Re: ROMs replacement

From: Gerrit Heitsch <>
Date: Mon, 08 Oct 2012 21:40:40 +0200
Message-ID: <>
On 10/08/2012 09:15 PM, wrote:
> On 2012-10-08, at 21:07, wrote:
>>> Could you upload a picture of the circuit as used?
>> PCB:
>> =====
>> On board and worn out with tens of rounds of de/re-soldering.. (full res - above 1MiB):
>> =======================================================================================
> Just in case you'd wonder.. the PCB doesn't show the last gate of LS11 tied to GND, neither VPP of the EPROM to VCC. Those I added on the assembled adapter manually.

As you know by now, I wondered... Also, I noticed that the trace for +5V 
to the LS11 is a bit on the long and winded side. I doubt that it makes 
a difference, but could you add a direct wire from pin 28 of the EPROM?

The next step, if this fails would be to take out the 74LS00 and bridge 
the signals so that you only have 1 char set and see if that makes a 
difference. (Take out the 74LS00 and put a bridge between pin 6 and pin 
2 of the now empty socket, assuming your schematic matches the PCB)


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Received on 2012-10-08 20:01:06

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