Apple II with video and (probably) RAM issues

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Apple II with video and (probably) RAM issues

I’d like to ask you for help with my Apple ][ board: As you can see [here]( (the upper one is without the ROMs, the lower with them), the board has some issues with the video output and start up process.

What has been tried:

- Using different monitors and TVs, including old CRTs
- Taking out the RAM
- all but row C
- all
- Taking out the ROMs
- only the Applesoft BASIC ROMs
- all but A5
- all
- Swapping around and the 74LS161 chips (D11-D14) or taking some of them out
- Reflowing connectors

What has been replaced:

- All chips but the ROMs (including the ones involved to the video circuit, according to the redbook)
- All transistors but the ones in the bottom left side
- All but the 44 0.1µF capacitors
- The timing crystal

Additional information:

- The values of the resistors are all as they should be according to the board.
- The power supply is home made for the EU, but it delivers the necessary voltages
- It is a 4th revision board
- All RAM chips are 16K

Sadly, I don’t have access to any

- oscilloscope
- multimeter that is able to measure a capacitors capacity
- another board

I really appreciate your help.

dorkbert's picture
Last seen: 7 hours 10 min ago
Joined: Apr 12 2009 - 16:33
Posts: 342

Last seen: 3 hours 35 min ago
Joined: Dec 20 2003 - 10:38
Posts: 463
Usually the first thing I do

Usually the first thing I do is reseat the chips. Lifting them up and pushing them down scraps off any oxidation on the legs and re-establishes contact with the socket.

Last seen: 4 hours 26 min ago
Joined: Aug 4 2015 - 14:30
Posts: 59
Contact Cleaner

A drop of Contact Cleaner in the sockets also helps.

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