[sdiy] The fatman is finished...

[Gabriel Lindeborg]

Great Scott!

I think your on to something, the AC voltage over the 7805 output 
(GND-Output/Pin2-Pin3)(the 7912 and 7808 reads 0V) reads ca 10V as does 
AC from Vss to Vcc on the uP. Then is it the regulator or a cap failing?


//Gabriel

Scott Gravenhorst wrote:
> There's more inline, but I do have one important question:  Are you sure the
> 5 volt supply is 5 volts, AND that it is properly regulated/filtered?  A
> supply with noise can have an _average_ DC voltage that could appear correct
> on a DMM, however if there's a problem with it, you might have 60 Hz
> appearing on the rail from bad filtering, wrong resistor size, or excessive
> load.  If your signal tracer has a series cap, try listening to the 5 volt
> (to ground) supply rail.  Or you could try to measure AC volts with the DMM.
>  There should be very little AC volts on the supply.  I don't have a spec for
> that, but measure that and let us know what it says...  This is another place
> where an oscope is wonderfully superior to a DMM.  If you've got a serious
> problem with 60 Hz noise, you'll hear it with the tracer and you'll see it on
> the DMM set to AC volts.
> 
> I've put other comments inline below...
> 
> Gabriel Lindeborg <gabriel.lindeborg at sverige.nu> wrote:
> 
>>Hi Crow!
>>
>>
>>>The Old Crow wrote:
>>>It sounds like the 8031 is not running.  Check to see if there is a
>>>processor clock at IC1 pin 18 (or 19, whichever is the internal osc
>>>output)...
>>
>>The up seems to be running as I get totaly different power up behavior 
>>when I remove the crystal.
>>
>>
>>>or check for the ALE strobe pulses at pin 30.
>>
>>The ALE output stays at a constant 0V as far as I can tell with the 
>>simple multimeter I got at hand.
> 
> 
> ALE (Address Latch Enable) will toggle with each bus access, so this will
> toggle very fast (megahertz rate) and you won't see it with a multimeter. 
> Here's where you need a scope.
> 
> 
>>>Are C2 and C3 the
>>>listed 33pF values?
>>
>>Yep, marked 33 anyway...
>>
>>
>>>Check for solder bridges, cracked traces, etc. in the 
>>>IC1/IC2/IC3 === MCU/latch/ROM connections.  Check IC4 connections as well.
>>
>>The soldering and traces has been scrutinezed w. a loupe, over and over 
>>again (I feel pretty confident w. the soldering as I have soldered for a 
>>living some years ago).
>>
>>I'll try to reburn the 2764... but then again the power up behavior 
>>should be constant if thats the problem, shouldn´t it?
> 
> 
> If you can burn, you should be able to verify.  No?
> 
> 
>>//Gabriel - I wish I had a scope at home...
> 
> 
> Borrow one ?
> 
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