Posted By
Macrofeet
on 2019-10-05
12:29:16
|  What is this plus 4 mod?
https://i.postimg.cc/m2DQ08fY/IMG-20191005-165949.jpg
https://i.postimg.cc/SKpYNG5t/IMG-20191005-170011.jpg
Hi, hopefully someone can help,
Question: What does pictured mod do on a plus 4?
keyboard keys seems slow if that's any help.
Back story: Found a couple of old plus 4's around parents,
1st pictured
working after carefully cleaning/reseating chips, pins etc. Has above mod & the motherboard/PCB is badly peeling like water damage on back the keys are slow
2nd
Non working, but motherboard has no sagging/peeling on the back
looks like TED and probably CPU dead red screen on power up but even after switching all chips one at a time and complete switch from working plus 4, i still get blank screen
I'd like to get the better looking board working ideally just wondered what the mod was for some sort of bypass ?
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Posted By
Patrick
on 2019-10-06
02:45:09
| Re: What is this plus 4 mod?
i can't see the pictures! something wrong with the URL?
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Posted By
Lavina
on 2019-10-06
02:56:44
 | Re: What is this plus 4 mod?
Try opening them in a new browser window
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Posted By
Macrofeet
on 2019-10-06
10:18:40
| Re: What is this plus 4 mod?
The mod migh not be very clear look right from the 4784 chip
extra resistors from capacitor
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Posted By
Lavina
on 2019-10-06
10:58:09
| Re: What is this plus 4 mod?
My buddy says that the photo on the link in your second post does not show any damage, it is factory default.
Furthermore, the “mods” that can be seen on the frist two links are not really modifications, you can find these in all machines like this or in another way. Those are not resistors but diodes which protect the portlines of the CPU against plugging in the serial cable while the computer is switched on. (Which is really not recommended even with this protection).
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Posted By
Macrofeet
on 2019-10-08
06:55:48
| Re: What is this plus 4 mod?
I will work up some better photos thanks for trying to help
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Posted By
siz
on 2019-10-08
15:27:31
| Re: What is this plus 4 mod?
That "4784" chip in fact is the 8551 ACIA. 4784 means it was manufactured in the 47th week of 1984. 
About those resistors/diodes: those were installed in the factory. Most of my plus4s has them.
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