Another C1P build

[ronin47]

So, after power-on, I still can't get the video to show up, UNTIL I touch the underside of the board at U65 (74ls123).

It is not perfect, with a"shimmering" instability, UNTIL I touch the circuit underside at U65.
Below is a what it looks like...

VIDEO 2.jpg


There is a thick 0V track on the outer edge of the board, and when I touch the circuitry under U65 the video somehow "stabilises" ???

VIDEO 1.jpg


So, I think I'm going to need an oscilloscope to identify the issues...

Also, I can't get the RESET line to toggle.
When I press the BREAK key, Pin 7 of U80 (LM393) toggles LOW to HIGH, but the RESET output on PIN1 does not.
C60 (50uF) was inserted the wrong way round (owing to strange marking of the - side)
I corrected this, but still the RESET stays HIGH. I've ordered a couple new 393's, will test this afternoon.
Should the RESET line stay LOW as long as the break key is pressed?

So U65 is where both sync signals come from according to the service manual. These are combined with the video 'data' in U70 to create the composite video signal.

You touching it sounds like capacitance is causing it to improve, might just be a socket or a solder joint that's a bit iffy. You might be able to use a scope probe (If you have one) and touching a pin at a time to see if you can cause the same effect and narrow it down.

Have you tried adjusting R58 to see if that helps?

On the subject of scopes, I would advise against getting a cheap handheld one if you're going to buy, some of them are useless for this sort of thing.

I would say that I've had a number of issues with certain ICs not working and swapping them about or using different types (LS/S or straight 74 logic) did solve some of my issues.

With regards to pin 1 of the 393, mine does this when I hit and hold break:

IMG20240620110006.jpg (3.56 MiB) Viewed 1757 times

The D/C/M prompt flashes showing it's done a reset. I get much the same when I do it without a CPU installed.

I have to release break in order to reset again.

[HOWARDHB]

Thanks for that!

R58 functions as expected - brighter / darker video...

So the RESET line should PULSE low for 100mS, and then remain HIGH until the BREAK key is released and pressed again?

I've ordered a bunch of spare IC's, so will spend some time checking pins / sockets / solder joints.

I have access to a storage scope at work, so I'll ask if I may borrow it this weekend...

Also, I've ordered a couple of 6502's, and some 28C16 EEPROMS from EBAY... delivery in about 4 weeks though

And... I found this keyboard on a local auction site for a 100 smackers..

KBD.jpg (94.44 KiB) Viewed 1752 times

I have no idea of it's origin, however, It has the original key switches that OSI used, including the latching CAPS-LOCK switch.
Complete with an 8U space-bar, with the EXACT stabiliser that fits the holes on the KlyBall pcb!!!!!!
(A slight modification to the "links" underneath will be necessary, due to the height differece of the Cherry MX key-switches, but that will be easy to 3D print)
The key caps are almost identical to the C1p, the main difference is the SHIFT keys are only 1U size. (OSI SHIFT keys are 2U)
Good fortune me thinks!

[ronin47]

Thanks for that!

R58 functions as expected - brighter / darker video...

So the RESET line should PULSE low for 100mS, and then remain HIGH until the BREAK key is released and pressed again?

I've ordered a bunch of spare IC's, so will spend some time checking pins / sockets / solder joints.

I have access to a storage scope at work, so I'll ask if I may borrow it this weekend...

Also, I've ordered a couple of 6502's, and some 28C16 EEPROMS from EBAY... delivery in about 4 weeks though

And... I found this keyboard on a local auction site for a 100 smackers..


KBD.jpg


I have no idea of it's origin, however, It has the original key switches that OSI used, including the latching CAPS-LOCK switch.
Complete with an 8U space-bar, with the EXACT stabiliser that fits the holes on the KlyBall pcb!!!!!!
(A slight modification to the "links" underneath will be necessary, due to the height differece of the Cherry MX keys, but that will be easy to 3D print)
The key caps are almost identical to the C1p, the main difference is the SHIFT keys are only 1U size. (OSI SHIFT keys are 2U)
Good fortune me thinks!

With regards to BREAK, I press and hold it, the signal goes low for about 100ms then goes high again without me releasing the BREAK key.

As soon as I release it, it's ready to do a reset again.

Sounds like your 28C16's are coming from China. I got mine from Ali Express, took about a fortnight to arrive, but I got extras in case of failures, though they all worked just fine.

That keyboard is a good score, though the only thing with the Klyball is that it's designed for the Cherry keyswitches, so they may not fit if you intend to harvest them, though if you're just using the keycaps you may be good to go

I almost never find that sort of stuff!

[HOWARDHB]

Ok, so I've replaced U58 (was a 74ALS00) with a 74S00 and now the oscillator starts reliably.
Graphics is stable...

However, no clock (02) on the processor pin 39...
Is there a jumper I've missed because I can't get continuity to anywhere else than U20 (74ls138) pin6, U21 (74ls04) pin 3, and U14 (6850) pin 14.

Where does the processor clock O2 originate?

...edit

Reset does work, a 100ms low going pulse.
Clock is now healthy on pin 39 of the processor, I can see the address and data lines toggling but video is still filled with random chars.
A faulty 40 pin socket did not connect pin 39 to the chip!

clk ok.png (3.19 MiB) Viewed 1735 times

[ronin47]

Oh the processor clock circuit had me doing a merry dance!!!

Glad yours was a simple solution. Glad to hear reset is playing ball too

Do you have the CPU installed yet?

[HOWARDHB]

Yes, processor is installed with SYN600 and BASIC4 rom.

The display is filled with random chars and pressing break key does nothing....except, sometimes when re-applying power, the display will fill with random chars but the video is darker and the chars are smaller, but stable...

sometimes.png (2.89 MiB) Viewed 1721 times

...then when I press break the screen clears and other random chars fill the screen, and a slight "shimmering" is evident...

afrer break.jpg (3.86 MiB) Viewed 1721 times

Where to start looking?....

[ronin47]

But you don't have all the ROM's installed do you?

[HOWARDHB]

Only Basic4 and SYN600.

[bxdanny]

Maybe one of the ROM socket pins has the same problem that the clock pin on the 6502 socket had? It would be on the SYN600 socket, if the screen is not clearing. Or maybe both ROM sockets. The change in character size indicates that the latch at $D800 is changing state, namely U72, pin 7. That chip's outputs are supposed to be cleared to 0 by a reset signal (which connects to pin 1), so if you see the small characters ("48 character mode") when you power on, it's not getting that signal.

[HOWARDHB]

Thanks @bxdanny, I will check the sockets...