Fixing Obtronix Apple I clone

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Fixing Obtronix Apple I clone

I have two kits of Apple I from Obtronix. I've built one but is imposble to do run.

When i power on, i can see in all the screnn full of characters (@M ...). If i push reset button the screen refresh and again full of characters. If i push clear only one @ is on the left top of the screen.

+12V -12V +5V and -5V are OK.

I've exchanged all the integrated circuits, one by one, without solve the problem, so the problem must been in resistors or capcitors.

I have voltimeter and oscilloscope. Somebody can help me to fix my Apple I?

Thank you

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Are you sure its broken? Typ

Are you sure its broken? Type 300.310 on the keyboard and see what happens. Your video sections seems to work OK.

Dave...

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Since the Obtronix Apple 1 is

Since the Obtronix Apple 1 is almost an Apple 1, you need to follow the same sequence. First, you need to press the clear button and clear the screen. Next you need to reset the 6502 to start it running. When you do this, you should see a \ followed by the cursor (a blinking @) on the next line. Is this what you see?

Vince

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Testing my Apple I

When i power on the computer i can see al the screen full of characters with a lot of @ blinking. Only are blinking @.

If i press clear, only a blinking @ is on the top-left of the screen.

Next i press reset, and the blinking @ change to other column and row.

If i type 300.310 there is not reply. I can't see the characters that i type.

resman's picture
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Keyboard?

You may have already tried a different keyboard, but if not its an easy check. On the Apple 1, the video section and the CPU section are almost completely separate subsystems. The good news is your video section seems to work. Find a pinout description of the 6502 CPU. With a logic probe or oscilloscope, probe the clock pins, phi 0 and 1. If they are not toggling, review your crystal and clock generating connections. If they are toggling, start checking the address lines. It should be trying to fetch from the ROM. Check all your ROM data and address lines for continuity and good logic values.

See how that goes.

Dave...

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Testing the Apple I

In 6502-pin37 trhere is not signal clock.
I can find signal clock in CL (7425-pin13 at position B7). You can see it in the schematics from the Apple I Manual.

7425-pin12 goes to 6502-pin37.
7425-pin12 output 7425-pin13 when Strobe=low (7425-pin15) and Select=high (7425-pin1).

7425-pin15 is a continous signal.
7425-pin1 is a continous signal with not periodic pulses.

With the polimeter i can measure the folloing voltage levels:

7425-pin12 and 6502-pin37 (are connected) 1.67V
7425-pin15 1.76V
7425-pin1 3.38V

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Looking for the problem

I think there is not chip with problem, because i exchanged all them one by one and testing the computer every chip changed.

I think there is no problem with oscillator because i can see clock signal 1Mhz in 7425-pin13.

I think there is not problem with voltage level because video subsystem is working and i can read 5V -5V 12V and -12V in the board.

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Did you know that the keyboar

Did you know that the keyboard that came with the obtronix apple 1 will not directly plug into it? It is made to fit the apple II not the apple 1 and it needs to have a special cable, you can not plug it directly into the keyboard socket.

Do you see the \ after clear and when you press reset? This will help to tell what is going on. If you get the \ then the obtronix is properly resetting and the Woz monitor is displaying the \ character.

Vince

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The problem may be the keyboard

I didn't know that. I'm connecting the obtronix keyboard directly using povided cable.

I tried to use a Apple II+ keyboard but some chip in te keyboard has been burned.

I can't see the \ when i press clear and then reset.

Do you know how can i use obtronix keyboard with my Apple I?

Thanks

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Keyboards pinout

Apple II ASCII keyboard pinout

+---| |----+
+5v | 1 16 | NC
Strobe | 2 15 | -12v
~Reset | 3 14 | NC
NC | 4 13 | Data 1
Data 5 | 5 12 | Data 0
Data 4 | 6 11 | Data 3
Data 6 | 7 10 | Data 2
Gnd | 8 9 | NC
+----------+

Apple I ASCII keyboard pinout

+---| |----+
~Reset | 1 16 | +5v
Data 3 | 2 15 | Data 7 (connected to +5v)
Data 2 | 3 14 | Strobe
Data 1 | 4 13 | NC
Data 0 | 5 12 | Clear Screen
Data 4 | 6 11 | -12v
Data 5 | 7 10 | +12v
Data 6 | 8 9 | Gnd
+----------+

Well, if this is ok, i'm going to build a bridge to connect the keyboard to the Apple I.

Do you think that the keyboard can be the source of the problem?
What can i break in the Apple II+ keyboard when i connect it to my Apple I and i press clear or reset button?

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A new step

Yet i don´t have the keyboard converter so i'm testing te Apple I without keyboard.

The problem is the following: the clock signal don't arrive to the cpu.

Pin 15 in the 74257 in B7 need to be 0V and is 2V. Pin 13 is the signal clock input and the pin 12 is the signal clock output to the 6502. If pin 15 is 0 then pin 12 output signal in pin 13.

Well, if i connect pin 15 to ground and i clear screen and reset the computer i can see \.

Why pin 12 in 74257 in B7 don´t have 0v? I'll follow testing the computer and making a keyboard converter.

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Something i don´t understand

I've removed chips in B5, B6, B7 and B8 (74257) and chips in A9 and A10 (8T97). Now in pin 15 of the 74257's sockets i have 0v.

If i insert any chip in a socket (74257 in B5,B6,B7 or B8, or 8T97 in A9 or A10) now i still having 2.5v in pin 15.

Why?

Pin 15 for chips in socket B5,B6,B7,B8,B9,A9 and A10 is only for input to enable DMA and is connected to the expansion bus slot (i have anything i the slot).

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If you see \ then the apple 1

If you see \ then the apple 1 clone is working.

The \ is generated by the Woz monitor in the PROM's when you press reset. So, if you see a \, then it is WORKING.

If you attached the keyboard directly, It looks like data2 and data3 took 12V and -12V from the clone into the keyboard. This could have damaged the keyboard.

Do not be surprised if you damaged the keyboard. I know that the maker of the kits did not let people know that the keyboard was not directly compatible with the clone. I wonder how many kits were damaged because of this?

Vince

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