Thursday, December 26, 2019

Methodical testing of Control Logic board - part I - movements

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PUTTING THE DRIVE INTO READY STATUS AS PRE-THREADED TAPE It is possible to thread tape manually through the machine and onto the take-up r...
Sunday, December 15, 2019

Bad chip that I had already replaced - 74LS08PC

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TRACING A DIFFERENT PROBLEM I found my 'ready to move' latch on the control board being forced to reset but as I traced the signal...

Single shot chip takes a dive - not so amusing distraction

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MYSTERY FAILURE OF CLOCK TRIGGER CIRCUIT The following circuit is given a set of pulses with a 60Hz rate, which should produce properly sh...
Thursday, December 12, 2019

Putting the correct 74LS08PC chips onto the board

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FIXING THE CLOGGED HEADS OF MY HAKKO FR300 DESOLDERING GUN My desoldering gun sucks the solder through a fine opening in the tip, but it c...
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Wednesday, December 11, 2019

Beeping out the rest of the Control Logic board to verify traces and schematic, found a big problem

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MISSING AND BONUS COMPONENTS VERSUS SCHEMATIC I spent some time reconciling the components found on the PCB and in the schematics. Once I ...
Sunday, December 8, 2019

Seventh chip replaced, testing resumes at a snail's pace

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After replacing the bad 74LS05N chip, I repeated the test to verify that the BACKWRAP output signal would float high if hooked to a suitable...
Friday, December 6, 2019

Continuing debug of control logic board

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I proceeded to push the L/Rew button by temporarily grounding the appropriate input, while watching the state machine for an advance to WAIT...