Serial number 320 built - one niggling issue to resolve

[Carl Claunch]

PiDP10 up and running, looking great. No issues with the LEDs.

When I run the test program and check the switch operation, the switches for bit 22 on the top and bottom row will produce an output for the switch to the left as well as itself In other words, I see a 6 when I should see a 2. The switch for bit 4 on the bottom row has the same behavior. 

I ran a quick check of all the diodes looking for a shorted one, but none detected. Microscope inspection of all solder joints also failed to find the issue. I will keep hunting in my spare time, but this only impacts toggling in values thus low impact at this time. 

[Bradford Miller]

I had a similar problem, where I couldn’t see the solder bridge using a magnifier, but it was there, regardless, between the pair of diodes that you note the confusion between: the pads (cathode on one, anode on the other) are VERY close to each other. A continuity tester should find it.

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[Bob Eager]

Check the multiplexer chip for the switches (I forget which one). Remove and reinsert it carefully. There have been cases of shorts between adjacent pins in the actual socket, if the chip is off centre.

[Michael J. Kupec]

> On Jul 13, 2024, at 3:46 AM, Bob Eager <warp...@gmail.com> wrote:
>
> Check the multiplexer chip for the switches (I forget which one). Remove and reinsert it carefully. There have been cases of shorts between adjacent pins in the actual socket, if the chip is off centre.


Thats why I threw away the cheap spring sockets and used machine pin sockets instead.
Did same on my PiDP-8 and PiDp-11.

Have a great Day!
Michael J Kupec
Sent from my iPhone

[Carl Claunch]

I had checked the chip carefully when I inserted it, but verified with a continuity tester that pins are not shorted.

Instead, it was the expected solder bridge between two diode pins. Completely undetectable on the stereo microscope as I very carefully inspected everything.

I used a continuity tester to find the diode connected to the switches causing the misread, as well as the switch to the left that was activated in error with the misbehaving switch. Indeed, the two very close pins between the two diodes had electrical connection, even if I couldn't see it. I did correct the issue and the switches work just fine now.

Installing the power keyswitch option next.