[sdiy] The fatman is finished...

[Gabriel Lindeborg]

Nope it´s me failing, right?

It's an cheap dmm, 5V DC should read 10V AC (and 7912 and 7808 
measurements weren't 0V as I thought).

I´ll get my hands on a scope and a eprom burner later...

//Gabriel - feeling stupid ;-)

Gabriel Lindeborg wrote:

> 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 ?
>>
>> ---------------------------------------------------------
>> - Where merit is not rewarded, excellence fades.
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>> - What good are laws that only lawyers understand?
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>>
>> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>> -- Linux Rex         | RedWebMail by RedStarWare
>> -- FatMan: home1.gte.net/res0658s/FatMan/
>> -- NonFatMan: home1.gte.net/res0658s/electronics/
>> -- Autodidactic Master of Arcane and Hidden Knowledge.
>>
>>
>