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CT-1024 Terminal Manual?

I think I 'may' have found a video incompatability that may make the CT-1024 not work with a 'bog standard' monitor - although I need a bit of time to think through the implications.

The original Radio Electronics construction articles can be found at http://www.swtpc.com/mholley/RadioElectronics/RE_CT_1024.htm in particualr the February edition http://www.swtpc.com/mholley/RadioElectronics/Feb1975/RE_Feb_1975_pg30.jpg identifying the video output specifications. The article states that the video output pulse is 2.25V with a 1V sync pulse. This is not what I would expect for a video signal. I am used to 1V with a 0.3V sync pulse. There also may be some issues with the number of lines (frame rate) being different to a 'standard' monitor (whatever one of those is...). Again I need some time to think about this.

The voltage levels can be fixed very simply with a small plug-in adapter board on the video output of the CT-1024. The number of lines issue I need to think about...

Just some thoughts in passing based upon what I have read today.

Dave
 
On the assumption that it is the video signal to the monitor that is the problem; we should be able to 'prove' this by trying various tests to check that the CT-1024 functionality is as expected (albeit it may be difficult to see the results on the monitor). This should give us confidence that a large amount of the CT-1024 logic is actually working and we just need to look at getting a stable and readable picture on a monitor!

I am assuming that all the switches, push-buttons and expansion cards (memory, URT, CURSOR control and screen read) have been removed and all we have is the main board to work with.

Download the data sheet for the 2513 character generator from http://amigan.yatho.com/2513.pdf.

You can see on page 7-46 what characters should appear commesurate with the settings an address lines A4 through A8 (corresponding to 2513 pins 17 through 22 and CT-1024 connector J8 pins 11 through 6).

Because a memory board is not plugged in, the data lines from the memory board (address lines A4 through A8 to the 2513 character generator) are floating. This state appears to generate an '@' character which corresponds to A4..A8 being at a logic '0' level (although why not all '1's giving a '?' I do not know at the moment - possibly to do with the internal circuitry of the 2513 character generator?)

By temporarily joining each address line in turn to +5V and then 0V via a 10 kOhm resistor - we should see the character that is displayed on the screen change.

First of all connect J8 pin 11 to +5V via a 10 kOhm resistor. This should correspond to the character for 000001 or 'A'. Disconnect J8 pin 11 from +5V and connect it to 0V via the 10 kOhm resistor. The displayed character should once again return to 000000 or '@'. Disconnect J8 pin 11 totally.

Repeat the above paragraph for the following pins in turn:

J8 pin 10 - 000010 character displayed should be 'B' when the pin is connected to +5V via the 10 kOhm resistor.
J8 pin 9 - 000100 character displayed should be 'D' when the pin is connected to +5V via the 10 kOhm resistor.
J8 pin 8 - 001000 character displayed should be 'H' when the pin is connected to +5V via the 10 kOhm resistor.
J8 pin 7 - 010000 character displayed should be 'P' when the pin is connected to +5V via the 10 kOhm resistor.
J8 pin 6 - 100000 character displayed should be ' ' (i.e. the blank or space character) when the pin is connected to +5V via the 10 kOhm resistor.

If this works out - then we have pretty much proved the character generator, parallel to serial converter logic and part of the divider chain.

Dave
 
In the above post I am using the 10 kOhm resistor to limit any fault currents should you accidentally touch the wire onto the wrong place to prevent damage to your CT-1024. Thinking about the value a bit, 10 kOhms may be a bit high. 2.2 kOhms may be a bit better...

You should also be able to work out that by connecting multiple J8 pins 11 to 6 to +5V or 0V will give you a 6-bit binary pattern that will correspond to the display of a specific character identified within the 2513 character generator data sheet.

Assuming all is well to this point - I would propose that we next check out some of your switches.

I assume that your J10 has the Page 1, Page 2 and solid cursor switches connected to J10 pins 1, 2 and 6 respectively?

Connect the black (negative) lead of your multimeter to the 0V/GND of the power supply and set the multimeter to a 10V d.c. range (or whatever is convenient to read 5V).

With 'PAGE 1' selected; the voltages on IC27 pins 13 and 10 should be 0V and +5V respectively.

With 'PAGE 2' selected; the voltages on IC27 pins 13 and 10 should be +5V and 0V respectively.

