Post #4384216

2026-08-04 21:57 UTC

@nottinghack@hachyderm.io Specifically on the +20v unregulated section, either that could just be that it is very old or because something made it blow We reformed the capacitors on a variac, checked over the PSU and made sure it gave out correct voltages, which it amazingly did, and got to work Of course, the fuse was blown due to a problem on the +20v unreg line, thankfully the genuinely amazing Philpem was there and found the closest matching service manual and found the wiring harness diagram, after several more blown fuses and multiple replaced tantalum capacitors later, we had +20v up! But oh dear, no lights or signs of life, after some more checks, +/-15v regulated was being tanked and was thus taking out the +5v where all the logic and the power LED lived, shortly after this Phil had to head home and myself, having been shown the ropes continued on an hours long task of finding dead tantalum caps on the +/-15v and later +5v, replacing, powering on, more dying and replacing more; eventually, we had all lines coming up, it was powering on, making a bleep, and showing a glowing display, and clearing it on PAGE being pressed Sadly, it wasn't doing much else

Replies (1)

@crashtestdev@woof.tech 2026-08-04 22:08

It really wasn't doing a whole lot, it bleeped, PAGE cleared the screen, and not much else So I consulted the service manual, I initially looked at the keyboard, in theory in LOCAL mode or with TX/RX connected we should hear a bell similar to the one we hear at startup when CTRL + G is pressed, but alas nothing, checking the serial line on a scope, and sure enough, nothing! My first point of call was the keyboard, whilst PAGE was doing something, this existed outside of the keyboard matrix and was a switch which connected straight to the minibus backplane which contained all the control electronics Oh yeah - this machine is build before the advent of microprocessors, it's combinational logic boards on a passive backplane all the way down! A similar construction to contemporary minicomputers! After spending hours looking at the keyboard to understand it, I was rather blown away, this keyboard uses a 7 bit counter (using a 4 bit counter IC with some flip flops to extend it), feeding the lower 4 bits into a 4-16 line decoder which pulsed each row, and the upper 3 bits into an 8-to-1 multiplexer which scanned each column, when a key is pressed and the decoder pulses the row whilst the multiplexer reads the row, the output of the multiplexer goes low, stopping the clock going into counter, and the 7 bit number on that counter - it's the ASCII value of the key you pressed! #tektronix #tektronix4010 #vectorgraphics #terminal #vintagecomputing

Open ##4384472