[sdiy] Question regarding IC replacement in Akai AX80 (was: Akai AX80 weird PWM behaviour . . . )

james meagher w.james.meagher at gmail.com
Sun Jul 15 08:07:04 CEST 2012

> It's actually probably supposed to provide a squarewave to some circuit.
> The fact that it shows as 2.1V is more of an artifact of the meter used to
> read it.  Check with an oscilloscope.

I was checking the Volts because that's how it was marked on the
schematic - I didn't think to put the scope on it. When I put the
scope on Pin 13 of the other relevant IC's I get a nice square wave on
the scope. However, Pin 13 on IC22 shows a barely perceptible square
wave - almost a flat line. I did notice that the square waves on the
other IC's showed a bent, top leading edge . . . I have no idea if
this is normal, or a sign of some larger issue with the current.

Scope images of Pin 13 on IC's 21, 22, and 24 available here:

> Have you got a good reason for suspecting they are faulty?  Unless you're
> *certain*, leave them alone.  If they are faulty they will most likely get
> red hot within seconds, from past experience.

Admittedly I don't have much good reason Gordon. My patch memory banks
are not holding their data and the original battery that's still in
the board shows a solid 3.2V on my meter. I am waiting for the new
battery with legs to arrive to replace the original one. I just
figured that if the price wasn't too high I might as well order these
at the same time because I'm not a big fan of shipping charges on
multiple separate purchases (I'm in Canada), or waiting for parts to
arrive. If I install the new battery and it doesn't solve the problem
I'll be kicking myself for getting the RAM chips at the same time. If
I get the RAM chips but don't need them I won't kick myself at all for
having needlessly got them.


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