If your PAGE 1/PAGE 2 switch has a centre position; the voltages on IC27 pins 13 and 10 should be +5V and +5V respectively.

Set the PAGE switch to 'PAGE 1' when you have finished with the above tests.

With the 'SOLID CURSOR' switch OFF (i.e. flashing cursor); IC8 pin 4 should be +5V.

With the 'SOLID CURSOR' switch ON (i.e. a block cursor); IC8 pin 4 should be 0V.

Set the 'SOLID CURSOR' switch to OFF when you have finished with the above tests.

Turn the power supply OFF to the CT-1024. Wait a bit and then put the memory board back in. Turn the CT-1024 back on.

You should see 'garbage' on the screen as the RAM has powered up with semi-random contents.

Temporarily pulse J3 pin 1 to ground (this should home the cursor).

Temporarily pulse J3 pin 8 to ground (this should clear the screen and leave a flashing cursor in the upper-left of the screen). Of course the definition of a flashing cursor is a bit suspect if the monitor is not synchronised properly!

Turn the 'SOLID CURSOR' switch ON. The flashing cursor should stop flashing and become a block cursor (or in your case, the lines that were flashing should stop flashing and be lit permanently).

Turn the 'SOLID CURSOR' switch OFF. The flashing cursor should appear again.

Next, select PAGE 2. The screen should display random 'garbage' characters again as the above 'clear to end of frame' has only operated on the visible page at the time (i.e. half of the memory contents).

Temporarily pulse J3 pin 1 to ground (this should home the cursor).

Temporarily pulse J3 pin 8 to ground (this should clear the screen and leave a flashing cursor in the upper-left of the screen once again).

If this works OK then we have checked out the basic operation of the memory and the cursor comparator logic.

The next installment will perform some cursor moves - although I will let you do some testing first and see what you come up with. It is pointless to go any further unless the above checks out. In the meantime, I will think about the video voltage levels and timing a bit more...

Dave
 
I got a bit worried there - the browser crashed and I thought I had lost the whole post :-(

Auto-save to the rescue :)

Dave
 
Thanks for this Dave... I don't know if I have any spare resistors kicking around.. but should be easy to find. To be honest, I have not seen any evidence of a cursor with boards in or out. It could be up in that gibberish area above or below. Perhaps it's better to go after the video so we can see everything properly? Would that adapter be hard to create?
 
A trip down to Radio Shack sounds on the cards... (We have Maplins in the UK).

If it is a voltage level issue - then no, the adapter will be dead simple (two resistors - and possibly a zener diode - at the most). You may even be able to use a 250 Ohm linear potentiometer (the same trip to Radio Shack?). Wire one end of the potentiometer to the video output from the CT-1024 and the other end of the potentiometer to ground. The output signal to the monitor is then taken from Ground and the potentiometer's wiper. The closer the potentiometer's wiper is to the video output wire from the CT-1024 then the higher the video voltage will be to the monitor. You could try this as a simple test if you wanted - you won't damage anything as it is unpowered. As you turn the potentiometer towards the 'ground' end - the 'whites' on the screen should start to dim and eventualy disappear. You may need to re-tweak R38 again...

If, however, the problem is both voltage level and timing related - then the above will not work (we are only fixing one of the problems not both of them).

The reason I am suggesting trying the tests in the previous post is to give us both confidence that the CT-1024 is at least working and that there are not loads of simultaneous problems that we are trying to chase down at the same time (which will juse send us round in circles).

The advantage of performing the tests that I have suggested above is that it should give us a clear screen with a flashing cursor (albeit potentially screwed up). If you have lots of random characters on the screen then you are correct that we won't be able to discern the garbage from the cursor. However, if the screen does not clear when it should - then there is something else faulty which may be preventing the video display from appearing correctly anyhow. We are also following the original "testing and calibration" procedure to some extent (with a few extra tests of my own thrown in for good measure).

Besides - I am now going out for an evening Curry and it is still early in Vancouver!

Dave
 
I have been unable to track down any video Standard that has the claimed voltage levels that the CT-1024 outputs. The oldest/closest I can find (for the US NTSC market that is) is RS-170 with a +1.0V (white), +0.075V (black), 0.0 (blank), -0.4V (sync) = 1.4V pk-pk. This is later reduced to +1.0V pk-pk.

