Re: TM506

Hugh Vartanian

Hey, Stephen,

No need to invoke any deities here (to the "praying" sign-off in a recent
post), or to threaten your new instrument with re-incarnation as a paper
weight! As previously stated, no rocket science is involved. If you can
build guitar amps and handle logical/conditional functions in software,
this will all yield to you! Pull the data sheets for those chips (love the
truth tables), read up on multiplexed displays (previously covered in an
earlier post), probe around with the scope a bit (assuming you have access
to one*) and you will figure it out.

Same with the transistors in the mainframe. Know that the "don't fix
anything that isn't broken" adage ought not be scoffed at. It will be
better to understand and troubleshoot what you have with some directed
surgical intervention to start, rather than draining your time and energy
changing a bunch of stuff that doesn't need changing, or breaking other
things that aren't now broken, but for the intervention.....

Caveats to this judicious change-them-all strategy, surely are the "known"
failure rate of certain components based on history, and whether you are
close to something known to be an issue (i.e. 4 hours into mechanical
disassembly). (I confess to being, within reason, an all-or-nothing
capacitor changer!)

*A multimeter on dc and ac ranges will tell you a lot in a pinch, are
signals stuck and/or are they doing "something", but please reference
the name of this newsgoup and get a scope if you don't have one. With the
scope, work to pick a sensible signal to trigger on, like the common pin
for the first display, presumably out of the 74145 chip (ok, I haven't
looked at the schematic, but guessing from the chip datasheet!). Just like
debugging a program, start a trace at a breakpoint in the code and probe

Good luck, keep doing the research (multiplexed displays, linear power
supplies, transistors, tek manuals and circuit descriptions, this group and
its history, etc.), ask questions when you are stuck, etc. The problems
will yield.

We love this stuff, as if you couldn't tell.

-Hugh V.

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