| Posted By
Flaviosr
on 2021-03-13
06:09:04
|  Drama! Apocalypse! Tragedy!
Dear All,
I am trying to repair ANOTHER Plus/4 with the help of Diag64!
Yesterday I had different errors:
° once the computer showed the screen with the various tests but it hanged immediately after starting the control of the HIGH RAM;
° normally it stopped at the second step of the LOW RAM control, with blue background.
For this reason I ordered four SN74LS257BN and I put them on socket BUT now the computer simply gives me a black screen... obvously there is something I do not understand.
The seller has about 1000 positive feedbacks at 100% and I woudl trust him... could it be I have ordered the wrong chips (I have ordered what's written on the old ones).
Another issue is that I am completely not able to remove a chip without cutting its pins so the old ones are trash... 
As you have understood I am not a tech but another strange thing is a different voltage (equal for all of them) for the ceramic capacitors near the RAM chips than another working Plus/4... 
Thank you for your help,
Flavio
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Posted By
Flaviosr
on 2021-03-20
15:45:37
| Re: Drama! Apocalypse! Tragedy!
I have the doubt that there is a bad soldering somewhere but I am not able to completely read the schematics.
I have been able to check the continuity from the top of the socket of many of the pins...
But I am missing some:
U9: pin 10
U10, pins 4, 7, 13
Can somebody tell me where to measure the continuity of this pins...?
Thank you very much
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