[sdiy] The fatman is finished...

[Scott Gravenhorst]

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.

Gabriel Lindeborg <gabriel.lindeborg at sverige.nu> wrote:
>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.
>>> - Hydrogen is pointless without solar.
>>> - What good are laws that only lawyers understand?
>>> - The media's credibility should always be questioned.
>>> - The only good terrorist is a dead terrorist.
>>> - Governments do nothing well, save collect taxes.
>>>
>>> -- 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.
>>>
>>>
>> 
>

---------------------------------------------------------
- Where merit is not rewarded, excellence fades.
- Hydrogen is pointless without solar.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- The only good terrorist is a dead terrorist.
- Governments do nothing well, save collect taxes.

-- 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.