[sdiy] The fatman is finished...

[Scott Gravenhorst]

Gabriel Lindeborg <gabriel.lindeborg at sverige.nu> wrote:
>Hi Scott!
>
>Scott Gravenhorst wrote:
>
>> Vss to Vcc ?  Do you mean Vcc to ground?  Noise should be rather low, well under
>> 0.5 volts AC.
>
>Vss is circuit ground, the same as GND as I understand it...
>
> > I see.  Well, a simple check would be to get a new 9 volt battery and 
> > test it. It should read very close to 9 volts with zero volts on the
> > AC scale. If not, the meter needs to be fixed, battery replaced or
> > used either as a wheel chock or as a target for pistol
> > practice.
>
>Cheap dmms, as mine, show 9V-ish DC and 18V-ish AC (or 0V if switch the 
>cables) on a 9V-ish battery. I think they just double the measurement 
>and do some simple intregration. The AC power supply I'm using measures 
>a fine 13V-ish AC. Anyway I could not hear any low frequency sound (I'm 
>on 50Hz/230V-ish) with a signal tracer.

Ok, well, this *probably* means there isn't a problem there.  Looks like you're
down to the EPROM or other digital IC problem.  If the "hum" (50 Hertz) were there
and significant, should be able to hear it.  I wouldn't trust that DMM too much.  A
DMM set to read AC volts ought to have a capacitor in series with the meter leads
(internally) to block any DC present.  Sounds like that isn't the case.

>
>//Gabriel - Back to suspecting the eprom and scrutinizing the solderings 
>and components.

Yep.  I'd been shipped one bad EPROM from PAiA.  They immediately replaced it.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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