Re: VIC-20 IF BOARD

From: Gerrit Heitsch <*gerrit_at_laosinh.s.bawue.de*> Date: Sat, 26 Apr 2014 17:47:02 +0200 Message-ID: <535BD4F6.2080801@laosinh.s.bawue.de> · gerrit_at_laosinh.s.bawue.de

On 04/26/2014 05:43 PM, Ruud@Baltissen.org wrote:
> Hallo smf,
>
>
>> Can you dump and upload the rom somewhere?
>
> I tried to read the EPROM but I think it is brooken. Every time
> after a read my burner reported verify errors. And worse, the first
> 30 bytes are zero. It has a Z80 on board so the certainly the first
> few bytes must contain something.

Try it again with a 1N4148 between Pin 28 of the EPROM and the burner. 
This will lower Vcc of the EPROM to about 4.3V which, with some EPROMs, 
lets you still read data that would otherwise be gone due to age.

If that makes a difference but the contents still look broken, try a 
second diode in series to the first one. If that still doesn't give you 
the correct data, it's gone.

  Gerrit

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