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
>