35 votes
Accepted

What is the Commodore 64C "France version" and why does it need a beefy resistor?

As noted in the question, the resistor is there to allow something to consume more current without voltage dropping too much. But what consumes more current may not visible in the schematics. France (...
Justme's user avatar
  • 30.4k
25 votes

Did anybody use PCBs as macro-scale mask-ROMS?

The HP9100A had a ROM which used inductive coupling between adjacent layers on a 16-layer PCB to store data: http://www.hp9825.com/html/the_hp_9100_rom.html. This approach apparently reached a density ...
malte0811's user avatar
  • 351
20 votes

Did anybody use PCBs as macro-scale mask-ROMS?

IBM used punched mylar circuits as ROMs. 0's and 1's were encoded by cutting some traces, circuits were probed through small inductors. http://www.righto.com/2019/11/tros-how-ibm-mainframes-stored....
Grabul's user avatar
  • 3,627
19 votes
Accepted

What was the first computer board to be wave-soldered?

The modern PCB, as we know it, was a war time development and so was wave soldering as a way to lower production cost while maintaining consistent quality. All this predates computers, so when ...
Raffzahn's user avatar
  • 218k
18 votes

Did anybody use PCBs as macro-scale mask-ROMS?

DEC had a bootstrap ROM module for PDP-11's with 32-words of memory: BM792 Unibus Module. Each bit position had a diode. If the diode was snipped out it flipped that bit from 1 to 0. Experienced users ...
HABO's user avatar
  • 721
8 votes
Accepted

How did wave soldering work?

(There is a rather complete Wiki-article about) While it is not used as much nowadays, Still widely in use, just not so much with fine electronics. then passing the board over a standing wave of ...
Raffzahn's user avatar
  • 218k
8 votes

Did anybody use PCBs as macro-scale mask-ROMS?

While I am sure it has been done, keep in mind that concurrent with the beginning of the microprocessor era was also the beginning of the EPROM era. According to the linked Wikipedia article, the ...
manassehkatz-Moving 2 Codidact's user avatar
5 votes

Reverse engineering an old 40-pin connector

With the continuity checker, a pencil, and graph paper, you can usually reverse-engineer a single-layer circuit board like this without even powering it on. First you reverse-engineer the PCB into a ...
Jacob Krall's user avatar
  • 2,309
5 votes
Accepted

Need help with lifted pads/traces on a TRS-80 Model 100 PCB

Preface: So far it's hard to see anything on the pictures at all. No offense, but from the descriptions it seams as if your skills are not up to the task. So having someone with sufficient knowledge ...
Raffzahn's user avatar
  • 218k
4 votes

How did wave soldering work?

The PCB is coated with a solder mask. That's usually the green shiny layer on the surface of the PCB. There are openings in the solder mask on places that need solder. So the solder only sticks to ...
Justme's user avatar
  • 30.4k

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