RX02 / DSD440 / SA801 problem

From: Tom Leffingwell <tom_at_sba.miami.edu>
Date: Thu Mar 7 11:20:43 2002

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
Received on Thu Mar 07 2002 - 11:20:43 GMT