From a timing perspective - it would appear as though the CT-1024 outputs an almost NTSC compatable signal with the expectation for an interlaced monitor (i.e. half of the lines are output in one frame with the other (identical) half in the next frame). If your monitor is non-interlaced then all bets are off.

What manufacturer, make and model of monitor are you using?

The monitor shown in the photographs accompanying the CT-1024 are (as I have read) a Sanyo VM4209 (although I have been unable to locate any technical details for this monitor on the web).

Based on what I have read today - trying to match the video voltage output by the CT-1024 to the specific details of the monitor you are using should work - providing the monitor is interlaced. If the monitor is expecting a non-interlaced signal - then it may be expecting all 525 (ish) lines to be displayed in one frame (which is not the case with the CT-1024).

Dave
 
Right now I'm linked up to a Commodore 1702. I do have that Panasonic vm4509 but no difference in display there. Also tried my Apple /// monitor. What is throwing me is the original video connector.. like I said it was one of those small earphone style numbers. Ive never seen an input on any tv or monitor like that.

I did try some experimentation. The machine definitely reacts to the switches. On one occasion I fired it up with only the cursor board in and actually briefly got a blinking cursor for two seconds, about five lines down in the field of gibberish. Ibalso noticed that when I pressed the EOF button a number of the gibberish characters would change.

With the mem board in, I get a single illegible line of gibberish where the top of the screen should be. There is, if you look closely, a reaction when you press certain buttons. But it returns to same as before when released. Keyboard and shorting keyboard pins produces nothing.

I kind of wonder about bad ram.. is it safe or possible to do the piggyback test we used with my PET?


daver2 said:
I have been unable to track down any video Standard that has the claimed voltage levels that the CT-1024 outputs. The oldest/closest I can find (for the US NTSC market that is) is RS-170 with a +1.0V (white), +0.075V (black), 0.0 (blank), -0.4V (sync) = 1.4V pk-pk. This is later reduced to +1.0V pk-pk.

From a timing perspective - it would appear as though the CT-1024 outputs an almost NTSC compatable signal with the expectation for an interlaced monitor (i.e. half of the lines are output in one frame with the other (identical) half in the next frame). If your monitor is non-interlaced then all bets are off.

What manufacturer, make and model of monitor are you using?

The monitor shown in the photographs accompanying the CT-1024 are (as I have read) a Sanyo VM4209 (although I have been unable to locate any technical details for this monitor on the web).

Based on what I have read today - trying to match the video voltage output by the CT-1024 to the specific details of the monitor you are using should work - providing the monitor is interlaced. If the monitor is expecting a non-interlaced signal - then it may be expecting all 525 (ish) lines to be displayed in one frame (which is not the case with the CT-1024).

Dave
Click to expand...
 
I recon the Commodore 1702 should work (assuming connected to the front-panel composite video connector). You have tried adjusting the vertical hold control on the monitor haven't you?

I don't think the connector is relevant. The CT-1024 was designed (in part) to be connected to a modified television - so the constructor could have used any old type of connector they liked.

Randomly pressing buttons with random cards inserted doesn't help diagnose the problems. Only a logical progression will.

If you think about it - it can't be a RAM fault if we have the RAM board (and all of the other optional cards) removed. My hypothesis is that if the main board doesn't work on its own - it can't have anything to do with the add-on cards as they have all been removed. The problem(s) must lie with either the power supply and/or the main board.

If you can't get a stable picture on the screen without the option boards present - the fault must lie somewhere with the timing chain/counters and/or synchronising logic. Once we have solved the problem with those - we can move on to the next problem(s) in sequence. We can only fault find on the RAM board when we know for a fact that the main board is solid.

My advice is to add the smoothing electrolytics as we have discussed and to perform the relatively simple tests I have already suggested to see what happens.

I have now read up on how the vertical and horizontal synchronising pulses are generated - but there is no point looking into this until we have some answers to the basic operation (i.e. are some of the basics working at all).

I noticed some earlier posts you made on YouTube. It is interesting to see that some of the characters appear to be "well formed" - but there is a lot of what I would call "intermittent operation" - may be from bad solder joints, possibly suspect capacitors or power supply problems. But this is me jumping to conclusions...

Dave
 
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