pins and all the signals going in, as though I have the main clock fixed, I can't help but think that if a clock signal of any sort going into the video circuit is off, then I just won't get a proper signal coming out.

The lack of a back porch in the video signal does bother me too, so if anyone out there with an oscilloscope and a Klyball 600D could provide a picture of their video signal for reference it would be a huge help.

Thanks.

[jbtech]

Hi, here are a couple of CRO images from mine, not terminated so output level is over 2V but the timing should be correct:

Video lines: there is a front and back porch and sync looks correct at about 5us

IMG_2133.JPG (3.57 MiB) Viewed 284 times

Video frame, I just held a key to fill the screen with characters so the last line with characters is the cursor position

IMG_2136.JPG (3.83 MiB) Viewed 284 times

Vertical interval expanded

IMG_2139.JPG (3.64 MiB) Viewed 284 times

Hope that helps, regards John.

[ronin47]

Hi, here are a couple of CRO images from mine, not terminated so output level is over 2V but the timing should be correct:

Video lines: there is a front and back porch and sync looks correct at about 5us

IMG_2133.JPG

Video frame, I just held a key to fill the screen with characters so the last line with characters is the cursor position

IMG_2136.JPG

Vertical interval expanded

IMG_2139.JPG

Hope that helps, regards John.

Thanks so much!!

My video signal, though at the correct frequency, I don't seem to have either a front or back porch, so that's again suggesting an issue with something in the video circuit, as I can see pixels in the rolling image, but it's clearly got a problem with vertical sync as I can see the horizontal is fine on my scope.

I'll get checking the ICs that form the video circuit and any clocks that need to be present.

[ronin47]

OK, so some progress. By removing U61 I was able to get this:

IMG20240319130246.jpg (4.68 MiB) Viewed 257 times

Which didn't make sense until I realised that the HSYNC clock, 15.63Mhz is derived from U60, but the VSYNC is derived from U61.

Checking U61 I found that the C15 signal (60Hz) used for VSYNC originates at U61 and does arrive at U65 pin 1 and VSYNC should come out of pin 4, so I lifted that pin and got the same result as pulling U61.

Since U61 feeds 60Hz to U65, I was expecting to see a VSYNC signal of 60Hz at pin 4, but instead I see 15.63Khz again.

Surely I should see both 60Hz and 15.63Khz separately at U65 pins 4 & 12 respectively, and also at pins 12 & 13 of U70? I just see 15.63Khz at both.

I have checked for shorts between pin 4 & 12 but they are fine.

Any ideas welcomed

[jbtech]

So, if you have 15kHz at pin 4 of U65 but you're sure /HS and /VS aren't shorted together and the input at pin 1 of U65 is correct at 60Hz -

check for other possible interaction e.g. pins 2 and 3, 10 and 11 should be held high, make sure they are not toggling at 15kHz due to a shorted track etc.

Likewise make sure the +5V and ground to the IC are correct and not floating or carrying noise.

Failing that try replacing the IC! Good luck, regards John.

[Klyball]

what happening at pin 8 u43

[ronin47]

OK, I have figured out what was wrong video wise and now have a working video circuit

So U65 was getting 60Hz at pin 1 but throwing out 15.65Khz on pin 4. The only way this could have been an issue is if the LS123 was faulty, which I knew it wasn't (I'd tested it), so that just left C8 and R3 which is the external capacitor/resistor combo controlling the part of U65 that creates VSYNC.

R33 was unlikely to be wrong or faulty, I mean it's just a resistor, and that was all good.

However it turned out I had C8 in the wrong holes as I misinterpreted a diagram I was given that looked like this:

Screenshot 2024-03-19 at 22.42.45.png (141.19 KiB) Viewed 240 times

I used the hole marked in red for C8 as I though it was highlighting it should go there, when in actual fact I should have used the holes either side of the red mark.

With it correctly located:

IMG20240319222739.jpg (3.45 MiB) Viewed 240 times

I now get this on-screen with no CPU fitted:

IMG20240319223254.jpg (4.58 MiB) Viewed 240 times

Which I think proves the CHARGEN and video RAM is working.

Sadly with the CPU fitted I see this:

IMG20240319222236.jpg (4.39 MiB) Viewed 240 times

And that's with or without ROMs installed, so there is something else to investigate as I'm guessing that's a crash of some sort.

BTW pressing break does cause a reset signal at the CPU and the screen twitches, but goes no further and doesn't change.

Currently I only have 2 RAM ICs installed and the 2 for video RAM. I do have the remaining RAM ICs so might just swap the 2 out.

At least now I have a clear video image to work with for the next steps of troubleshooting, and as always, any tips welcomed

[Mark]

See "What happens to my C1P upon RESET?" @ viewtopic.php?p=4500#p4500

Are you getting ACIA access after RESET? Um... U14 6850 Pin 9 / U17 'LS139 Pin 12? If so then check for bad low 1K RAM U31/U45 as the screen won't clear if the stack doesn't work. D/C/W/M? display depends on BASIC ROMS.

Good Luck!

[jbtech]

Hi, I'm not sure offhand if I mentioned this before but looking at one of your earlier photos - if you only have 2 RAM ICs fitted (plus the video RAM) make sure they are the pair nearest the edge of the PCB, not nearest the middle.

- Just in case... Regards, John

[ronin47]

Hi, I'm not sure offhand if I mentioned this before but looking at one of your earlier photos - if you only have 2 RAM ICs fitted (plus the video RAM) make sure they are the pair nearest the edge of the PCB, not nearest the middle.

- Just in case... Regards, John

Thanks John, I didn't realise that, I will swap them around.