Apple 1 : bad 2504s and problem to reset system

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Joined: Apr 18 2016
Posts: 7

Hi,

I’m new so I introduce myself. I'm Cyril Moulin from France. I collect and restore Apple computers. I have 15 differents Apple computers like Apple II, Macintosh 128k, Next Cube and many others. I'm very happy that you approved my request for membership.

I'm currently building an Apple 1 and i have 2 problems (it seems that it’s how we learn and it's true!) :

-A problem with bad 2504s, which was resolved. Attached, you will find the approach that I have used to identify bad 2504s. I tried to do something simple in case someone else would have the same problem; it certainly needs to be improved.

-A problem with the computer section, which isn’t resolved. i populated the computer section and soldered motherboard jumpers as described by Mike Willegal. When powering up, I have the same display as the video section and @ flashing at the top left when the screen is cleared. But when I reset the system (temporary jumper pin 1 / pin 9 of keyboard connector), nothing happens and the backslash doesn’t appear.

Pin 1 of keyboard connector isn’t connected to anything on the motherboard. I don’t understand how it can act.

On this forum, I read that someone had the same problem but I haven’t found a solution.

Is anyone have a solution to this problem ?

Thank you very much for your feedback.

Best regards,

Cyril

AttachmentSize
14 Power up display.JPG2 MB
15 Clear screen 1.JPG1.62 MB
16 Clear screen 2.JPG1.2 MB
Logigramme.JPG47.06 KB

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speedyG's picture
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Joined: Nov 16 2011
Posts: 2377
Re: Apple 1 : bad 2504s and problem to reset system

Hello Cyril56200,

welcome to the board....

thanks for the chart! I guess that will help several members while building their replicas.

first let's correct one mistake:
pin 1 of the keyboard connector is connected to pin 40 at the 6502 cpu !

according to the pictures you have taken it seems to me that probably the backslash
has disappeared but the prompt seems to be there....

otherwise check connection between pin 1 at keyboard connector and pin 40 at cpu....
check if pin 40 at the cpu is regular +5V and drops to 0 Volt when the pin 1 at keyboard connector is shortened...

so the question would be ( similar to the preclusion in the building instructions
that otherwise some characters might apear occasionally according to next paragraph of the manual )
is there a keyboard present at the keyboard connecter and did you try to enter anything at the keyboard ?
I miss at this posting confirmation to that fact....

second i quess mike_willegal, who is also member in this platform, will overtake the torch
assisting this debugging procedure.....

sincerely
speedyG

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Offline
Joined: Oct 9 2011
Posts: 1046
Re: Apple 1 : bad 2504s and problem to reset system

I'm going to ask an important question...

What is the date code on your 6502? Newer ones from the 90's and up don't work in the A-1 design without board changes.

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Joined: Apr 18 2016
Posts: 7
Re: Apple 1 : bad 2504s and problem to reset system

Hello speedyG,

Thanks a lot for your quick answer.

You're right : pin 1 of the keyboard connector is connected to pin 40 at the 6502 cpu.

I checked what you suggested me. I get +5v at pin 40 and it dropped to 0v when the 1 pin at keyboard connector is shortened.

I also connected the keyboard (working) and after clearing the screen, I can't enter anything.

Thank you very much for your help.

Best regards,

Cyril56200

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Joined: Apr 18 2016
Posts: 7
Re: Apple 1 : bad 2504s and problem to reset system

Hi Corey986,

Thank you very much for your help.

Here's what is written on 6502 :

C014377
R6502-34
8047
R6502D Mexico 0466

I don't know if this is a date code. I can ask Rob at Unicorn Electronics, where i bought it.

Thanks for your feedback.

Best regards,

Cyril

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Joined: Jan 4 2015
Posts: 68
Re: Apple 1 : bad 2504s and problem to reset system

Do you have a spare 6502?

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Joined: Apr 18 2016
Posts: 7
Re: Apple 1 : bad 2504s and problem to reset system

Hi snazzify,

I don't have spare but i also thought that 6502 could be bad and required to order another one.

Thanks a lot.

Best regards,

Cyril

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Joined: Apr 18 2016
Posts: 7
Re: Apple 1 : bad 2504s and problem to reset system

Hi Corey986,

I had Rob's answer. 6502 is before 1980.

Offline
Joined: Oct 4 2014
Posts: 64
Re: Apple 1 : bad 2504s and problem to reset system

The old trick to identifying the manufacturing date of chips is from the 4 digit run code.

In this case, it is 8047

This decodes to 80 ==> 1980 and 47 ==> 47th week of 1980

Bonne chance, mon vieux.

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Joined: Apr 18 2016
Posts: 7
Re: Apple 1 : bad 2504s and problem to reset system

Hi IEEE-802,

Thank you very much for this explanation.

Best regards,

Cyril