7 Mar
2002
7 Mar
'02
3:20 a.m.
On Wed, 6 Mar 2002, Tony Duell wrote:
There are 2 board versions that use the 40 pin ASIC
shown in my manual --
25136 and 25229. They are pretty similar, so I can give some more hints
withoug further information
I have the 25229.
OK, what I'd do is use a logic probe to look at
pins 25,24,23 of the ASIC
while the head is supposed to be moving. You should see square waves on
all of them. Of course if you have a 3 channel (or more) logic analyser
you can make sure they actually look like stepper motor drive waveforms.
All I have is an HP 54615B 2-channel scope, so I can't look at all three
at the same time, but they all had square waves while it was attempting to
move.
Otherwise, look at the outputs of the appropriate
sections of 1B. If one
of those isn't switching, change the 7404 (this is not a likely fault,
though).
I got square waves out of here. I didn't compare the inputs and outputs,
I just checked to see that a square wave is coming out, instead of seeing
if it was inverted. I've never seen one fail like that though, but I
could go back and check it.
Finally look at the collectors of the appropiate
sections of 1C. Most
likely one is never going low, in which case change the ULN2074.
I checked pins 8, 9, and 16; if I read your diagram right, those should be
the collectors. All them produced the square wave as well.
You mean you don't have a small screwdriver?
I've removed dozens of ICs
with just a small screwdriver. The trick is to work from both ends of the
socket and keep the chip as level as possible. That way you won't bend
the pins.
I do...the last time I used it was on a set of RDC19202-303's (resolver to
digital converters). They cost about $1,800. I didn't mess anything up,
but came close. At that point I decided I'd quit using the screw driver
method on things that aren't easily (or cheaply) replaceable.
However, I think it's time to stop swapping parts
around and to actually
use some test equipment.
I agree...
Any idea on what I should try next?
Thanks,
Tom