Also C302 and C303 are glued together on and on to the board...Perhaps
they are not quite touching, but they look close...

Is this a potential problem

--- In tr-707@yahoogroups.com , "Boompsie" <dj_boompsie@...> wrote:
>
> Which pin is clock on the 40H174 Can I do this without a scope
>
> I replaced the 54517p so I know it is not the case...It does the exact
> same as before I replaced the chip.
>
> Is then the 40H174 the problem There are only equivalent
> replacements for that one if I remember correctly, that I have found
> anyway...
>
> All connectors look and test fine...
>
> Testing this thing is hard being that it (the boards) doesn't sit well
> outside the case.
>
> I really appreciate your help,
> Jesse
>
>
> --- In tr-707@yahoogroups.com , Gordon JC Pearce <gordon@> wrote:
> >
> > Boompsie wrote:
> > > I have a friend's 707 that constantly lights up all lights but
> > > functions fine otherwise...I took the switchboard out of mine
and put
> > > it in his 707 and all works fine so I know the problem lies in the
> > > switchboard.
> > > I'm kind of guessing the problem might be in the transistors
(115 67F)
> > > q301-q304, though it's a guess. Does anyone have any experience
with
> > > a problem like this
> >
> > Ok, there are a couple of things it could be. Let's dig out the
> service
> > manual, and scoot over to page 10 (707-svc10.tif).
> >
> > Firstly, I don't think it's the four transistors. This would
cause one
> > group of LEDs to be either on all the time, or off all the time, and
> > would probably not all fail at once.
> >
> > Now I know you know how multiplexing works, but for the people on the
> > list who don't here's a quick run-down. You've got a grid of LEDs,
> with
> > all the anodes (positive) connected together in rows and all the
> > cathodes (negative) connected together in columns. When you want to
> > switch on a particular LED, you connect the column to positive and
the
> > row to negative, and the LED comes on. Great. Now to make it useful
> > what we do is cycle between which row is on very quickly, and change
> > which columns are connected to ground when we do so. Persistence of
> > vision takes over, and we have a stable display.
> >
> > Ok, so what drives the columns, then Well, there's a driver chip
> > (M54517) which appears to be just a bunch of Darlingon transistors
in a
> > chip, and a latch. I'd be slightly surprised if all the trannies in
> the
> > driver chip failed at once too (although not *that* surprised...),
but
> > I'd be paying close attention to the 40H174 latch. Check that the
> clock
> > pin is being clocked, and that data is making it all the way to the
> data
> > in pins and appearing on the output.
> >
> > It may well be that it's a dry joint at one of the connectors, so
check
> > those carefully too.
> >
> > Gordon
> >
>